Sciences : histoire orale

WUENSCH Bernhardt, 2001-01-09

Sophie Jourdin — 2011-11-18T12:26:13Z

Bernhardt Wuensch is Professor of Ceramics with the Department of Materials Science and Engineering at the Massachusetts Institute of Technology. He received his Bachelor and Masters degrees in MIT's Physics Department, and his PhD in Crystallography. He has been at MIT since his undergraduate days with a short interlude at the University of Bern, Switzerland.

Professor Wuensch has given us an interview full of interesting observations both on the history of Materials Science and Engineering and on the history of MIT.

BERNHARDT WUENSCH (BW) : Materials have been around for a long, long time. Glass making was already a flourishing industry in Egypt in 5,000 BC. Pottery is usually one of the landmarks in the evolution of civilization. In fact we are used to designating the level of a particular culture by the materials they used. Neolithic, bronze age, iron age, and this will probably be known as the silicon age. It is a witty observation I can lay no claim to, but it is valid. But the difference between what we know as materials science and engineering today is that these older crafts, and such they were, were strictly empiricist. They did not understand what was happening. To use ceramics, my field, as an example : the word ceramics is derived from the Greek keramos, which means burnt stuff. You take a plastic blob of clay and throw it in a fire ; and suddenly it becomes hard, maintains its shape and becomes impervious to water. Exactly what goes on in that process, called sintering, was not unravelled until the mid-1950s. All sorts of complicated physical and chemical changes take place. The clay minerals that make up most clays, predominantly kaolinite and montmorillonite, are hydrous silicates. The water of crystallization goes off, organic material that is invariably present in clay gets burnt off and then little bridges begin to form between the crystallites. These grow and coarsen, and gradually, rather than having a few grains that are tenuously stuck together, you have grains that are bonded with big vacancies in between the grains. And then the grains grow and the boundaries between them grow and some of these voids become enclosed in the solid. It is a tremendously complicated process driven by diffusion and vaporization processes that we now understand. But the early refractories industries, the clay industries, were based purely on empiricism. And when a particular mine closed down and the supply of kaolin dried up, the processing industry had to start all over again, and work out new procedures from scratch.

In the area of materials, and I would now include metals, ceramics, polymers, and more recently electronic materials, not just semiconductors but also magnetic and optical materials, the four main classes of materials, underwent a transformation from empiricism to something founded on a firm basic understanding. When these materials made the transition from a low-cost, high-volume, primarily structural material (steel in the case of metals ; basic structural ceramics, sewer pipes ; bath room fixtures, dishware and so on in the case of ceramics) to something that was very high-tech, a case where the development of a particular device was limited by the materials available, and improving them required knowing precisely what went on. And what justified this effort was that this was a transition to a very high-technology, high value added application. So, in the case of metals one went from steel girders as metals of construction to high-temperature alloys that went into jet engines and things of that sort. And to achieve those properties and to push those limits required a fundamental understanding of what was going on. In the case of ceramics that transition came perhaps 10 or 15 years later. And some of the driving forces for that transition...

ARNE HESSENBRUCH (AH) : Which decades are you referring to ?

BW : For metals the 1940s and 1950s, for ceramics the 1950s and 1960s. The real breakthroughs there were first driven by magnetic oxides in the very late ‘40s early ‘50s. That began with the radar developed during the war effort. One had to use materials that were magnetic but also electrically insulating because the high-frequency electromagnetic radiation employed would induce currents in an electrically-conducting material causing detrimental heating.

Another application of magnetic oxides was the random-access computer memory, developed here at MIT by Jay Forrester. The material employed is typically a ferrite, and these are double oxides of a general composition, AB2O4, where one of the ions or perhaps even both is a transition metal ion carrying a permanent magnetic moment. Typical compositions today might have five or six different cation components in them – some to control the conductivity, some to create a direction of easy magnetization, some to impede grain growth as the materials is sintered (because you would like small crystallites to prevent the material from splitting up into magnetically twinned domains). And these materials are engineered on a solid understanding of the physics and chemistry of the materials involved.

The other great impetus came with the advent of the space program, and in particular the development of materials for rocket nozzles and for reentry vehicles. I was in graduate school in those days, the early 1960s, and worked summers at a company involved in the nosecone project for the Apollo program. The initial approach to the problem, to get rid of all the heat caused by the vehicle entering and reentering the atmosphere, was to make it out of a gigantic casting of copper – copper being a good thermal conductor and the heat would thus be conducted away into other regions. But that was not terribly efficient : these things were huge, 10 feet in diameter : gleaming and shining, marvellous pieces of technology and materials processing and development. The next stage, largely developed by the company that I spent the summers with, a collaboration that lasted for 15 years, used ceramic materials because they have much higher melting points. 2500-3000 degrees centigrade is not uncommon for simple ceramic materials such as aluminum oxide and magnesium oxide. Simple low-cost materials, but very refractory, very high melting points. But they have one liability and that is that they are very brittle. So the technique that was worked out by the Space Systems Division of AVCO Corporation, in Wilmington, Mass., was again to make a massive ceramic forging of something like magnesium or aluminum oxide, and then avoided the brittle problem by using a refractory metal such as molybdenum or tungsten, formed in the shape of a honey comb – that would provide the strength and resistance to fracture. So this was a composite material. And then, as goes on in many industries, the final and ultimate solution was to make it out of plastic !

Figure 1. Hans Bethe.

This was a theory that was in part developed by one of the great figures in physics : Hans Bethe at Cornell University, who worked as a consultant at AVCO. He developed the theory of ablation. One can, for example, take an ice cube and direct a blow torch on it, and even though ice melts at 0 degrees Celsius, the ice cube will sit there coexisting peacefully, well not peacefully, but coexisting with the blow torch flame, because the flame melts the ice and distils it off as steam and that soaks up the energy. The ice behind that rapidly changing interface survives the nearby high temperature. Well, the notion with the plastic heat shield was exactly the same. The plastic would char, ignite, and burn away, but what was underneath that decomposing layer was at a low temperature and the vehicle and the astronaut inside were protected. So that was an evolution of use of different materials as the understanding of the properties evolved.

To recap : in the early days of the field we saw this transition from an empirically based technology, variable and not controllable, to an era when the fundamental physical properties were understood on the basis of rational chemistry and physics and applied sometimes in extremely complicated contexts – to a case where one could design and improve materials and push limits. At that time, the field was aligned very much along specific classes of materials. There was a metals industry, there was a Journal of Metals, there was an American Society for Metals. There were industries : US Steel and so on. They were based on metals, and even particular sorts of metals. The same was true of ceramics. There were very large refractory companies that made abrasives and grinding wheels. Norton in Worcester, Massachusetts, was one example. Their whole product line was crystalline ceramics. Corning Glass, as the name indicates, was working with amorphous oxides.

There was, and still is, an American Ceramic Society, a Journal of the American Ceramics Society, departments of ceramics or ceramics engineering. And so there was a complete system of education, professional identity, industries, and academic enterprises that were centered upon one particular class of materials.

It happened a little bit later with polymers. The polymer program here at MIT sprung up in very different ways. Curiously, a large part of it was initiated in Mechanical Engineering, simply because the development of the new fibers, nylon and rayon, required a completely different set of machinery to spin and weave these fibers. They had very different physical properties from natural fibers like silk and wool. So again the need for a transition to a new, higher class, engineered sort of material required mechanical engineering – people to learn something more about polymers in order to process them. But again, back in that era, apart from synthetic fibers, when you thought of plastics you thought of some inexpensive kids' toy that would break in 36 hours and you did not really care because it cost next to nothing. Or you thought of polystyrene foam coffee cup, but you did not think of high-technology conductive or optical materials. And that has now become the case.

And then finally with the transistor and electronic devices, one of the great revolutions in our culture. The additional class of materials, silicon, electro-optical materials, came into being.

Finally it dawned upon people that even though these were materials with different properties and problems, having to be processed in different ways, everyone was really doing the same thing. They were looking at the connection between structure on all of its scales, from electronic and atomic arrangements to the arrangements of crystallites in a solid to more massive structures such as iron reinforcements in concrete. Everyone was looking at the connection between structure on all its scales and the way a material behaved. Increasingly, engineers had to learn to use these different classes of materials in concert. My favorite example is an electronic chip. It has a ceramic substrate, usually aluminum oxide, on which electrically active semiconductor elements are deposited and then etched and shaped and changed in composition. You need to have that thing talk with the outside world, so you need metal contacts in order to connect the electronic components to some circuitry. And then to protect this very small-scale structure, you encapsulate the whole works in a polymer. So, for someone to design such devices, he or she had to be familiar with all four major classes of materials, and the interfaces between them and how they behaved. The devices would not be possible without that sort of understanding. Or on the more science-oriented activities : someone who is operating a sophisticated instrument like a Secondary-Ion Mass Spectrometer to measure very shallow composition gradients on the scale of Ångstroms, or someone who is using a sophisticated electron microscope of ultrahigh resolution that allows you to actually see the individual atoms (actually more rigorously : projected columns of atoms in thin film form). They could call themselves a metallurgist, a ceramist, or an electronic materials person, merely depending on what sort of material they put in their instrument. Techniques were the same – sure : the information they were trying to extract and the uses to which it was to be put differed, but still they would all do the same thing independently of the particular class of materials. So that was really the birth of a materials science. It was when this concern with structure and properties began to transcend different classes of materials and the technology required that materials were used in concert. Now there are companies, particular the semiconductor companies that are involved with all these materials, and people have to understand the basic science of the classes of materials and the engineering.

Figure 2. Schéma du tetrahedron

The Merton Flemings tetrahedron of materials science, structure, properties, processing, and performance [cf. figure on the right]. To me processing and performance are pretty synonymous, but this is a very current view nowadays. The older view, and it is one that I still like because of the similarity between properties and performance, is a two-dimensional matrix with the classes of materials as one way of slicing the field and then materials science and engineering as orthogonal cuts to this : the concern with the properties and the processing and performance of materials from all of the four major classes. It is interesting that the older societies, such as the American Society for Metals, which used the acronym ASM, still uses the acronym, but it is now called “ASM International : the Materials Society”. So they have pushed metals alone off at arm's length. They are staying with the times.

AH : What about the demand for interdisciplinarity ? I have heard accounts that materials science as a uniter of all these different strands was primarily a political decision. It is very difficult to unite across departments of a university, and so interdisciplinary laboratories were created from above, in which this interdisciplinary work could take place. In other words, in addition to the development of a logic of the field itself, there may also have been an outside demand pulling the different strands together.

BW : Probably one of the great difficulties in any university setting, particularly a busy one like MIT, is that people are involved in a certain set of problems that they are very knowledgeable in and very excited about, and they can find more than enough for themselves to do. This means that you are perfectly happy working in a particular area and perhaps even achieving prominence in it, but you are really too busy to reach out and think about collaboration. This was particularly true when there were walls between academic disciplines and departments that were far more impenetrable than they are now. There are several observations that might be made. First of all, I think the evolution of materials science and materials engineering as a name in the academic enterprise is something that happened naturally. It was not created by decree. Many of the people who worked in metals had backgrounds in chemistry, and that is also true of many of the people who were transforming ceramics science, developing a ceramics science from empiricism. They primarily had chemistry backgrounds and more rarely a background in physics. But the people doing condensed matter physics were really anxious to be at a frontier and not do practically-oriented engineering investigations. Again the old generalizations don't stand up, but for most people this was the case.

Figure 3. Josiah Willard Gibbs.

Looking at the people who started the ceramics program here, the one I am most familiar with, one of the founders of the Ceramics Society was W. David Kingery whose background was in chemistry. He was a chemistry undergraduate at MIT, and did his doctoral work under the one solitary ceramist in the Department of Metallurgy. Kingery stayed on and became an Assistant Professor. All his friends and colleagues counselled him against it because there would never be more than one ceramist in a department of metallurgy, and he or she had better be interested in the refractories used in steel making. Similarly, a very influential person in the development of the Department of Metallurgy and in Metallurgical Engineering was John Chipman, who was Department Chair for a number of years and the leader of the Department during the critical years of evolution from empiricism. He used thermodynamic understanding, something that had been around for many years, since Willard Gibbs, in order to bring rationality into steel making. That was an enormous contribution to the entire field. Kingery did the same with ceramic materials.

AH : When was this ?

BW : In the case of Kingery this was in the late 1950s, and the developments in steel were about a decade earlier. The Department of Metallurgy gradually became more diverse because the junior people brought in had wider interests than the narrowly metallurgist interest of the people already there. When I entered the Department in 1964, there were two people who had just joined. One was Harry Gatos, one of the founders of the Materials Research Society, one of the first major materials-generic societies. He was brought in from the Lincoln Lab to work on the growth of large single crystals of silicon semiconductor materials which had the purity and the mechanical perfection to have the desired electrical properties. There was a young Assistant Professor whose name was Gus Witt who came to work with an electrochemist. Casting around is probably too strong a term, because he was not looking for something to do. But the person he had come to work with, Phil de Bruyn, had left MIT. He was South African and had a Dutch wife and wanted to return to that cultural setting. So Gus was left without a home. In those days a young faculty member did not usually get a 6 or 7 figure start-up grant of expenses for capital, but rather had to align him- or herself with a senior faculty member who, because of their standing and reputation, were well-endowed with funds. So Gus Witt collaborated with Harry Gatos on the semiconductor program. That was the nucleus of the semiconducting and electronic materials part of the department.

I guess the main point I am trying to make with all these examples is that, at least at MIT, this did not happen artificially by decree. It was a natural evolution. This was not always the case. Once the notion began to grow and to make sense, I think it is fair to say that there were some universities that changed the name of their department to be in keeping with the times. Some universities, for example, had developed strong programs in metallurgy and ceramics, where the two existed side by side in two separate buildings. So this is the first observation : that the evolution in many cases was natural.

AH : And that this was a generational change ?

BW : Partly a generational change, but partly also driven by this transition from empiricism to a rational scientific basis. One of the things that MIT faculty in that period were very, very good at was this process of breathing new rationality and sound scientific fundamentals into many engineering disciplines that were really not far beyond empiricism. The science, chemistry and physics that they introduced were not really terribly sophisticated by today's standards. They had the knack of seeing the opportunity to bring this rationality into a field which otherwise lacked it. I mentioned the materials people, but there were people doing the same thing in other fields, in electrical and mechanical engineering and so on.

AH : And the theoretical tools that they were beginning to share were things like thermodynamics ?

BW : That is right.

AH : Any other theoretical tools that were beginning to be shared in the same period ?

BW : There is another interesting theoretical overlap. I began as a physicist but did my doctoral work in crystallography with one of the world's great figures in that field, Martin Buerger, who was a mineralogist in the Department of Geology, now EAPS (Earth, Atmospheric and Planetary Science) – not earth, fire, and water ! Geologists had a long tradition of descriptive crystallography for minerals found in the field. They too became more analytical. There was a period in the early 1900s when at places like the Geophysical Laboratory under the Carnegie Institution of Washington, worked out phase diagrams for materials that were of geological importance : silicon oxide, aluminum oxide and so on. These were the major rock forming systems but these also turned out to be the materials that ceramists were digging out of the ground. And once you have dug them out and ground them up, they become a ceramic powder. The materials scientists, the ceramists and metallurgists were interested in making things, so they had an eye on kinetics and on how things changed upon application of heat and pressure.

The systems that they worked with were relatively simple, chemically and structurally. The geologists however, were concerned with anything that Mother Nature had provided, so they delved into these enormously complicated silicates and other sorts of minerals, impure, all sorts of solid solution and chemical substitutions, incredibly complex structurally. But it was a static record. It was relatively late that they began to actively investigate phase transformations, something dynamic. The metallurgists and ceramists had been working on solid-state diffusion, oxidation, and corrosion processes for 20-25 years before the geologists became interested in measuring diffusion rates in silicates. They did so in order to understand the transformations that took place in rock implacements, particularly under pressure and hydrothermal conditions. And conversely, the aim was also to interpret the thermal history of the rock with knowledge of the kinetic rates. So there were two complementary views : one of complex materials and a static picture along with the materials science people who were working on similar issues but in a more dynamic sense with simple materials.

AH : It can almost be mapped by today's standard textbook. There will be chapters on the four major classes of materials : metals, ceramics, and so on ; and then there will be chapters on the properties (thermodynamics, electrical, optical, magnetic). And each of these chapters corresponds to the theoretical tools that were beginning to be shared by the communities you mentioned in the 1950s and 1960s. Would that be a reasonable way of describing it ?

BW : Yes. And another chapter that every textbook on condensed matter has to start out with is structure. This is atomic-scale structure in crystals and amorphous materials, but also microstructure : dislocations, imperfections, and vacancies. These control a great many properties to a larger extent even than the intrinsic properties of the material. Also interfaces. Unfortunately if you are writing a comprehensive textbook you cannot spend too much time on this sort of thing. My field of interest and passion – crystallography – is one that is often slighted. I took a lot of ribbing from my colleagues when I joined the Department of Metallurgy : “You are going to have it easy. There are only three kinds of crystal systems : body centered cubic, face centered cubic, and complex !” There was some truth as a basis for that kind of sardonic view. Even today the great majority of materials used in ceramics are cubic. Not all, but the majority are structurally simple.

But then you asked about, since this was becoming valuable in technology, valuable to government enterprises based on those technologies, once the value of this interdisciplinary work was perceived, were there ways to encourage people to work in this interdisciplinary mode ? There were indeed. In the late 1950s, there was an effort to do this that arose in the Department of Defense, from an agency then called DARPA (Defense Advanced Research Projects Agency). This was shortly on the heels of the discovery of the transistor and the great potential for this device in electronics and communication, and therefore in defense. The people in DARPA had the wisdom to realize that, in order to capitalize on the electronic properties of semiconductors, one would have to understand the chemistry of producing these materials and the way of growing single crystals of unprecedented perfection. This brought in the chemists, it brought in the crystal growers and the materials scientists. You also needed to understand the physics of these very complicated electronic structures and the way of controlling them through doping and through creation of proper interfaces. The only way to make any progress on this was to bring together in one place people who were interested primarily in solids but who came to this area bringing the perspective, instrumentation, and the skill and expertise of their particular discipline with a view to collaboration in a very close fashion – that is, not only formulating but also conducting the research. It was probably the late 1950s, before I came on the scene as a faculty member, that DARPA went around to probably a dozen or more research universities – saying : Hey, do we have a deal for you ! We would like to come and make a building for you in which you might care to house the majority of your people working on problems in condensed matter. Initially, the emphasis was on semiconductors, because that was the driving force for this investment. I believe twelve sites or so were selected, perhaps initially ten with two created later. But that was the origin of our Building 13, directly behind the great dome. That building was constructed during the early 1960s and we moved into it in 1965. It housed a great part of the Department of Metallurgy and Materials Science, as the name had evolved by then. Each name change was won at great expense by the Department Chair, since obviously people who had been trained as metallurgists resisted. That united them in a way that nothing else in academia could have done. You can imagine the furor arising from our grand alumni when the word metallurgy disappeared altogether.

In any case, the new Building 13, the Center for Materials Science and Engineering housed, on its 4th and 5th floors, a major portion of the Department of Materials Science and Engineering : the entire ceramics and electronic materials groups, the polymers group (which grew and increasingly took residence on the 5th floor). The electrical engineers, those who were interested in the materials aspects of devices, were on the 3rd floor. On the 2nd floor were the administrative headquarters and the condensed matter physics group. The latter has grown considerably since that time. Parenthetically : this new creation was the second major interdisciplinary laboratory at MIT – the first was an outgrowth of the Radiation Lab that developed radar in the famous wooden Building 20, since deceased, and Building 24. It is now called the Research Laboratory of Electronics. At the end of the war many of those people who had been brought together for purposes of the defense effort dispersed and went back to their home institutions. But some stayed on and that was the birth of the Research Lab for Electronics. This was another benchmark in the evolution of interdisciplinary work. In this case it was primarily Electrical Engineering and attendant design - some materials work. That came into being shortly after the war, early 1950s.

The charter for the Center for Materials Science and Engineering (and the organization had slightly different names at different institutions) was that first you will conduct materials research in a highly interactive and interdisciplinary mode – and faculty from as many as seven different departments at MIT had participated in the programs. These workers were to be grouped together in teams called Areas of Thrust in early semiconductor research, but later broadened considerably. The other thing that was visionary was the realization that in order to conduct first-class research one needed sophisticated, first-class equipment – constantly evolving and growing more sophisticated. This was too expensive to obtain for any single faculty member or small group of faculty. And moreover, for it to be effective and working at capability, it required support staff. So, the second mandate besides creating these funded, collaborative, and interdisciplinary research teams was to establish central research facilities. For a time, the Center had as many as 12 different central facilities. The next thing the sponsors did was to seek to convert young faculty to this interdisciplinary mode of operation. In order to do so they provided seed funding. It was an unabashed attempt to seduce young faculty into these interdisciplinary teams !

AH : Seed funding refers to a couple of years' funding which would then be taken over by the hosting university ?

BW : No. The Center operated under a block-funded federal budget. Seed funding was intended to provide an opportunity for a young faculty member, someone who might otherwise not be attracted to participate in the interdisciplinary teams. To develop this connection they wanted to get to them early and make it worth their while to not identify only with their peers in their own department. The hope was to fold such young faculty into one of the Areas of Thrust. There were also some features of this program that were almost without precedent : a great deal of local autonomy was given to the Director of the Center. The Director decided what problems to address on the basis of the resources unique to the particular host university. Rather than having these Areas of Thrust (generally speaking there were three or four) monitored by some program director in Washington, they were monitored locally. And this Director presumably would be gutsy enough to pare off the team members who were not interacting sufficiently or whose expertise was no longer needed for a new direction to be taken. It was a thoroughly enlightened view that somebody on the scene would be better equipped than someone down in Washington. This is not true, even in individual research grants, today. The NSF gives grants on the basis of promise, and once you have received the grant you can change minor details, but you cannot start off doing ceramics and then suddenly decide to do fruit fly genetics – at least not without major questioning from the NSF division. Other agencies, the Atomic Energy Commission, and then the Department of Energy, wrote not a grant but a contract : and you had to be very specific about your research. You had to prepare a work statement from which you could not depart without permission of the program director.

This made the Materials Research Laboratories very lean and fast on their feet. If something came up, they could change direction instantly. One of the great success stories here was in high critical-temperature oxide superconductors. When Bednorz and Muller made their earth shaking discovery [of superconductivity in ceramic materials], any number of people dropped what they were doing and began bootlegging efforts to identify these phases and understand this peculiar behavior – which is still not well understood. The Director of our Center for Materials Science and Engineering at the time brought together everyone at MIT who was interested in these materials, and obviously that number was rather substantial, and selected individuals to develop an area of thrust. And with one or two months' notice another Area of Thrust was cancelled : one concerned with defects in semiconductors. Now that may seem like a very courageous thing, but in fact many of the people working on these defects were also interested or even more interested in superconducting materials. People were working in everything from growing single crystals of the materials for basic property measurements. People in condensed matter physics ended up using these crystals – some very, very critical measurements in magnetic ordering and magnetic correlation lengths. That was the first clue that something in the magnetic moments of copper ions was critical to this behavior. Other materials scientists were interested in learning how to make polycrystalline specimens, so that the superconducting properties could be used in making better magnets. Since these were not metals, unlike all previous superconductors, it was not at all clear how you would wind them into solenoids to make high-strength magnets. That particular part of the effort at our Center led to the first US patent granted for processing of an oxide superconductor, and in fact it eventually led to a very successful spin-off company.

The only other thing that needs to be said about the program is that it evolved over time. The typical tour of duty of the Director was five years because by that time the necessary decisions had offended enough people for a new Director to be brought in. The change came towards the end of the Eisenhower administration, when Eisenhower coined the famous phrase : the military-industrial complex. There was a growing concern that the military had control of and sponsored much work, such as basic research in the space program, and that this belonged more properly in the civilian sector. So, at that time, the leader of the Senate, Mike Mansfield, tagged onto the Defense Appropriation Bill an amendment named after him, that confined the military to weapons systems and maintenance and support of armed forces. But they should not be in a position of supporting basic science. That is also interesting historically because one of the prime sources of funding for basic research prior to that had been the Office of Naval Research. They supported a lot of very fundamental science that had only indirect long-range connections with naval defense systems. So the amendment brought about momentous changes : the National Science Foundation's budget was beefed up ; it grew exponentially. I think NASA was set up at approximately this time. It absorbed space programs that had been conducted under the auspices of the Air Force and the Army – I think it is fair to say with considerable overlap and duplication. I think that also the Atomic Energy Commission and the Department of Energy came about then too. The military aspects of atomic energy stayed in the hands of the military, but the peaceful uses were spun off to the civilian agency.

What happened to the Materials Research Laboratories ? The NSF was very impressed with the success of this approach. The whole justification of it is that the net effect should be far and away above what could be achieved single investigator grants. And these investigators might or might not collaborate. There was arguable evidence that this was the case. The NSF toured these Materials Research Laboratories and announced that they would take over the sponsorship of the program.

Things stayed in this form until about seven years ago (1994), when there was some concern that, successful as the program was, it appeared to have become an old boys' club, in that there was no sunset clause. True, the programs were reviewed every three years with a major site visit lasting several days ; proposals were critically reviewed by outside referees, as is the case with any research proposal. Nevertheless, there were some materials activities at universities that were better than others, perhaps because of a critical number of faculty involved and also, one might say, because of the quality of these universities. I am aware that this may sound smug and immodest, but the situation was ripe for sour grapes, and there was a lot of grousing. Politically, a lot of states realized that a way to give the state economy a boost was to start up a research university that attracted industries and created jobs leading to tax revenues and so on. So there were sour grapes. And the MRL program had indeed gone on for a long time. It was competing with a similar program that had been created during the Reagan era. This was created as a response to Reagan's address with words to the effect that we needed to get this country going again, to be competitive and to rev up the economy. The NSF went to Reagan with a proposal to create something called Science and Technology Centers. Very similar in concept to the Materials Research Centers, with two exceptions : 1) they had a sunset clause in them (seven years) ; and 2) they were to focus on a specific problem, and could not shift and change, grow and evolve. They had a much greater emphasis on the outreach to technology and to the professional community : newsletters, training courses, bridges to industry to implement the technologies were integral to the Science and Technology Centers. So we had MRLs (successful, but oh, what have you done for us lately), and the S&TCs. And about seven years ago, just after a director of the NSF had resigned and the directorship of the Materials Research program had changed hands, Congress decided that the entire program should be looked at anew. As the result of a study that took place over a very, very short period of time, the system was changed into something called the MRSECs (Materials Research Science and Engineering Centers). I love the name because as an acronym it is gender blind : they can be either Mrs. Ecs or Mr. Secs ! A masterful political ploy. They supplanted both the Materials Research Laboratories and also the Science and Technology Centers. The funding level remained pretty much at a comparable level. Now there is a notion that, for the older programs, the bar should be raised consecutively at the time of renewals and there should be a chance for creation of some new MRSECs. This is taking place : some of the older MRLs have lost their support and new programs have come into existence, as MRSECs.

So much for institutional support ! But that was a conscious effort to advance materials research in general but also to deliberately foster this interdisciplinary, collaborative mode of work on materials.

AH : You have talked about the theoretical developments, from the institutional perspective, and the funding. Is there a story to be told about the history of the instrumentation ?

BW : When one discusses the history of instrumentation one immediately gets very specific. There are tools such as electron optics that have had a wide application from medical science to inorganic materials research : physics, chemistry, and geology and so on. It was a tool with unprecedented resolution. But it gets very specific. It is true of the way I have operated on my own research path. I always kept an ear to the ground to new apparatus that might provide something new in terms of precision, resolution, or more flexibility, or permit doing something that could not previously be done. Often, these new instruments came into being in fields that were distinct from your own area. Apparatus has become increasingly complex, and companies have made new designs and developed them to a high level. The advent of powerful computers have changed research in a major way. The speed and means of collecting data, the way in which it is analysed, the sort of analysis of a problem that can be undertaken have all changed in ways that could not have been anticipated a few years earlier.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Bernhardt Wuensch », par Arne Hessenbruch, 9 January 2001 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article133.

—

Entretien avec Bernhardt Wuensch, par Arne Hessenbruch, 9 January 2001

Lieu : Dibner Institute, USA

Support : enregistrement non précisé

Transcription : Arne Hessenbruch

Edition en ligne : Sophie Jourdin

WHITTINGHAM Stanley, 2000-10-30

Sophie Jourdin — 2011-11-11T22:33:28Z

Michael Stanley Whittingham is one of the main figures in the history of rechargeable batteries. From the late 1960s until now he has examined promising materials for use as cathode, anode, or electrolyte. He pioneered the use of titanium disulfide for cathodes, now commonly used. He also initiated the concept of intercalation. This term refers to the insertion of positively charged ions into the cathode material. In a rechargeable battery, Li+ ions are typically inserted between layers of the titanium disulfide cathode while the battery is being charged, and then de-intercalated during discharge. That the process of intercalation and de-intercalation of ions leaves the basic structure of the host material intact, so that the charge and discharge can take place repeatedly, was an understanding forged in the 1970s and early 1980s, and in which Whittingham played an important role. He has also been prominent in the field through the editing of its main journal, Solid State Ionics, from its inception in 1981.

Whittingham went into management for a number of years (1984-1988), while the field forged ahead. Japanese companies, in particular, made great strides in the commercialization of lithium titanium disulfide rechargeable batteries. When he rejoined battery research, the Japanese lead was becoming dominant, embodied in a raft of patents.

Since 1988, Whittingham has explored further materials with a view to improving batteries still further, both with regard to size and to performance. This will not change drastically the way in which the energy economy is currently organized (for example, the electrical vehicle is not around the corner), but smaller and more powerful batteries will impact upon the cost and design of portable electronics.

Biographie détaillée

STANLEY WHITTINGHAM (SW) : I graduated with a PhD in solid-state chemistry (from Oxford).

BERNADETTE BENSAUDE-VINCENT (BBV) : So you were trained as a chemist, mainly ?

SW : Yes.

BBV : And why did you go to Stanford, with Prof. Huggins ?

SW : Because in my time almost everyone from Oxford came to the States for one or two years. That was expected if you wanted an academic or an industrial job. It changed a lot... 1968. And why Stanford ? It was on the West Coast, California had sun.

BBV : And your PhD was on tungsten bronzes ?

SW : That's right : tungsten oxides and tungsten bronzes.

BBV : And how did you choose this topic ? It was not that popular ?

SW : No, I think Oxford always had a very active program in solid state. There were three or four faculty there interested in solid-state.

BBV : Who was that ?

SW : Peter Dickins was my advisor ; and J. S. Anderson was head of the department. And Jack Lunette was also there, and he was interested in the theory of calxes. So initially we were studying (?) catalytic activity, and how all that changed with the changes in the electronic properties of the material. There was a great deal of interest in the crystal structure, or rather the band structure, that controls the catalytical activity.

BBV : So it was mainly for catalysis in Britain ?

SW : Right. And we chose a very, very simple reactant : mainly oxygen atoms, and we just looked at how they recombine at the surface. And this was at the time of Sputnik and the US Air Force paid for the research.

BBV : Even the research conducted in Oxford ?

SW : They paid through their London office. Because they were interested in how various species (?) reacted outside their space ships.

BBV : So it makes sense in fact.

SW : Right. And that was the topic of my masters degree mainly. And then we looked at the same materials as catalysts potentially for gas production. And the Gas Council paid for that research. But within a few months of me starting the research, they struck natural gas in the North Sea.

BBV : And you stopped the project ?

SW : No, they said : we are not really interested in what you are doing anymore, but you have got the money. Do what you want and don't bother us too much.

BBV : And in those days money was easy to get ?

SW : Oh yes, you turned down money in those days.

ARNE HESSENBRUCH (AH) : You mean this was the case between the oil crisis and the discovery of natural gas in the North Sea ?

SW : No, they discovered gas in the North Sea before the 1973 oil crisis.

AH : Why did the money flow easily ?

SW : Well, the money came from the Gas Council and they made gas basically from coal. So they wanted a better catalyst to convert. Natural gas avoids all that messy stuff. The rest is really history. London cleaned itself up because they stopped burning coal.

BBV : And then, when you moved to Stanford who was there ? And how was the lab ?

SW : I worked for Bob Huggins there. And that was quite a switch. In England, France, and Germany, solid-state chemistry was a respectable subject. Chemistry departments did solid-state chemistry. In the US you could count the number of solid-state chemists on the fingers of one hand. So I went to a materials science department, not to a chemistry department.

BBV : Was Huggins considered a solid-state chemist ?

SW : He was a materials scientist with a PhD form MIT and he set up a new centre for materials research at Stanford. His interest was in solid-state electric chemistry ; how ions move in solids and things like that. And at that time the Ford Motor Company had just discovered that sodium ions move very fast in a material called beta-alumina. Sodium ions move almost as fast in that solid as they do in a liquid.

BBV : So it was the time of the beta-alumina ?

SW : Yes. Ford published their data in 1967, and I went to Stanford in 1968.

BBV : Did you continue your research on tungsten bronzes there ?

SW : Yes and no. I measured the conductivity of beta-alumina. That is what we tried to do. We has to have electrodes that were reversible to electrons, so we could get a current, and to the ions that were moving. So we paid attention to bronzes that had sodium in them, to metallic conductors, to see if they would make good electrodes. So we have narrowed the Oxford work into the Stanford work.

BBV : And how did you develop the batteries using tungsten bronzes.

SW : I arrived at Stanford in February. In May or June of that year Bob Huggins left to go to Washington to run this whole suite of advanced research centres of materials (?) of which MIT is the last surviving. So he went there and manned those for about two and a bit years. I remained at Stanford and continued my research on the basics. And about the same time, there were others in the medical field who were interested in batteries for pace makers and things like that and there was a number of good silver iodide conductors... (?). And it struck us that sodium or potassium had an advantage over silver because they yield a bigger current. And that is where we got the interest in actually using them. Beta-alumina as the electrolyte and we thought of sodium and some oxides as the electrodes.

BBV : And how did you come to your favourite, titanium disulfide ?

SW : Ah, that is a jump.

BBV : Yes, because you took the patent out in 1973.

SW : Right. While I was at Stanford a number of other people, in particular Hector Ball, who was Professor of Applied Physics and associated with the Materials Department. He was contacted to find people to go to Exxon who were starting up a new corporate research lab. Exxon really had very few chemists and physicists at the time. So I did an interview at Exxon and one at Cornell, and I was offered a job in the Materials Science Department at Cornell, not the Chemistry Department. About a third or a half of the faculty in Materials Science Departments in the US are physicists and chemiusts... they have PhDs in physics or chemistry, not in materials science.

BBV : Incidentally, do you think that physicists have had an impact on your field ?

SW : Oh yes. At Exxon they made me a very nice offer. What they had built up was an interdisciplinary group. It was led by Fred Gamble, who had also come from Stanford. His interest was in superconductivity. And that was the first wave of superconductivity. What we tried to do then was to look at (?) tantalum disulfides. And by intercalating different molecules between the sheets of tantalum disulfide we could change the superconductivity transition temperature. So, tantalum sulfide became superconducting, I think it was at 0.8 degrees Kelvin. By putting in different molecules you could raise it to about 6 Kelvin. It turns out that the one that could raise it the highest was potassium hydroxide. And my first job was to try to understand what was going on. And what I found out was that basically potassium ion structure was particularly stable in TaS2-... It behaved like a salt ... there was again of energy ... (?).

AH : Where was this new Exxon lab placed ?

SW : It was across the street from a refinery in Linden, New Jersey, along with a raft of other chemical and solids research labs. Basic research. And the goal was to be prepared since oil was soon going to run out. My part was energy-related systems, other than petroleum and chemicals.

AH : It was set up in 1972 and you were there from the very beginning ?

SW : It may have been set up in 1971, but basically yes.

BBV : How many people worked with you on this project ?

SW : The group headed by Fred Gamble : there was about six of us. Each one of us had a different background. Fred Gamble himself was something like a physical chemist, there was an organic chemist, some were physicists.

AH : Presumably you had plenty of funding for equipment and the like ?

SW : In those days, if you needed something for your research you asked for it, and it would be there in a week. Money was no issue. They invested in a research laboratory like they invested in drilling oil. You expect one out of five to pay off.

BBV : Was it perceived as a long-term project ?

SW : Yes.

BBV : And what did that mean : 10 years ?

SW : 5-10 years. Industry has changed considerably since then. I would say after about 7 years they began to ask : well, what is going to come out of this ? By that point we had moved from tantalum sulfide, which is really no superconductivity material. We were looking at lighter materials : titanium sulfide. And we were looking at lithium, not potassium, because it turns out that potassium is very dangerous. And some time in this period a Japanese company had come out with a carbon fluoride battery which they used for fish floats. They fish at night and they need to see where their floats are. And that was a primary battery. This was the beginning of interest in lithium batteries.

BBV : So the initial interest came from Japan ?

SW : Well... we thought we could do something better. It was a high-voltage, one-shot, then you throw it away. And Exxon was only interested in rechargeable systems. They were looking to the electrical vehicle.

BBV : From the very beginning ?

SW : As soon as we started. We were only in energy, but we told them that we may have a battery and they immediately jumped to the notion of an electrical vehicle. And they in fact built – well it must have been in the mid-1970s – a 3W and diesel hybrid vehicle running on the roads.

AH : Presumably the Japanese were also interested in the EV at this early stage ?

SW : No, they were not interested at all. In the mid-1970s some Japanese companies started selling calculators with solar systems built in.

AH : In other words, they focused only on smaller batteries than those employed for vehicles ?

SW : Yes. And it is important to make the point that no battery company came up with any inventions. Every invention coming from Japan came not from a battery company. They had a device they wanted to take to the market. Sony, Sanyo. It is a straight busines. They do not stray from where they have been.

BBV : And from where did you get your techniques in intercalation chemistry ? Did you receive training in this already in Oxford ?

SW : Well, the tungsten bronzes are quite similar in this respect sodium, lithium, or hydrogen in and out. There was interest in electrochromic displays in the late 1960s early 1970s and so we were all familiar with them. You have tungsten dioxide and you put in in acid adding a bit of zinc. It generates atomic hydrogen and turns into a solid going from yellow to blue.

BBV : Yes, but when the mixed conductors started, I think there was something of a change in intercalation chemistry.

SW : Yes.

BBV : Was there any feedback from your research at Exxon to intercalation chemistry ? Or was it isolated as a completely industrial research lab ?

SW : No, I think we had a huge impact. At the time Bell Labs were doing similar things. They were located close to us, they were a similar group, also with many individuals from Stanford. We were competing head-on for a while, also in publications. If you look at our publications on the battery, you will see a lot of basic science with no mention of batteries at all. Exxon clearly did not want to disturb their aura (?).

AH : What journals did you publish in ?

SW : Electrochemical Society, Materials Research Bulletin. But the electrochemical stuff came after the basic stuff. So much of the basic stuff went into the MRB which had a very strong reputation in those days.

BBV : So, you have been working on titanium sulfide for many years ?

SW : I started working on that when I joined Exxon in 1972, already in October. As soon as we started work on it we realized that it had very interesting physical properties. So my colleagues like Art Thompson ... (?). After a year we knew about that material than anybody in the world.

AH : May I ask a couple of questions about the early period before we get advance too far chronologically ? Would you please contrast the appearance of the labs at Oxford, Stanford and Exxon ?

SW : Sure. Oxford was an organic chemistry lab. We were in the old wing of the building, built probaly at the beginning of the last century. The walls are three feet thick. There was mercury all over the floor and under the floorboards. It was an antique place. But most of the facilities were there. It was all set up for solid-state work, because the head of the department was a solid-state chemist. We had some of the first NMR ... (?). It was, I would not say state of the art but, pretty good for those days. And what people don't realize is that there was no such thing as an electronic calculator. The computer we used took up a whole Victorian house and it had less power than one of those [pointing to a PC].

AH : What was your working day like ?

SW : If you were running an experiment you stayed there. There was no computer. If you were lucky you had a chart recorder. change temperatures... (?) You built your own equipment, you could not buy it.

BBV : Was the equipment different in Stanford ? Was it a shock ?

SW : Stanford was a new building. The Center for Materials Science had been built just a few years earlier. The building was new, most of the equipment was fairly new, though soime of it was surplus from (?). But the change was more going from a chemistry department to one of materials science. There were no fume hoods in the buildings. It was much more electronically oriented and obviuously the computers at Stanford were then better than those at Oxford. And after maybe a year there, a hand-held calculator costing about $95 came out. ..... (?)

BBV : And that was important for your own field ?

SW : Yes, because we wanted to measure how fast ions move. We made the first measurements over the first 5 or 10 seconds. You can do it with a chart recorder but it is very difficult.

BBV : And at Exxon ? Did you have everything you needed ?

SW : You had everything you wanted within reason. It was a new set-up and wanted to get it going right. Their attitude was that our time was much more expensive than the equipment.

AH : Were there more technicians at Exxon than the other two places ?

SW : No, I would say it was almost the opposite. Oxford had more support staff than any place in the US. We had a huge machine shop, a huge glass-blowing shop. And you had the old business of artisans in what were called shops. They would do new things for you, but they expected you to do anything routine by yourself. If it was complicated, they would do it for you.

AH : And in the US you would buy in ?

SW : Yes, there you tended to buy stuff. There was some support staff but nowhere near the same. These days there is almost no support staff.

AH : But the impact of the computer has generally speaking been more marked in later periods than the one we are talking about now, right ?

SW : Yes, when did the PC arrive ?

AH : I think it was about 1986.

SW : And I was at Exxon from 1972 to 1984. We came up with a battery patent early on. We had an incredibly good patent attorney. They would write up your invention and then ask you : why can't you do it this or that way ? And they came up with ideas for building a battery fully charged or fully discharged. TiS2 patent... (?)

BBV : And did you publish more patents or more articles during your time at Exxon ?

SW : More articles because one of the goals was to get Exxon better known as a research institution so they could hire better scientists. And there was some pride with the president of the company that he wanted to compete against Bell Labs. So he wanted us to be perceived as the labs of the energy business. One of the presidents was E.B. David (?) who subsequently became head of the board of Science Advisors or something like that. He wanted Exxon to be known as the best place in the world.

BBV : So they valued research over patents ?

SW : Both.

BBV : Was not there a tension between the two in the disclosure of results ?

SW : Yes. The publications did not mention batteries at all. So we made materials and we described how we made them. We then discussed their scientific behaviour, how they reacted with water, their thermodynamics. But anyone smart enough would know what we were doing. They soon caught on. And I think about 1975 or 1976 when the first patent started coming out we released the first paper in Science Magazine. And about the same time we also published ... (?). Because up to that time people in the battery business did not know what intercalation was. ...

BBV : Did you attend the Belgirate, Italy, meeting in 1973 that purportedly is the founding event of the community ?

SW : Yes, I gave two papers both of which went very well. And the other thing I remember is that Carl Wagner attended that meeting. He was very old. He basically put the field of corrosion on a scientific basis. He ought to have received a Nobel Prize.

BBV : Were there more Europeans there ?

SW : It was organized by Europeans, and I think there were more Europeans. And I remember that I was there with my wife and two young children. We bailed out half a day early because they said it was going to snow in the Alps, in order to go back to England.

AH : Were there any Japanese present ?

SW : Yes, I think there were a few.

AH : So you agree with the interpretation that this was a founding meeting ?

SW : Yes.

AH : One might also point to the beginning of the journal Solid State Ionics (1980) as the origin of a community ?

SW : Yes, but by that stage we were already having annual meetings.

BBV : Did the journal make any difference ?

SW : Do you want a bit of history of the journal ? The North Holland folks then had an office in the US. I lived in New Jersey two miles away from the publishing editor. They published the Belgirate proceedings. And this editor said : we need a journal in this field. I was one of those who said : no we don't.

AH : Why did you think that ?

SW : I thought there were too many journals already, even at that time. There were few compared with today of course, but even so. So he said, you prove that to us and we will pay you to do it. So Hans Becker (?) and I sent out a mail to everyone in the community, saying North Holland was going to start this journal and was there any interest ? I fully expected to get negative feedback hbut 95% wanted it. So North Holland played every nice game and we could not say no.

AH : Did the journal then not change anything much ?

SW : Yes, the journal changed a great deal because it pulled all the papers together in one place. Remember in those days there were no journals such as Chemistry and Materials. Solid-state chemistry had just started and that was more high-temperature. And there was the Materials Research Bulletin. So papers were all over the place. So they convinced us to go with it. I had my arm twisted to edit it. Within one year we went from single-column to double-column format and larger-size paper. It basically took off straightaway.

BBV : The whole community decided to publish in this journal instead of in the others you mentioned ?

SW : Yes. They kept publishing in other journals also, but they knew that here they would have their stuff recognized .

BBV : Was it a fast publication ?

SW : Five months. The goal was to get it out quickly. In those days the Materials Research Bulletin got things out in two months.

BBV : Let us come back to your career. Why did you leave Exxon in 1984 ?

SW : Exxon had one good thing about them. It was run by scientists and engineers, not by lawyers or MBAs. I will give you an example. When we had come up with the battery, the board of directors came to the lab to listen to us. And they then said here is the money, now go and do it. So they built an applied film group costing millions of dollars, a very good one. It was like a poker game : well we make a big dollar or we loose it. Their philosophy was that if you were a good scientist then you would also be a good director. So within a few years I became a lab director. I am not sure exactly when but at some stage they said : now you have shown that you can manage something you know, so we will now send you off to manage something you do not understand. That is why I went to an engineering facility, where I headed their chemical engineering. I was responsible for technology, for synthetic fuels in those days, chemical plants, raffineries. It sounded challenging at the time and I stayed there four years. At that time began the shale oil and coal gasification (?). It was a booming period. My job was to employ as many chemical engineers as I could lay my hands on. But soon the writing was on the wall and the slump was coming. We started laying off people. We went from roary-rosy days to (?). And I was doing no science myself then. I missed that and that is why I went to Schlumberger. My first boss at Exxon went to the Metallurgical division there.

BBV : What kind of research did you do there ?

AH : It was 1984-1988.

SW : Right. Schlumberger was in Richfield, CT, the lab was built and designed by a famous architect called Johnson, from Texas. One or two stories, glass, a very pretty building. You could not have your names on the doors or pictures on the walls unless they'd approve them. Schlumberger was then the Rolls-Royce of the oil field. They built very expensive analytical equipment which they put down oil wells to determine whether there was in fact any oil down there, what the rock foundations were like. They would put these probes worth millions of dollars down the well, pull them up very slowly and you would get wiggles and charts and things like that. And if they could reproduce the wiggles they would sell it. It was a very low-key company. In those days they probably made more money than all but two or three of the biggest oil companies. What they did not have was chemists, those who tried to understand what these measurements actually meant. They did have a large number of physicists and electrical engineers building the instruments. Then they decided to build up a basic rock science group, the job of which was to try to understand what was measured. And I went as head of the group, to bild up the chemistry activity with the engineers. One of the biggest electrolytes in the world is clay. It is clay in the formations that causes various forces to be formed in the earth and you can measure them.

AH : So you were not really moving to something completely new. This is the link to your previous field.

SW : Yes, but I had been doing management. At Schlumberger I was dealing with chemical engineers. But as my wife said, I was doing far too much travel. Schlumberger had labs in Texas, Connecticutt, Tokyo, Paris, and Cambridge, England. During my first year I was in the US maybe half of the time.

BBV : Is that why you stayed only four years there ?

SW : When I went there it was a booming organization run by a Frenchman (Ludeau ?). A whole book has been written about him. He died, and his chosen successor failed. There was a palace revolution. And a Scotsman was in charge, Ewan Baird (?), I think he is still in charge. At that point they were building a new chemistry facility in Richfield. They had put the foundations in, and he came in one day and said, no. Construction stopped. He ordered people back to basics. Schlumberger also had some TV stations back in France. They invested in other things. It was as if they only wanted to have Nobel Prize scientists : only the best was good enough. They did hire some outstandingly strong theoretical physicists. We looked at how oil flows through sandstone in rocks. Sprinkering (?) techniques ..very similar to how snowflakes build up on the window. Some people there did not like it : why are you doing this ? There was a reaction against basic science and people wanted to get back to building and improving equipment.

AH : Was the basic stuff modelling ?

SW : Yes, there was a strong modelling component and a measurement component. At that time we had about 30 people in this basic science group. We were told basically that we could become engineers or leave. We were given about 18 months. They were very generous. Some of the best people were in their 20s. Three of them were offered tenured professorships within a month.

AH : This is also the period of change from the mainframe to the PC.

SW : Yes, and Schlumberger was big on that. They had a Cray computer and Macintoshes. The theorists wrote their programs on the Macs and ran them on the Cray. Schlumberger also had e-mail, around the world. We were in touch with the Japanese and the French. That was really the first time that I used e-mail. They were well ahead.

AH : This must have been towards the end of your time there ?

SW : They had it from the beginning. Remember, they were well versed in how to get electronic information.

BBV : Did you go straight from Schlumberger to SUNY Binghamton ?

SW : Yes. At that time I decided that US industrial research activites had started on a down hill. Exxon had cut back on their basic research by about 50%. Seven years earlier they had doubled basically overnight. Then they had said : what would you do if we gave you twice as much money ? Give us a plan by Monday (that was on Friday). In my recollection we worked all that weekend. Within a week we had the doubled size.

AH : How would you account for the change in atmosphere, for the downturn in the mid-1980s ?

SW : A number of things : 1) oil prices had been going up but then they dropped ; 2) MBAs started getting into the business (short-termism ; now the stock price is more important than everything else) and then they looked hard at basic research. With regard to Exxon : it is a mammooth company. The corporate labs were under $50 million. When they doubled it, it got above $50 million. They rounded everything off into hundreds of millions. Anything under $50 million just did not appear in the balance sheet. 3) When the oil price went down there was no longer a sense of crisis. So you do not need any longer to investigate all the alternative forms of energy. Exxon had gone into solar, batteries, computers, a chip company. But Exxon did not really have the management expertise. At about that time Exxon sold all their battery technologies. They licensed them to a Japanese company, one American and one European. I think it was Sony in Japan. Exxon said : you mean you can not make $100 million a year on this ?

AH : It would seem that the price of oil is a really good indicator of the field of solid-state ionics ?

SW : Yes. When Exxon got out, the whole field got out. The federal government cut funding, thinking that if Exxon was not interested, then why should we be.

BBV : So how did the field continue ? Where did the incentive come from ?

SW : Europe was continuing. The Japanese had our technology. There were a few problems with it. They wanted a safe anode ; they could not use pure lithium. ... (?) John Goodenough came up with cobalt oxide. That is almost double the voltage. Sony combined that with an interpolation compound of graphite as the anode ; and came out with what is called (?). The Japanese now have some 90% of the market for all lithium rechargeables. Sony has the primary licence making sublicenses. I think the patent is running out any day now. A number of companies toyed with getting into the business. Eveready two years ago started a plant and found that they could buy the batteries cheaper in Japan than they could build them themselves. The Japanese just have such a long lead time.

AH : Your personal choice of going back to academia. There was no future in industry you said...

SW : There was no future in industry and I wanted to do my own thing. In the mid-1970s 9 out of 10 solid state chemists were in industry. About that time chemistry departments in this country suddenly realized that this is a field. We want these people. Now, 9 out of 10 are back in academia.

AH : What impact did the return of solid state chemists to academia have upon the field ?

SW : In 1987 superconductivity happened. All solid state chemist jumped on board. The result was this symposium. Meeting in New Orleans. The largest room in New Orleans was not big enough.... [too much noise]

BBV : The field suffered from the cold fusion affair ?

SW : Yes and no.... [too much noise] few people got involved in cold fusion

AH : Characterization ?

SW : Computerization has accelerated the getting of measurement results.

Most of these batteries have maybe one or two years. They last as long as the product itself. As far as environmental concerns : they are pretty darn good. [noise]

AH : Hybrid vehicles ?

SW : They are there. The Japanese have them. All that is needed is the political will to factor in the environmental advantages.

BBV : Oxide markets ?

SW : Electrochromic displays.

AH : Optimism when you started ?

SW : Optimism fuelled by end of oil. Now the end of oil is not in sight. But batteries are needed in the small electronic devices. The EV is not everything.

AH : Whom should we talk to : Frank, John Goodenough, Michel Armand.

BBV : Hagenmuller ? Steele ?

SW : Steele is still active.

AH : Fuel cell relevance ?

SW : Fuel cells are much more active in Europe than in the US.

AH : For political reasons ?

SW : No, .. [noise]

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Michael Stanley Whittingham », par Bernadette Bensaude-Vincent et Arne Hessenbruch, 30 octobre 2000 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article132.

—

Entretien avec Michael Stanley Wittingham, par Bernadette Bensaude-Vincent et Arne Hessenbruch, 30 octobre 2000

Lieu : SUNY Binghamton

Support : enregistrement sur cassette

Transcription : Bernadette Bensaude-Vincent et Arne Hessenbruch

Edition en ligne : Sophie Jourdin

STENSGAARD Ivan, 2001-03-08

Sophie Jourdin — 2011-11-11T21:40:34Z

Ivan Stensgaard received a PhD in physics from the University of Aarhus, Denmark, in 1977. He subsequently spent two years at Bell Labs in Murray Hill, New Jersey. From 1979 to 1998 he was Associate Professor at the Institute of Physics and Astronomy of the University of Aarhus. From then on, he has been a Research Professor at the Center for Atomic-Scale Materials Physics (CAMP).

From the 1970s onwards, Stensgaard has investigated surfaces. His primary tool before the advent of the Scanning Tunneling Microscope was ion scattering. His first publication investigated radiation damage in reactor materials, and soon he moved on to investigate other surfaces, such as platinum, tungsten, and silicon. He used both backscattering and channeling of ions to infer the reconstructions of crystal surfaces. Most of his research employed ions in the MeV range, but he has also worked with low and high energies.

Because of his extensive knowledge of surface structures and the tools used to gain knowledge about them, he was in a good position to judge the efficacy of the scanning tunneling microscope when it came upon the scene in the mid-1980s. In collaboration with Flemming Besenbacher and Erik Lægsgaard, he built up a research project (CAMP) that relies extensively upon this new tool.

In our interview, Stensgaard outlines the history of CAMP and describes some of the many uses to which the STM can be put.

IVAN STENGSAARD (IS) : In the early the days, the way I recall it at least, in the STM field, most people worked on semiconductors, where the advantage is that the corrugation revealed by the STM is generally much larger than on metal surfaces. That means that the demands on the equipment are much more modest. So it was easier to enter the field of semiconductors - and of course also the technological implications were thought to be greater in that field. But when we entered the field, which must have been around 1987, there were few groups working on metal surfaces. So although the STM was really recognized as an excellent tool, there had been some delay in really using this as a common tool in studying metal surfaces.

ARNE HESSENBRUCH (AH) : But during the period of '82-'87 you would have known about the STM ?

IS : Yes.

AH : And it was something that you perhaps watched ? You watched the development of this instrumentation and you were critical to see whether it would prove its mettle for you to begin to use it ?

IS : Yes. Well we were not, as I recall it, completely convinced that it would add a lot to the insight into metal surfaces. But as soon as we did enter the field ourselves, placed the instrument in vacuum and seen the results, we were immediately convinced. I'd say from then on it has been fantastic : it has been quite easy to achieve good results with just about any topic of investigation. One saw new phenomena almost regardless of what one studied—new and completely unanticipated phenomena.

AH : So you're saying "we" now, this is presumably the CAMP group. When did that gel ? Was that in '87 ?

IS : Yes, I do mean the CAMP group. But we began collaborating earlier. Historically, I think it was like this : I returned from the US and received this grant for building up an ion scattering facility for studying surfaces [referring to an earlier mention that is not on the tape – this part of the interview will be repeated in the near future]. Some years later, Flemming Besenbacher and I worked together on ion scattering from surfaces. We looked at small molecules, and specialized on the examination of hydrogen on metal surfaces. Then in the 80's, probably around '85 or so, we began to discuss in more detail this question of building a scanning tunneling microscope. Flemming took the initiative in those days and contacted Erik Lægsgaard. Erik was really the key person in building the STM here. And from when he started until he had a table-top version, giving atomic resolution on graphite, lasted only a few months. Of course it took longer to make an instrument fitting into a vacuum system, and so on.

AH : Did you make it locally ?

IS : Yes, everything here has always been homemade.

AH : You've never bought instruments from the outside ?

IS : No. We tend to claim here that our instrument is better than what we can buy. It may sound like boasting, but I think our results help prove the contention. The fact that we can work with extremely rudimentary vibration isolation, proves that we have an highly stable instrument.

AH : So what were the characteristics of the design – the Aarhus design ?

IS : Well, there are two basic ingredients in the construction : one is the scanner tube scanning the tip across the surfaces, and I think that was copied simply from the Binnig and Rohrer design.

AH : The empty cylinder.

IS : Yes. So, the larger problem was how to approach this scanner tube tip to the surface in a controlled way so that you would come close enough to draw a tunnel current without actually colliding. To begin with we had many ideas about some mechanical way of doing it with micrometer screws, but soon we focused upon piezoelectric materials. And I think, again, that it was Erik's idea to make an inchworm. This is a really strange story. We had a very small inchworm made : only a few millimeters in diameter - maybe 10-12 mm long. It worked well and a company called DME in Copenhagen wanted to commercialize our setup. During the discussions and negotiations with them, they found out that the inchworm principle was already known, and what was worse, it was already patented. That was a something of a setback - not for our in-house microscopes but for the efforts to commercialize it. The commercially available inchworms were much bigger and not nearly as elegant as ours. But the principle was patented, and the patent had a few years left before expiration.

AH : Oh, so the patented inchworm was not intended for the STM ?

IS : No. The patent was about 10-15 years old and had been developed for something else. Whether it was developed for one of the topografiners and what they were called, the instruments used prior to STMs, I don't know. We can check the patent.

AH : Well, the topografiner was invented at the National Bureau Standards now NIST and I don't think they would have taken a patent.

IS : We could check it.

AH : So you designed the inchworm in '87, just when you were making your first STM ?

IS : Yes.

AH : But your first STM did not have an inchworm.

IS : Yes, it was a mechanical approach.

AH : Where did you get all the information for making an STM ? Did you look at the publications of Binnig and Rohrer, did you go and see them ? Did you go to the IBM labs ?

IS : No, the way I recall it, we had no personal contact. I think everything was done just using the publications.

AH : And it wasn't particularly difficult ?

IS : Not if you had a clever man like Erik. The short time required to make the first STM also indicates that it was fairly easy. Of course in retrospect many aspects of building an STM seem easy, because we know just how piezos work and what to pay attention to. The game nowadays is really to make them as compact as possible, to make them work even with vibrations in the surroundings and so on.

AH : Yes, you were saying you had very elementary vibration damping. This is another characteristic of this design ?

IS : Yes. Exactly. When you visit other STM labs, you're frequently told that they have to work at night when there is no traffic. They have all kinds of vibration damping, entire vacuum systems hanging in rubber — springs from the ceiling or something like that. They have the microscope damped with magnetic or eddy current damping. And people had to stay quiet and not move about in the room and so on. That remained characteristic until at least ten years ago. By contrast, from the beginning we hung our microscope on three or four springs, or viton-o rings, which are really rubber springs. That's all ; we have no further vibration damping. And people can even touch the UHV chamber without interfering with the tunneling. So that has been the main characteristics of the instrument here : its ability to scan fast and under adverse conditions.

AH : Fast and robust. You have told us about the robustness, could you tell us about the speed ?

IS : Fast scanning is interesting also because it has opened up new opportunities compared to other microscopes. There are more fast-scanning microscopes today but to begin with we scanned faster than most others. We scanned at the rate of one second per image, where many others spent one minute per image. This gives you the opportunity to follow dynamic processes on surfaces by sequentially recording images and then replaying the images at a faster rate - in the form of a movie. That gives you a very vivid impression of what happens on the surface. You might object that a movie yields no new information, but it turns out to be a very good means of attracting attention to dynamic processes. Such phenomena miss easily when just examining static pictures. The eye is well-suited to spotting change, so that even when there is a lot to keep track of, say 20 to 40 entities on a surface, your eye will immediately pick it up a movement of any one entity. So this question of scanning fast and taking movies, is not just a question of presenting results in a nice way, it also gives you a better insight into what is going on.

AH : But you weren't capable of making movies off the bat in 1987 were you ? How long did you need to scan in 1987, roughly ?

IS : I don't recall it really. I think we could record images in seconds, but the problem was probably rather that saving and replaying images requires a lot of data storage, and in those days the hard disks were not very big. It was slow process simply to get an image from the hard disk onto the screen.

AH : Was your ability to scan quickly a desideratum in 1987 ?

IS : Early on we probably didn't focus on the time you spent recording. It probably didn't matter whether it was 1 or 20 seconds or so. But I see now [checking on the computer] that taking movies and things like that, must have started in the late 80's. Because we have publications at least from '91 where we have included, not movies because that wasn't possible, but results based on these techniques.

AH : And what sort of thing did you image ? Metal surfaces with adsorbed atoms ?

IS : Yes, of course the standard sample in those days (as it still is for testing an STM in air) was graphite. Of course we used that as the test that our STM was working properly. Having done that we moved rather swiftly in the surface science direction again. We examined some gold-plated plastics, simply to investigate the micro-roughness. The purpose was to test the coating of large mirrors of an x-ray telescope to be used in a satellite. We also investigated some biological samples. But we were really implementing the STM in a vacuum.

AH : You say you were immediately convinced, when you saw the images, that this was a useful tool. It was seeing the images that convinced you almost instantly ?

IS : Yes

AH : Why ? There are many problems with the imaging process of course, with the noise and the interpreting just what the tunneling current actually is referring to. On metals this is less of a problem than semiconductors. Was that a help to you ?

IS : Yes, to some extent it was. Let me just mention the first system we examined, to maybe make references to that. Once we got the microscope into a vacuum we continued our work on small molecules on a metal surface. The first system we examined was one I had investigated earlier using ion scattering. We had absorbed oxygen on a particular copper surface, a copper (110) surface. And it was known what happened to the oxygen, how the surface reconstructed. What was not known was how the process took place, and that was revealed immediately almost with the STM, because we could look upon the surface while the reconstruction took place, and we could make a movie and watch the process.

AH : That must have been exciting.

IS : Yes, and then I was at least totally convinced at that time that here was an amazing tool.

AH : So the problems that there might be with interpretation were really secondary to you, you said that even with all those problems, "it's still exactly what I need ?"

IS : Yes, you said that in the case of semiconductors it is more difficult to relate the STM-produced image to the surface corrugation. That is correct of course, but you could say that we had a similar problem on our hands with oxygen on a copper surface : were we imaging the copper or the oxygen ? And it turned out that we were usually imaging the copper. This posed the question : why not the oxygen ? And why is it sometimes just the other way around, that we image the oxygen and not the copper. So scanning on metals was not completely free of problems, at least not when you have the adsorbates on them. But if you image one clean surface with only one element present, then the interpretation is straightforward.

AH : What I'm trying to understand is that when you use a completely new tool, you cannot know whether it works.

IS : I think the problems of instrumentation were so insignificant compared to the insight gained, that we were absolutely convinced of the amazing utility of the instrument. That's the way I recall it, really. There was a trend in those days—probably through the 90's—from static to dynamic problems. Other methods, such as low-energy electron diffraction, high-energy ion scattering, x-ray diffraction, are better suited for static problems. You can induce a reaction on the surface, and then you can take your tool and find out how the surface has changed. But with the STM you had a tool with which to see the transformation from one state to the next. Later on, you could even follow single atoms moving on the surface. That was really amazing, and almost impossible with other techniques. Field ion microscopy has been able to do it in some cases.

AH : Before the STM, you were using tools like ion-scattering, but it was not the tool that defined your research. Now it looks like the STM defines the group.

IS : I don't really think that's correct. No matter what you investigate,
you have to take both things into account. You have to find an interesting problem amenable to investigation with your background, its relevance and so on. Then you have to consider the available techniques. You have to find a topic amenable to the techniques available to you. I think that also describes what we did with the STM. It is a question of resources. The microscope does not define the activities ; a natural development has rather taken place. I mentioned before that we first investigated small molecules on surfaces, and we have continued to do that. Our research has now diversified but it is still to a large extent coupled to chemical reactions and the like. We have studied surfaces in greater detail – also clean surfaces although clean surfaces are less interesting for STM research because one can get the information by other means. But when you grow metal on metal for example, what happens ? How do these atoms of one metal, influence the properties of a surface of another metal. How does the surface restructure ? And, to come back to my initial point, how do the chemical properties change ? What happens if we now adsorb oxygen, what happens if we carry out a chemical reaction, let's say oxygen and CO reacting on the surface. In all these cases there has been a connection to the initial questions.

AH : Have you expanded the number of chemical reactions you worked with ?

IS : Over the years we have worked with a number of chemical reactions, but in the last few years we have focused more on catalysis. We have for many years collaborated with Haldor Topsøe AS, one of the leading companies in the catalytic world. We have collaborated on a number of issues, in once case a new catalyst was developed on the basis of our results. We proved scientifically that the catalytic conversion works. Whether that catalyst in the end will be commercially available now depends on other considerations, such as the cost of producing a catalyst, its lifetime and so on.

AH : But you discovered new catalysts with the STM, is that what you're saying ?

IS : We discovered a system that turned out to have possibilities in catalysis. We could talk in more detail about that, but it's a story in itself.

AH : Okay. What can you do now with the STM that you couldn't do in 1990 ?

IS : There has been constant improvement in speed : the rate at which you record and replay images. And new designs have made the microscope usable under new conditions. It now works over a large range of temperatures and pressures. To begin with experiments could only be carried out at room temperature, whereas we now can work from 20K or so and up to maybe 150ºC (500K). This increase in the temperature range is important for the investigation of dynamic processes because the rate at which they proceed is governed by temperature. And if you wish to study a certain reaction or a certain diffusion property, you have to have the events happen at a rate you can follow. That means that you shouldn't have too many events per second, preferably no more than one event every few seconds. And you can normally do that by adjusting the temperature.
We can also work at many different pressures now. Early on we had to work either at atmospheric (ambient) pressure or else in a very high vacuum. We have recently become able to work in the full range of pressures from ultra high vacuum to atmospheric pressures and could in principle make the system work at even higher pressures, if it weren't for some windows unable to withstand atmospheric pressure. And that again is advantageous for catalytic research, since all catalytic processes run at high pressure and high temperature. In the surface science community there has always been arguments that their field would help improve catalysts and understand catalytic reactions. That is to some extent true, but there has also been a lingering skepticism whether the processes taking place at atmospheric pressure remain the processes governing chemical reactions while raising the pressure from 10-10 Torr to atmospheric pressure. So that has been an important result : that at least in the one case that we have done so far, the system behaves identically at high pressure and in an ultrahigh vacuum, it's exactly the same things that govern the processes.

AH : What do you have to change in the STM to make it amenable to the range of pressure and temperature ?

IS : Actually not much was changed ; it's basically the same setup. The only major change is that it is located in a minor vessel ; it's in a minor chamber with a smaller volume, which is the volume that is brought up to high pressure. The suspension system has changed also, but the basic STM is the same. The suspension system is still based on a few springs, and looks differently, but the system as such is really the same. And of course minor things like gold coating surfaces to avoid reactions of those, but the heart of the microscope is completely unchanged.

AH : Why didn't you do these things 10 years ago ?

IS : I think in the field of ultrahigh vacuum there have been so many extremely interesting topics that there simply hasn't been the capacity to look in other directions. We should bear in mind that when CAMP was established in '93, much more funding became available than before. And the group grew much bigger. And although to begin with we also focused very much on processes at low to high vacuum, then at least during the second period of CAMP (from 1998 onwards) we have been able to diversify. High pressure is simply a natural development out of our original research. When I refer to new fields, I mean investigating organic molecules and other biology-related issues. So our research program has really developed quite naturally.

AH : So you started CAMP in 1993 - you, Besenbacher and Lægsgaard.

IS : The history of CAMP is more complicated – it is related to changes in the funding of Danish research. A large insurance company, Statens Livsforsikringsanstalt, was sold and a fund, Grundforskningsfonden, was set up with the money from there : 1 or 2 billion Danish kroners. Interest from the capital there was to be spent on basic research in all fields. In those days the interest rate was high and leading to a fair amount of interest each year. They requested and received many proposals for research centers. I don't recall exactly but it was a very large number. And in the end they funded 23 centers in all kinds of science : medicine, humanities – Søren Kierkegaard. We got a center too, a collaboration between our group here at Aarhus and Jens Nørskov's group at the Danish Technical University at Lyngby. The group there focused mainly on theory, and Nørskov was the director of the center, as he still is technically. The reason the two groups joined in this project was that we had had a prior collaboration within another program called FTU, research for technological development. In addition Flemming had collaborated with Jens Nørskov on another topic. So we knew each other. A proposal was made based on the joint resources of these two groups and after some external referring procedures it was eventually funded.

AH : And the project was focused on the STM ?

IS : I think the scope was broader : the interaction between small molecules and surfaces, to some extent chemical reactions. Our tool of investigation was STM but the center as such was not a STM center, it was a center doing research in a specific field. And our tool of research was the STM.

AH : You mentioned that you had contacts with Topsøe and other companies. Have you had contact with chemists, people in chemistry departments ?

IS : We have, but not much.

AH : Are they not interested in this ?

IS : I think they are in many cases, but we work in surface physics, as it is called in Danish. The English term, "surface science", is more neutral. Of course what we do is to some extent surface chemistry. But our background is just physics. You could say that a center like this might just as well have been placed at an institute of chemistry. It just so happens that we had this collaboration, and that we had not had the opportunity to interact much with chemists.

AH : So it's not the barriers between physics and chemistry that are particularly high, it just hasn't happened ?

IS : It just hasn't happened. It might have worked out differently, had we had a common institute instead of a separate physics and chemistry institute. Some of the activities going on here might as well have been placed in the institute of chemistry and vice versa. Nowadays it's not that natural to have this division into two institutes.

AH : How far is it from here to chemistry ?

IS : It's just across the parking lot, 100 meters. We're even connected underground to them, although it takes a specific key.

AH : But you don't go to each other's seminars ?

IS : Very infrequently.

AH : This does seem surprising and in need of an explanation. No ?

IS : I think much of what we're doing is of interest to chemistry as such, but our institute is comparatively small. Chemistry and physics are amazingly broad fields and our small institute is only able to cover certain areas. It has just so happened that we work in a field without a natural counterpart in the institute of chemistry. There are no ill feelings on the other side of the parking lot ; it's not based on that.

AH : And what about chemists in general out there in the world ? Do you get resonances ? Where do you publish, for instance ?

IS : We publish in papers with as high an impact as possible. We have published very large number of Physical Review Letters during the period of CAMP, on very few occasions in Nature and Science also. But that is not that easy, and sometimes you feel it is more difficult being European than if you had been American, but that's another story. We publish of course also in other journals ; some material will go to Surface Science. Surface Science does not have that high an impact, but it is obviously a very natural journal for people working in surface science. In my opinion the quality is rather mixed, but these are the main journals that we choose. We do not publish much in European journals, or journals that are particularly European such as European Journal of Physics and European Physics Letters.

AH : For any particular reason ?

IS : Simply because impact and visibility are low.

AH : When you say that in Physical Review Letters the visibility is high, is it not limited to the physics community ? Isn't your work broader ?

IS : It's probably correct, but we have colleagues in other places working in chemistry departments. And some of them will also publish in Physical Review Letters. I think it is recognized as some natural place for good work, also. But we have also published in Chemical Physics Letters, there are also a number of publications there, but they're not quite as prestigious as Physical Review Letters.

AH : Are you under pressure to produce results of commercial interest and if so, does this conflict with your own interest in pure science ?

IS : I don't' think so. I don't think we are under much pressure in CAMP to produce results of direct relevance to industry. I do think that we in CAMP all see an extra benefit or satisfaction in producing something of relevance to the "real world” and not just to pure science.

AH : So when you get around to renewing CAMP for another five years, the grant-giving bodies will not look to commercial applications ?

IS : It won't come to that. The funding will stop after ten years. It's the general policy that centers such as ours may reapply only once, so that they run for a maximum of two periods. After two periods, they ought to find alternative funding and in some way become a more integral part of the institute. What will happen in two to two and a half years from now, I don't know.

AH : You are not worried ?

IS : Not terribly, I think some kind of funding will come. I think that the government has set aside some funding for integrating centers into their host institutions.

AH : The reason I'm asking these things, is that Jens E. T. Andersen at the DTU was telling me about tremendous pressures. The DTU has now a patent office, and renewal of academic contracts is subject to results in terms of patents rather than scientific publications.

IS : The emphasis on patents has definitely increased here also, but in my opinion it has not yet become a pressure. There is a greater emphasis on it, and some of that emphasis originates from the government. A new law was introduced in Denmark. Up until maybe a year ago, you had the rights to exploit your own inventions, even as an employee and civil servant. That has now changed so that when you develop anything patentable or otherwise exploitable, you have to first contact the university. Your invention will be assessed. The university decides whether it wants to patent your invention and exploit it. If it declines, then you are free to do it yourself. So you could say that maybe the timing is a little bit strange, because on the one hand you remove some carrots from the researcher and on the other hand you apply the stick to encourage work resulting in patents. I think the general political perspective is that a fair amount of knowledge of interest to industries is generated at the universities, but no good forum for the transferal of that knowledge exists. Maybe the thinking was that having the knowledge documented in patents would facilitate the transferal.

AH : Is it possible to pinpoint advances made in the field of catalysis over the last ten years related to the possibilities of the STM ?

IS : I think this story about developing a catalyst from scratch based on pure research is rare, almost unique. There are no more than one or two other examples. Normally catalysis has been a highly empirical field. Developments have mostly been trial and error - of course guided by different kinds of knowledge. But in the end it came down to trying something, modifying it, changing the stoichiometry or the ratios, optimizing and so on. The understanding of the catalyst emerged gradually out of this process. By contrast, ours is a clear case of going directly from scientific insight into the working of a catalyst to its development.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Ivan Stensgaard », par Arne Hessenbruch, 8 mars 2001 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article131.

—

Entretien avec Ivan Stensgaard, par Arne Hessenbruch, 8 mars 2001

Lieu : CAMP Aarhus : The Scanning Tunneling Microscopy Group, Aarhus University, Denmark.

Support : enregistrement non précisé

Transcription : Arne Hessenbruch

Edition en ligne : Sophie Jourdin

WHITESIDES George, 2002-01-28

Sophie Jourdin — 2011-11-10T17:04:18Z

George Whitesides

Mallinckrodt Professor of Chemistry, Harvard University

George Whitesides' group in Harvard's Department of Chemistry and Chemical Biology works on many topics : Biomimetics, Biosurface Chemistry, Complexity / Emergence, Materials Science, MEMS, Microfluidics, Micro- / Nanofabrication, Photonics, Polyvalency, Self-Assembly, Surface Science, and Tools for Biophysics and Biology.

BERNADETTE BENSAUDE-VINCENT (BBV) : Do you see any changes that you would like to mention in your field over the past 20 years.

GEORGE WHITESIDES (GW) : 20 years ago there was not any materials science in my field, which is organic chemistry. People made polymers, but they didn't really think in terms of materials, and all of this stuff of electronics and optics and unusual functions and biocompatibility and things like that were - some of them were not even concepts and some were not considered materials science because nobody thought about materials science. Materials Science in the last 20 years has come from something that was done with airplanes to be a real part of chemistry - that is really interesting I think.

BBV : Have chemists been involved from the very beginning or did they jump on the bandwagon later ?

GW : Well, no, I guess my sense would be that chemists were involved from the very beginning in the sense that they made materials. Because after all most materials in the world are actually made by chemists.

We have metals, but ceramics often come out of chemical backgrounds, and all of polymers come out of chemistry but they were thought of as being fibers or coatings or something else and the idea of thinking about them as materials - it's a re-naming but it was helpful for the field to think about how to organize itself intellectually among other things, and then what was a little bit of a change was that at the beginning the financial support was primarily from the DoD for its own purposes which was primarily metals and ceramics for airplanes and armor and hot-sections in engines and things of this kind. It is recently that this has changed. Chemistry and chemical thinking is an increasingly important part of materials science which means there is now some money which means it is worth the effort for chemists to think about that as a community they might want to be involved in. But chemistry has gone from an area dominated by the notion of making natural products to an area in which probably the two interesting areas are bio - and most people would say this is the biggest deal in chemistry at this point - and materials. Synthesis becomes an accessory technology which enables one to make these materials that you might want for either biological applications or materials applications.

BBV : And what about the electronic applications for chemistry ? Is there any future in that ? You have been working a lot in that.

GW : I think that is going to be one of the big deals in electronics. The argument there is that there is a certain specific way of thinking about electronics which is silicon and semi-conductors and that works fine. But my prediction is that there is going to be a new class of devices that is going to be perhaps slower but much cheaper, so that the ratio of benefit to cost goes up but primarily because the denominator goes down rather than because the numerator goes up. The notion with these and with optical photonics systems and with organic LEDs is low cost, ease of fabrication, the ability to integrate a bunch of different kinds of functions in the same thing whereas if it is all polymers you don't have to worry about compatibility between the 500-degree processing step and an ion-beam step or whatever it might be. That is organic chemistry. There are two components : one is the laser and the second is the coating. Optical recording now dominates a certain segment of that industry and it is entirely because what chemistry has made possible. CDs are the same thing. These are optical CDs but the older CDs were the same thing. I think chemistry has found opportunities in thinking about the collective properties of matter as opposed to thinking of the properties of individual molecules - it is a little bit of a revelation but it opens all kinds of doors.

ARNE HESENBRUCH (AH) : Shall we try to get at the history of the last 20 years ? What in your opinion has been the most important changes in the last 20 years ? You have been in the field for that long.

GW : It is more like 20 years. I really began to think seriously about materials science when I came to Harvard. At MIT I was primarily concerned with inorganic chemistry and catalysis. So I came here and became involved, but what made a big difference from our point of view was the development of self-assembling monolayers. Self-assembling monolayers were particularly interesting - and I think actually very interesting for many chemists because they made the point that you could design molecules and thereby control macroscopic properties. You make a kind of molecule and a drop of water beads on the surface and you make another kind of molecule and a drop of water spreads on the surface. So that idea of being able to engineer macroscopic properties based on molecular-scale synthesis was a pretty interesting idea and fairly new at the time.

AH : When ?

GW : That happened ... the first identification of SAMs per se was early '80s and forget exactly when, whether it was '83 or '84, and then the real understanding that you could put them together was done by Ralph Nuzzo - he did the first identification of these as structurally ordered systems. And then we did a lot of the work that connected them with materials ; we were actually working on it at the same time and we started publishing papers in the period of 88-89. So it's really only been about a decade. Now polymers have been around for a long time and we have been working on polymer surface chemistry in the late '70s. But we didn't really call it materials, we called it polymers and it was very hard to do because you couldn't really get a grip on it. You'd start with a piece of polyethylene and we used to put in chromic acid solution and that burned the surface and introduced a bunch of carboxylic acid groups which we could use for various purposes but it was very hard to characterize these things and the surfaces were pitted as a consequence, so we never really had a good grip on the density of surface functionality, the roughness of the surface or any of those things.

AH : What did you do to characterize ?

GW : We used XPS and we developed a whole series of techniques like contact-angle titration - which is an idiot idea but the notion that you make the drop more and more basic and you see if it spreads more and that tells you if there is an ionizable group. This is the kind of thing a chemist thinks of first but not a materials scientist with a metallurgy background because they don't know that carboxylic acid groups exist. Self-assembled monolayers still are, I think, the best of all the materials systems - and this is almost independent of field : ceramic, metal or anything else. If you want something which you can control in exquisite detail it is this. If you want to understand how you go from atomic and molecular level structure to macroscopic property within the range of things that it can do, nothing beats SAMs.

AH : And you knew this in the early '80s already ?

GW : No, what you knew in the early '80s was that there were ordered structures. Strictly speaking, well before that, the electrochemical guys had known that organic silver compounds adsorbed on metal electrodes. So that was well understood and they'd been used empirically for a bunch of things having to do with adhesion so there was, as in everything in science if you look backwards you find, lots of precursor phenomena. And then Ralph Nuzzo and a guy named Dave O'Lara(?), who were at Bell Labs at that point got involved in this and I think their initial interest (I actually never asked Ralph why he got into but I think it was partially because they needed ways of doing coatings of metals and - anyway they were good spectroscopists - and Ralph looked at these structures and recognized from the infrared spectra that they were highly ordered so that the idea was that it was not just going on the surface as scrambled eggs but that it was crystalline. And then we did physical organic chemistry. We took that platform starting in the early '80s and put functional groups on the terminal positions so that after the thyols formed mono-layers, you just saw a monolayer of the terminal functional group, and the hypothesis was that this would control wetting. And it did. Then the process from there was that in the early '90s we had the idea that one might be able to make patterns with these self-assembled monolayers and we had several approaches to this - the earliest one was actually an experiment I did with my own two hands - which was to take a piece of a gold dish (gold on silicon), put on a hydrophilic thyol so that water spread on it. We took a razor blade and put some scratches on it and redipped it in a hydrophobic thyol, so one ended up with scratches about a 100 microns wide they were hydrophobic in this sea of stuff that was hydrophilic then put drops of water on it and the interesting fact was that the water would not cross the lines. Had the characterization changed by then ? By that point the characterization was in pretty good shape, the combination of reflection infra-red and XPS did a lot of it. I forgot when people first saw STM images but it was ...

AH : The Nobel Prize, DI began selling in 1989.

GW : Right, and they were hard to see at the beginning because they require the tip to be far away, so it was not the first thing that was done, but people began to see crystalline rays (?). We had done a fair amount of work in the mid-80s on transmission electron crystallography. We'd taken awfully thin gold foils and run electron beams through them and seen diffraction from the organic mono-layers I think those were the first real structural indicators other than the infra-red spectras that they were united. So anyway, we started the business of stamping. I think the first paper was 92, 93, something like that. That became the basis for micro-contact printing and then for soft lithography and that brought an entire new community into it who are now on the other side of the electronic guys who are looking for new ways of getting around diffraction limits and looking for a different economics. And it has not yet made an enormous difference in microelectronics although it may well in this next stage of all-organic electronics. But soft lithography was probably the most important thing in moving the micro-fluidics community away from silicon to polymers. Now, in the long run whether the microfluidic systems we use for genomics are based on polystyrene or PDMS or what, remains to be seen - it will be whatever is cheapest. The basic idea that you did not need silicon, and in fact didn't want silicon or glass for microfluidic systems : all you wanted was that it was cheap, transparent, and easy to work with, and that is polymers. And now you put those kinds of things together with the idea of conducting or photoactive polymers and ever-increasing resolution of these printing and stamping techniques and the economics which are just phenomenally better than traditional methods when you don't need the kind of precision that the photolithographic methods bring, and you find all of a sudden that there is a new approach to making micro- and nano-structures. It is an interesting evolution. What about the biological ? Well, the biological has also been a big deal and the issue there is interesting on a couple of levels : one of them is that biology since the 60s, which is when practical sequencing first really started, has been profoundly reductionist. The whole notion is that you get the gene sequence and everything comes from that by some unknown process. That is not true of course. People now understand that it is not clear what one does with the information of the genome : which will be useful, how you combine that with proteomics, which will be useful in cell biology, which will be useful in knock-outs, which will be useful in the ... and so on. These are all interesting questions that we don't know the answers to. Biology is pretty complicated. In developing biology, as in any field, you need new tools. And new tools are microfluidic devices for genomics, new ways of manipulating cells which have to be in fluids.

AH : Could you put some dates on those new tools ?

GW : They were done in silicon in, maybe, the 70s. The guy who did this was named Andreas Manz who is now at Imperial College in London. At that time he was at Sandor ... Ciba-Geigy ... I forget.

AH : Basel, anyway.

GW : He was in Basel - I think he was in Ciba-Geigy. Of course it was an internal project so none of it was published at that point. He had two post-docs, one named Mike Ramsay, the other named Jed Harrison who were both migrant ; Mike to Oak Ridge and Jed to Edmonton, Alberta, where they started to make microfluidic systems. And that is really where microfluidics started. Other people, Roger Howe, did have an important contribution. In fact, Andreas made some of his first systems out of PDMS - unpublished stuff - he recognized the virtues of this nice elastomeric polymer even back then. But he couldn't publish it and I think the company wasn't very interested, so it sort of languished for a period of time and then this genomics came along and there was this need to find better ways to crank out data large quantities of data. Then there was a real need for microfluidic systems that were parallel with which you could generate lots of information. That was an enthusiasm that began to build in the 80s, late 80s, and people had been making devices using silicon microfab technology and it was clear it was just too cumbersome - it took too long ; they didn't have any control over the surfaces and then we among others made the point that if you use self-assembled monolayers you could get exquisite control over the interface between the materials world and the biological world. We have done a lot of this in collaboration with a guy named Don Ingber here at the medical school. This is in the late 80s, actually the most interesting part of this began came fairly rapidly after we began contact printing or that is when you saw some really neat things. So this was, I would say, 1994 or 1993, I forget when the research was done, but in that period of time. So that was one theme in this : that you could make the inorganic materials of gold films, or whatever they were supporting, you could make them compatible with biology using self-assembled mono-layers. But at the same time other people had begun to tinker with different ways of making micro-fluidic systems. I don't know that I can say what all the threads were, but certainly one of the threads was a discovery that we made that instead of using photolithography and clean rooms and all the rest of that you could do the design, print them out on a printer at scales that were perfectly useful for this kind of work and then you could design quite sophisticated systems. Other people were designing quite sophisticated systems at the same time using conventional lithographic methods. We made a point that you could do it very easily using these soft lithographic methods and that provided quite a stimulus, not to the generation of the final systems necessarily, but to the process of invention because lots of people used those rapid prototypic methods for trying new kinds of devices. This has also been an area where the industrial groups, particularly start-ups, have had a very big influence on things. Probably the first company that was a serious effort in this was Caliper. Caliper was a Larry Box(?) special and it's doing okay as a company. It is focused now on micro-fluidic systems for high-throughput screening for the pharmaceutical industry - it was one of the first to do that. There was a fellow named Lee Hood(?) who was named Hunkerpillar(?) - I think a bioengineer - developed a series of devices for sequencing of DNA and proteins which were commercialized by a company called Applied Biosystems which was one of the early darlings of the biotechnology industry, and those were not intentionally micro-fabricated - they just turned out so because you needed lot of them and small. They ended up making nice small systems - not very small but small systems. And then there was another thread to this which was the whole notion of high-throughput screening which had a number of connections that tied together. One of them was just the need in industry to do lots and lots of experiments in parallel the acceptance of 96 ??? plate formats which was the first of these. And then the idea of parallel synthesis, combinatorial synthesis, parallel synthesis which came partly from Bruce Merrifield – he got the Nobel Prize for solid state synthesis of peptides - and partly from a bunch of people including, at least I give credit to, a man named Mario Geysen as being the first person to do combinatorial synthesis, parallel synthesis, on pins. They weren't terribly small but he had that notion. Out of that came the whole idea of very large-scale parallelism in synthesis which had a requirement for making things small which led to new requirements for small systems. It is an interesting area, the bio-area, both because it has had an important impact on genomics and drug discovery and also because it provides a bridge between these two areas of biology and materials science. This is where they come into contact.

AH : You have put together elements of techniques and ideas. I presume that funding structures have had impact on the history also ?

GW : Yes. Most of the funding for materials science in the US has come from DARPA. DARPA also got interested in the biological stuff in the mid-80s, maybe a little bit later than that. Their driving concern was with biological weapons - biological defense. The United States does not have an offensive program but it was clear that there was a potential problem there and then in the late 80s there was a Russian defector and then in the early 90s another, Ken Alabakoff(?), who spent a lot of time talking about what the Russian program had done. It was clear that the Russians had had a very very large program in biological weapons and it really bothered people. So there was a growing effort to think about how to build sensors and analytical systems, how does one put together a defensive program in this. That ended up being an important bridge between the materials community (which was the DARPA community) and the biological world. One of the things that DARPA does very well as that when it decides to go into an area to put in enough money for a sufficient period of time that it is actually worth people's effort to go and learn how to do that because they can run programs that make a difference. They get, I think, a lot of credit for building the biological component for micro-fluidics and then of course a very large fraction of soft lithography was funded by DARPA and their interest in that was largely new methods of circumventing the natural limits in photolithography for very high-density electronics. It has not in fact changed that - I mean these techniques are not used for high density electronics - but I think they are going to be the basis for low density low-cost electronics, the organic stuff. I think this whole area is one that DARPA gets the major credit for. Had DARPA not put the money in it would not have happened or it wouldn't have happened the way that it has. NIH has been very resistant to doing anything in this because NIH only does science, it doesn't develop tools. I think it is an enormous strategic mistake on their part but they have basically been parasitic on activities funded by other parts of the government or funded in industry, in start-ups, for the tools that they use and the biological community uses. Then of course there has been some work in the NSF and DoE but not big programs.

BBV : So do you see the contribution of your group as providing new tools for materials science ?

GW : The biggest contribution is to make the connection between physical organic chemistry and materials science - that is the idea that you can design molecules, or design matter by synthesis at the molecular level, and thereby influence macroscopic materials properties. The second is to put together a series of tools, particularly self-assembled monolayers and soft lithography and illustrations of the uses of these in microfluidics and particularly in bio which have caught people's attention. This is an interesting strategic decision : we decided at the very beginning that we were going to proselytize for the area, so we made a really big effort to have anyone who was interested. We invited them to the lab and tried to teach them everything that we knew. It is one of those interesting philosophical issues in science : when you have something that is new and interesting you either try to hold it close or you try to spread it as widely as possible, and we really made a big effort to spread it because I thought it was going to be very useful. Quite a large number of people would come for two-three days or a week over the course of time and then these people have gone out and started programs and then of course the graduate students come and learn how to do these things and they go off and start programs. So, the dissemination has been quite rapid, primarily because it is very easy to do. That is another philosophical issue : I like to do research that is really easy to do because other people can do it. If you want to have an impact on the community at large it is easier if you keep the bar low to people getting into the area rather than making the bar high. So, minimal capital investment.

BBV : And how much time do students need when they come to be trained in the techniques of self-assembly ?

GW : Two days.

BBV : Two days ? It is kitchen experiment !

GW : It is kitchen experiment. You take some wafer and you dip it and you pull down the stamp(?). That is not complicated. And stamping is literally no more difficult than putting a rubber solution on a rubber stamp and putting it down by hand and pulling it off and it's done. It obviously gets to be more complicated than that but you've got the basics at that point. There is a little issue there, which is : you say this is trivial, and in a sense it is trivial, but it is trivial because some very smart students spent a lot of time understanding these systems and figuring out which ones worked so well that they could not be made to fail. That is the criterion. The simplicity at the end is the result of a lot of hard thought along the way not just by us but by the whole group of people who was interested in self-assembly and related areas. The second thing is the tools and the third is the notion of self-assembly. Generally, organic chemistry has been largely concerned with making molecules by putting together covalent bonds and self-assembly is how you make materials through non-covalent interactions. So it is a switch in emphasis. We are certainly not the only ones who've worked on self-assembly but we have probably been more emphatic in making the case that it is a technique that can be used in materials science than other people who have been concerned with making structures in solution or how proteins fold or other things of that kind.

BBV : It is striking that other groups doing self-assembly have had biomimetic inspiration whereas in your group it was not a leading ...

GW : Well, we do biomimetic stuff. If you talk to some of the people around, Mila Boncheva, who I think with a little luck you will meet, has made this wonderful device. You basically have a string of something and you put this in suspension, it folds up and one part of it becomes a high-frequency ring oscillator and the other part becomes a shift register. It's quite intentionally patterned on the idea of protein folding so it is biomimetic in that sense. But the major issue is the generic problem, which is to understand molecular recognition in biology because if you want a single process in biology that is important it is the recognition of a ligand by an enzyme-active site, or whatever - that is the reductionist end of the working part of biology. There has been lots of work on that - and then self-assembly came in, as a result of two things : one was to try to model biological recognition and interestingly this has never really worked. There is an enormous amount of molecular recognition that has gone on in methylene chloride solution, but of course water doesn't go on in methylene chloride, so in organic solvents a lot of good work has gone on which has led to systems that are pretty efficient in molecular recognition. But noone has come really close to duplicating the efficiency of biological molecular recognition in water because we have to learn how to handle the hydrophobic effect and we don't know how to do that yet. So that is one theme. The second theme was the stuff that Jean-Marie Lehn, Cram, and Pedersen from DuPont got the Nobel Prize for, which was just understanding the crown ethers of the right size would wrap themselves around a sodium ion. That was not really molecular recognition, but it was self-assembly ... well ... Jean-Marie calls this supermolecular chemistry, so it is chemistry beyond molecules. It was an important first step in making the case that it isn't just making covalent bonds that's important but these events in which things recognize one another and get together without making covalent bonds are also important. So these two things came together in self-assembly. One virtue of this place is that students are very good and very independent, and the groups are big so that we can have biologists, chemical engineers, physicists, organic synthetic chemists, and materials scientists. That makes it much easier to think about putting biology and materials science together, or organic synthesis and microelectronics ; you know x and y, where x and y come from very different directions. It is a lot harder to do that in smaller groups.

AH : Do you think there is any purpose in doing history of science ?

GW : Oh yes. Understanding what this funny activity is of creation. Hang on, I'll be right back - this last question is important ...

History of science. If you look at history of science you can see where interesting things came from. Now, the question is, can one learn something from the activity, and I think the answer is yes. The question that comes up in this area is, is it sufficient just to put different research areas together in order for good things to happen, or do you have to have a brilliant conception ? No, I don't think in this case one needed a brilliant conception. It was putting things together - with some luck - self-assembled monolayers were an experimental observation, they were not a theoretical prediction confirmed by experiment. It still amazes me that soft lithography works as well as it did. In any event, one can ask where ideas came from, and from that point of view the history of science is an enormous contribution. The question which is never clear is, to what extent are there lessons that you can learn from one success or one failure that you can carry over into other areas ; and in particular : what is the mechanism by which whatever lessons you learn are transmitted to the people who are the ones who in principle would benefit most, who are the people just beginning their careers, but who are in general the least interested in listening because they are eager to get on with it. They have their own usually not very well-formed theories as to how to do things and it is based more on their own particular instinct. A lot of their instinct, in fact, turns out to be replication of the experience in graduate school. That is probably the least perceptible but longest lasting lesson of the graduate career, because people tend to do their research the way they learnt to do research which was the way their research director did research. That stylistic issue comes across. In a sense, one of the great sadnesses of science is to look at people at the age of 50 and realize they have spent their entire career working on their theses with minor variations on themes. It is not a happy outcome. What they learnt was, don't step too far out of this particular circle ; just sit there and fret away with this stuff. So, I think there is enormous opportunity for the history of science to be useful, and even predictive if one could figure out what to do with the information. As we made a big effort to teach people how to use soft lithography, I think all scientific enterprises, particularly with fields that move rapidly, which is what science does : it is always looking forward and almost never backward, one needs some clever way of figuring out what the short-form lessons are from what you do, what you have learnt. But I don't think the user will study things. A book which I think is a very interesting example of history of technology which has made a big difference is The Innovator's Dilemma. Have you read The Innovator's Dilemma ?

AH : I haven't read it.

GW : You should read The Innovator's Dilemma. It is by a guy named Christensen, who is somewhere here at Harvard or MIT. It's history - history meaning business school history, but it's close enough - and the question is : look around and you find big technology changes, and how do companies react to that ? And the answer is in general : incredibly badly. And this book has really caused people to think about how they run their technology programs (in companies) because the failures are so stark that as a big company person it really does not give you a lot of confidence that whatever you are doing is going to survive. One of the lessons in this is this : the mantra in the United States is listen to the voice of the customer ; the customer will tell you what you do. And one of Christiansen's lessons, loosely re-phrased is that if the field is technologically changing the thing that will kill you is to listen to the voice of the customer, because the customer never wants change - the customer has people trained in some technique, they've got capital investment and so on and so forth : the last thing in the world they want is change. So you listen to your very conservative customer and some little company who wants to take your customer away or create new customers, is going to zip around on the side. Now the interesting issue for you all is, you are doing all this stuff and my guess is that websites may be interesting for other historians of science but I don't think it will make any difference to scientists. So what you need is a nice short book which summarizes all of this in terms of lessons. What are the lessons that you can draw from this ? What has succeeded in what circumstances and why ? And what are the risks, and what has failed ? People hate failing. So look around and what are the failures, and what did they not do that prevented them from competing effectively ? I think if you think about history of science rather as the business school thinks about its analyses in terms of something that's branded in terms of suggestions for the next generation or the current generation of operators rather than sort of a passive observation it might have more impact. I don't know whether you care whether it has more impact or not.

BBV : We care about our impact.

AH : I care a lot.

BBV : Thank you very much !

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec George Whitesides », par Bernadette Bensaude-Vincent et Arne Hessenbruch, 28 janvier 2002 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article130.
—

Entretien avec George Whiteside, par Bernadette Bensaude-Vincent et Arne Hessenbruch, 28 janvier 2002 : on history of organic chemistry and materials research and on the purpose of history of science.

Lieu : Prof. Whitesides' office at Harvard University

Support : enregistrement sur cassette

Transcription : Bernadette Bensaude-Vincent et Arne Heseenbruch

Edition en ligne : Sophie Jourdin

WHELAN Michael, 2002-12-12

Sophie Jourdin — 2011-11-10T15:51:51Z

Professor Michael Whelan.

BERNADETTE BENSAUDE-VINCENT (BBV) : Could you tell a few details about your own work on the experimental discovery of dislocations in 1956 ?

MICHAEL WHELAN (MW) : In the 1930s there was no experimental evidence for dislocations but theoretical predictions were built up about the way dislocations behave. What was really missing was any direct observations of dislocations, although slip lines on the surface of metals had been observed by optical microscopy. The question was how could that occurat the sort of stresses that were observed experimentally ? If you work out the stress required to push one layer over another as a whole, it is much higher than it would be if you introduce the concept of a dislocation. A dislocation is like a wrinkle in a carpet ; Peter Hirsch used this image. When the concept of a dislocation came to the forefront with many papers about the behaviour of dislocations, there were unbelievers, among the Russians in particular. At the Cavendish Laboratory in Cambridge in the group of W.L. Bragg they had suggested simple X-ray experiments to detect the small subgrains that were hypothetically formed in the plastic deformation of metals.

BBV : When did you start ?

MW : I started in 1954 with Peter Hirsch. He was a post-doc in Cambridge. He had got his PhD about 1950 using X-rays to study the textures of metals. They had developed a microbeam X-ray technique under the supervision of Professor W.L. Bragg and Dr W.H. Taylor. It was essentially based on X-ray equipment - a high intensity X-ray generator with a rotating anode produced a beam of about 10 microns diameter for taking back-reflections photographs from a small area of a deformed metal.

BBV : So in 1954 X-ray diffraction was still the dominant technique for studying dislocations

MW : When I started the X-ray machine was still in the lab and there was another student still using it, Chris Ball, who eventually emigrated to Australia, and I started in the same room as the microbeam X-ray machine. I remember him telling me - you don't have to worry about the scattered beams…. I tolerated it for about six months and then moved to another room. The work with X-rays had its limitations - you could not get a smallenough beam to examine certain metals, notably nickel and copper. The scattering is very weak with X-rays and typical exposures were about 24 hours. Anthony Kelly had the idea of going to one of the new electron microscopes that had been developed to do transmission electron diffraction. An electron diffraction pattern exposure time was only a few seconds. I was asked to investigate this electron microscope technique further. Some people had already worked on it. Heidenreich in particular at the Bell Telephone Labs in the USA, but not with the idea of actually seeing dislocations.

BBV : Did Heidenreich produce the first images of dislocations ?

MW : If you read my article you will see that Japanese had also produced dislocation images. The Japanese were interested primarily inmoire fringes, but if you look at some of the pictures thatProfessor Hibi took of mica and graphite, you can see that they contained dislocation images. But they didn't really understand the concept of a dislocation. I heard that from an eminent Japanese scientist, Professor R. Uyeda. We came from the X-ray side. We were interested in crystallography whereas many electron microscopists did not know much about diffraction. It was important to have a team which was expert in diffraction to move into this field.

BBV : You mean for interpreting images ?

MW : Yes, the theory that you need to understand how the electrons interact in a crystal which contains dislocations is essentially diffraction theory. It is more or less the same theory that you have for X-rays except in the difference of scale. The theory was well known to crystallographers. It had been developed in this country by Darwin and Bragg andby Ewald and von Laue in Germany.

BBV : Where did electron microscopy come from ?

MW : Electron microcopy was developed in the 1930s by the team of E. Ruska, M. Knoll and B. von Borries working in Berlin, and was initially used by metallurgists mainly to look at surfaces. Their interest initially was to extend what they did with the optical microscope, namely to examine surfaces. They made thin replicas of surface structure and examined them in the electron microscope. They had to shadow the replicas with heavy metals to obtain good contrast. This was the main area that metallurgists were engaged in during the late 1940s when electron microscopy started to be used again after World War II, with the exception of Heidenreich in the USA and Raimond Castaing in France, who developed microprobe analysis techniques.

BBV : Did you know Castaing and interact with him ?

MW : Yes, I wrote to him as a research student and sent him some of my electron micrographs. I met him first at a conference in Madrid in 1956 at the end of my second year of research. I remember him taking me for a ride in his car through Madrid. He was a scary driver. There was a session at an EMSA conference in Portland Oregon in 1999 that was devoted to the memory of Castaing.

BBV : Did you take your Ph D in physics or in crystallography ?

MW : In the physics department in Cambridge, known as the Cavendish Laboratory.

BBV : Did you consider yourself as a physicist or as a crystallographer ?

MW : A bit of both actually. I was interested in crystallography but Cambridge had traditionally a broad natural sciences undergraduate course. You studied for three years. In the first and second years you had to study a number of subjects, for example in my case physics, mathematics, chemistry and crystallography. In the third year I specialized in physics, but in the crystallography course during the first two years I got interested in X-ray diffraction. Therefore, when I started in the Cavendish Laboratory I decided that I would join the group working on X-ray diffraction.

BBV : When did you shift from X-ray to electron microscopy ?

MW : When I started. As I have said, Kelly had initiated the work, but he left the Cavendish to work in the USA. He had taken some transmission electron micrographs with Peter Hirsch and Jim Menter, who worked in the Laboratory of Physics and Chemistry of Rubbing Solids, a subdepartment of the Physical Chemistry Department at Cambridge. He had an electron microscope with which you could do selected area electron diffraction. Selected area diffraction was a relatively new technique at that time. It enabled you not only to take an image of the specimen, but also to insert an aperture into the microscope column, selecting an area down to about a micron or half a micron in size to obtain a transmission electron diffraction pattern. You had to have a thin specimen, about 1000 Angströms thick. The simplest thin specimen you could easily obtain at that time was beaten gold foil. It could be beaten down to about 1000 Angströms thickness. It would transmit electrons at that thickness but it was heavily deformed. They saw things in the images that they could not interpret. Peter Hirsch had the idea that they could be stacking faults on inclined planes. If you can see a stacking fault it ought be possible, he thought, to see a dislocation because the dislocation in a face centric cubic metal can dissociate in two partial dislocations, like a little ribbon with the space in between them being a stacking fault. So if you could see the fault you might be able to see the dislocation by virtue of the ribbon. That was the initial suggestion that Peter Hirsch made. It was simply a hunch. Experiments had to be carried out and interpreted. That was my job.

BBV : What kind of microscope did you use in 1954 ? Was it easy to get electron microscopes in research laboratories ?

MW : At that time the Cavendish Laboratory had two electron microscopes in the Electron Microscope group headed by Dr V.E. Cosslett. One was a pre-war instrument manufactured by the Siemens Company of Berlin in 1938. You could not do electron diffraction with it. It had been picked up in Germany by the British Army as a war reparation. Ernst Ruska developed the first electron microscopes in the early 1930s based on work done in the 1920s. The first commercial firm to produce a microscope was Siemens, who engineered a microscope that Ruska had basically designed. It was a two-stage magnification instrument with a single condenser lens. You could not do selected area electron diffraction with it. You need three stages of magnification for that.

I took some electron micrographs using this instrument. The resolution was not good, but some of the micrographs of beaten aluminium showed images of dislocations. This was not realised at the time. It was only much later, with hindsight, when the micrographs were re-examined, that dislocation images were recognised.

In early 1956 I was able to use the new Siemens Elmiskop in Dr Cosslett's group. This had much better resolution, and dislocation images were recognised in the summer of 1956.

BBV : What do we see on these pictures ? Picture 1 plate 404 and Picture 2 plate 1833.

MW : Plate 404 : This relatively low magnification micrograph shows the subgrain structure of beaten aluminium foil. Subgrain boundary walls are visible. These are made up of dislocation arrays. The subgrains are about 1μm in size. Inside the subgrains there are many extinction contours. These arise from dynamical electron diffraction effects due to buckling and thickness variations in the foil.

Plate 1833 : Here at higher magnification we see subgrains of size 1 or 2 μm in diameter. In the centre we see a cross-grid network of screw dislocations constituting a low angle twist boundary, on or close to the (100) crystallographic plane. In the next subgrain we see a slip trace (the contrast feature with a 90o bend). A dislocation has moved across the grain, first on one 111 plane and has then cross-slipped to another 111 plane, leaving behind the trace of its path. In imaging dislocations by so-called « diffraction contrast », we do not attempt to resolve the atomic arrangement. There is a strain caused by the displacement of atoms near a dislocation, and it is the region of strain that is made visible as a dark line by diffraction contrast.

Only one beam is used to form the image - here the directly transmitted beam. Other diffracted beams are removed by an aperture in the objective lens of the microscope. The dislocation images reflect the fact that electrons are scattered outside this aperture. This is diffraction contrast.

BBV : What does it tell you about the material ?

MW : You don't aim at resolving the atomic structure. Metal physicists think in terms of a sort of quasi-particle. They are not usually interested in details about the atomic positions. They are interested in the concept of a dislocation as a line defect with properties such as energy, line tension, inter-line forces. What you want to see is a line.

BBV : How can you sort out the line defects that are dislocations from other spots or lines ?

MW : With some experience you can easily identify dislocation lines. Other contrast features arise from artefacts. The instrumental resolution required to observe dislocation lines is not high.

It is of the order of 100 Angströms. To see atoms you need a resolution of about 1 or 2 Angströms. Modern instruments have this resolution. To image the crystal lattice, you need to include more than the directly transmitted beam. You include a number of diffracted beams and resynthesize the atomic image by using several beams. You can use modern electron microscopes to actually see the atomic arrangement with a very thin specimen. You can gain a sort of projection of the atomic lattice structure. But then again, you have an interpretation problem. The question remains - what does the image mean ?

BBV : On which metal did you first observe dislocations ?

MW : We first observed dislocations in aluminium foil.

BBV : Following your first observation and publications I guess that there was a great excitement among physicists that increased the demand for commercial microscopes

MW : In post-war years, the Siemens company improved on the design of their pre-war instrument and manufactured the Elmiskop 1. It was presented at the London International Electron Microscope Conference in the summer of 1954. The first to be delivered from the factory was acquired by the Electron Microscope Group at the Cavendish with a grant from Nuffield foundation. It was designed mainly for biologists. Although you could do selected area diffraction with it, there was an inconvenient system for energizing the lenses which made it difficult to obtain electron diffraction patterns initially. But after a few years Siemens modified the electronics to enable fine focus illumination to be used with electron diffraction. For many years the Siemens Elmiskop had most of the world market.

BBV : Was it difficult to operate the early electron microscopes ?

MW : Most of the difficulties in those days was preparing thin enough specimens. Also adjustment of the electron beam was done mechanically, requiring some agility of the operator. Nowadays adjustments are made by magnetic deflection. Practically the only thing which is still mechanical in modern instruments is the actual movement of the specimen stage.

BBV : How long did you take to familiarize yourself with the electron microscope technique ?

MW : There was an assistant in the Electron Microscope group Bob Horne who was in charge of the Elmiskop instrument. I seem to remember that he had never studied for an undergraduate degree but he had been an electronic assistant during World War 11. He told me that he had been involved in recording ground-to-air voice communications during bombing raids on Germany using wire recordes borrowed from the BBC. The recorded voices were broadcast again during later raids to confuse the enemys defence fighter aircraft ! He acquired skills in electronics during the war. We collaborated and the first papers were co-authored by Hirsch, Horne, and myself. Horne took the pictures. He operated the instrument. The difficulty for me was to get my own hands on the instrument. But there were three viewing windows on Siemens Elmiskop. The operators window and two side windows, so it was possible for me to observe through a side window. Later when we first saw dislocations, Peter Hirsch would be observing at the other side window. To record the movement of dislocations we attached an external ciné camera, recording through the front window. We needed not only an operator but also somebody trying to tilt the specimen to give it best contrast and somebody to operate the ciné camera. So three of us, Hirsch, Horne and myself worked altogether. Another difficulty was the availability of the machine. It was the only microscope in the university. I had an afternoon session per fortnight. During the rest of the time the instrument was mainly used by biologists. (Lord Victor Rothschild was one of them. He was an eminent biologist and was Chairman of the Agricultural Research Council. He was one of the few members of the Rothschild family who did not go into the family banking business. He stayed in Cambridge doing research, and later directed research at Shell laboratories and became an advisor to Margaret Thatchers government). But when we started obtaining exciting results we got more time on the instrument. Ultimately around 1957 we got our own instrument. And we had 2 or 3 of those instruments before we left Cambridge to come here.

BBV : So it was a rapid increase. How expensive were these instruments ?

MW : In those days you could buy one for about £8000. I remember Professor Nevil Mott coming - he was the head of our department - and looking at the first Elmiskop we obtained and he said - « ah, two houses ! ». In the 1950s you could buy a professoriel style house in Cambridge for about £4000. Money was obtained from various sources. Part of the money came from the Royal Society and the rest came from the Department of Scientific and Industrial Research. The instrument was for our groups use, but it was situated as an attachment to Dr Cossletts group ; so that his technicians could advise us.

Initially we had a beam of 100 microns diameter which is quite large. The images were of poor quality, but they were not much better than Heidenreichs images because he too had not used a double condenser lens. The initial emphasis was to look at electron diffraction patterns. So we had to use the single condenser illumination. One day Bob Horne switched the lens arrangement to the system that biologists, used but with which you could not do electron diffraction. We noticed that the images obtained very clear and picturesque. After a while we saw changes taking place in the image, and the dislocations started moving around. I called Peter Hirsch to come and have a look. He said we must get a ciné camera to record the dislocation motion. One of our assistants who had worked at the National Physical Laboratory and knew something about movie cameras, advised us on who to contact at the NPL to borrow a ciné camera. We mounted the camera on the microscope, put some high speed film in it and we made a ciné film of the motion of the dislocations. We produced a silent movie. Peter Hirsch and I presented the film at various conferences and we received requests from people who wanted to obtain a copy of it for teaching students. So we started a business in the Cavendish to sell it at cost price. We still have the negatives. Recently we put it on video. I showed this movie in Japan recently on a trip to raise funds for my college at Oxford. A generation of students has grown up, who have never seen this old movie. So it is entering a second life !

BBV : How many instruments did you get when you moved in Oxford in 1966 ?

MW : We bought a new Elmiskop. With the help of research students we had converted an instrument in Cambridge to study the energy losses of the electrons when they are transmitted through the specimen. We moved it to Oxford. Then with the help of another competent research student we built another instrument based on a design of Castaing which enabled energy filtered images to be taken. There was an old EM6 electron microscope already here in John Martins lab. But we were in a Department annexe on the ground level of another building.

BBV : Did you need a special environment for using those electron microscopes ?

MW : It was not a bad building. Because it was on the ground floor vibrations were minimized. Later we bought instruments with higher resolution that required special foundations, we had concrete blocks put on the floor to minimize any vibrations coming from traffic outside the building.

BBV : How did you teach electron microscopy ?

MW : I started giving a graduate level course on the dynamical theory of scattering to research students. At the undergraduate level initially there was not much teaching of electron microscopy. There was only brief mention of it, with no experimental work. That has now changed. Undergraduates can have practical classes in electron microscopy.

BBV : Do you remember when these practical classes started ?

MW : I don't remember exactly. Probably in the late 1970s. I used to give a course on optical and electron microscopy to undergraduates. But there was no practical work ; in the practical classes they could only take X-ray pictures. Now in the practical classes they use various electron microscopes, both scanning and transmission. Compare this with the days when we started with an instrument available one afternoon a fortnight.

BBV : What is the importance of electron microscopy now in this department ?

MW : It is used as a routine technique now in the department. Anyone working in any area of materials science can get advice from the electron microscope group.

BBV : Is it also the case for the Scanning Tunnelling Microscope ?

MW : That is a different technique, a surface technique. What is interesting is that they awarded the Nobel prize to Binnig and Rohrer for inventing the STM, and at the same time they awarded it to Ernst Ruska, the German scientist who developed the electron microscope in the early 1930s, almost 60 years before. There were in fact three people involved in this work in Germany, but the other two were already dead by the time the Nobel Prize was so belatedly awarded for the invention of the electron microscope.

BBV : What is your view of Materials Science ?

MW : It is a miscellany of problems all related to the way atoms behave collectively in the solid state and even to some extent in the liquid state.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Michael Whelan », par Bernadette Bensaude-Vincent, 12 décembre 2002 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article129.

—

Entretien avec Michael Whelan, par Bernadette Bensaude-Vincent, 12 décembre 2002

Lieu : Oxford Materials Department.

Support : enregistrement non précisé

Transcription : Bernadette Bensaude-Vincent

Edition en ligne : Sophie Jourdin

SCHWEBER Silvan Sam, 2001-08-27

Sophie Jourdin — 2011-11-10T14:32:16Z

Silvan Sam Schweber

ARNE HESSENBRUCH (AH) : Would you tell me what kind of physicist you were, please ? In order to illuminate your perspective on the history of materials science and engineering.

SAM SCHWEBER (SS) : Let me say a little about my background. I started my studies at City College of New York in 1944 as a chemical engineer. I migrated to chemistry, and in my last year at City College I took various courses in the physics department, one in particular with Mark Zemansky. It became clear that I had greater interest in physics than in chemistry, so I went off to the University of Pennsylvania in '47 to become a physicist. The kinds of courses that people took in those days were atomic physics, a required course offered by Harnwell, who later became the president of the University of Pennsylvania. He had written a book giving an overview of atomic physics. I had a course on quantum mechanics with Ufford, and also one on electricity and magnetism. Walter Elsasser was there, and I did a course on statistical mechanics with him. The person I got closest to was a man by the name of Herbert Jehle, who had an interesting background. He was originally German, a Quaker, who was trained by Schrödinger and obtained his PhD in the early ‘30s in Berlin. He knew Einstein very well and was very much interested in general relativity. Under his aegis I got interested in general relativity, I actually wrote a Master's Thesis on variational principles in general relativity. He suggested that I transfer to Princeton, which I did in '49. To complete the story of Jehle : being a Quaker, he got into trouble with Nazi Germany during the 1930s, and left Germany in 1938 to go to France. When the war broke out in 1939, he was promptly interned in Gurs as a German citizen. Eventually the Society of Friends got him out of the concentration camp in France and brought him to the United States, where he taught during the war at Harvard, and then moved to the University of Pennsylvania. He did lots of interesting things. He knew many people at the Institute of Advanced Study at Princeton, Einstein, Weyl, and many of the younger people in physics there, in particular Finkelstein and Wouthuyzen. . He also worked with Pauling on molecular mechanisms of identification in biology. He was an interesting and impressive man. I came to Princeton in September 49, right after the detonation of Joe 1, the first Soviet atomic bomb, at the height of the intensification of the Cold War and in the midst of debates over the hydrogen bomb. John Archibald Wheeler had disappeared and gone off to make hydrogen bombs, first at Los Alamos and later back in Princeton at what became the Forrestal Center. Eugene Wigner, whose research assistant I became, was there, as was David Bohm. The general tone was set by Wigner, who was really very much a phenomenological physicist. He was skeptical about making ultimate and general claims. During the war he had been very much involved in building piles, working with Fermi at the Chicago Met Lab. Actually, for a year before coming back to Princeton, he had been the head of Oak Ridge, trying to get people interested in nuclear power. When he came back to Princeton in '49, after the advances in quantum field theory by Schwinger and Feynman, he did not get involved in these things. The kinds of topics he encouraged were illustrated by the theses his students wrote. There was a somewhat older student than I, Ed Jaynes, who had written a thesis on ferroelectricity. Another of his students, Ted Teichmann did a dissertation extending Wigner's R-matrix theory, a generalized S-matrix approach to nuclear reactions. Probably the person at Princeton who influenced me most was David Bohm, whose Advanced Quantum Mechanics course I took during my first year at Princeton. He had just finished writing his Quantum Mechanics textbook. He taught a very beautiful course which took into account the recent advances in quantum electrodynamics. He was very interested in many-body theory at the time. He had had Eugene Gross as a PhD student the year before who had done a thesis on plasma physics. David Bohm had worked on the description of plasmas at the Berkeley RadLab during the War. He had come back knowing a great deal about plasmas. The question addressed was whether you could apply the insights of plasma physics to the description of the valence electron gas within a solid. Eugene Gross worked on the classical theory of plasmas. Another person who was finishing at the time was David Pines. He did the quantum mechanical formulation of plasma theory that eventually became the Bohm-Pines description of electrons in metals, a subject that Wigner was very much interested in, because back in the early 1930s he was one of the founders of solid-state physics with Seitz. Wigner had worked very hard on the treatment of electron correlations. The question was whether the plasma approach could give a simpler way of describing electron correlations — that is, whether a collective way of describing electrons in a metal was a more effective way of describing them than the quasi-single particle approach Wigner had used in the 1930s.

At Princeton physics and mathematics were rather close (Wigner was a professor in both departments). I became attracted to working with Arthur Wightman who was a young assistant professor at the time. This was particularly the case after David Bohm was not reappointed, and I started a thesis in (semi-)axiomatic quantum field theory with Arthur Wightman. Let me say something about the kind of training I received as a graduate student. Princeton was a little special in the following sense. The classes were small, as about 10-12 graduate students were admitted each year. The message conveyed to us was : "we invited you and think highly of you, and we want to give you every opportunity to realize your potentialities". There were no formal course requirements of any kind. Instead, there was a hurdle consisting of a very intense three-day written general examination which covered all of physics : classical mechanics, electricity and magnetism, optics, quantum mechanics, thermodynamics and statistical mechanics, special and general relativity. After that, there were two-three hours of oral examinations overseen by groups of faculty members. The onus was really on us to get acquainted with everything in physics. I had taken statistical mechanics with Wigner, and as mentioned earlier advanced quantum mechanics with David Bohm. I also took various courses in the Math Department - with Spencer, Schiffer and Feller, but in the absence of actual course requirements I just took what I considered useful. There was also the Institute ; after 1947 Oppenheimer was its head. There were joint theoretical seminars every Wednesday, and every theorist at the university would go out to the Institute. During the period I was in Princeton, from 1949 till 1952, most of the presentations were at the frontiers of quantum field theory. During the 50s the Institute was the finishing school for young theorists and all the bright young people trained in the US and overseas would come there. I remember people like Van Hove, Frank Yang, Bryce deWitt, Feldman, Karplus. During my second year at Princeton Murray Gell-Mann and Francis Low were there. I finished my thesis in the spring of 1952 and after I got my degree, I went up to Cornell in the fall of 1952. The atmosphere at Cornell was very different from that at Princeton. Freeman Dyson was there in 1952-53, and of course Hans Bethe. They were in the Laboratory of Nuclear Studies, which housed that segment of the department involved in high-energy physics. The Nuclear Lab had a separate building. There had been earlier tensions between solid state and nuclear/high-energy physicists that had resulted in a rift in the department. What was characteristic of my 1952-54 experience at Cornell was the intimate relationship between theory and experiment, something I had not felt at Princeton. I don't mean to say that there was no active experimental work going on at Princeton. Dicke was there doing positronium experiments and various other things, in retrospect it seems to me that there were no fora for interaction in the way that existed at Cornell. As a post-doc at Cornell I attended a solid-state class with Overhauser, a young instructor at the time as well as lectures by Bethe on advanced quantum mechanics. Cornell gave me a different vision of what physics is about. One came to realize that high-energy physics was different from solid-state physics - both in approach and in status. It had been a little like that already before the war, then in terms of nuclear and solid-state physics, but this bifurcation became intensified after the war. The differentiation also manifested itself in the requirements on graduate students. What it took to become an experimental or a theoretical physicist differed at Cornell and at Princeton in one respect : during their first two years every graduate student at Cornell took the same classes : mechanics, electricity, magnetism, quantum mechanics, solid-state physics, nuclear physics, experimental physics. Experimental physics, a year-course, was required of every graduate student. Cornell also had a set of examinations, but these were less intense than Princeton's. At Cornell, just as at Princeton, one was expected to know most of physics. The specialization was limited. Solid-state and high-energy physicists were all still members of the same department, and the curriculum required of all graduate students encompassed all of physics.

In 1954 I went as a research associate to Carnegie Tech in Pittsburgh. The atmosphere there was similar to the one at Cornell. There were some very good people there (the senior theorist was Gian Carlo Wick ; also in the department were Walter Kohn who had migrated from doing quantum field theory with Schwinger to doing many-body solid-state physics , and Julius Ashkin who had switched from being a theoretical physicist and became in charge of the Carnegie Tech cyclotron). I had to leave Pittsburgh after one semester and go back to New York, because my wife had fallen ill. I never returned to Carnegie Tech but accepted in the spring of 1955 a job at the recently established Brandeis - its first class had graduated in 1952. At that time Brandeis was essentially an undergraduate college, but it had a commitment to build a graduate school. In 1957 a graduate program in physics was started. The emphasis was initially heavily on theory because it is cheaper to hire and maintain theorists than experimentalists. In 1958 we started a summer school in theoretical physics that became well known and helped put Brandeis on the map. It was quite useful and ran through the late '60s. Partly by virtue of the emphasis on theory, the people we hired were predominantly engaged in field theory and general relativity. In 1957 Eugene Gross, who had been a student of David Bohm's, arrived, doing many-body physics. By 1960-61 it was recognized that we should have an in-house experimentalist program and experimentalists doing solid-state physics (Steve Berko) and atomic beams (Edgar Lipworth) were hired. The examinations to be admitted to candidacy for a PhD in physics at Brandeis were no different from the ones given at MIT or anywhere else in the country. Graduate students were expected to know what mesons and their properties were, even if they were to continue in solid-state physics. The training of graduate students was such that they did not have to make a decision whether they wanted to become experimentalists or theorists, and in what field, until the end of their second year of graduate studies. That continued until the mid-1960s. Entering graduate students mostly would want to become theorists, but if the faculty felt they were not quite strong enough, they would become experimentalists. It is certainly the case that by the early 1960s, one had a sense of sub- disciplines existing, that is that solid-state physics was a different branch from the rest of physics ; and that the same was true for high-energy physics. There were some overlap and mutual interests, for example in atomic physics where precision measurements involved quantum electrodynamics. Brandeis became well known in the late 1960s for doing experiments that determined the Lamb shift in positronium — Berko, Cantor and Mills did that experiment. Positron sources for the exploration of properties of the solid state is what Brandeis became famous for in experimental physics, and that was mostly due to Steve Berko. He had done positron physics before coming to Brandeis and really put positrons on the map as probes in solid-state physics. Until the 1970s support for all the research activities in the department came from two or three places : initially it was mostly the Office of Naval Research, then the National Science Foundation, and then the Air Force. There were no strings attached. You submitted an application and it was looked upon on its merits. The intent of the ONR and the Air Force was to have people trained, to have a pool of scientists available to meet national security needs and national educational and economic interests.

During the 1960s the size of the physics faculty kept on increasing, as did the number of students, and as did the funding by the national agencies. From the mid-'50s on, computers were housed in the physics department and computer science was taught by the department. Max Chretien, who had been a high-energy physicist, had slowly gravitated more and more toward what we now call computer science. By the late 50s, early 60s, the physics department offered several courses in software and in hardware. Computing activities took up an ever-greater role, partly because the high-energy people required it. But it was also simply a way for the department to grow.

By the early 1960s, we started having discussions at senior faculty meetings whether or not to hire a solid-state physicist rather then the brightest and ablest theorist. The demand of sub-disciplines had become assertive. That is the way the department is now run. There are sub-groups, semi-autonomous, quasi-departments. Discussions in the early 1960s still had a common background in questions such as : "what is physics really about ?" We had metaphysical discussions about what counted as more fundamental. By the late 70s and the early 80s, this kind of question had disappeared. It was now about where support can come from. This determined in part who would be hired. Another crucial questions became : "Where would graduate students be able to find employment, and what kind of training should they obtain keeping that in mind ?" It also became clear in the post-Vietnam 70s that only the very best theorists would find employment. And there was then a gradual shift of the balance of the department towards the experimental side and more students interested in experimental physics were admitted. Robert Meyer, an experimentalist who studies liquid crystals, came to Brandeis and started a program in that field. Gradually his group has become fairly large and one of his best graduate students has joined the faculty. Interest in using viral particles to test phase transitions and that sort of thing has become a part of the experimental activities of the department. There is also at Brandeis a research institute in biochemistry, molecular biology and biophysics called the Rosenstiel Center, that functions by having its research staff placed in various departments. Alfred Redfield, an outstanding experimentalist working in NMR, was appointed to both the physics and biochemistry departments. Over the last 15 years the focus of experimental physics has shifted toward biophysics, partly reflecting the fact that the greatest amount of support will be forthcoming in that area, and that graduate students obtaining PhDs in this area can go in many directions thereafter. The newest additions to the department in theory have been condensed matter physicists. There is a woman by the name of Bulbul Chakaborty who is a condensed-matter physicist, doing computational physics. I would say that she is now the leading theorist in the department doing that sort of thing. Two years ago we hired a young condensed-matter physicist by the name of Jane Kondev who has made a big difference. These are people well grounded in modern condensed-matter theoretical physics, and their interests are much wider than those of the high-energy physicists. They have the feeling that theirs is the way of the future ; that young physicists ought to be trained in this field when considering their employment upon graduation. What causes tension within the department is the fact even though there are on the faculty several outstanding high-energy theorists - people like Stanley Deser, Marc Grisaru, Howard Schnitzer - it has nonetheless become more and more difficult over the last 15 years to attract good graduate students. The very best go to Harvard, CalTech or such places. In a nutshell, that is what has happened in the Brandeis physics department. There has been a rethinking on what physics is about and what the mission of the physics department is.

AH : Is it a question of status ?

SS : Also.

AH : The way you described it was in terms of numbers of students. But are you also saying that solid-state physics used to be low status and that this has changed ?

SS : Yes, there is no question about that. I think that Brandeis, a secular university but founded, established and supported primarily by the Jewish community, felt that it had a certain mission. Clearly the conception of the university was such that "pure" contributions had a higher priority than applied ones, and in the sciences this meant theoretical physics and mathematics. Furthermore, as I said it is much cheaper to do theory and by virtue of the initial economic context at Brandeis, it was much easier to hire theorists rather than experimentalists. The initial bias was towards theoretical physics, and since until the mid-1970s high-energy physics was considered more "fundamental" than solid-state physics or what later became condensed-matter physics the theorists were either general relativists or field theorists. It was within the physics community at large that the question of status got rectified. It has to do with what solid state physicists did in superconductivity - using field theoretical techniques, and in particular recognizing the role and meaning of spontaneously broken symmetries in the description of the dynamics of such systems — that similar ideas were developed and then grafted onto quantum field theory in general, and a rethinking of the status of condensed matter took place. Phil Anderson was very influential in this both by virtue of his technical contributions, and because of his article in Science "More is different." There were great theoretical advances in the late 60s and early 70s, in particular, the re-adoption of quantum field theory as the seminal representation of microscopic phenomena, because gauge theories conjoined with the Higgs mechanism for symmetry breaking seemed to be the right way to describe both the strong and the electroweak interactions. This after 't Hooft showed that one can renormalize gauge theories even if they have broken symmetries This led to what is now called the standard model. But ironically what happened at the same time was a recognition that what had been thought of as renormalization is really something very different, namely, an effective way of putting all the high-energy effects into certain observable parameters at low energy. For the most part you will not see anything of the effects of the high-energy processes beyond the cut-off energy you have introduced to make the theory free of divergences. It implied that even though renormalizable theories still had a special status, renormalization qua renormalization was not quite so important. More fundamentally, it implied that most theories that we know of, be they quantum electrodynamics, electroweak theory, or quantum chromodynamics, are only effective theories. They have a limited range of validity, the range being essentially the masses of the particles, which you need to introduce into the theory in order to explain the data, and which therefore reflect the context (the available energies) in which you are doing physics. People began to recognize that to some extent the theories that condensed-matter physicists used to describe superconductivity, liquid helium, or some such system, was as foundational for its domain of validity as the standard model was for the 0-200GeV range of subnuclear entities - the quarks, gluons and leptons.

AH : But that is an argument that will not be accepted by an older generation of physicists. I mean, this is the kind of thing that Paul Forman argues against, right ?

SS : Well, I would put it differently - and it is not meant pejoratively. Most physicists have become like chemists, in that they are exploring novelty in the world. They are creating new things, or new systems with new properties. And the power of the theory is such that they can actually pinpoint the elements that will give you the kind of qualities or properties that you want. There is still a subset of condensed-matter physicists who see their job as testing foundational issues - for example, "Under what circumstances is describing certain processes as a Bose-Einstein condensation appropriate ? How does this depend on the number of particles involved ?" - However, the foundational theories involved are not questioned. Since the 1970s more and more condensed-matter physicists think that conceiving of nuclei in terms of quarks is irrelevant. An atomic physicist doing experiments that determine the Lamb shift in various atomic states to some amazing accuracy, measurements that indicate structure at a smaller scale, does nothing of great consequence for chemistry, for most phenomena in chemistry do not depend on effects to that order of precision.

There is a further observation. Since the late 1970s the impact of computers has been very great. It is a striking fact about both experimental and theoretical physics that much computer modeling takes place. People are now trained quite narrowly in modeling on the computer, so that computational physics has become a third branch of physics. There are so few things that one can do analytically by virtue of non-linearity that one has to do it on the computer. The results are really quite impressive. The rise of the role in the training of students in computer modeling is really very striking.

AH : Does that have a bearing on the solid-state vs. high-energy physics issue ?

SS : In theoretical high-energy, the impact of computers has been on how to deal with the complexity of perturbative calculations when you start to have 2 to 3 hundred diagrams to evaluate. You have programs where you draw the relevant Feynman diagram and the computer will grind out the finite radiative corrections at given energies or whatever else you are calculating. When you are concerned with real experiments and you have to compute radiative corrections and cross-sections, you people rely very much on computers, the calculations having become so complex. The use of computers among string theorists is much more having access to the web so that you can download the latest pre-prints available from Los Alamos. They log in every morning to learn what new preprint is available. From a sociological point of view the web - and the Los Alamos archive - has democratized high-energy theory : a researcher in Pakistan or Ghana has the information as readily available as the one at SLAC. Also there is a general recognition that physicists need to know a great deal about computing, if only because at the end of their graduate studies they could land a job on Wall Street if they are adept and innovative in modeling on the computer. I think you are right in saying that the older generation still feels that high-energy and elementary particle physics is more "fundamental" than condensed matter physics. I think it is quite painful for my colleagues in high energy theory at Brandeis to consider the possibility that once they retire the university will likely not replace them with someone in their field. They have invested their lives in this field. In high-energy physics and cosmology, where practitioners - still - set their own internal agendas, work gives meaning to lives in a way that is - probably - not the case in condensed-matter physics. For a condensed-matter physicist, solving a difficult and important problem is an impressive thing, and brings about many rewards both personal and communal, including the possibility of a Nobel Prize. The same is true for the high-energy physicists but in addition there is the feeling of being some kind of secular priest, for they believe that they are reading and writing the book of Nature, and formulating something ultimate about the world.

AH : That is certainly the way I perceived it as an undergraduate of physics in Freiburg, Germany, starting in 1978. Pure physics was supposed to be independent of the demands of society. It had nothing to do with the demands, say, of the nuclear industry or the military. That seemed to be the credo, whether it was correct or not. Solid-state physics was very small, and it was openly commercial. The solid-state physics institute actually paid students a salary to write their theses. It attracted some students but it repelled even more. Does that ring a bell ?

SS : In the US, the autonomy of physics departments was greater. There was a system of governmental funding until the end of the Cold War. One did not have to go to industry to get support for your students. In chemistry, funding for research and for students has always come in part from industry. In that field, a faculty member, as the principal investigator, would get a grant or a contract from a particular chemical or pharmaceutical company to carry out specified investigations of great value to that company and in this way obtain the funds to carry out the research and support his postdoctoral fellows and graduate students. In physics, it would not be unheard of during the 60s and 70s for a graduate student to go to Lincoln Lab or Oak Ridge to do his PhD thesis there, but it would have been very unusual to obtain a PhD for work done in an industrial setting.

As an answer to your question : The older generation of physicists might deplore the fact that string theorists lack knowledge of general physics, because their field of activity is so close to mathematics. It is not that they look down upon it, but it is felt that as long as string theory is without empirical relevance it is not really physics. Since the 1980s there has been a great deal of exchange of techniques and knowledge between quantum field theorists and condensed-matter physicists, partly because experimental techniques have become so good that one can devise one-dimensional and two-dimensional systems. The exploration of two-dimensional field theories is thus of great interest to both sets of practitioners. They exchange insights about conformal field theories. But both are concerned with the constraints and relevance of experimental data. String theory thus far has little to say about experimental findings.

AH : Do young people who enter into high-energy physics nowadays also have these - shall we call it lofty aspirations ?

SS : I really don't know. There is some split. One type are the theorists who try to figure out what it means if the experimentally measured value of the m meson anomalous magnetic moment no longer agrees with the standard model calculations. Does it imply super-symmetry ? String theorists are not likely going to do that. They count states in black holes, so the division is more where you stand in relation to actual experiments.

AH : I don't understand the historical development of solid-state into condensed-matter physics. Could you explain that ?

SS : Solid-state physics was principally concerned with solids, primarily metals and semi-conductors. Gradually it became clear, partly due to field-theoretical methods, that what you learn about Fermi systems is equally applicable to electrons in solids and gases and liquids composed of He3 at low temperature.

AH : So it was an expansion ? When did this take place ?

SS : In the late 1950s and early 1960s. This is when field theoretic methods became powerful tools in the treatment of many body systems. This was also the time when Bardeen, Cooper and Schrieffer solved the superconductivity problem and when experiments on He3 were being done. You ought to ask Paul Martin or Henry Ehrenreich about this. There was a period in the middle 1950s to early 1970s when these field theoretical methods become standard components of the solid state physicist's toolkit. And since the field theoretic Green's function methods used allowed the consideration of the properties of the system as a function of temperature, phase transitions became an essential part of the field. Thus all phases - liquid, gases, solids - became the concern of the field.

Interestingly, there is a parallel development in nuclear physics. After the establishment of the Standard Model, nuclear physicists recognized that they had fallen upon hard times trying to understand nuclei in terms of nucleons, that the challenge was to understand how to go from quarks and gluons to mesons and nucleons. The field theoretical methods were used to understand the properties of nuclear matters, and diffused to such esoteric topics as neutron stars, and the collapse of supernovae. Incidentally, the development in that field in the United States can only be understood if it is remembered that the physicists who became high -energy physicists had been at Los Alamos during World War II and the most distinguished of them populated PSAC (the President's Scientific Advisory Committee) and setting the priorities for governmental support of the various fields of science. This began to change already in the late 1960s.

AH : Already ?

SS : Look at PSAC : In the 1960s there were almost no chemists on it. The support of science before and after Vietnam was different for many reasons. First of all there was the 1969 amendment of senator Mansfield about funding by the department of defense. Vietnam also marks end of the expansion of physics. The number of annual PhDs in the field began to decline.

AH : Where did Materials Science and Engineering enter into your world ? I imagine that when the interdisciplinary laboratory came into being at MIT in 1960, you must have noticed it. Did it look like physics to you ?

SS : We noticed it. The experimental approach resembled work in physics departments. But it was also like chemistry. My colleague and friend, Eugene Gross, had an interest in the statistical mechanics of polymers. I heard from him about polymers and polymerization. I went to the chemistry department colloquia. In particular, I remember a lecture in the mid-1970s by a polymer chemist from PennState in which he talked about designing polymers with specific electric and optical properties. The use of quantum mechanics to understand not elementary but complex systems and to make it the basis of a "molecular engineering" intrigued me. Later I discovered that Slater had such a vision already in the late 1920s after the advent of quantum mechanics.

In 1973 we had another crisis because of the Arab-Israeli war and the oil crisis. This led to extensive investigations of solar cells - Henry Ehrenreich was head of the committee that was in charge of these activities. He went around to various departments asking what kind of materials are required to obtain such and such an efficiency. By that time materials science conceived in this "applied" way was recognized as a valid field of inquiry.

AH : So it became known to you as a problem, but not as a discipline ?

SS : Right. We did not see these activities as belonging in a department called Materials Science. No, I associated it more with polymer chemistry and with semiconductor physics. I think it came into greater prominence through these solar cells investigations, in these designs for capturing solar power.

AH : We are talking about the mid-1970s now ?

SS : Yes.

AH : And Brandeis does not have a Materials Science department, but much work done there could now well be done in a department with that name.

SS : Correct. Let me put it this way : I have some interest in the limits of computation. How far can you reconstruct the world if I tell you the foundational theory and the entities make it up ? Where does computational complexity put a stop to your efforts ? Every once in a while I go to Harvard to listen to material scientists talking about the design of materials by modeling on computers. What is striking to me is how uncritically they accept the foundational theory as formulated in their computer codes. They just model.

AH : Complexity is in a way also pure vs. applied. If you have the true foundational theory, then in principle you can calculate everything from it.

SS : Yes, until you are stopped by the complexity of the calculation.

AH : Right, and my point is that thinking about the world in this way is tantamount to accepting the notions of pure and applied science.

SS : To overcome the computational complexity you have to cleverly make assumptions simplifying the calculation. Organic chemists designing complicated biological molecules make up little models with hook-like forces and it works very well. The challenge to the theorist is how to justify such assumptions.

AH : I am trying to fit what you have told me to the demise of the pure vs. applied model. For instance in materials science, many people will tell you that the notions are outdated or that they are simultaneously doing both.

SS : I would argue that quantum mechanics differs from everything else in that it gives a highly accurate and stable foundational theory on the atomic level that can't be tampered with. Heisenberg called it a closed theory. You also know the basic entities populating that realm, i.e. electrons and nuclei. There is a confluence of theory and ontologies. In electroweak theory you can compute the anomalous magnetic moment of the electron to an unheard precision : of one part in 10 to the 10th. You never need that accuracy in materials science and what I am trying to say is that the foundational theory is secure. That is the reason that pure and applied no longer exists. Nobody doubts the accuracy, veracity, efficacy, and efficiency of the foundational theory. There is nothing these people do that probes the foundational theory.

AH : I imagine that an imaginary particle physicist in the 1950s would have said that one ought to find the foundational theory beyond quantum mechanics.

SS : Even though people really felt that the Schrödinger description of atoms is a limiting version of the more foundational theory, you did not have the means to show this. The 1960s provided the means to show that with the re-conceptualized notions of what renormalization means. Not that it is easy, but the foundational theory has been secured. More than that : any foundational theory beyond quantum mechanics must recover all the successes of the standard model : for example, the ability to account for the Lamb shift in hydrogen to the known accuracy, to account for the magnetic moment of the leptons to the known accuracy,...

AH : It seems to me that the meaning of pure has shifted. When materials scientists tell me that they do pure and applied at the same time, they refer to calculating local densities of states and energy levels of an atom moving in a groove of a surface or some such thing as pure. But from the perspective of the old high-energy physicist that is not pure.

SS : Okay. I would phrase it differently : I would call it pure if the intellectual agenda is set by the practitioners without external considerations. Of course, with this definition of purity even high-energy physics - even though the practitioners set their own intellectual agenda - is not pure because it is supported by the government, etc. The same is true for people investigating the onset of turbulence. Clearly there are industrial applications, but that community also sets its own agenda and rewards research very much as high-energy does. It is a question of autonomy. Purity simply reflects the state of autonomy.

AH : So the shift in the meaning over time is interesting.

SS : It is difficult to phrase this - I can make it ad hominem. Your activity as an historian of science gives meaning to your life. You are trying to find out something ; it is personal and there is an intellectual commitment going beyond earning a living. I am not sure that a person at DuPont trying to figure out a better plastic gives much meaning beyond that of monetary reward and job security. There is of course the personal gratification if the challenge is met and the problem solved - and something useful is created - but I believe that success does not answer the quasi-metaphysical questions. So purity has something to do with going beyond what pertains to the economic and sociological sphere. I don't know how to make it sharper than that. Something about extradisciplinary rewards.

AH : The importance of which has declined ?

SS : In every field. Not just physics or history of science.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Sam Silvan Schweber », par Arne Hessenbruch, 12 décembre 2000 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article128.
—

Entretien avec Sam Silvan Schweber, par Arne Hessenbruch, 27 aout 2001

Lieu : non précisé

Support : enregistrement non précisé

Transcription : Arne Hessenbruch

Edition en ligne : Sophie Jourdin

PETTIFOR David G., 2002-12-13

Sophie Jourdin — 2011-11-04T15:31:52Z

David G. Pettifor
Director of Materials Modeling Laboratory, Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK.

DAVID PETTIFOR (DP) : Professor Hirsch told me that you might be interested in the fact that I wrote a short biographical sketch about the founder of our department, William Hume-Rothery (H-R). When he died in 1968 the TMS (The Minerals, Metals and Materials Society) in America set up an award, the William Hume Rothery Award for distinction in the science of alloys. This award has been given out every year. At the time of the millennium they decided it would be nice to have a special symposium to evoke H-R's science. Since I am based in Oxford, I was asked by the Committee to give a presentation, a biographical sketch. That was very interesting for me.

BERNADETTE BENSAUDE-VINCENT (BBV) : What is your background, in physics or chemistry ?

DP : I had registered at University to read Chemical Engineering, because I loved the chemistry laboratory at school. Fortuitously, I bumped into my old physics teacher just before the start of the university year, who persuaded me that physics was the most fundamental of the sciences. So I changed my mind and went into physics. I did my first degree in South Africa at the University of the Witwatersrand in Johannesburg, where Professor Frank Nabarro had built up a strong department of physics. I found my first three undergraduate years of classical physics pretty boring, being challenged mainly by some inspiring young lecturers in the Mathematics department. Fortunately, in my honours year we had excellent lectures in quantum mechanics and solid state physics. I was awarded a National Postgraduate Scholarship and came over to Cambridge at the Cavendish Laboratory in October 1967 to do my Ph.D. with Volker Heine in theoretical condensed matter physics. By the time I visited Oxford as a graduate student, H-R had already died, so that I never met him. So I found it intriguing to research a bit into his life and science, using manuscripts and correspondence in the Bodleian Library and interviewing his daughter Jennifer Moss. Here is the paper (D.G. Pettifor, "William Hume-Rothery : His life and science", in E.A. Turchi, R.D. Shull, A. Gonis eds. The Science of Alloys for the 21st Century : A Hume-Rothery Celebration, TMS, 2000, p. 10-32). H-R was the holder of a professorial chair in metallurgy endowed by the Wolfson Foundation.

BBV : What is the Wolfson Foundation ?

DP : Isaac Wolfson was a merchant trader in Manchester who set up Great Universal Stores (GUS), a mail order company, in the interwar period. He became very wealthy and was interested in supporting science and education. For instance, there is a Wolfson College in Cambridge and one also in Oxford. H-R got the first Isaac Wolfson Chair in 1966. Now there are Wolfson Chairs in various other universities around the UK.

H-R basically was a chemist. He did his undergraduate degree in Oxford. You know the story : he was totally deaf. His family wanted him to enter a military career but meningitis contracted in 1917 left him totally deaf. He wanted to go to Trinity College in Cambridge where his father had been. But Trinity wouldn't accept him because he was deaf. He then came to Oxford's Magdalen College in 1918 to read Chemistry. On the advice of Frederick Soddy, he went to do his Ph.D. at the Royal School of Mines at Imperial College, London. He worked in Metallurgy with Professor Harold Carpenter. He specialized in the stability of intermetallic phases. They do not follow normal valence rules. In seeking for a solution to the stability of intermetallic compounds, H-R developed the concept of electron concentration as a controlling factor in structural stability. He got his Ph.D. from the University of London in 1925. In that thesis he came up with his famous electron per atom rule for the structure of noble metal alloys with sp-valent elements. At that time chemists had simple chemical valence bond rules. For instance, sodium chloride forms a stable octet system NaCl. So how to explain that intermetallics had crazy stoichiometries, like the sodium tin phases Na4Sn, and Na3Sn2 ? That was the start of the so-called Hume-Rothery rules. That was seminal work. [The "Hume-Rothery rules" on alloy phase behaviour were published in the early 1930s. The first two rules emphasize the importance of the atomic size factor and the electrochemical fact respectively, whereas the third rule concerns the role of the electron concentration (or electron per atom ratio)]. In Oxford the chairs have to be attached to colleges. Because metallurgy was considered as a ‘dirty' subject it was not attached to a proper, well-established college. St. Edmund Hall, on the other hand, was a very poor college, a not well endowed college. In the 1950s, they were trying to build up their reputation academically rather than just being famous for their rugby players and oarsmen. So when the metallurgy professorship was passed round the colleges, St. Edmund Hall picked it up so that the Isaac Wolfson chair is held at St. Edmund Hall. H-R was there, then Sir Peter Hirsch was there and I am there now. In retrospect, it has brought great prestige to the College because all the metallurgists at St. Edmund Hall have been elected fellows of the Royal Society.

BBV : Is metallurgy still prestigious now ?

DP : As you know, during the past forty years metallurgy departments around the world have transformed to embrace materials in general. This is reflected in the history of our own department where the undergraduate course was re-titled ‘Metallurgy and Science of Materials' shortly after the arrival of Sir Peter Hirsch as the new Isaac Wolfson Professor in 1966. Then shortly before his retirement in 1992 the name of the department was changed to simply ‘Department of Materials'. Nevertheless, metallurgy still plays a key role in the department with outstanding, internationally-funded research being performed on developing new process routes for metals and alloys. When this department was created industrial sponsors wanted undergraduate programs to train people for industry rather than the setting up of a purely research institute. In practice, our undergraduate numbers have always remained small (around 30) in comparison to the physicists, chemists and engineers with their annual intake of two hundred students each. Our sizable faculty is heavily supported by our successful graduate programs and postdoctoral research. Expansion to the green-field site at Begbroke was successfully carried through by our previous Head of Department, Brian Cantor, who persuaded the university several years ago to buy a recently constructed but then vacated laboratory 5 miles outside of Oxford. It is where we have spin-off companies with young researchers. The Oxford department is by far the top materials department in the country according to the latest research assessment exercise that the UK universities had. That is also true for teaching. It is not however, the biggest one.

BBV : Which is the biggest one ?

DP : This depends on how the counting is done, as many courses are joint with engineering departments. But, on undergraduate numbers, Birmingham, Imperial College and Manchester would be amongst the front runners.

BBV : Could you go back to the beginning of your own career ?

DP : At the time I joined Heine's group, the measurement and calculation of the band structure of how electrons move in materials was a major topic. I was given the project to develop an electron theory to explain the structure of transition metals. It was a theoretical project but it was a well known experimental fact that if you go across the transition metals series from yttrium to zirconium, niobium, molybdenum, technetium, ruthenium, rhodium and palladium the structure changes from hexagonal close-packing to a body centric cubic packing, back to hexagonal and then cubic close-packing. There was a theory, the so-called Engel-Brewer theory, that correlated the crystal structure of metals with the number of valence s and p electrons in the system. H-R did not believe in it.

At that time the Cavendish Laboratory in Free School Lane was a very exciting place to work. Phil Anderson, who later got the Nobel prize with Mott, spent 6 months in Cambridge each year. Brian Josephson, who got the Nobel Prize for superconductivity, was the young star in our group. And Sir Nevill Mott was the fantastically charismatic leader of the Cavendish. They used to come to the seminars and inspired us younger researchers. Well I was very fortunate to be able to crack the problem I had been set, showing unambiguously that the structural trends across the transition metal series were driven by the changing number of valence d electrons, not the s and p electrons as claimed by Engel and Brewer. This work brought me for the first time directly into contact with the metallurgical community, in particular Larry Kaufman and his CALPHAD group who were developing a semi-empirical thermodynamic technique for predicting the phase diagram behaviour of multicomponent alloys. After completing my thesis, I then went down to London as a post-doc in the Physics Department at Imperial College. I had still not resolved my future career path, so shortly afterwards I went off to Tanzania to teach on a two-year contract at the University of Dar es Salaam. I did not want to go back to South Africa. In South Africa I was involved in student politics. I didn't want to go back as a white liberal. After two years in Dar es Salaam, I realized that emotionally and scientifically I wanted to work in Europe or in America. I returned to Imperial College for a year, then back to Cambridge as a post-doc for 4 years. During that time I did my work on the binding energies of the transition metals, performing some of the first-ever Density Functional Theory (DFT) calculations of total energies. In 1978 Bell Labs invited me for 6 months as a visiting scientist. I went to Bell Labs clearly with the idea of sorting out the underlying theory for the heats of formation of metallic alloys.

BBV : Well this was more or less like physics. When did you shift from theoretical physics to materials science ?

DP : I think I've never shifted in the true sense. I come from physics, but I have always had a very broad vision that encompasses the ‘dirtier', more complex world of the metallurgist or materials scientist. I deal with atoms and electrons. My colleague Adrian Sutton has been educated in this department. He is a materials scientist. He is more in tune with the microstructure, the mechanical properties of materials, which for myself have never been really close to my heart. I am much more into the chemistry, the growth of films, into the nanotechnology. My research starts from the fundamental quantum mechanical Schroedinger equation, but I have always enjoyed the challenge of extracting the essential physics, making simple models for explaining, for instance, the heats of formation. If you mix atom A with atom B, Pauling would say that a charge flows from the more electropositive atom to the more electronegative atom, thereby setting up an ionic bond. Therefore, if you have just this attractive ionic term, elements A and B should always mix. In practice, nearly half of all binary systems do not mix. In the mid seventies a Dutch physicist who worked at Philips, Andreas Miedema, came out with a simple generalization of the Pauling predictions for the heats of formation. You don't have just an attractive term but also a repulsive term and by a very clever adjusting of the parameters he could separate the sheeps from the goats, he could separate the alloys with positive heats of formation from those with negative heats of formation. Still the concepts he was pushing were ionic. My early expertise was in metals where concepts of ionicity and the ionic bond do not really make any sense due to the perfect screening by the conduction electrons in a metal. Whilst I was in Cambridge I had performed these first-principles density functional calculations - what everybody does now - what Walter Kohn got a Nobel Prize for. These density functional calculations allowed me to derive a rigorous understanding of the different roles played by the s, p and d electrons in transition metal bonding.

BBV : Did you start with transition metals ?

DP : My thesis took the fundamental scattering theory of electrons in metals and transformed it into a computational tool that allowed me to predict the structural changes across the transition metal series. You are looking at extremely small energy differences between one structure and another. The mathematical transformation that I did from scattering theory to the tight-binding model of Jacques Friedel, allowed the correct prediction of these very small energy differences.

BBV : What do you call a model ?

DP : Well, this is what physicists spend their whole time constructing and solving. We make approximations. When I came to Oxford ten years ago I set up the Materials Modeling Laboratory. People wanted me to call it the Laboratory for Computational Materials Science. I said no. Computing, solving numerically quantum mechanical or classical equations, is not the key step in providing insight into the complex world of materials and their properties. The critical step, the creative step, is finding a model that encompasses the dominant mechanisms of the complex process one is wishing to describe. Only then can we write our computer program to provide quantitative answers. Hence, I kept the name Materials Modeling Laboratory. But they laughed at me and said : Here you go with your plasticine.

BBV : So what is a model ? I guess it is not a small plasticine shape that you were trying to do.

DP : A model is an attempt to extract the essential ingredients, the dominant mechanisms that you feel responsible for what you want to explain. For example, you can take Walter Kohn's equations. They had transformed a many-body problem into a simpler one-body problem. I would not call that a model. That is a theory, the so-called Density Functional Theory (DFT). These equations are however, still very complicated. In order to be able to simplify these equations, we use a chemistry description. We imagine bonds between the atoms. We reduce very complicated equations by using a chemical bonding picture that is familiar to all undergraduates.

BBV : Do you mean that you transformed a matter of calculus into something visual ?

DP : No, although the underlying physics can be visualized in terms of chemical bonds, the model remains analytic. Take the heats of formation, for example. People at IBM and all around the world started DFT calculations with the help of computers : In order to calculate the heat of formation of a mixture of rhodium with palladium, for instance, they compared the total energy of the separate metals, namely 1,000,000 units of energy say, with that for the alloy namely 1,000,000.1 units of energy. The question was what is responsible for that very small energy difference of 0.1 ? I developed an analytic model. It was not based on the Pauling-Miedema model of ionicity but was based on the idea of the importance of the strong, covalent bonding between the valence d orbitals in transition metals. I can do that on the back of an envelope. Solve that model analytically and make the prediction that the heat of formation should change sign while you go through the transition metal series, depending on the average number of valence d electrons in the band. That model was published in Physical Review Letters 42 (1979) 846 and there was a lot of controversy. The established community did not like it.

BBV : Why did they refuse it ?

DP : I tried to work in the spirit of what Wigner and Seitz did in 1933 when they applied quantum mechanics to the problem of bonding in metals. They solved for the binding energy curve of metallic sodium. They replaced the atomic polyhedron in the metal by a sphere which is a good approximation that you can solve. What they did in the early days of quantum mechanics for the sp-valent alkali metals, I generalized when I was in Cambridge to the case of the elemental transition metals. For the binary alloy the picture I had in mind was originally that of Miedema's model. It suggested that if you mix a metal A with a metal B, then you start by cutting out the Wigner-Seitz sphere for metal A and the Wigner-Seitz sphere for metal B and bring them together to form the alloy. I started with that model and tried to show that within DFT you could get an ionic term and a repulsive term like in Miedema's picture. But that was not possible. I realized that I could not justify Miedema's model and I went back to the more chemically intuitive tight-binding model, championed by Jacques Friedel at the time.

BBV : Could you clarify what you mean by analytic model ?

DP : Consider making a model able to predict the heat of formation of transition metal alloys. You start with a real transition metal. It has two types of valence electrons : free electrons and electrons more tightly bound to their parent atoms. The latter are more like the electrons in diamond, in the carbon atom. They overlap and give strong, covalent bonds. If you look at which element has the highest cohesive energy, it is not carbon, diamond or graphite, but actually tungsten which is a transition metal. It comes not from the free electrons but from the tightly-bound d electrons. The model relies on three simplifications that help understand the changing energy when A and B mix. The first simplification is the assumption that the d electrons are the critical electrons whereas the s and p can be neglected. The second simplification is that we assume a constant density of states throughout the d band. We don't want to calculate the exact electronic structure. The third simplification is that we assume that the atoms remain neutral, i.e. there is no net flow of charge from A to B on the formation of the alloy. I call it a model because it is a simple representation of reality, but it is a mathematical model. It is not a qualitative representation. It is a rigorous model because we try to make it internally consistent.

BBV : Which of these assumptions were controversial in your model ?

DP : The third one was critical. Miedema was unhappy about it. There was a big fight at Bell Labs with the person I worked with, who was also unhappy about this lack of explicit ionicity within my model. Nonetheless, I got permission from my bosses at Bell Labs for my paper to go out with myself as the sole author. But to show you the power of scientists at Bell Labs at that time : I went to Imperial College as a new lecturer with my paper already accepted by the Physical Review Letters. Soon afterwards the editor wrote to me saying there was someone at Bell Labs who was submitting similar results. We would like you to withdraw your earlier paper and write instead a joint paper. I wrote back and said I am sorry but this question had already been officially resolved whilst I was at Bell Labs. So it came out just with my name on it. Finally, scientists at IBM Laboratories in Yorktown Heights did DFT calculations and confirmed the basic assumptions of my model.

Such models are important. You asked me why as a physicist I work in Materials Science. People in Materials Science found they could understand the concepts and use them to help design less brittle, more ductile alloys, for example. 15 years ago scientists and engineers at Oak Ridge National Laboratory were attempting to stabilize cubic close-packed phases of the titanium alumini rather than the naturally occurring tetragonal or hexagonal binary phases which were very brittle at room temperature. I had recently ordered the structural database of binary compounds within a simple two-dimensional structure map. Conventionally, structure maps had been constructed by taking coordinate axes to reflect those physical properties which were deemed important for controlling structural stability : for example, the difference in electronegativity of the two elemental constituents ∆X, the difference in atomic size ∆R, or the average number of valence electrons per atom e/a. During the early 1980s Pierre Villars had constructed such three-dimensional maps (∆X, ∆R, e/a) in an effort to separate the binary compounds into distinct structural domains within the map. Unfortunately, the structural separation was not good because these maps relied solely on the classical coordinates of electronegativity, size and number, neglecting completely the quantum mechanical character of the valence orbitals (which describe the bonding hybrids or ‘hooks' that stick out from the atoms to form directed bonds). I realized that if we were to present the structural data in a user friendly fashion for the alloy developers, then we could not use physical coordinates (that required at least four dimensions !) but instead must use a single phenomenological coordinate. This I obtained by running a string through the periodic table, as shown in Picture 1.

Picture 1.

Pulling this string apart orders all the elements with respect to each other, so that two dimensional maps can be plotted for any given stiochiometry (see Picture 2). These maps suggested to the alloy developers how best to alloy their binary titanium aluminides to drive the pseudobinary into cubic domains of stability. They found that these cubic phases were indeed less brittle than the original tetragonal or hexagonal phases, but alas they were still not ductile enough to fly in a jet engine ! This required the expertise of traditional metallurgists who subsequently found clever processing routes to control the microstructure of the alloy. Nevertheless, these two-dimensional structure maps are very powerful pedagogically. The string is the simplest representation that keeps the chemistry by grouping like elements in sequential order. I would call this a model.

Picture 2.

BBV : So would you call the Mendeleev periodic table a model as well ?

DP : I don't have such deep philosophical thoughts. I would call it a table and I call that a string. So maybe it is not a model. But the periodic table is a representation of reality that topologically orders all hundred elements within a matrix that rationalizes their chemical properties. Similarly, this string helps order empirical data on compounds, thereby allowing the search for new alloy phases with improved mechanical properties.

BBV : Is it the kind of models that you are doing at the Materials Modeling Laboratory ? What is the role of modeling now in Materials Science ?

DP : When I came here ten years ago the idea was to set up a Materials Modeling Laboratory that was unique at that time. We wanted to go the whole way from quantum mechanics up to the engineering level within one laboratory. (Picture 3 : hierarchy of models). I have colleagues who do the modeling of processes, for instance, the solidification of metals, or the spray forming of metals. Obviously they use continuum modeling rather then quantum mechanics. The goal was to get this community to talk together. The chemists doing drug design had always had good contacts with fundamental ab initio theorists. But the drug design did not really get beyond the atoms, they did not have to worry about the microstructure. My community had a quantitative basis from which to start. So we could solve the density functional equations on huge computers and get binding energies, heats of formations, and even phase diagrams from first principles. Going from the electronic world through to the world of atoms, then up through the microstructural domain to the continuum world, the idea was to bridge the gaps between these different modeling hierarchies. Ten years ago people started talking to each other but there was not much interaction, except in the polymer world where the chemists had made the most advance in so-called multi-scale materials modeling. But it was also political because at each length-scale there was a different community, loosely corresponding to a different discipline. During my inaugural lecture in Oxford ten years ago, I plotted the vertical scale as drawn in Picture 3 to show that our lab had to be interdisciplinary.

Picture 3.

BBV : Practically how did you interact ?

DP : I introduced the Friday lunchtime seminars. The MML (Materials Modeling Laboratory) seminars are different from the department colloquia. These weekly seminars were a learning experience for all of us. My colleagues in the department saw them as highly successful in integrating the modeling and experimental work within the department.

BBV : So is it by this way that your own research belongs to materials science ?

DP : Yes, I believe very strongly in the goal of multiscale materials modeling where the ultimate driver is to understand and control the processing and properties of materials.

BBV : What kind of models did you work out in this department ?

DP : With multiscale modeling we got funding several years ago from DARPA on the chemical vapor deposition of diamond films. That brought together a team involving a chemical engineer for modeling the flow of gases through the reactor, a materials scientist for modeling the growth of the film, and us in Oxford doing the quantum mechanical atomistic studies on the dominant growth mechanisms at the diamond surface. In America that particular program was called virtual integrated prototyping, VIP. That was a very exciting dynamic program. It was unusual for non US scientists to get funding from DARPA. The same project to model the CVD growth of films was considered as too ambitious in this country by the Engineering and Physical Sciences Research Council (EPSRC). We have just put a new application into the DARPA spintronics program that is centered on deriving interatomic bond-order potentials to bridge the gap between the electronic and atomistic modeling hierarchies.

BBV : It seems that the Americans have been extremely important to you.

DP : Yes, DARPA has been important in supporting this work on bridging these gaps. Also it was the Americans who funded the work on the structure maps. The US Department of Energy gave me money that allowed me to take a sabbatical. When this lab was set up ten years ago we got funding from Hewlett Packard Laboratories in Palo Alto for two modeling postdocs and one experimental postdoc. They are currently funding a postdoc to model the writing with an electron beam in phase change materials for atomic resolution storage.

BBV : How do you see nanotechnology ?

DP : I am obviously in favor of it. I am involved with a colleague in this department, Andrew Briggs, on quantum computing in collaboration with people in Cambridge and from the Clarendon Laboratory on the other side of this road. He got a big grant last year. He is looking at different ways of building solid state quantum computers. One of the ways is based on putting nitrogen inside a fullerene inside a nanotube of carbon. Nitrogen has a spin which is a good quantum bit. There was an excellent discussion meeting about quantum information processing a month ago at the Royal Society. The science coming out is absolutely amazing. Even if we don't have a quantum computer in twenty years time, it is pioneering science. The concepts are totally different from classical computing. That is only one part of nanotechnology but it is a very exciting area.

BBV : Do you think that nanotechnology can bring more coherence into the cluster of research fields covered by materials science ?

DP : Tony Evans, probably the most cited materials scientist in the world, currently at Santa Barbara, was the chair of the Panel of Assessment of materials science departments in this country. He started his presentation stating that "Materials science is an enabling science". If it is a science that enables engineers to make things, it is not about to gain coherence as it spreads and dilutes itself into more and more fields such as biomaterials and nanotechnology. May be it will disappear from most universities as a unique undergraduate discipline in the future, as the core disciplines of physics, chemistry, biology and engineering set up interdisciplinary courses and modules. For the present, however, here in Oxford our multidisciplinary materials science course is becoming increasingly popular with school applicants, who enjoy the mix of physics, chemistry and engineering that we offer.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec David G. Pettifor », par Bernadette Bensaude-Vincent, 13 décembre 2002 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article127.

—

Entretien avec David G. Pettifor, par Bernadette Bensaude-Vincent, 13 décembre 2002

Lieu : Materials Modeling Laboratory, Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK

Support : enregistrement non précisé

Transcription : Bernadette Bensaude-Vincent

Edition en ligne : Sophie Jourdin

HIRSCH Peter, 2002-12-12

Sophie Jourdin — 2011-11-04T14:03:56Z

Professor Sir Peter Hirsch.

—

BERNADETTE BENSAUDE-VINCENT (BBV) : Could you tell me about how metallurgy developed in Oxford and how it grew into Materials Science ?

PETER HIRSCH (PH) : Let me first say a few words about the way I see the early developments of Materials Science in the UK. There were various trends that came together after the War. First of all there was Professor Nevill Mott in Bristol, developing Solid State Physics. His interests included inter alia defects and how they influence properties of materials. He had important activities on properties related to point defects and on the photographic effect. In the course of these studies they also developed techniques for visualizing dislocations. The group included Charles Frank, a physical chemist by training who was a material scientist par excellence. He developed a theory of crystal growth. Then there was Nabarro who worked on dislocations. So in Bristol they worked on defects, dislocations, crystal growth, the photographic effect, and also optical properties of crystals.

BBV : Where were they based ?

PH : In the Physics department at Bristol University. It was Solid State Physics. The electron theory of metals was developed there too. And Jacques Friedel was there for some time. In my opinion Solid State Physics opened the way to Materials Science. In parallel with this there was the group in the Metallurgy Department in Birmingham, lead by Alan Cottrell. He is much more of a materials scientist than I am. He was subsequently instrumental in developing Materials Science in Cambridge. His activity in Birmingham was very important because his group attempted to explain mechanical properties in terms of disclocation theory. And the third trend was what happened here in Oxford through Hume-Rothery's classic work on electron phases of alloys. He stimulated work on electron theory of metals and alloys in Physics Departments elsewhere. He was trained as a chemist.

BBV : So it came out of these three trends ?

PH : These are the main three. I may be unfair to other groups but these were the most influential groups.
There was some Metal Physics going on in the Cavendish Laboratory after the war. Bragg, who was Head of Department was of course an X-Ray crystallographer. In order to understand the intensities of diffraction spots on an X-Ray diffraction photograph, it had to be assumed that the crystals were not perfect, i.e. that crystals consisted of mosaic blocks. This was based on a theory by Darwin (1914) of the intensities of diffracted X Rays. Bragg published a note in the 1940s on the relationship between strength and particle size (mosaic blocks) in crystals. There were two groups in the Cavendish in the Metal Physics field when I came in 1946. One was Bragg's little group which developed the bubble-model, typical of Bragg's simple but brilliant ideas. Another group was Orowan's Metal Physics group which studied plasticity, fracture, creep, those sorts of topics.

BBV : It is in the Cavendish Laboratory that you started your career, isn't ?

PH : It was 1946 when I joined and there were several activities. My own work started from Bragg's interest in work hardening (when you deform a metal it becomes stronger). I actually went into the Crystallography Department of the Cavendish to work on a PhD problem that Bragg gave me. It was conceptually very simple. If you take a metal and work it, does it break up into smaller blocks ? Bragg always had very simple and brilliant ideas. If the crystal breaks up into smaller blocks (subgrains) the diffraction pattern consists of individual spots from each little subgrain. If you make the beam small enough you illuminate such a small number that you will get a few spots on the diffraction ring, whereas, with too large a beam diameter you get a continuous ring due to overlapping spots. You can count the spots (on discontinuous rings) and deduce the size of the particles. That was the project. It did actually work for heavily cold worked aluminium. We derived a particle size of 2 microns. By the time we managed to do all this by X ray diffraction, Bragg had lost interest in it. He did not actually supervise me. Bragg was interested in proteins at that point. My formal supervisor was W.H. Taylor who was head of the Crystallography Department. His interest was the structure of minerals.

BBV : When you worked in Cambridge did you consider yourself as a crystallographer ?

PH : I was a physicist working in a department of crystallography. In those days most conventional crystallographers determined crystal structures. I was one of the relatively few people not doing that.
By the time we found that cold worked aluminium breaks into subgrains, Heidenreich at the Bell Laboratories published the first pictures of metals by Transmission Electron Microscopy (TEM). He observed directly the little subgrains in heavily beaten aluminium foil. That depressed us very much because we needed exposures of many hours for our x-ray diffraction photographs, while he had a ten second exposure with his electron microscope. So we went into this field of TEM and finally we saw individual dislocations. This had a big impact because there were many metallurgists who did not believe in dislocations, who considered them as figments of the imagination of solid state physicists working out theories in tremendous detail without much supporting experimental evidence. With our technique you could see dislocations directly and see them move. And we made movies. I remember showing a movie at MIT to Bert Warren who was a well-known X Ray crystallographer. His comment was symptomatic of many metallurgists. Seing is believing. We converted people.

BBV : In terms of institutions could you describe the shift from Metallurgy to Materials departments ?

PH : There were many Metallurgy departments in this country : Sheffield, Birmingham, Imperial College, to mention a few. The activities of the groups that I mentioned gave an impetus. But an important impetus came from the United States. Bill Baker and Herbert Holloman in particular had this vision of multidisciplinary activities leading to the development of better materials, whiskers, ceramics etc.. An enormous amount of money was spent at General Electric, and Bell Telephone and the Ford Motor Company. When Alan Cottrell became Professor in Cambridge that was the real beginning of an institutional effort to develop Materials Science in this country. In my opinion that was the defining moment. Alan Cottrell left Birmingham in 1955 and went to work at the Atomic Energy Authority at Harwell where he worked on uranium and materials for nuclear reactors. Then he became Goldsmith Professor of Metallurgy in Cambridge in 1958. He started projects on ceramics and composite materials. Tony Kelly joined him to work in these areas. Alan Cottrell ‘s interest in composite materials probably stemmed partly from activities in the US but mainly from his own views on strong materials. He also supported work on superconductors. His initiative to work on different types of materials was probably the beginning of the shift from metallurgy to materials science in Universities in this country.

BBV : Could you tell something about the implementation of Materials Science here in Oxford ?

PH : The department of Metallurgy and an Honour School in Metallurgy were started by the University in 1957. Jack Christian wrote a paper on the early history (Materials World, April1997) when the department celebrated its 40th anniversary. You see from this that Hume-Rothery started as a chemist and worked in the Inorganic Chemistry Department. But he was interested in metallic phases. The idea of a separate department arose gradually. Jack Christian was appointed as demonstrator in 1951 and initially lectured on metallurgical topics to chemists. Metallography was a supplementary subject in the Chemistry Honour School. Then the Pressed Steel Company at Oxford established a readership in metallurgy named after George Kelley. Hume-Rothery became the first George Kelley reader in 1954. Jack Christian was appointed lecturer in 1955, then John Martin came from Cambridge and joined in 1957, followed by Angus Hellawell. There was a move to increase the Engineering School and to develop a Department of Metallurgy. Francis Simon who was professor of physics here was keen to establish something on the lines of the Laboratory for the Study of Metals in Chicago, which was famous in those days. Chicago was a research institute, not a teaching department, just a research institute for postgraduates. This is what Simon had in mind for Oxford. However, the industrial advisors expressed the view that we needed to educate metallurgists to go into industry. British industry wanted a teaching department. Monty Finniston, who was at the time the head of the metallurgy division at AERE Harwell and later became chairman of British Steel, made approaches to the Wolfson Foundation for financial support. The result was the establishement of the Isaac Wolfson Chair in Metallurgy which Hume-Rothery held until his retirement in 1966.
At the same time the condition that the Wolfson foundation made for giving the money for the Chair was that the University Grants Committee, an organization distributing the money from the Department of Education to the Universities, should provide the funds for the building. Funds were provided by the University Grants Committee and the building was opened in 1959. Initially the Honour School was a Joint Honour School in Chemistry and Metallurgy, which subsequently became Metallurgy. There is an interesting quote in Jack Christian's paper which indicates the University's unease with technology at that time. The Honour School should teach « no more technology than is involved in the degree courses of chemistry and physics » and it stated that « the man who has studied pure science at a university can take up technology on entering industry much more easily than one who has studied technology can later take up the pure science which may be required for his work ». It was still quite difficult to really expand engineering and to get a proper engineering metallurgy course at that time. The research that was going on here was on alloy phases (Hume-Rothery's research) ; John Martin worked on mechanical properties of alloys ; Angus Hellawell worked on solidification studies ; Jack Christian worked on phase transformations - the martensitic transformations - of metals and alloys, and also on plastic deformation of body centred cubic metals. So that was the development of metallurgy in Oxford before 1966. Clearly this department was a metallurgy department rather than a materials department. But Hume-Rothery's work was influential in encouraging solid state physicists to become interested in metals. He stimulated the understanding of the structures of metals and alloys on the basis of the fundamental electron theory of metals. He empirically developed some structure rules. He hoped that electron theory of metals would enable the prediction of the structures of metals and alloys and appointed a theoretical chemist, Simon Altmann, to work in this area.

BBV : And then you came in this Metallurgy department. Why did you move from Cambridge to Oxford ?

PH : I came in 1966. I was a physicist who had worked on electron microscopy of defects in materials. I had the opportunity to take a Cambridge chair or an Oxford chair. I decided to go to Oxford for two reasons. 1) I had been in Cambridge quite a long time (23 years) and a change opens new vistas. 2) The challenge was much greater here and my own predilection was always for building things up. The Cambridge Metallurgy department was a large and successful department built up by Alan Cottrell. In Oxford there was really a nucleus of a department (a distinguished one) and in principle one could do a job to build it up.
I had already built up a large research group in the Cavendish in Cambridge. When Bragg switched his interests to proteins (Perutz, Kendrew et al) Orowan left and went to MIT. I don't know the details but my impression is that Bragg did not work hard enough to get Orowan a senior permanent job. So the Metal Physics group in Cambridge folded up. Bragg's own little group folded up too. We made a significant effort to set up a new Metal Physics group at the Cavendish. The vision behind this was : We now had a technique to enable us to actually see with the TEM what is going on inside metals and one could see the defect distribution after deformation or irradiation of the material. One could then determine in principle what the properties of the materials were. That was the Holy Grail. There were three steps : 1) to try to understand the properties of the defects and how they interacted ; 2) to try understand how they control the macroscopic properties ; 3) if one understood the basic relation between defects and properties then one could eventually go further and predict what processing should be done to optimise properties. That was the vision but while we were successful in the first step, there was only limited success in the second step, and we never got as far as the third step.
When I came to Oxford, my aim was to get this technique of TEM - to see what goes on in the materials - transferred to a metallurgy/materials department. I wanted to get it closer to applications to « real » materials. Whereas physicists work on models, - on pure copper for instance, a metallurgy department should be looking at materials of interest technologically, such as alloys that are much closer to practical needs. My aim was to apply TEM to technologically interesting materials, real materials rather than the model materials that we looked at in Cambridge.
When I got here I did attempt to build up Materials Science. Right from the beginning my aim was to shift from metallurgy to materials science which should cover all kinds of materials and applications.

BBV : Where did this project come from ?

PH : There was no model course. We had to build this up incrementally. When I first came the University provided three new permanent posts, very generously. One was for Professor Whelan, to establish the electron microscopy group. One went to John Hunt, a solidification expert who had worked at Harwell and Bell Laboratories ; and another one was for Geoffrey Groves who worked on ceramics. Gradually we built up a Materials Department by securing more appointments. You have to realize that when I came in 1966 the number of staff was very small (4 faculty plus the Professor).The course developed gradually and changed from metallurgy to materials science. In the early years a considerable part of the teaching was carried out by research assistants or fellows supported on research grants or fellowships. The research activities were built up first, and the research groups then helped in the teaching of the Honour School.

BBV : When did you officially change the name of the department ?

PH : That was much later, 1990. The name of the Honour School was changed to Metallurgy and Science of Materials in1969 (The University would not accept "Materials Science" because Materials was not an adjective !).

BBV : Did you appoint chemists as well ?

PH : We didn't appoint chemists to teaching posts. We appointed metallurgists and physicists. But we did appoint a chemist to a research post in the department, in high resolution electron microscopy. When I retired in 1992 the department consisted mainly of metallurgists or materials scientists and physicists or ex-physicists. We appointed inter alia people who had expertise in semiconductors, superconductors, magnetic materials, materials processing, corrosion. Gradually we extended the scope of the courses in the department. The one sticking point was polymers. For a very long time we could not get a good polymer scientist. It has changed now. We now have two polymer scientists.

BBV : Did you have contacts with John Goodenough who came to the chemistry department in 1973 ?

PH : We did have contacts but we probably did not make the best of the opportunity. In this department we were more interested in the effect of microstructure on materials, metals, ceramics, semiconductors, superconductors, magnetic materials etc., rather than e.g. in the intrinsic magnetic properties of perovskites and other materials. Our interests were not sufficiently close. We became a Materials Department in that we were concerned with the effects of microstructure on properties of a wide range of materials of technological interest and with the effects of defects on devices. The work on superconductors was initially on low temperature superconductors, but later on high temperature superconductors, and the more recent studies focused on processing. There was some interaction with the Inorganic Chemistry Laboratory on electron microscopy of catalysts and superconductors.

BBV : Did you keep a close link between courses and research in the department ?

PH : Yes. We started as a metallurgy department. We built up a number of research groups, and the expertise in some of these, e.g. semiconductor and magnetic materials, enabled us to teach courses on these topics and broaden the curriculum to Materials Science. At some point we had a group working on cements, and this too led to a course in the Honour School. And there were always undergraduate and postgraduate courses on materials characterisation, where we had particular strengths. In the 1980s, I became more interested in the output end, in getting closer to the engineers.

BBV : Did you train students in engineering ?

PH : The engineers had their own faculty to teach materials to Engineers. But we did some teaching for them, and over some years they taught polymers for us. In the mid 1980s we started a joint course with the Engineers on Electronic and Structural Materials Engineering, changed to Engineering and Materials in 1992. This led to closer collaboration with the Engineers in teaching and research.

BBV : Did you also have contacts with the nuclear physics department in Oxford ?

PH : The only contact we had with the Nuclear Physics Laboratory in Oxford was on their proton microprobe, a materials characterisation tool, and fairly recently this activity was transferred to our department.

We had a lot of contacts with Harwell. From 1973 onwards I got very much involved with the study of the integrity of pressurized water reactors through the Marshall Committee. From 1982 to 1984 I became part-time chairman of the Atomic Energy Authority. This period had a strong influence on me. I felt the need to produce materials engineers, not only materials scientists. I learned during my period with the Atomic Energy Authority that the education of engineers in materials tended to be relatively poor. And this could result in inappropriate component design or manufacture. These problems sometimes led to costly mistakes. In order to develop a joint activity between engineers and metallurgists we got some support from the engineering department. To cut a long and difficult story short, we took an opportunity which presented itself around that time in the form of additional funding for engineering courses from the Government to start a course on Electronic and Structural Materials Engineering.

BBV : Was it in the 1980s ?

PH : Yes.

BBV : Did you then feel the need to add « engineering » in the name of the department on the lines of the departments in US universities that are called Materials Science and Engineering with an emphasis on the E of Engineering ?

PH : What happened here is that we developed a multiplicity of courses to provide more options for the undergraduates to increase our intake. The courses were Metallurgy and the Science of Materials, then Metallurgy, Economics and Management (1979), and finally Engineering and Materials. There is close collaboration between us and engineering through the teaching and contacts in research. This depends on individual contacts of course. In the 1980s we set up with the Engineers the Oxford Centre for Advanced Materials and Composites (OCAMAC) to foster collaborative research and contacts with industry. There is now also strong collaboration with people in chemistry and physics on a number of research programmes. We have become much more interdisciplinary, if you like. We have always considered ourselves as a bridge between the Science and Engineering Departments, with contacts with both. The fact that Physical Science and Engineering are all part of the same faculty in Oxford is advantageous to us. We did consider changing the name of the Department to Materials Science and Engineering - but that was unacceptable to the Engineers who considered Materials Engineering to be their responsibility. So we decided to change the name in 1990 to "Department of Materials".

BBV : It seems that your story is quite different from that of the US materials departments.

PH : I think that it is different ; you are quite right. Here the initiative to have Materials Departments came from academics, whereas in the US the development was led by Industry, and industrialists promoted Materials Science in Universities. (This does not mean that no materials science was going on in industry in the UK - e.g. the carbon fiber work at Farnborough.) I think it started in Cambridge first. We came along in the late 1960s. By that time there were materials science activities going on in many departments, at Imperial College and Birmingham, for instance. We could not claim to have inspired Materials science in the UK. We came along and did our own brand. There were many departments, but they were on a small scale. Concerning the definition of Materials Science I am with Merton Flemings. Structure, properties, processing, performance/application. I think it is the engineering applications that are fundamental. The philosophy of the department here was to get theoretical and practical people together. People able to develop models with people who really know what applications are important. And industrial links were fostered. It is still the philosophy today, even more so. In the last few years after my retirement the department has gone from strength to strength in that direction. There is now another site in Begbroke, five miles away from Oxford centre. It provides opportunities for collaborative research between the Department and Industry.

BBV : Where did the money come from ?

PH : The funding for work in the department came partly from the University, the Research Council and Industry. Some from charitable foundations, e.g. for building expansions. We had a large budget from the Research Council. That is another important aspect, somewhat similar to the US picture.

It is difficult to attract undergraduates to read Materials Science and Metallurgy. Enormous efforts have been spent on attracting more undergraduates, most of them not very successful. (But a recent appointment of a Schools Liaison Officer seems to be effective.) Materials Science is not a school subject, although elements are introduced into some of the school examination papers e.g. the physics curriculum. The number of courses and options that we offer in Oxford has helped a bit but it remains a problem. Some small departments in the UK were able to survive because they had a large research activity (supported on non-University funds) compared to the undergraduate activities. But in the UK as a whole some Materials Departments have closed or have been amalgamated with Engineering Departments. The change of name of department from Metallurgy to Materials does not only reflect the change in content of the courses. It is also pragmatic because metallurgy has an old-fashion ring about it and materials science is a much broader subject likely to attract more students. The image of materials for computers, aeroplanes and cars is more exciting than that of dirty blast furnaces in the steel industry.

BBV : What would you say about multidisciplinarity in the development of this department ? More specifically could you compare the situation here in Oxford with this diagram published by the National Academy of Science in 1969 with a hard core in mathematics physics and chemistry and applications around ?

PH : I would agree with this : mathematics, physics and chemistry are basic inputs in Materials Science with applications in ceramics, polymers, and so on. But in these days I would include materials for medical applications. There is somebody in this department working on biomedical materials for implants. There is also a large group in Cambridge. There is a big scope for materials in medicine, particularly for prostheses.

BBV : Finally would you consider yourself today more as a physicist or as a material scientist ?

PH : I think I am physicist who « saw the light ». True physicists would no longer consider me as a physicist. I consider myself as a materials scientist because my interest is in the effect of microstructure on the properties of materials. I am interested in quite complex materials, with potential applications e.g. high temperature intermetallics, and in modelling their complex mechanical properties. I ended up as a materials scientist. But there are materials scientists who would consider me to be a rather theoretical materials scientist. In the later years of my conversion I supported and promoted materials processing in the department although it took me rather a long time to get to this view, to appreciate the importance of this field, and to realise the need and potential for modelling.

BBV : What is your concept of materials science ?

PH : I am close to Merton Flemings's concept. To me materials science is an enabling science. We study material composition, structure, properties and processing for applications in engineering. There is now a strong group on processing here. Not only casting but various kinds of processing like spray forming, coating, making magnetic and superconductor devices etc. There are also two lecturers working on polymers now.

BBV : Does polymer synthesis now belong to Materials Science ?

PH : Polymer processing and modelling properties belong to materials science, but synthesis of new kinds of polymers - I doubt if this is a proper activity for a materials department, although it would be quite appropriate as a joint research activity with Chemistry. That would be my view for what it is worth. But composition, structure, properties, performance, Merton Fleming's picture, defines Materials Science.

BBV : What about the recent addition of end-users to this picture ?

PH : Yes end-users are important but I would consider that this links in with performance. The interaction with industry is important. Quite apart from the problem of funding it is vital for materials science, as an enabling science.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Peter Hirsch », par Bernadette Bensaude-Vincent, 12 décembre 2002 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article126.
—

Entretien avec Peter Hirsch, par Bernadette Bensaude-Vincent, 12 décembre 2002

Lieu : Materials Department, Oxford University

Support : enregistrement non précisé

Transcription : Bernadette Bensaude-Vincent

Edition en ligne : Sophie Jourdin

HIRAO Kazuyuki, 2002-08-29

Sophie Jourdin — 2011-11-04T13:08:55Z

Kazuyuki Hirao.

—

HERVE ARRIBART (HA) : In which discipline did you take your degree and your Ph.D.?

KAZUYUKI HIRAO (KH) : I was trained in Inorganic Chemistry.

BERNADETTE BENSAUDE-VINCENT (BBV) : Why did you decide to go into Glass Science ?

KH : Well, you know, the Chemistry Department of Kyoto University is very old, 100 years old. When I had to select a laboratory, I was interested in inorganic chemistry. I belonged to the Chemistry Department but only one division of chemistry was Glass or Ceramics related to inorganic chemistry.

BBV : Did you publish books in inorganic chemistry ?

KH : Yes, I published two textbooks on Inorganic Chemistry intended for undergraduates. One of the textbooks was translated but another one I wrote myself in Japanese.

BBV : Do you have to teach inorganic chemistry ?

KH : Yes at the undergraduate level.

BBV : And do you have to teach a course in Materials Science ?

KH : Yes I have 3 courses a week : one of them is Glass Science, the second is Advanced Materials, and the 3rd one is Inorganic Chemistry. Inorganic Chemistry for undergraduate students, Glass science and Advanced Materials for graduate students.

BBV : There is no department of Materials Science at Kyoto University ?

KH : Materials Science partly belongs to chemistry. My department is called Department of Materials Chemistry. But Materials also belongs to Metallurgy. They have a department of Materials Science which is totally separated from us. We have no common class between Materials Science for chemists and Materials Science for metallurgy. We have to collaborate in the future. The Department of Materials Science also belongs to the Department of Mechanics. Chemistry and Mechanics are totally different. Polymer Chemistry is also separated. We still have to build up the new class of Materials Science. In Japanese universities, it is not usual to have interdisciplinary Materials Centers. It is usually divided. It is not good for research. Because equipment is shared.

HA : What kind of instruments ?

KH : TEM, SEM, X Ray, spectroscopy. At least in nanotechnology we ignore the boundaries between polymer science, metals, ceramics and glass. It will be possible to develop the new materials perspective.

BBV : Do you think that this traditional university system prevents you from doing Materials Science ?

KH : It is difficult to change. If you want to change anything, you will have to obtain agreements from all the professors in our departments. University professors are very conservative.

HA : Still, Professor Soga did endeavor to change the system while he was here.

KH : Yes, but in Japan if one single professor is against the change, then there will be no change at all. We don't usually have a majority decision making system.

BBV : Are the students more attracted by Materials Science in general or by Chemistry and Physics ?

KH : The entrance examination is about Industrial Chemistry. Almost 250 students are admitted. After one year, in the 2nd grade, they will be distributed into three different courses. Three classes divided mechanically. In the 4th grade they chose to enter into one the laboratories of the department. Four graduate students choose to enter in my laboratory every year. Kyoto University is a very big university. We have almost 47 chemistry professors for 250 students. 150 graduate students. Two Nobel Prizes came out from this department. It is a prestigious department.

HA : Could we come back to your PhD subject ? How did you choose it ? Was it Professor Soga who proposed it ?

KH : Yes it was about Glass Science. Thermal properties of glass.

HA : From your list of publications I can see that you have worked on many, many fieldswhile working in Professor Soga's laboratory.

KH : Yes I have been mainly interested in computer simulation of making glass structure and predicting optical properties of glass. I started computer simulation early in the 1980s. It was too early. The computer capacity was very small in the 1980s. Now we have a big project on computer simulation program and we get $5 million over five years from the government for it. Owing to the progress of computers, we can make glass structure containing 10,000 atoms.

HA : Then why did you move to non-linear optics instead of mechanical properties or low temperature behavior ?

KH : It is a good point. One major advantage of glass is transparency. Its major disadvantage is brittleness. Optical fibers are a very important because electrical wires are very limited in speed.

HA : So by the end of the 1980s you guessed that the future of glass for a large application would be optical glasses.

KH : Now we are very lucky. We are also interested in the mechanical properties of glass at the nanolevel. We are dealing with elimination of the nanobubbles. It is very important for industrial companies.

HA : So you got in to the glass making process ?

KH : Yes.

BBV : Was it industrial demand that prompted you to work on optical properties in the 1980s ? Or was it your own initiative, your choice ?

KH : In this period the optical properties were not important for glass industry. Now many glass companies are interested. So now we have a lot of industrial contacts. Before next year we intend to produce 3 commercial optical glasses called photonic glasses. For this, we need connections with venture business.

BBV : Do you mean that you conducted all these researches on optical properties without industrial support ?

KH : No, only in the beginning. Now we get a lot of industrial support. But now I get a lot of budgets from three kinds of government projects, not only from industry. We have 3 projects. One is computer simulation. One is on photoactive glass in cooperation with foreign countries. So we have a lot of post-docs in my laboratory. The third one is the nanoglass project.

HA : Could you tell us about this nanoglass project ?

KH : The government launched a nanotech program that covers a variety of projects : nanometals , nanopolymers, carbon nanotubes, nanocoatings, nanoparticles, nanosimulation and the nanoglass project. For the latter, we get $30 million for 5 years approximately.

HA : How do you spend this amount of money.

KH : Most people involved in the glass project are coming from industry, from Asahi Glass, Hoya, Nippon Electric Glass, Central Glass, Okamoto Glass, Nippon Yamamura Glass, Hitachi, ... 11 companies sent us 15 researchers whose salaries are paid by the project.

HA : How many people are working in your nanoglass project ?

KH : 100 people including the supporters. They join in Tsukuba consortium, from Osaka Institute and several university professors also support us.We have some large equipment.

HA : When did this project start ?

KH : We had a preliminary year and the project itself started in 2001.We have got a number of results. For instance CVD deposition. We also succeed in making very low optical loss glasses. We have reached 0.005dB/cm. This glass will be very useful for making waveguides. In Tsukuba we use two kinds of femtosecond lasers working at 1 kHz and 200 kHz. By using these femtosecond lasers, we not only write in waveguides but also we make crystals from glass, for example silicon crystals from amorphous silica.

HA : Last time you mentioned that you also have a laboratory in China working on crystal growth.

KH : That is right. And we have also made a lot of semiconductors, single crystals in glasses by using this material and we made photonic crystals, which can be used as optical filters.

HA : Where does the money for this nanoglass project come from ?

KH : From NEDO. It is part of METI (Ministry of Economy, Trade and Industry). No connection with AIST although METI also supports AIST. We also made a very tough glass whose strength is very high, 2 times that of standard glass. With the femtosecond laser we made very small dots, nanosize dots, that stop the cracks. We have already succeed.

HA : Was it enough to make these tiny holes on the surface ?

KH : They are under the surface. Also by using the interference technique we have made a lot of dots.

HA : I understand, it is beautiful glass but too costly for bottle makers.

KH : Of course it is not for bottle makers ! Also we have found a cheap process to make AWG (array wave-guide grating) by using the femtosecond laser. AWG are very useful for optical telecommunications. Until now, they were very expensive to make. We also managed to make a nanoglass thin film for CD. The storage medium can be a cobalt oxide-based glass, for example. When we apply a nanoglass coating on this recording material the blue beam is shrinked to ¼. This is a lens effect. We have now this optical disk standardized by Hitachi. So you know that Shuji Nakamura ; a Japanese researcher, has discovered the blue laser diode. In my case by using this blue laser diode, the recording capacity is approximately increased by a factor 4, because the beam is much smaller. And in the field of optoelectronics, we have made 3 dimensional devices including both electrical and optical circuits. We use gold containing glasses that crystallize under laser beam. Three dimensional wires can be obtained, together with optical waveguides in the same device.

HA : So this program seems to be essentially telecommunication oriented.

KH : Yes NEDO asked us to make such devices. Otherwise they would cut the financial support.

BBV : You mean that the budget is according to your practical results.

KH : Yes.

BBV : What kind of connections do you have with venture business ?

KH : For optical properties we have to make such connections. Otherwise we could not do it on university money or government money. Venture business have a lot of demands in optical properties of glasses. For instance some fibermakers make lenses inside optical fibers. With my technique of femtosecond laser we can make lense in fiber. There are many such innovations of interest for business, although optical properties are not directly related to optical devices.

BBV : Do you mean that you only do research and no development ?

KH : Optical properties are synchronized with optical devices. There is no linear sequence from optical properties to technical devices, from basic research to applied science then development. We have to work in synergy.

HA : So do you consider yourself as a materials scientist because you are dealing with devices ?

KH : Yes we have to make connections with venture business and industry. For doing this kind of research we have to build a wide network. So many venture businesses are connected with me and they are eager to be.

HA : Where does the money come from ? From big industrial companies ?

KH : So far my devices did not cost much. If one day we have to develop a costly device, the Japanese governement is able to support us immediately, at least for two or 3 years. The Japanese governement is encouraging this kind of cooperation.

HA : Do you also collaborate with foreign companies ?

KH : With Schott in Germany. They have sent a researcher here. And Corning is also willing to collaborate. In the USA glass professors are not so many in optical devices. Here we have more than 50 professors of Glass Science

BBV : Do you send students to the USA ?

KH : Not right now.

HA : Where do you locate the leading centers in your field ?

KH : I guess Osaka is the center. Glass science originated in Osaka National Center.

HA : You told me last year that you run many laboratories. How many ?

KH : I have 6 laboratories including one in China, one in Osaka, one Tsukuba ... 300 people altogether. There are autonomous and eager to make things because optical devices is a very promising field. So I don't have to be continuously behind them. There are so many things to do such as inkjet using semiconducting cadmium selenide nanoparticles. The color changes depending on particle size.

HA : This is not glass. Is it ?

KH : Yes it is, because nanoparticle CdSe particles are made in micelles and encapsuled by glass using sol-gel chemistry. The fluorescent yield increases nearly 10times using these nanoparticles. Silica sol-gel coating is necessary ; otherwise the semiconductor particles aggregate to each other. Encapsulated particles are then deposited by inkjet to make displays. We do this development by collaborating with venture business.

BBV : So you seem to work as a partner of venture business, as a manager of projects rather than as a traditional scientist supplying science for applications downstream.

KH : Yes my aim is really to make optical devices. This is what we have to do. We teach Glass Science. But in laboratory research we have to make devices. Traditional professors are not interested in devices ; I am. But you see, in Japan I don't have to move to an industrial company to make such devices.

BBV : Is it part of your obligations as a university professor to make devices ?

KH : No, teaching is the only obligation. We just have to teach and take care of the students.

BBV : Does the university system recognize your devices ?

KH : Yes now the government recognizes patents.

HA : So you feel that you are in a better position at the university because you have the freedom of choosing your topics of research and you have the money that you need for them.

KH : Yes I am very lucky.

BBV : How do you select your research projects ?

KH : The keywords are glass and optics. We have a lot of choices. One criterium is to use the femtosecond laser.

HA : You mean that you can use it to change glass composition ?

KH : If we use samarium doped glasses we can change the samarium3+ to samarium2+ with the femtosecond laser. So glass composition is very important for me. Not just to make new glasses and measure their optical properties. If we make a new glass it is to make a new device by using a new technique. We also made electrical lithography by plasma etching for nanodevices, in Osaka.

HA : On our webpage you also mention that you are working on hybrid materials.

KH : Yes usually at the macroscale, it is difficult to combine organic and inorganic components. Nanohybrids work better by using chemical reactions with micelles. Professor Tetsuo Yazawa at Himeji Institute of Technology University made a lot of nanohybrids that can be used for gas filters, for membranes, solid sensors and solid electrolytes. Conductivity is very high in the nanohybrids. Both electronic and ionic conductivities. And hybrids are also useful for glass capsules for drug delivery. So we started that kind of research on hybrids within the nanoglass project.

BBV : Do you try to compete with other materials in your nanoglass project ?

KH : No, glass offers unique advantages. We can overcome polymers. Glass is the only transparent material even at the nanoscale. I forgot ! Athermal glass is very important. We achieved athermal glass-ceramics we have to apply pressure to control the size of the nanoparticles and the growth. So nanoglass is unique and very useful.

HA : I can see that your project works very well. But do you remember any failure in your research career ? It is also instructive for our project on the history of Materials Science.

KH : For the Photoncraft project we are at the middle point so we have to submit. The nanoglass project started one year ago. We have to make an effort, otherwise budget might be cut.

HA : This morning Professor Soga told us that he considers himself as an educator rather than as a glass scientist. Is teaching and training also important for you ?

KH : You cannot separate teaching and research. Education and laboratory work together. In the field of glass, just making optical devices is a good education, a good training. Now we are training a number of students through the nanoglass project.

BBV : Do you mean that the nanoglass project is in itself a kind of training ?

KH : Yes, for graduate students. When I present the results of our nanoglass project to company presidents, they are essentially grateful for our work as educators because we train the researchers from industrial companies. Helping each other is very important.

HA : Does it mean that you are no longer interested in basic research and basic education ?

KH : No. Presently I am making devices but maybe in a few years I write a new textbook of glass science because they are so many new glasses that all conventional glasses are obsolete. This textbook should be written in English.

BBV : You want to write a textbook of Glass Science, not of Materials Science in general ? Are there any Japanese textbooks of Materials Science ?

KH : Yes and we had written one.

BBV : One final question : Do you see differences in the research styles of various countries ?

KH : In Europe originality is important. Here it is rather collaboration and harmony. We are more modest, more humble. Collaborations, mutual help and mutual learning, Interdiscipinary philosophy is my project aim.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Kazuyuki Hirao », par Bernadette Bensaude-Vincent et Hervé Arribart, 29 aout 2002 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article125.

—

Entretien avec Kazuyuki Hirao, par Bernadette Bensaude-Vincent et Hervé Arribart, 29 aout 2002

Lieu : Department of Materials Chemistry, Kyoto University

Support : enregistrement non précisé

Transcription : Bernadette Bensaude-Vincent et Hervé Arribart

Edition en ligne : Sophie Jourdin

HAGENMULLER Paul, 2001-06-12

Sophie Jourdin — 2011-11-03T15:23:16Z

Paul Hagenmuller, born in Alsace in 1921, developed solid-state chemistry in France. He first initiated a research program at the University of Rennes (1956-60). In 1960 he set up a dynamic laboratory in Bordeaux. In 1964, Hagenmuller organized an international conference dedicated to the relations between structure and physical properties in oxides of the transition elements. The meeting gathered together chemists, crystallographers and solid-state physicists and prompted the establishment of an international community of solid-state chemists. In Bordeaux, Hagenmuller became the head of a research school working, at the interface between physics and chemistry, on the relation between atomic/electronic structure and physical properties, with a strong emphasis on industrial applications.

The Bordeaux research school has attracted scientists and students from all over the world (both developed and emerging countries) and many brilliant chemists of the next generation such as Jean Rouxel were trained in Bordeaux. Paul Hagenmuller retired in 1994. A jubilee celebration was organized at the Maison de la chimie in Paris in 1997. In 2001, his 80th birthday was celebrated in a special issue of the journal Solid State Chemistry.

HERVE ARRIBART (HA) : Pouvez vous retracer votre formation, vos débuts dans la carrière ?

PAUL HAGENMULLER (PH) : Depuis que je m'intéresse à la science je me suis préoccupé de la physique. Je me suis demandé pourquoi les matériaux avaient telle ou telle couleur, tel ou tel comportement électrique, magnétique, optique ... J'ai donc été porté vers la physique, plus tard vers la mécanique par extension, dès que j'ai entrepris mes études de science. Ces études ont eu lieu en 1940 à l'université de Strasbourg, repliée à Clermont Ferrand. Mon statut était celui d'un réfugié politique puisque j'avais quitté l'Alsace pour échapper au système politique allemand et parce que je me refusais d'être un jour mobilisé dans l'armée allemande. A Clermont, pour des raisons financières j'ai fait le choix de la chimie, séduit par la diversité des méthodes de préparation mais choqué parce que la chimie était alors très descriptive et n'était pas encore une science déductive, de réflexion.
Sur place, je suis entré en résistance, je faisais du sabotage. J'ai été arrêté en 1943 et envoyé en camp de concentration à Buchenwald. Là j'ai appris à me taire. J'ai travaillé sur les V2. J'ai appris le russe avec les prisonniers russes ; j'avais de bons contacts avec les communistes allemands. Puis j'ai été envoyé à Dora où c'était plus dur.
Après la guerre, André Chrétien m'a proposé un sujet de thèse sur la formation de nitrites complexes en solution aqueuse, puis une recherche sur la réduction de divers oxydes par des hydrures d'alcalino-terreux. J'ai accepté parce qu'il y avait un appareil mathématique. Puis au lendemain de ma thèse je me suis dit : il faut que je travaille sur des choses plus concrètes, les matériaux. J'ai voulu revenir à mes anciennes amours les matériaux. Je suis parti au Vietnam dans le cadre d'un accord avec la direction de l'enseignement supérieur et moi. Je partais pour deux ans 1954-56, au moment où la France se désengageait et voulait garder des relations culturelles. Au retour il était entendu que je pourrai choisir un poste de maître de conférences parmi ceux qui étaient disponibles en chimie. Ces deux ans de Vietnam ont été pour moi une période de décantation, de réflexion. Et quand je suis revenu j'ai voulu, d'une part, me préoccuper de physique ce qui suppose la détermination des structures atomiques - pour comprendre les propriétés physiques il faut savoir quelles sont les positions des atomes - et, d'autre part, il faut une certaine habileté à préparer des matériaux par des techniques nouvelles fort différentes.

HA : Quelles étaient alors les relations entre physique des solides et chimie des matériaux en France ?

PH : Aujourd'hui la physique s'est beaucoup rapprochée de la chimie parce que, de part et d'autre, on a compris que c'était indispensable pour faire des matériaux à propriétés spécifiques intéressantes sur le plan de la science fondamentale et intéressantes aussi sur le plan des applications. Au début des années 60, on en était à se chercher. Moi, j'avais fait un choix très clair : faire une chimie orientée vers la physique, plus tard vers la mécanique. Maintenant c'est devenu presque de routine, ne serait-ce que par ce que les chimistes pour bien connaître leurs matériaux sont obligés d'utiliser des méthodes de caractérisation physiques. La physique s'est imposée dans les perspectives de la recherche comme par les nécessités quotidiennes : savoir où sont les atomes et les électrons.
Donc au retour du Vietnam mon objectif était d'associer la physique et la chimie. J'ai eu la chance que dans mon poste à Rennes il y avait quantité d'excellents étudiants, mais en chimie personne ne voulait faire de la recherche sous prétexte qu'il n'y avait pas de moyens. J'ai décidé que j'allais lancer des thèses dans ce domaine à l'interface de la physique et de la chimie. On a d'abord tâtonné. On a travaillé sur le bore, sur les hydrures. Parmi les études réalisées à Rennes se trouvait la réduction d'oxydes par l'hydrure de lithium. On était intéressé par les hydrures de bore et d'aluminium qui comportaient des liaisons dites pont-hydrogène originales. Ceci m'a donc amené à réduire le V2O5 par l'hydrure de lithium et nous avons constaté qu'il y avait des phases intermédiaires qui devaient être les futurs bronzes de vanadium et de lithium, qu'on a appelées plus tard b et g. La phase a étant la solution solide de lithium dans V2O5. Alors j'ai pensé que ces matériaux étaient intéressants : s'il y a là un domaine d'existence, les propriétés physiques doivent varier à l'intérieur de ce domaine et si, par chance, ce domaine est suffisamment grand on peut faire ce qui est plus difficile dans les solutions solides limitées, de type oxydes non stœchiométriques. On s'est préoccupé de manière systématique des bronzes de vanadium qu'on a préparés par voie synthétique. Dans les années qui ont suivi - de 1960 à 70, j'étais alors à Bordeaux où un grand nombre de chercheurs de Rennes m'avaient suivi - on a préparé un grand nombre de phases de bronzes de vanadium par analogie avec les bronzes de tungstène qui avaient déjà été signalés. On a fait systématiquement des études magnétiques et électriques pour caractériser le mode de conductivité. Il est apparu que lorsqu'on insérait le lithium dans le réseau, on remplissait les états électroniques du vanadium, qui forment la bande de conduction. Les électrons devenaient donc de plus en plus délocalisés au fur et à mesure que leur nombre augmentait et on passait d'un état semi-conducteur à l'état métallique.

BERNADETTE BENSAUDE-VINCENT (BBV) : Quelles étaient vos relations avec le groupe de Robert Collongues ?

PH : Collongues avait été élève de Georges Chaudron, comme André Michel, Paul Lacombe, Jacques Bénard. J'avais d'excellentes relations avec Collongues. Nos domaines se recouvraient partiellement sur la non-stœchiométrie mais on avait des approches différentes. Lui enlevait des ions, nous on faisait de la chimie d'insertion. Collongues aimait bien se singulariser par rapport à moi mais dans la pratique nous avions la même politique sur des matériaux différents. Il y avait chez lui le même désir de systématique et de réflexion en profondeur. Collongues considérait que la bonne expérience était importante mais qu'elle devait illustrer une réflexion de fond. Il pensait que la science était avant tout la réflexion intellectuelle.
J'ai fait de la chimie sous pression à la manière d'un tailleur : choisir une structure cristallographique, écrire la formule d'une composition chimique, puis la stabiliser dans un degré d'oxydation élevé. Après avoir discuté la structure puis la formule, on préparait sous haute pression. C'était du design pour la conductivité électronique, les propriétés magnétiques, ou les propriétés magnéto-optiques et plus tard également pour la conductivité ionique.
Nous nous intéressions systématiquement à l'évolution de toute propriété physique originale en fonction de la composition et de la structure. Un nœud important dans cette évolution fut le colloque organisé à Bordeaux en 1964 sur les oxydes d'éléments de transition.

HA : Quelle fut la portée de ce colloque de 1964 ?

PH : Ce fut le moment où s'est constituée une communauté internationale de chimie du solide. Le colloque a rassemblé les chimistes qui nous étaient familiers, des cristallographes (Erwin-Felix Bertaut, Charles Guillaud), des physiciens (Jacques Friedel). Parmi les étrangers Mike Sienko, John Goodenough du Lincoln Laboratory au MIT qui est venu pour la première fois à Bordeaux ; des Allemands : Wilhelm Klemm, Rudolf Hoppe, Harold Schäfer ; des Hollandais, des Belges, etc. Il est apparu qu'une conjugaison des méthodes de mesure physique, des méthodes de détermination structurale et une certaine flexibilité pour les changements de composition, pouvaient permettre d'optimiser un certain nombre de propriétés physiques. D'abord le magnétisme, ensuite il y a eu la ferro-électricité - comment accroître la distortion ferro-électrique et par voie de conséquence la polarisation ; enfin, la conductivité ionique, d'abord dans des matériaux isolants au point de vue électronique et ensuite dans des matériaux dits cathodiques utilisables dans des batteries parce que conducteurs mixtes.
Je dois dire que ce qui fut déterminant pour l'avenir de la chimie du solide ce fut la venue de John Goodenough à ce congrès parce qu'il a popularisé parmi nous l'idée de l'importance de la liaison chimique. On a compris qu'on pouvait renforcer ou atténuer la liaison chimique en modifiant la composition, en particulier en jouant sur la liaison antagoniste. Par exemple si on compare le zirconate de baryum avec le titanate de baryum, la liaison baryum-oxygène est renforcée dans le zirconate par rapport au titanate. Inversement si on remplace dans le titanate de baryum, le baryum par le strontium comme la liaison strontium -oxygène est plus forte que la liaison baryum-oxygène, la liaison titane-oxygène est affaiblie, ce qui peut amener une variation très forte de la polarisation en fonction de la température, juste en dessous de la température de Curie. Et on peut avoir ainsi des matériaux aux propriétés intéressantes.

HA : Le rapprochement de la physique et de la chimie avec une orientation vers les applications constituerait-il donc l'identité de la chimie du solide à cette époque ?

PH : Oui nous avions un besoin civique de justifier les crédits que nous demandions par une application dans la vie économique. De plus, le travail avec des industriels fait naître des problèmes inattendus qui sont des challenges et qui sont nourrissants.
Une deuxième date importante dans l'institutionnalisation de la chimie du solide est 1978. Sur mon initiative la Société française de Chimie a créé en 1976 une division de chimie du solide, dont j'ai naturellement été le président. J'ai organisé la même année un premier colloque national de chimie du solide à Nantes. Sur ma proposition et sous ma présidence s'est tenu à Strasbourg en 1978 le premier congrès européen de chimie du solide, organisé par Jean-Claude Bernier (Strasbourg a été choisi pour une raison stratégique,). L'intervalle entre deux congrès consécutifs est maintenant de 3 ans ; le huitième congrès européen a lieu en juillet 2001 à Oslo.

HA : Quel était l'état des relations entre science et industrie en France à cette époque ?

PH : Il y avait une tradition de collaboration en métallurgie et en chimie : Chaudron et ses élèves, Lacombe, Bénard étaient très impliqués. Robert Collongues l'était aussi dans le domaine des monocristaux. Mais il y avait une forte hostilité syndicale au nom des grands principes : il ne faut pas mettre la science au service des grands intérêts privés. Les choses se sont atténuées à la veille de l'élection présidentielle de 1981. J'ai eu la visite de M. Kahane, longtemps doyen à Orsay, qui s'était rallié à la collaboration avec l'industrie privée. Cela a facilité cette évolution qui, de ma part, ne rencontrait aucune résistance car j'étais un scientifique et je n'avais pas à me poser des problèmes de déontologie qui me paraissaient un peu artificiels. Mais une partie de mon entourage était réticente à travailler avec l'industrie.

HA : Est-ce la crise pétrolière de 1973 qui a contribué à anoblir le rapprochement entre science et industrie ?

PH : Oui. Du fait de notre préoccupation entre propriétés physique et composition, nous avons été conduits à travailler sur des composés non-stœchiométriques d'intercalation et nous avons constaté après 1973 qu'il y avait possibilité d'intercalation ou désintercalation à basse température grâce à l'électrochimie comme on le faisait aux Etats Unis. Exxon et Bell étaient plus concernés que nous par la crise de l'énergie.
Les recherches sur la conductivité ionique ont été encouragées par la crise de l'énergie. Après la zircone déjà exploitée par Nernst, puis étudiée par la NASA et par Collongues ; il y avait eu AgI. Puis il y a eu l'alumine-b qui a suscité de nombreux travaux. CGE a dépensé beaucoup d'argent. L'alumine-b est un matériau très particulier. J'étais très sceptique. On a abaissé la température de fonctionnement, mais c'est encore trop haut pour un véhicule électrique. Et puis le soufre attaque la membrane. Finalement on a renoncé, pensant qu'avec des batteries au lithium on irait plus loin. Les derniers efforts de développement visaient plutôt le stockage d'énergie en période creuse. Les nasicons eux ne sont pas attaqués et ils présentent un avantage au plan fondamental car leur structure est plus simple. Ils ont de bonnes performances, qu'on pouvait maîtriser avec une juste proportion de sodium.

HA : Pouvez vous évoquer vos travaux sur la conduction ionique ?

PH : Avant 1973, on a publié un grand nombre de documents sur des conducteurs ioniques. On s'inspirait comme modèle de réflexion des bronzes de tungstène bien que la plupart des travaux publiés à l'époque fussent des études structurales et que les bronzes de tungstène soient métalliques. On avait également préparé une série de nouveaux bronzes de tungstène. Ce travail s'est étendu à des bronzes oxyfluorés, à des bronzes de vanadium et de molybdène contenant les deux cations vanadium et molybdène plus le sodium et le lithium. Puis au début des années 1970, on s'est attaqué aux premiers bronzes de manganèse NaxMnO2 et puis aux bronzes de cobalt KxCoO2.
Sur ces entrefaites il y a eu la grande crise pétrolière de 1973. Les pays occidentaux ont eu peur de manquer d'énergie et donc on s'est occupé de sources d'énergie non fossile et de stockage d'énergie. Un certain nombre de gens ont voulu faire des batteries. Exxon et la Bell Telephon, Whittingham et Murphy en particulier, ont travaillé sur ces matériaux non plus comme nous l'avions fait vers 500°C avec des phases en équilibre thermodynamique mais à basse température par intercalation ou désintercalation électrochimique.
Une spécialité à Bordeaux c'était les fluorures conducteurs. On remplaçait systématiquement l'oxygène par du fluor parce qu'il a la même taille et présente une liaison plus faible. On pouvait ainsi atténuer les interactions magnétiques. Comme pour la zircone, on dope les fluorures systématiquement. Watanabe avait déjà préparé les premières batteries au fluor.
Jean Rouxel s'était intéressé à l'époque où il était mon élève aux sulfures, aux sulfures à couche en particulier. Entre les couches de FeOCl et FeSCl par exemple, on pouvait intercaler beaucoup de choses, comme l'ammoniac ou les amines. Jean Rouxel a préparé NaxTiS2, un matériau qui avait été préparé par Rudorf à Fribourg, qui le considérait comme une curiosité. Mais Rouxel a très vite réalisé qu'il devait y avoir un domaine d'existence. Or il s'est avéré que Li xTiS2 avait un large domaine d'existence. Jean Rouxel a poussé dans cette voie et il a étudié un grand nombre de sulfures et sélénures à feuillets alors que nous nous intéressions plutôt aux oxydes. Il y avait une sorte d'accord empirique entre nous : Nantes les sulfures, Bordeaux, les oxydes. Nous avons étudié des matériaux sur le plan de la synthèse, dans des conditions d'équilibre thermodynamique plus que par intercalation désintercalation.
Il y a une grande variété de méthodes topologiques ou non de relative basse-température qui permettent d'obtenir des matériaux nouveaux. Mettre un mélange très fin de poudres sous hautes pression pour que se déclenche une réaction brutale qui prend fin lorsque l'un des deux constituants initiaux a disparu. Donc c'est un échauffement brutal suivi d'une trempe. Ce qui permet d'obtenir des borures ou des silicium stables seulement à haute température.
Beaucoup de ces matériaux sont métastables mais on peut les utiliser dans des dispositifs.
Jean Rouxel a apporté beaucoup dans le domaine des réactions d'intercalation-désintercalation. Les oxydes lorsqu'on les désintercale perdent des électrons cationiques. C'est une oxydation cationique. Lorsqu'on part de LixCoO2 vers CoO2 on perd des Li+, mais on perd également des électrons qui proviennent des niveaux d. Mais pour les séléniures, ce sont les niveaux anioniques qui sont les plus élevés. Et lorsqu'on oxyde, c'est l'anion qu'on oxyde. On passe de Se2- à Se- et de Se- à Se pour des raisons de stabilité de liaison. Et Jean Rouxel a montré qu'il y avait une évolution graduelle pour les éléments 3d à l'état de sulfure entre TiS2, qui a une structure à couches, et CuS2 qui a une structure avec un ion S de type pyrite. Il a fait une analyse précise dans les cas douteux où les niveaux cationiques et anioniques sont à peu près de même énergie. L'analyse très fine des distances inter-atomiques lui a montré si c'était le cation ou l'anion qui était oxydé. Il a également fait beaucoup de choses sur les bidimensionnels qui sont ici hors sujet.

HA : Qu'est-ce qui a manqué en France alors que les compétences étaient là pour donner l'impulsion sur les batteries au Lithium ?

PH : Il y a un très grand nombre de batteries réversibles au lithium pour des applications diverses depuis les montres jusqu'aux batteries de taille moyenne utilisées par les militaires pour observation spatiale avant bombardement. Mais le marché important, c'est le véhicule électrique, non polluant. Du moins en partie car on s'est résigné au véhicule hybride. Le véritable marché ce serait la voiture électrique -éventuellement hybride- ce qui suppose des batteries de grande taille. Probablement l'électrolyte sera un polymère PEO imprégné d'un sel de lithium avec un gros anion, type matériau Armand. La cathode sera probablement riche en cobalt ce sera un matériau voisin de LixCoO2, plutôt un oxyde qu'un sulfure parce que la tension est plus élevée. Mais pour l'anode ce n'est pas encore évident. Si on pouvait faire mieux que les composés d'intercalation du lithium on serait content. Mais actuellement il n'y a pas encore de solution. Il y a donc premièrement un problème de matériau qui freine cette évolution. Deuxièmement il y a un problème de prix. Ajoutez à cela qu'une batterie au lithium doit être scellée car le lithium est sensible à l'atmosphère et vous voyez que ce n'est pas évident. Une solution concurrente est la batterie hydrogène consistant à stocker l'hydrogène dans un alliage métallique et puis à libérer l'hydrogène. Ce modèle permet des puissances plus élevées que la batterie au lithium mais là aussi il y a un problème de vieillissement car après un certain nombre de cycles, l'alliage s'oxyde car l'oxyde est plus stable que l'hydrure. Ce problème n'est pas encore résolu avec un coût acceptable pour l'utilisateur. A cet égard, il y a une coupure entre le scientifique et l'utilisateur.

HA : Concernant les relations entre physique et chimie qu'est-ce qui a favorisé le rapprochement ?

PH : Les physiciens ont fait des efforts pour parler un langage plus proche de celui des chimistes. J'ai parlé déjà de John Goodenough. Nevil Mott aussi était un homme qui s'exprimait dans un langage compréhensible pour un chimiste. Par exemple, lorsqu'il a obtenu des transitions isolantes par changement de composition au sein d'un domaine d'existence, on comprenait ses préoccupations et il comprenait les nôtres bien qu'on raisonne sur des modèles un peu différents. On est ainsi arrivé à préparer dans des bronzes de tungstène oxyfluorés des matériaux qui sans changement de structure manifestaient une transition métal-isolant. Les physiciens ont fait des progrès. L'équipe de Friedel était très préoccupée de parler un langage qui nous était commun. Je pense à Denis Jérôme, Claude Berthier à Grenoble.

HA : Le travail de physiciens sur la caractérisation très fine vous a-t-il aidé ?

PH : Je me souviens de discussions à Orsay sur les hexaborures. Les physiciens voulaient des matériaux qu'on appelait thermo-ioniques - mais c'est un mot malheureux : on devrait plutôt dire thermo-électronique - c'est à dire ayant un faible potentiel d'ionisation et susceptibles de cracher un jet d'électrons relativement puissant sous tension faible. On en a fait une étude systématique et on a essayé de préparer des cristaux.

HA : Et quel était l'enjeu ?

PH : L'enjeu était d'avoir ponctuellement un faisceau d'électrons puissant, par exemple pour des soudures, des soudures localisées. Outre la collaboration avec les physiciens d'Orsay on a aussi collaboré avec ceux de Grenoble. Plus que ceux d'Orsay, les physiciens de Grenoble avaient un langage très compréhensible. Il y avait un grand homme à Grenoble, Louis Néel. Il avait publié son travail sur le ferrimagnétisme en s'appuyant sur des modèles structuraux très clairs. La répartition des cations entre les sites tétraédriques et les sites octaédriques de la structure spinelle. Donc on comprenait pourquoi on avait des interactions d'abord anti-ferromagnétiques - ce qui constitue la base du ferrimagnétisme - entre des sites tétraédriques A et des sites octaédriques B, et pourquoi l'aimantation résultante était accrue lorsque le réseau prévalent contenait des cations avec beaucoup d'électrons d célibataires. Tous ces travaux - encouragés par les recherches militaires - ont permis une collaboration très fructueuse avec Grenoble. Je pense à Bertaut en particulier. Nous avons été encouragés, par exemple, à faire des études basse-température par Pauthenay qui nous a dit : c'est aux basses- températures qu'on détecte les phénomènes peu énergétiques.
Alors c'est l'époque où nous avons manqué le prix Nobel - Je dis cela en plaisantant, bien sûr !-. Nous avons préparé les premiers oxydes purs de Cu3+ : par exemple SrLaCuO4. Nous avions une telle habitude des solutions solides qu'on pouvait imaginer de préparer une solution solide avec La2CuO4 contenant du Cu2+. Mais pour nous, les solutions solides, c'était du travail secondaire. On cherchait à préparer des oxydes purs. Si on avait été préoccupé des solutions solides on aurait pu trouver des oxydes contenant à la fois du cuivre Cu 2+ et 3++. Comme par routine on caractérisait tous nos matériaux jusqu'à la température de l'hélium liquide, on aurait trouvé la supraconductivité. On ne l'a pas fait parce qu'on voulait des phases pures et non pas des solutions solides.
Bernard Raveau l'a fait avant Alex Müller. Il avait un objectif : comprendre ce qui se passait au point de vue des corrélations. Passer d'un semi-conducteur à un métal. Müller était un très grand physicien. Il a été surpris aussi mais il a tout de suite expliqué. Raveau a fait ses solutions solides. C'est même moi qui ai transmis sa publication au M[aterials] R[esearch] B[ulletin] mais j'ai regretté à l'époque qu'il n'ait pas fait de mesure à l'hélium liquide.

HA : Après avoir évoqué vos collaborations en France, pourriez vous parler de vos liens avec l'étranger ? Vous avez été précurseur pour les relations scientifiques avec les pays en voie de développement comme la Chine, le Maroc et l'Inde. Quelles étaient vos motivations ? Comment voyez-vous la science des matériaux dans ces pays ?

PH : J'ai toujours été persuadé que la science devait être internationale. Cela me distingue de beaucoup de mes compatriotes. Je suis toujours étonné que l'on fasse des quêtes pour aider la recherche en France sur le SIDA. Toute la recherche sur le SIDA, toute recherche de pointe est internationale et ce n'est pas parce que la France dépensera un peu plus d'argent que nécessairement, il y aura des progrès significatifs. La science doit être internationale.
J'ai donc eu des liens d'abord avec les pays développés car dans ce type de relation on se fait connaître mais aussi on apprend. Je suis allé souvent aux Etats Unis, moins par enthousiasme culturel, que parce qu'on y rencontre des gens de qualité. J'ai rencontré Goodenough, Al Cotton... j'ai rencontré à Berkeley ou à Stanford des gens de grande qualité. J'ai eu des relations suivies pendant un temps avec la Grande Bretagne mais les Anglais ont un sentiment de quant à soi. J'espère qu'avec le temps la Grande Bretagne va évoluer vers une intégration dans l'Europe. Les Allemands sont très favorables à cette intégration. Dès 1961 j'avais pris l'initiative d'emmener tout mon laboratoire en Allemagne pour un voyage de 15 jours. On est allé à Stuttgart, Karlsruhe, Heidelberg, Darmstadt, Giessen, Göttingen etc.. On a été très bien reçu par Wilhelm Klemm avec qui j'ai toujours entretenu d'excellentes relations. Mais ses élèves étaient jaloux. Les Allemands se sont sentis bousculés parce qu'un peu jaloux de gens qui faisaient beaucoup de bruit. Ils avaient une bonne tradition de chimie préparative, en relation avec l'industrie. Les Allemands ont compris que pour faire des matériaux nouveaux il fallait des techniques nouvelles comme la haute pression. Mais leur but c'était la performance tandis que le nôtre c'était de stabiliser des structures électroniques peu usuelles, grâce à la synthèse. Les Allemands se sont senti un peu gênés. Les gens leur disaient : vous utilisez des équipements de haute pression mais ce que vous faites c'est de la botanique alors qu'il faudrait réfléchir. Le but d'un équipement est de faire des matériaux à façon pour répondre à des problèmes déterminés. Les collègues allemands avaient un autre point de vue et je regrette qu'il n'y ait pas eu davantage de liens.
En revanche, toujours parmi les pays développés, j'ai eu beaucoup de liens avec l'Europe de l'Est. Pour deux raisons. D'abord, il y avait des gens de qualité chez les Soviétiques, les Polonais et les Tchèques. De plus j'étais un peu agacé de cette Europe coupée en deux du fait de la guerre froide. Donc je trouvais raisonnable qu'il y ait une présence de la France là où c'était relativement facile, c'est à dire la science. C'était intéressant pour eux et pour nous car nous avons eu de ces pays des personnes remarquables. J'ai eu des relations systématiques avec des laboratoires à Prague, Cracovie, à Moscou, à Kiev, Novosibirsk, à Sofia. Avec la Roumanie, c'était impossible car Madame Ceaucescu interdisait aux scientifiques de discuter avec des étrangers.
Avec les pays en voie de développement, la situation change d'un pays à l'autre. J'ai eu des relations avec le Maroc parce que l'université de Bordeaux et l'université de Rabat avaient des liens traditionnels. Je suis allé y faire cours. Il y avait de très bons étudiants je les ai encouragés à faire une thèse. Le nombre a crû considérablement. 30 ou 35 Marocains ont fait des thèses avec moi. J'avais une politique de sélection impitoyable ; je prenais les meilleurs et je les surpayais. Je voulais qu'ils n'aient pas de souci matériel pendant leur thèse. J'ai eu des liens plus occasionnels avec la République du Congo et quelques Tunisiens mais ils préféraient Marseille.
Avec la Chine j'ai fait un choix politique. J'ai compris que la Chine était un potentiel économique et humain. La France devait être présente à un moment où la Chine était exclusivement tournée vers les Etats-Unis. Je suis allé souvent en Chine. J'ai fait venir des étudiants chinois en les choisissant bien sûr excellents. Mes espoirs ont été dépassés par le succès car ils ne sont pas retournés en Chine mais partis au Canada ou aux Etats-Unis comme professeurs ou dans l'industrie. Ils se sont bien débrouillés. Maintenant c'est différent ; une majorité d'étudiants chinois reviennent en Chine.
L'Inde est aussi un pays avec lequel j'ai eu des relations. C'est une société où le savoir est respecté, une science de caste malgré l'abolition officielle des castes. Thaïlande, Malaisie, Indonésie...j'ai privilégié les pays asiatiques par rapport aux pays africains car la culture asiatique favorise la réflexion métaphysique et par conséquent scientifique. Néanmoins j'ai eu aussi des collaborations avec le Brésil, le Chili et l'Argentine. Le but étant d'aider ces pays dans leur développement industriel. Je suis d'ailleurs membre de l'Académie des sciences brésilienne depuis 1988.
Vis à vis des étudiants du tiers monde, j'ai toujours considéré comme ma responsabilité de leur donner une thèse originale et non pas, comme on le fait souvent, de leur faire remplir des vides dans le laboratoire ou de servir de main d'œuvre. Les étudiants du tiers monde que l'on fait venir en Europe il faut bien les choisir et bien les former pour qu'ils deviennent des maîtres.

HA : Je serai curieux de connaître votre point de vue sur l'évolution de la chimie des matériaux et le rapprochement avec la biologie.

PH : Je ne me sens pas compétent dans l'interface chimie/biologie. Mais mon expérience à l'interface physique et chimie me rend plutôt sympathique cette perspective d'une ouverture de la chimie vers la biologie. Elle est défendue par Pierre Pottier, Guy Ourisson, Corriu.
Sur l'interface physique/chimie, cela s'est moins bien passé. Peut-être que je n'ai pas su convaincre. Quand on prêche, on se fait des adeptes mais aussi des ennemis. Cela est vrai au CNRS. Celui qui prêche secoue les caciques, les gens en place. Quelqu'un comme Fernand Gallais était fermement hostile à mon projet d'interface avec la physique. Par contre j'ai rencontré beaucoup de sympathies du côté de Pottier, de Jacques Livage.
Pour revenir aux oxydes supraconducteurs, il s'agit d'un cas intéressant de collaboration entre physiciens et chimistes. Très vite, j'ai compris que l'on avait plafonné et puis à un moment donné il était clair que Tc était d'autant plus élevé que la bande de conduction était plus étroite. Et plus la bande de conduction est étroite plus le matériau est instable et a tendance à se dismuter en donnant un mélange de deux phases. J'ai compris cela très vite mais beaucoup ne l'ont pas compris. Il y a donc eu un emballement. Il a rapproché les chimistes des physiciens. Il est dommage que personne n'ait proposé un modèle simple permettant aux chimistes d'innover de manière simple comme on avait innové dans le domaine de la conductivité ionique, du magnétisme, de la ferroélectricité, des magnéto-optiques ... ou même des composites thermo-structuraux. Il a manqué quelqu'un qui propose un modèle intuitif liant les propriétés à la liaison chimique. Goodenough aurait pu le faire mais il était trop vieux, trop pressé de publier des matériaux miracles. Les matériaux miracles sont difficiles à reproduire. Celui qui essaie il n'a pas le même four ... Ces matériaux sont métastables, ils ne sont jamais parfaitement purs. Ils n'ont jamais le même nombre de lacunes d'oxygène. Donc ce n'est jamais parfaitement répétitif. Cela exclut toute réplication sérieuse parce qu'un matériau n'est utilisable industriellement que s'il est relativement simple à préparer et à utiliser. Telle est la raison de l'échec de la diode Josephson sur laquelle IBM a dépensé beaucoup d'argent. A l'époque j'étais d'ailleurs conseiller d'IBM.

BBV : Est-ce qu'il y a eu des matériaux sortis de vote laboratoire qui ont été industrialisés ?

PH : Il y a d'abord eu les varistors. J'ai fait beaucoup avec la Thomson CSF dans ce domaine. Il y a eu LixCoO2 et puis il y a les céramiques composites de R. Naslain : fibres de carbone infiltrées par SiC qui permet de travailler à des hautes températures pour les matériaux de rentrée de la fusée ou du satellite dans l'atmosphère. Car lorsque l'engin revient dans l'atmosphère, il y a un risque d'oxydation. L'astuce consistait à infiltrer - non pas déposer en surface - SiC à partir d'une phase vapeur. Alors à l'air SiC s'oxyde en donnant SiO2 qui s'infiltre dans le matériau à base de carbone et permet de le prolonger.

BBV : Pourriez vous préciser quelles étaient vos relations avec l'industrie et comment elles ont évolué ?

PH : J'ai toujours eu des relations avec l'industrie. Quand j'étais à Rennes j'ai été contacté par Raymond Paul, un des responsables de la recherche à Rhône Poulenc et il m'a vivement encouragé à travailler avec Rhône Poulenc. J'ai eu plusieurs bourses de thèses payées par l'industrie - parfois il fallait publier des résultats plus tard. Rhône Poulenc a payé la thèse de Michel Pouchard sur les bronzes de vanadium au début des années 60. Ensuite il m'a paru tout naturel de travailler avec l'industrie. J'ai travaillé avec Saint-Gobain sur les verres, en particulier sur les verres conducteurs du lithium et du sodium avec Levasseur, sur les verres sulfurés à base de B2S3. Les verres sont un matériau merveilleux. Ils ont une composition qui est flexible. Vous tombez un peu à côté, cela n'a pas d'importance les propriétés ne sont guère modifiées. Vous n'avez pas le problème des matériaux cristallins où, par suite de la moindre erreur, de la moindre difficulté de préparation, une deuxième phase d'impuretés se forme à côté. Là il vous reste une phase. D'autant plus qu'on peut préparer les verres par trempe brutale donc énormément de matériaux sont vitreux alors qu'il y a 30 ou 40 ans c'était différent.
J'ai eu beaucoup de liens avec l'industrie locale : Aérospatiale et SNECMA, avec SNPA (société nationale des pétroles d'aquitaine : ancêtre d'Elf) sur comment purifier le gaz de Lacq...Ma porte était toujours ouverte, on élargissait le champ de nos recherches à la demande car l'industrie n'est pas un boulet.

BBV : Est-ce que ces liens étaient encouragés par le CNRS ?

PH : Le CNRS était informé bien sûr. Et puis quand on est devenu un laboratoire propre en 1966 Curien était très favorable aux relations avec l'industrie. On a un des contrats avec Saint-Gobain, avec Rhône Poulenc devenu Rhodia, avec Ugine Kuhlman devenu Péchiney. Nous avons même eu des liens avec General Electric aux USA pour les borures, avec BASF sur le di-oxyde de chrome pour les bandes d'enregistrement.

BBV : Quelles sont les méthodes et techniques utilisées dans votre laboratoire ? Et comment ont-elles évolué au cours de votre carrière ?

PH : Au début le B-A-BA c'était la diffraction X. Puis pour bien comprendre la structure on a eu un équipement pour des monocristaux. On a préparé des mono-cristaux pour déterminer les structures. Maintenant on a fait de gros progrès et on peut sur des spectres de poudres lorsque la poudre est de bonne qualité déterminer la structure par les méthodes Riedveld en faisant des hypothèses simples sur la structure la plus probable. La diffraction X a été fondamentale et a débouché ensuite sur la microscopie électronique en transmission qui permet de voir les défauts locaux. C'est merveilleux. La diffraction X était une méthode à grande distance. Par contre la microscopie électronique en transmission vous donne les défauts localisés et étendus. C'est une préoccupation que j'ai eu beaucoup à propos de non-stœchiométrie. Quand on passe d'une phase perovskite ABO3 à une phase brownmillérite A2B2O5, on perd de l'oxygène. Alors à haute température les lacunes d'oxygène sont désordonnées. A température plus basse, elles s'ordonnent en fonction du cation B. Quand c'est du fer ou du gallium, un cation isotrope, on a soit des tétraèdres parce qu'il y a pas de lacune, soit des octaèdres car les lacunes marchent par deux. Donc dans une structure brownmillérite on a une séquence octaèdre,-tétraèdre, octaèdre-tétraèdre, et dans la structure perovskite c'est octaèdre-octaèdre-octaèdre. Alors on peut trouver à condition de faire des recuits à température assez basse - quelques centaines de degrés - des phases intermédiaires avec 2 couches octaèdres, 1 couche tétraèdre, 3 couches octaèdres, 1 couche tétraèdre. Et bien sûr quand on chauffe le désordre s'installe à cause de l'entropie d'empilement. On a étudié de manière systématique comment on passe de défauts isolés aux défauts ordonnés, étendus. Et cela a des conséquences au point de vue de la conductivité de l'ion oxygène. Parce que maintenant on a de nouvelles préoccupations. On veut par exemple extraire l'oxygène de l'air par des membranes de perovskite lacunaire ou détruire les traces de CO en oxydant par l'eau. Dans ce cas, vous avez CO2 - qui est quand même moins toxique que CO, sauf sur le plan idéologique - et vous avez de l'hydrogène. On utilise des perovskites lacunaires qui doivent être conducteurs de l'oxygène - ce qui est normal - mais aussi conducteurs électroniques car le transfert se fait sous tension donc il faut que les ions O2- migrent à travers les lacunes de la structure. Il y a donc un aspect pratique pour les capteurs d'oxygène, la purification des gaz. Les Norvégiens utilisent ces méthodes massivement pour transformer le gaz de la Mer du Nord en un gaz exempt de CO. Norsk-Hydro dépense des sommes considérables pour cela. J'ai été invité pour parler avec les gens impliqués par ces recherches.
Donc pour résumer : nos efforts se sont situés à l'interface entre physique et chimie et se concentraient sur l'étude des relations entre composition, structure et propriétés avec la perspective d'applications industrielles.

Fin de l'enregistrement

haut de page

accueil du site

Pour citer l'entretien :

« Entretien avec Paul Hagenmuller », par Bernadette Bensaude-Vincent et Hervé Arribart, 12 juin 2001 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article124.
—

Entretien avec Paul Hagenmuller, par Bernadette Bensaude-Vincent et Hervé Arribart, 12 juin 2001

Lieu : Paris, France

Support : enregistrement sur cassette

Transcription : Bernadette Bensaude-Vincent et Hervé Arribart

Edition en ligne : Sophie Jourdin