Sciences : histoire orale

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.

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

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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.

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« 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

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.

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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.
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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

BOILOT Jean-Pierre, 2000-12-12

Sophie Jourdin — 2011-10-28T12:00:58Z

Jean-Pierre Boilot worked on b-alumina in the 1970s and subsequently on ionic conductors within the framework of chimie douce.

BERNADETTE BENSAUDE-VINCENT (BBV) : Quel fut votre parcours individuel ?

JPB : Je suis entré au laboratoire Collongues en 1971, étant assistant à l'Ecole de céramique de Sèvres où j'enseignais la chimie. Mon sujet de thèse portait sur l'alumine-b plus exactement sur les gallates. On cherchait à améliorer la conduction ionique en remplaçant l'aluminium par du gallium. On connaissait, bien sûr, les travaux de Yao et Kummer et on savait déjà échanger les ions sodium par d'autres. Mais ceci n'a constitué qu'un chapitre de ma thèse qui devait en avoir 5 ou 6.
Après j'ai eu un rôle très particulier : travailler à l'interface de la physique et de la chimie. Cette expérience de collaboration de la physique et de la chimie du solide, c'était une innovation. Seul Yves Le Car avait commencé avant moi. Lui avait un financement industriel, avec CGE qui est devenu Alcatel. Cette collaboration est issue de discussions entre Robert Collongues et André Guinier qui était responsable d'un groupe de physique du solide à Orsay au bâtiment 510. Le Car a commencé à faire de la diffusion des rayons X, organisation des ions de conduction dans alumine-b. J'ai poursuivi dans cette voie. La collaboration s'est étendue. Je passais 50% de mon temps au labo Collongues et 50% en physique chez Guinier et chez Jérôme, un autre groupe de physique du solide qui faisait de la RMN. Une grande partie de ma thèse concernait des problèmes fondamentaux : comment les ions s'organisent, ordre désordre, stœchiométrie.

BBV : Quels étaient les modèles théoriques à l'époque ?

JPB : Peu de choses pour comprendre les mécanismes de conduction. C'est venu plus tard. Les physiciens durs ont attaqué le problème plus tard.
J'ai soutenu ma thèse d'Etat en 1975 devant un jury très impressionnant : Jacques Friedel, Jean Rouxel, Michel Fayard, qui est devenu directeur du secteur chimie au CNRS, Jeanine Théry et Robert Collongues. Je me souviens avoir été mauvais, je n'étais pas fier de moi.

BBV : Avez-vous poursuivi sur alumine-b ?

JPB : Oui de 1975 à 82 j'ai travaillé avec Gaston Colin, cristallographe et avec Philippe Colomban qui est arrivé au labo Collongues. Je l'avais eu comme étudiant à l'école de céramique. On a travaillé essentiellement sur deux aspects : alumine-b stœchiométrique et alumine-b''. Même type de base : compréhension, organisation des ions en utilisant les paramètres fondamentaux du solide : répulsion entre ions, transition au désordre etc.

BBV : Y avait-il alors une communauté française de chercheurs sur l'alumine-b ?

JPB : Oui, il y avait des séminaires organisés ici à Polytechnique par Bernard Sapoval->http://pmc.polytechnique.fr/bs/english.html] et Hervé Arribart. Les gens ici ont commencé à travailler sur l'alumine-b avec des porteurs de protons et ils utilisaient la RMN.
Donc si l'on fait le bilan de ces 10 ans, il y a deux caractéristiques propres à ce sujet

- C'étaient les premières recherches fondamentales menées parallèlement à la recherche industrielle car CGE en France, Ford, General Electric aux USA faisaient des recherches plus appliquées sur les accumulateurs sodium-soufre. C'était particulièrement motivant de voir qu'il y avait des possibilités d'application.
- Deuxième caractéristique : c'était la possibilité de travaux à l'interface physique-chimie. Ces deux aspects là se retrouvent plus tard dans les recherches sur les supra-conducteurs au cours des années 90.

BBV : Aviez-vous des contacts avec l'industrie ?

JPB : On avait des contacts avec CGE et on allait parfois à Marcoussis voir M. Dumas de CGE. Mais on faisait de la recherche fondamentale.
Des contacts avec l'industrie, il y en avait sans doute au labo Collongues. Mais je n'étais pas au courant. Par contre, au laboratoire Collongues, Didier Goureyet était plus proche des préoccupations industrielles, tout en étant en recherche fondamentale.

BBV : Avez-vous ressenti un certain pessimisme industriel sur l'alumine-b au cours de ces années ?

JPB : Non, il y eut une effervescence de 1970 à 76. Le pessimisme est venu après. Il y avait peut être des problèmes pour les gens qui ne travaillaient pas sur le sujet. C'est faux de dire qu'il y avait un pessimisme dans les années 70. Pour les années 80, c'est une autre histoire. Plus de problème d'énergie, d'autres problématiques sont arrivées : utiliser des systèmes. On savait que les batteries sodium-soufre ne seraient pas commerciales. Elles ne le seront peut-être jamais. Donc du point de vue industriel, c'était un tout petit peu moins motivant.

BBV : Avez-vous participé aux congrès internationaux des années 70-80 ?

JPB : Bien sûr je pourrai vous donner la liste. C'est un autre aspect important : il y avait une compétition internationale, essentiellement avec les Américains, avec les gens de General Electric - Roth - et les gens de Bell Telephon. J'ai commencé à participer en 1976 Schenectady ; 1979 Lake Geneva (USA), Gatlinburg (Tennessee) en 1981, Grenoble en 1983, Lake Tahoe en 1985 ; Garmisch en 1987. Outre cette série des Solid State Ionics il y avait Rome (1976) et Saint-Andrews en Ecosse, en 1978. A chaque fois on avait des papiers dans ces conférences.

BBV : Y-a-t-il eu une évolution ou réorientation de vos recherches sur cette période ?

JPB : On a pousuivi les mêmes pistes de recherche sur les deux alumines-b.
Philippe Colomban, chimiste, s'est consacré à l'élaboration des mono-cristaux d'alumine-b. Seuls deux groupes au niveau international savaient faire la synthèse des alumines-b : Colomban au laboratoire Collongues et Farrington chez General Electric. C'était un procédé à haute température avec quelques subtilités chimiques pour parvenir à faire l'alumine stoechiométrique. Mais il n'y eut pas de brevets sur les mono-cristaux. L'objectif était purement fondamental car les applications se faisaient sur un milieu polycristallin, céramique.
Parallèlement à partir de 1978, on a commencé à travailler sur d'autres conducteurs ioniques qui pouvaient remplacer l'alumine. Ils faisaient partie d'une série qu'on appelait nasicons : c'étaient des phosphates ou des phospho-silicates avec des ions sodium.
Le choix du sodium repose sur des arguments très simples : il faut un ion monovalent, de la bonne taille. S'il est trop gros il ne diffuse pas facilement ; s'il est trop petit (cas du proton ou du lithium) il vient se coller sur le réseau ; ou on a une interaction trop forte avec les anions (les chimistes disent trop polarisants). Les meilleurs ions sont Na+ et Ag+. Ensuite le choix dépend des applications. A cette époque là le problème était le stockage d'énergie, on visait des accumulateurs de haute puissance pour faire du stockage. Les critères de densité d'énergie massique portaient le choix sur les éléments légers, donc le sodium plutôt que l'argent.

BBV : Est-ce que la crise d'énergie a infléchi les recherches au labo Collongues ?

JPB : Peut-être mais à cette époque j'étais trop concentré sur ma thèse et je n'avais pas de vue d'ensemble. Pour revenir aux applications, les nasicons ont eu moins d'intérêt car ils sont moins stables, ils résistent moins bien au sodium liquide. Ils n'ont pas eu le succès de l'alumine-b mais des gens travaillent encore dessus. Il y a eu beaucoup de travail sur cette famille : diversité de compositions et de phases. Elle présente un intérêt pour la compréhension des paramètres fondamentaux du solide mais moins que l'alumine-b.

BBV : Rétrospectivement considérez vous que ce travail sur les nasicons a été positif ?

JPB : Oui on aurait peut-être pu arrêter un peu plus tôt. On a travaillé là dessus de 1978 à 1984 mais toujours en parallèle avec l'alumine-b. C'est un travail qui se faisait à Polytechnique où je suis venu en 1981. C'est un sujet qu'on a développé ici avec Colomban, toujours en liaison avec les physiciens du solide (Collin) d'Orsay dans le groupe de Robert Gomès qui avait pris la succession de Guinier.
Après on a pris un virage vers les sols-gels. La transition s'est faite par le biais des nasicons. On avait dans l'idée d'élaborer des phases amorphes pour conducteurs ioniques. Elles étaient dérivées du nasicon. On a préparé les premiers verres organo-minéraux en s'inspirant des conducteurs ioniques type nasicons. Notre modèle à nous était le conducteur ionique. Puis on a eu des résultats intéressants sur ces matériaux, sans rapport avec la conduction ionique. Ces hybrides organo-minéraux, à la frontière entre organique et minéral sont faits à température ambiante avec une chimie douce.

BBV : N'est-ce pas un paradoxe que de la chimie à haute température du labo Collongues sorti une chimie à température ambiante ?

JPB : Oui à la même époque Jacques Livage faisait des gels V205.

BBV : Qu'est-ce qui a motivé votre virage vers les verres ?

JPB : Du point de vue industriel, l'alumine-b c'était moins motivant et, du point de vue fondamental, on avait fait le tour. De plus, je démarrais un groupe ici à Polytechnique, c'était le moment de passer à un nouveau projet.

BBV : Est-ce que ce virage vers les verres organo-minéraux a changé votre place dans la recherche ?

JPB : Au niveau du CNRS, non, car on appartient toujours à la famille chimie du solide. Mais on a eu des contacts industriels nouveaux avec Saint-Gobain (Silor). Bien sûr pendant deux ans, on a eu un peu de ralentissement dans la production de publications. Mais le virage se fait bien.

BBV : Quelles sont les activités de votre laboratoire actuellement ?

JPB : Actuellement on est toujours sur la chimie douce. En plus des hybrides organo-minéraux, on travaille sur des objets nanométriques. On part de molécules et on essaie de construire des solides à partir de ces molécules. Ce sont essentiellement des matériaux pour l'optique : lasers ou stockage de l'information optique.

BBV : Quelles sont les techniques que vous utilisez ? Sont-elles totalement différentes de celles qu'on utilisait au laboratoire de Collongues ?

JPB : C'est de la chimie classique avec des béchers mais pas de haute température. C'est bien différent des labos d'alumine où on avait des fours à 2000°C. Le labo Collongues était surtout tourné vers l'élaboration de matériaux alors que maintenant on fait surtout de la caractérisation. Comme maintenant on dispose de nombreuses techniques, on peut faire des thèses sur la caractérisation avec peu de chimie.
Ce que m'a appris l'alumine-b c'est qu'il faut faire de la chimie. C'est le matériau qui est intéressant. C'est le message le plus important. Toutes les avancées qu'on a eues au laboratoire Collongues, c'est parce qu'on a su faire de la synthèse de matériaux avant et mieux que les autres. Notre premier travail est de faire de l'innovation en matériaux, mais on a beaucoup de collaboration en physique.
Notre troisième thème est la pile à combustible. Il est arrivé avec un ancien du laboratoire de Collongues : Philippe Barboux. Il travaillait sur les films minces de céramique et prépare maintenant des membranes conductrices ioniques pour les piles à combustibles. C'est donc un retour à la tradition d'origine.
Mais il y a un lien entre les verres, les particules nanométriques et les piles à combustibles. Ce sont toujours des procédés à basse-température. On travaille sur la diffusion de molécules comme autrefois on travaillait sur la diffusion des ions.

BBV : Combien de personnes travaillent dans votre groupe ?

JPG : Actuellement notre groupe de chimie du solide comprend 10 personnes et il est l'une des composantes de l'UMR-CNRS intitulée Laboratoire de Physique de la matière condensée qui comprend 50 personnes.

BBV : Quels sont vos liens avec l'étranger ?

JPB : Nous avons gardé des relations avec Bruce Dunn de UCLA (nous avons ici un chercheur permanent qui a fait son post-doc là bas). Nous avons également une collaboration avec un laboratoire allemand. Pas de programme européen, c'est trop de paperasses.

BBV : Comment voyez-vous la chimie du solide française sur la scène internationale ? Est-ce qu'elle n'a pas d'une certaine manière fait obstacle à l'essor d'une science des matériaux en France ?

JPB : C'était suite au démarrage de la physique du solide. Il y a avait a deux pôles de chimie du solide en France, celle de Hagenmuller à Bordeaux et celle de Collongues à Paris. L'une plus mandarinale que l'autre. Des gens comme Rouxel, je les mets dans la famille Hagenmuller. En fait, si on prend les labos actuels de chimie du solide, ce sont tous des descendants d'Hagenmuller ou des descendants de Collongues.
Les deux écoles sont tournées vers la science fondamentale plus que vers les applications. C'est totalement différent de l'approche science des matériaux aux USA. Elle n'existe pas en France. L'approche Materials Science est plus tournée vers les applications. En France, il y a eu beaucoup de recherche fondamentale. L'originalité française n'est pas dans la collaboration avec l'industrie mais dans l'approche physique, dans la collaboration entre chimistes et physiciens du solide. Je défends l'approche française. Si les gens avaient été très proches du milieu industriel, je ne crois pas qu'on aurait été aussi forts en chimie du solide.

BBV : Peut-on associer une coloration politique à cette discipline ?

JPB : Traditionnellement en France, les physiciens sont plutôt à gauche et les chimistes plutôt à droite. Quant à la couleur de ces deux écoles de chimie du solide, je dirais que Hagenenmuller était un gaulliste bon teint ; il serait plutôt proche de Pasqua aujourd'hui ; Collongues, lui, était plutôt centre droite, bon vivant.

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Pour citer l'entretien :

« Entretien avec Jean-Pierre Boilot », par Bernadette Bensaude-Vincent, 12 décembre 2000 Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article121.

—

Entretien avec Jean-Pierre Boilot, par Bernadette Bensaude-Vincent, 12 décembre 2000

Lieu : Ecole polytechnique, Palaiseau, France

Support : non communiqué

Transcription : Bernadette Bensaude-Vincent

Edition en ligne : Sophie Jourdin

ARRIBART Hervé, 2001-02-19, 05-29, 02-20

Sophie Jourdin — 2011-06-16T07:31:17Z

Hervé Arribart is the Scientific Director of Saint-Gobain Recherche, an international company of French origin with an emphasis on glass manufacture. He took his PhD from the Ecole Polytechnique in Paris in the mid-1970s and subsequently researched ionic transport using nuclear magnetic resonance. In the late 1970s he worked with Jean Rouxel's group at the University of Nantes. In 1981 he joined the company Elf to work in research and development. In 1985 he moved to Saint-Gobain, where at first a large portion of his research was closely related to the practical problems of production. In 1990 he started a laboratory (a joint venture of Saint-Gobain and the CNRS) on the basic science of glass surfaces, using a diverse set of tools and especially the Atomic Force Microscope. In 1999 he moved to the more managerial position of Scientific Director. Hervé is also on the staff of this project.

2001-02-19 :

HERVE ARRIBART (HA) : I studied at the École Polytechnique in Paris. The selection to the school is done mainly on mathematics. But during my studies I learnt to appreciate physics in particular. I decided to pursue research in solid-state physics. It was a good place to study physics. While in my last year as an undergraduate I did a Diplome d'Étude Approfondie in parallel (an intermediary between an M.Sc. and a PhD typically done for a year before starting one's PhD studies). In Orsay, near the École Polytechnique, there is a very famous place in solid state physics, a lab started by Jacques Friedel - a great name in solid-state physics. I followed this course and afterwards I did the PhD at the École Polytechnique in the field of condensed matter physics. In principle I ought to have started with a topic distant from materials science. I extracted spin-polarized electrons from semiconductors. This was in 1974.

ARNE HESSENBRUCH (AH) : How did one extract spin-polarized electrons in 1974 ?

HA : It is true of all solids, but in semiconductors it is especially interesting that when light falls upon a surface there is a coupling between the spin of photons (in classical physics : the polarization of light) and the spin of electrons. Electrons in the upper layer absorb light photons depending upon the spin. If by some technique you can extract electrons from the conduction band of the semiconductor, you can find ways to select electrons of specific spins. This was quite important at the time because at big-science institutions such as LEP [Large Electron Positron collider] or SLAC [Stanford Linear Accelerator Center], there was a need for spin-polarized electrons. And of course you then needed solid-state physics to do it. But the man who in principle was my supervisor decided to do something else. His name is Claude Weisbuch, and he is now a good friend of mine. For a few years he was the scientific director of the French Department of Defense. He is still working in solid-state physics, in the optics of semiconductors. But he decided to do something else and Bernard Sapoval, another professor at the lab, proposed that I work on new materials. At that time there was little contact between solid-state physics and solid-state chemistry. The idea was to link up with chemists. This is why very early on in my career I had contact with chemists. We worked with Parisian solid state chemists on a new material. We found a new way to draw single crystals of an already existing material. It was very nice because we could examine transport and NMR phenomena. And the material, a copper vanadium sulfide exhibited astonishing properties : a large spread of conductivity that one can measure in a standard experiment. We suspected that this was due to mixed conduction properties. Mixed conductivity refers to conductivity by both electrons and ions. The experiment appeared to verify our a priori suspicion. This gave me the possibility to present a model for mixed conduction in this material and to understand the influence of ion transport and electron transport. I also used NMR in order to understand which ions moved. It turned out that the copper ions moved. So, this was the subject of my first thesis. At the time, in France, there were two theses. The first one was called "thèse de troisième cycle". The second was the "Docteur es sciences". This degree does not exist any longer. The thesis that is done now is shorter.

I decided to continue to work with chemists. I decided to combine NMR and transport measurements. I changed my collaborators, turning to two different groups. In my PhD there had been two chapters on NMR. But I wanted to study proton transport. I had two reasons. One was that protons give a strong NMR signal. The second reason was that two reasons had been given for proton transport. In one, protons move in individual jumps. In the other the proton is a part of a more complex molecule such as the ammonium ion (NH4+) or hydroxonium (H30+). In the former case we can see the transport phenomenon as a result of molecule rotation and proton jump. The molecule would turn and the proton jumps to the neighboring molecule, which again turns and so on. This was called the rotation-jump model. The second model was for the whole complex ion to jump. This was called the vehicle model because the whole molecule acts as a vehicle. So I worked with one group of chemists in Nantes, at the Institut de Matériaux de l'Université de Nantes. It had just been created by Jean Rouxel, a chemist. With them I worked on a substance called antimony acid - a solid. I was able to show using NMR that transport occurred in this case with rotation-jump. Protons used H30+ as a complex rotator. I was also able to show that the jump was due to quantum mechanics within a certain temperature range. It was not the usual ion transport of classical mechanics.

AH : A tunneling effect ?

HA : Yes, this is one aspect of protons, because protons are very light ions allowing for this quantum effect. The other material I studied was ammonium beta alumina. This was the standard beta aluminium in which the sodium had been ion exchanged with ammonium. This material was very interesting from the perspective of NMR. All kinds of ionic motion took place at different temperatures. At the lowest temperatures, that of liquid helium (1-4K), there was rotational quantum motion. As the temperature increases the motion becomes classical.

AH : If I may make a comparison with Stanley Whittingham here. You were working on some of the same materials, you were using some of the same tools (NMR), but you were asking very different questions, right ?

HA : Yes, that is true. I was not at all involved in the application. For two reasons : French chemists were interested in materials and did not look to the application. And chemists were between me and the application, so I had no contact with attitudes such as Whittingham's. I was very happy working on the solid-state physics problems.

AH : And we are talking about the late 1970s now ?

HA : Yes, I began the proton transport research, I think, in 1976.

AH : And it went on for how long ?

HA : For five or six years.

AH : And you lived in Nantes ?

HA : No, I remained in Paris while collaborating with the Nantes group.

AH : Were you employed in Nantes ?

HA : No, not at all. At the beginning I was employed at the Ecole Polytechnique as a research assistant, and then I was hired by the CNRS - in 1977.

AH : So, the CNRS paid your salary, you were able to do basically whatever you wanted, and you collaborated with Jean Rouxel and coworkers because you found it interesting ?

HA : Yes. It was a chance to work with an outstanding chemist. French chemists were really very good. The problem, as we just said, was that there was little interest in application.

AH : What did you do next ?

HA : After my PhD thesis, I found it interesting to go to industry.

AH : I imagine that there were many advantages and disadvantages to leaving academia for industry. For instance, where was status greater, what paid better, where were working conditions better ?

HA : First of all, it was rare, even more so than today, for CNRS people, or people within the public system, to go to industry. I cannot give you a clear answer about my motivation - it was not even clear to myself at the time. I did get a higher salary in industry. I also had personal reasons for leaving Paris and going to the Elf company. I went to an Elf research lab in the Southwest of France, in a very nice place in the Pyrénées. I had small children at the time and it was much better for them to grow up in the countryside and in a very nice climate. I was also curious. So the decision involved many elements. And anyway, it was not irreversible. The CNRS allowed me to take a three-year leave after which I could have gone back. With regard to the working conditions : I was of course less free than I had been at the CNRS, but I found it more stimulating because there were a lot of different problems on the horizon, arriving almost every day. We could easily get the necessary equipment at the CNRS and at Elf, so there were no differences there.

AH : The restrictions at Elf had to do with what you were allowed to study ?

HA : Yes.

AH : What did Elf want you to do ?

HA : In principle I was hired to work on solid-state sensors. Because it was not in the direct line of my previous work I proposed that I work on solid-state sensors and ion conduction. We developed a family of sensors named ISFETs (Ion Sensitive Field Effect Transistors). It was a new kind of transistor at the time but now it is very common. You control the electrode using field effects, opening and closing the circuit between the two other electrodes. This is the way the transistor works. My idea - not an original one - was to replace this way of controlling the electrode, the gate, to replace it with a membrane, selective to such and such an ion. If you put the device in a solution containing the ion for which you have designed the system, the membrane will be charged. This charge will change the state of the solid-state transistor. It worked all right for protons. We could use the device to measure pH and afterwards we just had to change the nature of the membrane, choosing a different solid electrolyte, such as calcium fluoride.

AH : Your toolkit remained the same and you still used NMR ?

HA : Not NMR, but yes. You need large samples in order to do NMR. So it was mainly electrochemistry and surface analysis. This was between 1982 and 1985. But as I told you, in industry new projects can arrive almost every day. I had developed some skills in electronics using instrumentation at the École Polytechnique. Elf applied for a patent for a medical analysis system, a small instrument to be sold to private practitioners, as opposed to hospitals. This had nothing to do with solid-state ionics. But the people working on this project needed someone who knew about electronics, and so I got progressively more involved. After one or two years it had become my main project. This worked very well. I was very proud to design an electronic system that required no manual setting. It was set in the factory forever. This was a critical issue, because we thought that doctors could not be expected to deal with electronics - and I am sure that we were right in this. So there was nothing to check or calibrate - the system was self-calibrating. So it worked very well, and after only two or three years Elf built a plant and people were hired. But in 1984 and 1985 there were big changes in chemistry. And there was a great redistribution of all chemical industries. And Elf, that had been an oil company, in this period expanded to become also a chemical company. As a result a lot of the more diversified lines of business lost in importance. Many projects like ours were discontinued. But because we were already quite advanced we found a way to keep going. In fact it was Dupont de Nemours that found that our system was complimentary to some of theirs. The result was that Elf shipped the patent and everything else to Dupont. For a few months I considered following the project to Dupont and to the United States. In the end I decided against. I still wanted to work in solid-state physics and not to work completely in the instrument making business. But for one or two years I continued as a consultant.

2000-05-29 :

HA : For both personal and professional reasons, I decided to stay in Paris, and then Saint-Gobain offered me a position, working in a new research field : polymer adhesion on glass and other materials. It was a new topic for me too. At the time adhesion was not even considered a science. It was before Pierre-Gilles de Gennes's Nobel Prize in polymer adhesion [1991]. It was rather considered an art. Even though I had no background in the field I was interested. What interested me in the Saint-Gobain proposal was that real breakthroughs were to be expected in the science of adhesion when two materials are brought into contact. In fact this was my first real industrial experience. Of course CNRS had not been an industrial experience at all, and even at Elf I was always in the research lab. As I explained, my work at Elf had nothing to do with the industrial activities. I never visited factories. At Saint-Gobain I had to do this, at least in the beginning.

AH : Did you not say that your development of the medical analysis system resulted in the setting up of a plant ?

HA : Yes. I did participate in the design of the plan, in order to make it efficient. But I had no role in the plant itself after construction. It was also a small plant for high-tech activity.

AH : You had nothing to do with the fabrication side of it, situated in the plant – merely the R&D before the plant became functional ?

HA : Yes, exactly. Saint-Gobain of course has many plants all over France and Europe, and even the United States. But at that time, the company was still franco-français [French through and through] in its general spirit and culture, despite the many factories in other countries. There were only French directors and the system was based on the French system of education. There is a hierarchy from the École Polytechnique through the École des Mines and the École Centrale to lesser schools, and you carry the status of your school within you for the rest of your life. I remember that I strongly felt the weight of tradition when I first joined the company. It is true that winds of change were already blowing then, but they were barely noticeable and needed a couple of years before really expressing themselves. But eventually the company changed its culture, and now the company considers itself an international one. I think a deep change has taken place during my 15 years with the company.

So, anyway, this was the first time I gained experience of the industrial aspect of research. My first task was to examine and synthesize different kinds of adhesion in Saint-Gobain's products and processes. I decided to simultaneously pursue fundamental reflection and a practical approach, helping the factories improve their processes. This was a very instructive experience. I learnt many things although I am not sure that I helped the factories all that much. I certainly learnt for myself that I preferred to stay within R&D and not to progress into production. On the fundamental side, I developed a network of contacts in public labs in France and the US. This became useful later on. After three years in the field, and having created a small research lab, I decided to gain some distance from the practical aspect of my work. It was also obvious to me that fundamental research was required first. Progressively the idea came to me to propose the creation a special laboratory dedicated to the basic aspects of polymer adhesion - and of course also to related issues such as the surface science of glass. But I knew that Saint-Gobain was not ready to have a laboratory for basic science by itself, so my idea was to set up a lab jointly with the CNRS. This was in 1988. From the administrative point of view this was feasible : a number of such joint ventures already existed, an example of which is Rhône-Poulenc. Of course I had to convince both Saint-Gobain and the CNRS of the utility of the project which was not straightforward. Although I managed to convince Saint-Gobain in a manner of hours, CNRS needed more prompting.

AH : Would you explain the nature of Saint-Gobain's research before your proposed laboratory ?

HA : It was a quite common kind of R&D geared towards problem solving. Helping the development of new products and solving problems within production.

AH : So the research agenda was driven by questions arising out of production ?

HA : Yes, and my idea was to get a more fundamental understanding of the questions which would enable us to help with such questions in a much better way.

Figure 1. Saint-Gobain Recherche, Paris

At Saint-Gobain I had to sell the idea primarily to the Vice-President of R&D. He took the decision just before retiring. The CNRS process was more complex. It has a democratic organization where decisions are taken by committees. The members consist of both elected researchers and individuals named by the Ministry of Research. They are divided up into different scientific sections. So here I had to convince a diverse group of people, and not just one person, as at Saint-Gobain. As I mentioned, I had developed a network of relationships in the fields of adhesion and surface science and now this turned out to be useful. I knew that many people approved of my research agenda. My project was accepted without much fanfare, but it still took a while because of the administrational hoops that a proposal has to jump through within the CNRS. They meet only twice a year, and every decision has to be validated by the CNRS directors and so on. It took maybe 12 months. The laboratory started on January 1, 1990. But there was only a building and neither instruments nor people.

Figure 2. Joint lab : Saint-Gobain Recherche & CNRS

The three yellow arrows point to the units of the joint lab within the Saint-Gobain Recherche building.

In the meantime I conferred with scientists in many other labs trying to recruit people. Of course the CNRS could not order people to go, so I had to entice scientists away. I estimated that I needed three scientists from the CNRS in addition to three scientists from Saint-Gobain. Two of the latter had already worked with me, and they followed me to the new project. A further researcher came from somewhere else – it was a young Chinese woman. We also had two or three technicians and some PhD students. Altogether, it took a year or so to gather everyone together. We also had to buy instruments and the process of getting the laboratory shipshape lasted altogether something like 2 years. We began to actually do some research in late 1990. And from then on the activities progressed rapidly. In two to three years we reached a plateau of 20 people, a level that had been stipulated by the CNRS. A third of the people had come from the CNRS, a third from Saint-Gobain, with PhD students constituting the last third.

AH : Where did they come from ?

HA : The latter were doing industrial PhDs (Contrat à Durée Déterminée) with Saint-Gobain, and their salary came jointly from the French Ministry of Research and from Saint-Gobain. Of the entire staff, about half each came from chemistry and physics. It was crucial that we develop knowledge and expertise in both these fields. Later we also developed an interest in mechanical problems.

Figure 3. The SPM from Park Scientif Instrument

AH : What was the instrumentation ?

HA : There was a conjunction of the beginning of our lab with the very early days of scanning probe microscopy. This new kind of instrumentation offered a very exciting opportunity. There was a risk in this. We purchased the first Atomic Force Microscope (AFM) ever in France. We bought it from Park Scientific Instruments. Later we built the first AFM for UHV purposes. There were many people then who thought the instrument had no future, so it was a risk to invest time and money in it.

AH : Why did people think it had no future ?

HA : The objection was that it was not clear that atomic resolution could actually be achieved with the AFM. It was not until 1993 that Binnig showed true atomic resolution.

AH : Well, yes, but before he had claimed to achieve atomic resolution. In 1993 he only claimed that so far he had been mistaken and only in 1993 did he achieve true resolution. Is that not right ?

HA : Yes. But in 1993 the community was convinced. The reason I did not hesitate was that atomic resolution was not actually the big issue for our purposes. Even a resolution of 1 nanometer amounted to a great deal. Much could be done with such a resolution in the field of adhesion, and also in fracture mechanics and surface chemistry.

AH : I have the impression that since 1995 or so many people argue that atomic resolution is not really that important, and that in the early 1990s it was still considered the holy grail. So you were unusual in that you had this attitude so early ?

HA : You are right that atomic resolution had a special ring to it in those days.

AH : Did you emphasize the issue of atomic resolution in your application to the CNRS ?

HA : I am not sure. Even today, nobody has achieved atomic resolution in glass. So it would have been a hard sell, also then. The same goes for polymers. And those two were our substances under investigation.
There is a difference between STM and AFM. They obey two different logics. The STM has remained a tool of basic research, in surface science. The AFM, even early on (and this would be interesting to discuss with Calvin Quate or Gerd Binnig), there was a hope that it could be useful, for example in other fields of science, such as mine, or in technology, such as process control, microelectronics, semiconductors, and so on. Generally speaking, in early phases there are always many people who think that a novelty will never become common. We have to remember that in 1987 or 1988 solid probe microscopes were still big and unwieldy instruments. Of course miniaturization had set in by 1990, but it was a novelty. Only very few people were convinced that the AFM would become so common. Calvin Quate is one of the few. The STM has revolutionized basic research on metals and semiconductors. There was a reaction against it, because surface science was done using diffraction techniques working in reciprocal space. Surface scientists were formed in this mode of research. They resisted the change, feeling that newcomers would enter their field without the kind of abstraction that had hitherto been key to access to the field. Working in ordinary space was too easy ! Of course it has not actually become easy because the instrument has brought its own problems, and there are still people working with diffraction and in reciprocal space. The two complement each other.

AH : So this is the background against which your decision has to be seen. You went out on a limb.

HA : Yes. The beginning of my lab coincided with the first commercial scanning probe microscopes (SPMs). We had to grasp the opportunity.

AH : How did you know about the AFM ? Was it a very visible instrument at the time ?

HA : No. I knew about it from publications, but in order to actually see an instrument, I had to travel to California - although I guess I could have seen one at IBM Zurich. There was an STM at Marseille, because two physicists there (Salvan and Humbert) had worked at IBM Zurich, and they had brought one back with them. But they had no experience with the AFM. So I went to the US and visited the very few labs with AFM, both academic labs and the start-up companies of PSI [Park Scientific Instruments] and DI [Digital Instruments]. At Stanford University I met Calvin Quate and at UC Santa Barbara I met Paul Hansma.

AH : Was there a relationship between Paul Hansma and DI ?

HA : I don't remember. But at any rate it was not as close as the one between Quate and Park. I think Park was a former student of Quate's.

AH : So you purchased an AFM from Park. What about the other kinds of instrumentation you purchased for your lab ?

HA : Yes, we had to get other instruments, partly because it took a long time for the AFM to arrive. I had to go to the US to compare the DI and the Park instruments, and I discussed it with the physicists and chemists in our lab before ordering, and then we had to wait for the delivery – maybe 4 months or so. We got a 40% discount, because we were the first French customers, and they hoped that we would open the French market for them. I had very good discussions with Quate, and I think he trusted me to be a good advertisement for him in France. I think we paid 400,000 French Francs, so that the catalogue price was in the order of 800,000 French Francs [approximately US$100,000].

We bought also an infra-red spectrometer, in order to study molecular grafting on oxides. This we used as a complement to the AFM. And as I said in a previous part of the interview, our approach was to combine the traditional surface science (very clean surfaces) with “true surfaces” interacting with the environment. The infra-red spectrometer, XPS (X-ray Photoelectron Spectroscopy), and LEED (Low-Energy Electron Diffraction) were good tools for the traditional surface science approach working in UHV Ultra-High Vacuum). And also HR-EELS (High-Resolution Electron Energy Loss Spectroscopy). Our choice was risky, but it turned out to be correct. Our decision to build bridges between the two approaches was taken in 1992 or 1993. Quite early on in our project we built a surface force apparatus (SFA). It is not at all an AFM – there is no concept of high resolution, but it is similar in that you can get a direct measurement of the force interacting between two objects only a few Ångstroms apart. The idea is to make the measurement quantitative in order to study whether the interaction is due to van der Waals or electrostatic forces. In fact this project took six years – not for technical reasons but simply because we had to get the right people.

AH : Each instrument had its strengths and weaknesses in terms of resolution and the scale of the surface analyzed. And each instrument required special skills. The AFM, for example, requires quite some expertise to disentangle signal from instrumental artifacts, right ?

HA : Yes, artefacts were a real concern at the beginning, when we all had very limited experience. We had to pay much attention in order to ascertain the results.

AH : Can you explain how one separates signal from artefact ?

HA : There are different kinds of artefact. One that now seems quite natural but was hard to understand then is the tip effect. If the surface under examination has sharper topographic features than the tip, then the tip will be imaged rather than the surface. We had trouble with this kind of artefact. In fact, when studying tin oxide deposits on some substrate we got very nice images that we at first interpreted as small crystals having the similar orientation. We were very excited to find a growth mechanism of specific orientations on isotropic surfaces such as glass. I decided to present this result at a small meeting in Davos, Switzerland. The topic there was in fact “The AFM for Technological Applications”. Famous scientists attended, including Calvin Quate, Jim Gimzewski, and Heinrich Rohrer. There were only some 10 people there, because this was very early, maybe 1991. The night before my presentation, I began to wonder that the result was really too beautiful to be true. I telephoned my lab and asked people there to turn the sample by some angle and do the experiment again. That way, the features should have changed if they belonged to the surface. But they did not, and so we knew that the features belonged to the tip. So I did not present that particular slide in my talk.

AH : So rotating the sample by some degree is one way of identifying artefacts.

HA : Yes, that will eliminate this kind of artefact, the tip effect. There are also adhesion artefacts, some of which have been solved in the meantime thanks to new recording techniques such as the tapping mode.

AH : Digital Instruments has a patent for the tapping mode, right ?

HA : Yes.

AH : So the Park instrument that you bought did not have the tapping mode ?

HA : No it did not. The tapping mode did not become available until 1993 or so. Later on, Park Scientific Instruments did do something similar, but they may not call it tapping mode. The DI patent covers the name. And in the straightforward contact mode many artefacts were possible ; for example when looking at soft materials and polymers surface scratches easily occur. If you do that you image the substrate only. One way to identify this effect is to scan again with a smaller tip-surface interaction. In some cases you will find miniature small squares where the surface had been damaged in the course of the first scan. Some artefacts are very common, others are quite specific and harder to identify.

AH : In what you have explained, the identification of artefacts is internal to the instrument itself. It is not that you can go and compare the results of an AFM scan with those from a different instrument ?

HA : You can change the tip, and you should identify artefacts unless you are very unlucky to get the same tip. Everybody understood that the AFM has great potential not just as an imaging instrument but also to measure adhesion, hardness and so on.

AH : Using force-distance curves ?

HA : Yes, force-distance curves. This turned out to be very useful for us. For instance in order to understand the electrostatic interaction between oxide and a silicon nitride tip under water. This was original work. For example, in polymer adhesion we checked if it stayed on the substrate and what scratching would do. Of course such ideas were floating around at the time.

AH : Were you important to the subsequent spread of the AFM in France ?

HA : Yes, people came to our lab. Another lab, at the Institut Curie, that got an AFM at almost the same time. For a while we were a small community but then gradually we grew larger and larger. Yes, we were the pioneers. It was exciting.

2001-02-20 :

HA : I went with one of my sons who was 11 years old at the time to see Park Scientific Instruments. There were no more than 10 people working there, in fact I think it was more like three. It was very small and familial. We discussed and had tea. I enjoyed discussing with these people. It was nothing like an established company.

AH : What did it look like ? Did they work out of a garage ?

HA : Something like between a home and a garage. It was a small house. Even Digital Instruments started out like this. Already in those days DI, and especially Virgil Elings, was much more commercially aggressive, but they were very small too at the time.

AH : Did you stay in touch with some of these guys ?

HA : I stayed in touch with Calvin Quate for five or six years, until 1996. After that I lost the contact but he will probably remember me because we had many discussions. It was curious to see his impact upon materials science. In fact it was very difficult for him to get the first paper on the AFM accepted in Physical Review Letters. Some of it was considered just a pure mechanical profilometer. It had good resolution but it was not really anything new. His project now is very interesting from what I can tell reading his articles in the scientific journals. And he really is a very nice person. Maybe the last time I saw him is when I invited him to give a talk at Saint-Gobain Recherche.

AH : So you stayed in touch with him in the early 1990s, while you were developing your own AFM. I guess the use of the AFM changed the project from what you had originally envisaged ? Did you continue using all the other tools or did you focus exclusively on the AFM ?

HA : We used the other tools.

AH : What did you buy for your laboratory ?

HA : Infrared spectrometer, XPS, HR-EELS (High Resolution Electron Energy Loss Spectrometer), LEED. Quite quickly we had three AFMs. I wanted to develop a PSTM working in the infrared but unfortunately that particular project died because the physicist we had working on it left.

AH : What journals show the history of these instruments best ?

HA : In the beginning it was mainly in the general physics journals such as Applied Physics, Applied Physics Letters, Physical Review Letters, Surface Science. Now there are specialized journals. A journal like Journal of Scientific Instruments is not so important in this respect. Langmuir is also important for soft matter.

AH : Do any of these journals have review articles ?

HA : I am almost sure that all of them do.

AH : We were talking about the various instruments you had in your lab. How did you apply them to your research project ?

HA : The idea was to have two parallel approaches. We were mainly interested in adhesion, molecular grafting and so on. One approach is the classical view of surface science, the ideal surface approach. The other is the REAL surface approach, taking the environment as a part of the system.

AH : Not working in Ultra-High Vacuum (UHV) ?

HA : Yes. But we were trying to make the two approaches meet.

AH : So when you started working with the AFM in UHV, the point was to simplify the experiment ?

HA : Yes.

Figure 4. UHV Chamber et AFM in UHV Chamber

If a probe were to be introduced directly into the UHV chamber, it would take days of pumping to achieve UHV. Instead, it is first introduced into an antechamber, whereupon a vacuum is produced there. Only then can walls be opened without reducing the UHV too much. By pushing the rods labelled 1 and 2, the sample is transported in successive stages into the central chamber. Several instruments are attached to the chamber, including an XPS. On the right, an AFM can be discerned in the UHV chamber.

AH : How did the various instruments complement each other ?

HA : The spectrometers provided structural information. They give a chemical signature. One point of interest was silver on magnesium oxide. In order to have a simple model of glass we chose to study this problem within pure single crystal. We had the probe in situ in the same UHV chamber where we had the instruments to add the deposition techniques. In the case of silver it was just thermal evaporation. We wanted in situ real-time studies of the atoms arriving upon the substrate, the oxide surface. There were two models in this problem. One was that the atoms remain isolated or form small islands, so that the growth process is two-dimensional, so that you first get a perfect monolayer before a second layer is started upon. The other is that growth is three-dimensional with occasional collapses into flatness. To study this it is of course useful both to look directly and to use diffraction techniques. But in order to understand the process you need to grasp the interaction between the silver and the oxide. And only spectroscopic techniques will help here. We always tried to look at a problem from two differing points of view – in this case geometrical and chemical.

AH : You make it sound easy. You just use one tool and you get the topography, and then you use another and you get the chemical composition.

HA : Well of course it is not at all easy. It was very difficult because for instance, the STM works very well when you have a smooth surface but when you have corrugation it becomes much more difficult, because this corrugation interferes with the instrument. In spectroscopy you integrate over the size of the beam which is much larger than the surface scanned by the AFM. So you have to do many different experiments to see what effect the temperature has and so on. You also have to model the interaction. This was a little known problem. What is the mechanism of very small silver clusters on magnesium oxide with other silver clusters in the neighborhood ? It was a new problem. So it took time to understand the system.

AH : What is the measure of success ? It was partly CNRS, so you were under pressure to publish ?

HA : Yes.

AH : And since it was partly Saint-Gobain you had to get patents ?

HA : We had to do both. It was an interesting exercise in communication. In my position as head of the lab, I could not use the same words, the same way of presenting things when addressing different audiences. From time to time it was necessary to gather the scientific and the industrial people together under one roof.

AH : And what language did you speak then ?

HA : Fortunately everyone was happy with this lab, so it was not quite so difficult. The conditions were good. Nonetheless your question is quite correct. It was interesting.

AH : How did you convince Saint-Gobain that this would have a pay-off ? And how did you negotiate long- and short-term goals ?

HA : The short term was a problem. It was not straightforward to plan a new product for the company. The pay-off was very diffuse and difficult to identify. One way of motivating the directors was the argument that we trained very good PhD researchers for Saint-Gobain. And this was not expensive for Saint-Gobain, because they shared all the expenses with CNRS. Up until now this has not been a problem.

AH : Stanley Whittingham told me that in the last 15 years or so there has been a tremendous shift in company planning towards the short term in industry. Partly this was due to the MBA education and the fanning out of this new generation of business administrators into all nooks and crannies of industry. As a result the long-term disappeared, because everything had to fit into the financial year so that you have something to show to your shareholders.

HA : It is true that this has taken hold in industry. We had the good fortune that it was not very developed in Saint-Gobain. But also, the time required for the development of new glass materials just is acknowledged to be greater than that in electronics or informatics. When we start new projects, we are simply not able to show a product six months later. So we are less exposed than people in other fields, but the general development that you alluded to certainly has taken place. Maybe our situation will also change in the future. We may be excessive.

AH : Has the accountancy changed for you ? Did you have to write annual reports ? And has it changed over the last ten years ?

HA : In general ?

AH : Well, for the CNRS I can sort of imagine it. In academia you would specify the number of publications that you have produced and that is the measure. End of story. And that is very simple accountancy. But if you account to a company, keeping in mind the increasing influence of MBAs : did you have to account for your expenses in ever greater detail ?

HA : I do not think there has been such a change in the last decade.

AH : And do you write annual reports ?

HA : Bi-annual. But I am not in this lab anymore ; I left two years ago.

AH : Okay, so during the 1990s up until two years ago you wrote biannual reports to the company and in that period the structure of the reports did not change.

HA : That is correct.

AH : Did you have to specify just how much money you spent ?

HA : Yes, but also there, no change took place. And I always reported to the same person within Saint-Gobain. He was basically content with what we did, so it was never critical. It is true, it might have changed with a different person in charge.

AH : So, how did the instrumentation change throughout the 1990s ? The AFM became commercially available to an ever greater extent, you were able to buy many more things off the shelf. Is that true also of all the other instruments ?

HA : Yes, there are different aspects to your question. We used to build many instruments ourselves, and this was of great use for training. And this has changed. A reason the French PhD has been shortened is that equipment is being bought and not made in-house. That is a general trend. Science is changing as a result, because using a commercial instrument is not the same. When you develop an instrument yourself you know exactly how to get the result. In the specific case of AFM/STM : probably the AFM has been developed much more than the STM. In the STM the major breakthrough was with the driver and that was quite early. I think it was possible to purchase an STM driver already by 1992. Variable temperature was a little more difficult, but it was certainly available by 1994. Different ways of scanning and acquiring information were developed. Otherwise the evolution was purely technical : cheaper, and more diverse (such as an STM expressly for electrochemical research). By contrast the AFM has developed rapidly. Tapping mode and other modes where you measure not only the distance but also hardness, conductivity, adhesion, chemistry. It has become possible to map all these parameters. This explains why more and more people use the AFM.

AH : It has also become cheaper, right ?

HA : Yes.

AH : It has certainly become more user-friendly, adaptable to different circumstances.

HA : Yes. For the STM : there have very beautiful studies made of the coupling between tunneling and modulation. You might modulate the tunneling current with light for instance. You can even leverage the spin of the tunneling electrons. So you can do beautiful physics. But this contributes little to the democratization of the technique.

AH : I have the sense that Calvin Quate, by contrast, is working hard to increase throughput.

HA : Yes, that is right. There can be two reasons for doing that. To make the investigated part of the surface larger – of use in the semiconductor industry. And to shorten the time required for a scan. He is trying to use the system technologically.

AH : Okay. Two years ago you left your lab. Your own lab. Why ?

HA : I wanted to try something new and I was lucky to find someone who was well capable of taking over and for whom I have a lot of respect. He is from a different background. So now it is a different group. I became the Scientific Director of Saint-Gobain Recherche. There are two parts to the job ; one is to be the scientific manager, the other is to establish contacts in the outside world, and to promote innovations within the company, for instance with the marketing people.

AH : You were promoted ?

HA : Yes.

AH : And you have become slightly removed from lab work ?

HA : Yes, completely, I am now involved in organizational work.

AH : In fact, our project resembles your job in the sense that we stand back and look at the scientific research and try to gain a perspective ?

HA : Yes, you could say that.

Fin de l'enregistrement

Pour citer l'entretien :

« Entretien avec Hervé Arribart », par Arne Hessenbruch, 19 février, 29 mai et 20 février 2001, Sciences : histoire orale, /spip.php ?article47.

Pour citer l'entretien :

« Entretien avec Hervé Arribart », par Arne Hessenbruch, 19 février, 29 mai et 20 février 2001, Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article47.

Lieu : dans le salon (les 19 février et 29 mai 2001) et dans la petite salle de réunion (le 20 février 2001) du Dibner Institute, Etats-Unis.

Support : enregistrement sur cassette.

Transcription : Arne Hessenbruch.

Édition en ligne : Sophie Jourdin, Sacha Loeve.