Sciences : histoire orale

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.

ANDERSEN Jens E.T., 2001-03-06

2009-12-21T23:53:02Z

Jens E. T. Andersen est chercheur au Département de Chimie de la Technical University of Denmark à Lyngby. Dès 1992, il utilise une technique inaugurée par Dieter Kolb et Richard Nichols un an auparavant : le microscope à effet tunnel en milieu liquide, appelé également « STM in situ » ou « microscopie électrochimique à balayage » (SECM pour Scanning ElectroChemical Microscopy). À partir de 1995, Jens E. T. Andersen a étendu la gamme de ses usages du STM in situ de l'électrochimie à la biologie, en imageant des protéines adsorbées sur des surfaces. Il a organisé trois conférences sur la technique du STM in situ en 1994, 1996 et 2000.


Autorisation de diffusion

ARNE HESSENBRUCH (AH) : Could you give us an overview of your academic career ?

JENS E.T. ANDERSEN (JA) : I studied chemistry and physics. I majored in chemistry and got a bachelor's degree in physics at the University of Copenhagen in 1987. I did the Danish equivalent of the PhD for three years in surface science at Preben Juul Møller's laboratory at the University of Copenhagen, doing metal on insulator surfaces. I finished in 1991, after which I got a post-doc at the University of Cambridge, with Dr. Richard Lambert - he is now a professor at the Chemical laboratory. I worked for a year and a half on a catalytic effect denoted as NEMCA, Non-Faradic Electrochemical Modification of Catalytic Activity (figure 1). We wanted to investigate this effect, invented by a Greek scientist in the late 80's, and we wished to check this under UHV conditions. Then I saw this advertisement for a Danish position to implement a technique called in situ STM. Not just STM, but in situ STM, or electrochemical STM. You see in 1990, as far as I recall, or 1991, Prof. Kolb (University of Ulm) and Richard Nichols (University of Liverpool) found that you were able to operate an STM while the atoms were submerged in a conducting liquid, in an electrolyte, like water. This was a sensation. We used LEED (Low Energy Electron Diffraction) imaging to study electronic details of electronic diffraction, but it was very difficult, especially because we needed UHV conditions. It seemed absolutely sensational that one could image something like that under ambient conditions in air in a liquid, just by electrochemical control of the STM tip. That was brilliant, and this really aroused some interest in me. I took this position. I applied with Per Møller at the Institute of manufacturing and engineering here at the Danish Technical University in 1992 to get the job and I was successful. We continued for two years developing the instrument together with DME. So the purpose with this project...

Figure 1. Non-faradic electrochemical modification of catalytic activity (NEMCA) Principle.

AH : So when you started out with surface science, did you know about STM in the late 80s. It was not of very great interest ?

JA : Well it was interesting as such, because we all speculated : is this technique really able to image atoms. What is it that we really see in the images ? Are these blobs really atoms ? But I think in the mid 80's it became evident that you could image a silicon 7x7 reconstruction, and this convinced me that this was some kind of atomic resolution. So it was all a technique that was developing.

AH : So you even knew about the STM in the early 80's. You'd heard about Binnig and Rohrer and you kept an eye on it, but you were not convinced. The blobs had to be...

JA : Had to be something to do with metal conduction bands and the band structure of metals. Semiconductor structures, and maybe more subtle to interpret. But with the silicon 7 x 7 reconstruction it seemed sort of convincing.

AH : And was this common in surface science, or maybe even in chemistry ?

JA : I think it's more or less a part of the education that you keep an eye on some of the new techniques. You see, the question always arises : what is an atom in reality ? At that time Transmission Electron Microscopy was the prominent technique of atomic studies. But it has become less prominent in the light of STM, because the latter is fairly easy to use and also less expensive. But then again one asks, is it really atoms ? At that time lots of people were speculating and still there is not a convincing theory describing all the details of the tunneling experiments.

AH : I presume that by the time Binnig and Rohrer had gotten the Nobel prize in 1986, then there was no doubt that these blobs were atomic resolution. Everyone agreed about this. But there was still not commercial STM's on the market, you couldn't have used STM's yourself.

JA : I'm not really sure, the Nanoscope, was that in 1980 ?

AH : Late 80's. Digital Instruments was only founded after the Nobel prize.

JA : But when they received the Nobel prize I presume they invented Atomic Force Microscopy in the same year ?

AH : 1986, right. But you would have had to build one yourself, and Joergen Garnaes over there [across the road] in the early 90's he was building his own. And he could only buy one off the shelf in 1992, and there was no longer a point in building one.

JA : In 1991 DME was putting the instrument on the market, but I think Digital Instruments, they were much earlier. I think Besenbacher, who was the Danish pioneer, built his own instruments in the early 80's, mid 80's. He's recognized as a real scientist of developing STM also to convince scientists that this is really a technique of the future. I think he made a really impressive contribution there. So I think he did that in the mid-80's, he must have because I started out doing surface science in 1987, and he was well known in the field at that time. [Actually, Besenbacher, Lægsgaard, and Stensgaard built their first STM in 1987.]

AH : So in your own work in 1987, what tools did you use, what characterizing tools did you use ?

JA : I used the most common tools, low energy electron diffraction and electron spectroscopy, Auger electron spectroscopy, electron deposition for building up atomic layers, and high resolution EELS (Electron Energy Loss Spectroscopy).

AH : The whole palette ?

JA : Not x-rays. X-rays is a common surface technique of elemental analysis, but we analyzed by AES (Auger Electron Spectroscopy). I think I was also one of the only ones in Denmark doing high-resolution ELS and analyzing surface optical phonons on insulators. This is a fairly difficult technique, and Preben Juul Møller, I think, was the only one who had the instrument at the time. And together with 2 Chinese guys we made it work properly. So we got some interesting surface optical phonon studies of metallic insulator surfaces. The interface of insulators and metals.

AH : Would you describe how that works ? The instrument, and what you had to do to get it work.

JA : The difficulty is, that it is a very narrow electron beam of low energy and you have to focus it delicately - it's a very delicate focusing problem. You have to optimize with an electrometer where you measure all the currents at the equipment and then you try to focus into the detector, which is a fairly difficult process, and the manufacturer couldn't really tell you how to do it. Just told us optimize, use optimizing procedures. And we were three people, working on this for three months, and then we made it work by a systematic optimizing approach. You can never do anything by trial and error. Optimizing by statistical methods, experimental planning basically. We used the instrument for a fortnight each, and we did as well as we could, a sort of competitive method of achieving the best signals, and suddenly we got the same signals as the manufacture's best signal. But I think it's quite a struggle, and too much of a struggle in comparison to the information you get out of it. But it was fun trying to make this very delicate instrument working. This is interesting for low energy electron studies, when you can do spectroscopy of something like phonons, that's quite interesting I think. And one of the Chinese guys, Guo Qinlin he's now a professor in China with a group of 30 people, and the other one, Dr. Wu Mingcheng, he went to the States and was employed in Texas A&M, College Station and he is still living there. So he did quite a good job and produced very exciting results, it was really good experimentally, brilliant. But then the technique you can study surface optical phonons, and overtones of these optical phonons, it can give you an idea about the electronic structure of the surface of insulators.

AH : So, is this a common thread for you to use new techniques try to stay abreast in most recent technology and use them to find out about surfaces ?

JA : In the sense that they can give us new information inside of how Nature is working, then it's interesting. Some new techniques emerged, I think, that are not that much of a help to something that we know already. When it's complementary, they can be the sort you need to advance only slightly. Some of the really new exciting technologies can do something that was not possible before, such as the in situ STM, where you can study atoms in an electrolyte medium.

AH : And you started using the in situ STM when you got here in 1994 ?

JA : 1992.

AH : But you had an interlude in Cambridge, and you didn't work on the STM in Cambridge. What tools did you use then ?

JA : Mainly mass spectrometry and Auger. I think we may have used electron energy loss spectrometry. Oh yes, we also used thermal desorption spectrometry together with the mass spectrometer to study molecules desorbing off a surface. This was quite an interesting project and we had a close collaboration with the Greek group who invented this technique.

AH : In Athens ?

JA : It may have been the University of Athens. Constantinos Vayenas was the head of the group. And Ioannis Yentakakis was our collaborator at the time. He went to Cambridge and we started this phenomenon under UHV conditions. We succeeded and I was happy to see what was going on, and we went as far as we could interpreting their method. They have brilliant articles in many famous journals where they show how this effect was working. When we got it running under UHV conditions it was not a significant effect, we could not be convinced that this was as brilliant, as they told us it should have been. To this day, a lot of work is going on to study what exactly this NEMCA effect is. So we didn't really finish the project completely because I left for another position, but I got enough information as to decide not to build a career on it. It was something really exciting, a new science and a new idea, a new and novel effect you can study in detail and resolve all the chemical mechanisms. But I think it was fairly simple. It was an increase in oxygen production by the material that was used for the electrochemistry - it was sort of solid state electrochemistry. And a zirconium dioxide ionic conductor where you can pass oxygen ions through a material by electrochemical potential differences. You can also desorb oxygen off the surface, and of course if you got an oxygen consuming process at the surface you will consume the oxygen produced by the material. And in my mind it was all coming from the material, but my colleagues were not quite convinced, so we disagreed a little.

AH : So you agreed to disagree in the end.

JA : Yes.

AH : How did you get to work in Cambridge in this period ?

JA : Well I had been working with Dr. Preben Juul Møller at University of Copenhagen in surface science and it was sort of a natural continuation of the career. You have to apply for vacant positions abroad, and I was maybe overdoing it a little applying for a position at Cambridge. Richard Lambert knew Preben Juul Møller very well. He was familiar with his work on insulators. So I had been working on insulators and metallic surfaces contacts for 3 years and I knew what it was about. And I think also very quickly, within half a year, we constructed the necessary UHV improvements to study this NEMCA effect together with Ian Harkness, a scottish PhD student who made a brilliant job of constructing this electrochemical cell for UHV conditions. It's not trivial to make this sort of system, but we did it within half a year. And then we got a whole year of studying the NEMCA effect which worked quite well. But of course I was extremely surprised and happy that I could get this post-doc position at Cambridge.

AH : The laboratory life at Cambridge is very similar to that of the University of Copenhagen ?

JA : Yes.

AH : Same kinds of equipment same level of funding ?

JA : The funding is better at Cambridge. More students available for the studies, but equipment is similar. The level of science is also basically similar, teaching is probably a little better at Cambridge. I haven't followed the graduate courses, but to my knowledge some of the people there were really brilliant. The young PhD students were really brilliant scientists.

AH : Were you a member of a college ?

JA : No, I was not affiliated through the colleges. I did try to become a member of some of the colleges, but as a post-doc you are not supposed to interfere with college life.

AH : So the people you talked to were people in your field, in your lab.

JA : Yes it was a highly professional and competitive working environment and I think a very good time.

AH : Was it also a lot of fun ?

JA : Well, it was hard work – I am not sure about fun. I had my family with our daughter aged six months. Also my wife was not too happy, it was one of the reasons why we left a little early. We were supposed to stay for 2 years, we left after 1.5 years. My wife also wanted to go back because it was tough when I was working from 9am until late in the evening. She didn't really have anything to do apart from taking care of our daughter. And she has a Masters in music and rhetoric and wanted to use her education. It was a little too boring for her, I think. But for me it was excellent.

AH : And so you went back to the in situ STM ?

JA : Yes, I started with the STM when I arrived back in Denmark. I had never worked with the STM before.

AH : But you had kept an eye on STM all the while.

JA : Oh yes, as a surface scientist you always look out for interesting techniques that are competitive to what you have in your field. And when I saw this atomic resolution in an electrolyte, I couldn't believe it, because you can't imagine the struggles you have to go through to make a metallic surface clean under UHV conditions. And once it's clean you have only approximately half an hour to make all your studies because it adsorbs all the gases even under UHV conditions. Approximately one hour you can keep your surface clean under UHV conditions. By contrast, with the arrival of the STM you suddenly were able to study atoms under brilliant conditions (ambient conditions) with a low cost instrument and you can even deposit atoms electrochemically. You can study the metallic overlayer at atomic resolution while it is being constructed atom by atom. I just couldn't believe my own eyes. My colleagues and the PhD students had a good laugh and they said : “So, you're going into in situ STM submerged surfaces. Well, you will need a diving suit.” I assured them that “No, no, no, it's atomic resolution.” They didn't believe me. We discussed the article and I have to say that even Richard Lambert was really surprised that this was possible.

AH : So you were one of the people that convinced others that this was possible, that this was real.

JA : Well it seemed real. If there is a paper in Physical Review Letters my attitude is always to take it seriously ? And you can study also the references in the particular paper by Richard Nichols. You can see in the references that they had been struggling with various modifications of STM to get this result. So it seemed very convincing to me.

AH : But if someone like Lambert was critical, he must have had a good reason. And you say that...

JA : It's so difficult to get a clean metallic surface and it's so highly reactive towards gases in the background and it will destroy the clean surface in a matter of minutes and then suddenly you can have water on top of the metal adsorbing to the metallic surface and you can still observe your atoms. At first nobody really understood, and they said okay it was an aqueous monolayer or something like that, we observed under liquid conditions. Of course this is not what Nichols told us - It's really metallic atoms deposited electrochemically, you can see atom by atom building up. No doubt !

AH : So Richard Lambert didn't develop a new STM really, he just used it ?

JA : Well he did acquire an STM for UHV studies at a later stage. Maybe he got it while I was there, but he was convinced that this was a technique he also had to consider for catalytic studies.

AH : But he didn't build his own STM. You take an STM off the shelf and use it for new studies.

JA : But it wasn't much off the shelf for UHV conditions. I think there was one Swiss company building UHV equipment for the STM.

AH : So a UHV chamber with an STM inside as a package ?

JA : Yes.

AH : And the job here was advertised for in situ STM you said ?

JA : It was advertised in a Danish union journal. Magisterbladet, I think. Or maybe it was in Ingeniøren.

AH : So the people here, they must have trusted the new technique also.

JA : Well you see, Danish Micro-Engineering produced the instrument already before I arrived. I think they sold 10 or 20 air STM equipments around Europe. So they wished to develop the STM. They considered this to be a minor problem and they employed me to do the job. As a matter of fact, Per Møller who advertised this position wasn't really familiar with science as such, but the purpose of implementing this technique was to use it for bulk electrochemical studies. So he would more easily be able to study corrosion processes under the real conditions in an electrolyte. He also wanted to use the instrument to automate electrochemical deposition. You know, he is an expert in plating. So we would like to optimize plating processes, let's say pulse plating and things like that. We wanted to study such things with the instrument. He also wanted to build small metallic machinery, something like submarines swimming about in your veins, depositing medicals at the right spots.

AH : Nanomachines ?

JA : Nanomachines. Within 10 months we got the desired atomic resolution and we finished development of the instrument. I'm saying we because Carl-Erik Foverskov, an instrument maker at the institute, he made the design for a bi-potentiostat. Actually, I must mention that I visited Richard Nichols. I think that without his help we would have taken much longer.

AH : Where was Richard Nichols ?

JA : Richard Nicols was employed at Schering, in Berlin. Schering is a pharmaceutical company, and they were taken over by a French company, Atotech. He stayed in Berlin for a number of years doing in situ STM. But he helped me out with some of the problems. I visited him in Berlin and he participated in our conferences. He was invited to help us out, and he also delivered some of the gold samples that were necessary to obtain atomic resolution. So he was very helpful. Within 10 months, we improved the DME instrument, got atomic resolution, and it was ready for distribution, ready for sale. They needed maybe six more months before they were ready to sell the instrument.

AH : What was the connection between the Danish Technical University and the DME in your job ? You said there was a DME that started the job how did they influence the DTU ?

JA : The connection was Per Møller, the center leader. He was head of the Center for advanced electroplating at the DTU. In Denmark, such a center must be a collaboration between DTU and a company. I think there must be something like 3 institutions involved. I don't know which was the third, but I think it's Danish Plating Industry, something like that. So it was a joint venture. I think we succeeded. But I remember that Møller wasn't too happy about the outcome, because he wasn't really interested in the scientific achievements. And we even made this instrument work for pulse plating, varying electrochemical potentials up and down very quickly. This influences the instrument, so you lose the imaging, but we could maintain the imaging while doing pulse plating.

AH : What did you do next ?

JA : Then I was employed with Professor Ulstrup, who's a bioinorganics scientist. I never expected to be involved in bio-something. But then suddenly I found myself in the imaging of proteins. I still don't know what a protein is. [Laughter] Today I do know a little about this field. We started a joint venture with Per Møller, and we applied for the [Danish] National Technical Science Foundation and got a three-year project. We were supposed to image proteins, and yet we uncertain about what we saw in the STM images (figure 2). But we knew some other group in Europe was grappling with proteins because if you can image proteins, you can image the molecule of life. That's really a big thing. It took quite a while but we succeeded.

Figure 2. In situ STM image of azurin adsorbed on gold(111).

From Esben P. Friis, Jens E. T. Andersen, Yu. I. Kharkats, A. M. Kuznetsov, R. J. Nichols, J.-D. Zhang, and Jens Ulstrup, 1999, « An approach to long-range electron transfer mechanisms in metalloproteins : In situ scanning tunneling microscopy with submolecular resolution », Proceedings of the National Academy of Sciences of the United States of America, vol. 96, n° 4, pp. 1379-1384 (figure 7). Quoting the paper : « individual molecules and a submolecular central feature of brighter contrast are clearly visible ». Copyright © 1999, The National Academy of Sciences.

AH : Which groups ?

JA : Professor Kolb in Ulm. Well, he is working not on proteins as such. Dr. Davis at Oxford and his group. Prof Allen Hill, also Oxford. They are the prime investigators in Europe I think. They have come up with some of the best results, including the imaging of proteins. So we've been working in parallel towards the same goal and we arrived there sort of simultaneously.

AH : And when did you succeed ?

JA : 1996 I think.

AH : Were in touch with Hansma ?

JA : Not as such, but I asked him for some preprints, and he sent me some piles of preprints and said "I'm happy you're working in this important field." He encouraged us very much and we invited him to our conference last year in 2000, but he was not able to attend. But he's done very good work and I think encouraged us to continue what we were doing.

AH : So these workshops. How did they start. Who took the initiative ?

JA : That's professor Ulstrup. 100%. He took all the initiative. When he saw this instrument and that we were able to image proteins he became very excited because he's a theoretician doing electrochemistry on metalloproteins. He has developed protein electrochemistry together with Allen Hill but from a more theoretical point of view. And then he's got me and the group to do the experiments. This way he could develop his theory. He took the initiative and then we've got lists of Danish companies and foundations who supported the first workshop. It's no problem to obtain funding for this purpose, I think. We even got funding from the Danish National Research Foundation. You know the Carlsberg Foundation in Copenhagen, they've got a house of science, the Royal Danish Academy of Science and Letters. And they supported us so we could use the premises of their Foundation. There was I think 60 people attending the workshop, in 1994.

AH : Was it a conference on STM in general ?

JA : No it was on in situ STM, electrochemical STM, also called scanning electrochemical microscopy. Allen Bard at the University of Texas, Austin, invented a similar method, and he denoted it as SECM - scanning electrochemical microscopy. So there are various denotations of this technique. We say in situ because we image while it's occuring.

AH : What sort of people came in 1994 ? What fields did they come from ?

JA : Well we invited people to display their results in STM in general and we did get some contributions that were not really in situ. It's definitely not under water, it is not in an electrolyte. We accepted more or less a wide range of contributions because there were overlaps also with in situ in many fields : solid state depositions by vacuum evaporation can also be considered as in situ, and can be made as comparison to some of our in situ experiments. But the purpose was to promote in situ STM. We still believe that in situ STM is superior to regular STM. The availability, information, methods, and scientific results you can obtain are more varied, there are many things you can do. So we would like to promote this technique and of course you can also image proteins in air, but we would like to image molecules in their own environment, which is electrolyte environments. And I've also considered to image viruses and things like that. At the present stage we have imaged proteins satisfactorily, and we have been promoting in situ STM also in the year 2000 to make people understand that this is really something worthwhile.

AH : Have you had a conference every year since 1994 ?

JA : No, only in 1994, 1996, and 2000.

AH : Were the people who came in 1996 all in situ STM people ?

JA : Almost yes.

JA : It was absolutely the most important groups in Europe represented at this congress and some invited speakers from the States also present. I think there were a couple of students from Japan, but no speakers from there.

AH : How many people came in '96 ?

JA : There was around 60 people – same as in 1994.

AH : And in 2000 ?

JA : The same

AH : Any change in composition of attendees in 2000 ?

JA : No, the same groups were represented. The focus was more bio-oriented in 2000 because now the issue was protein superstructures. Bio-inorganic imaging, that was the purpose, so there were some new groups.

AH : Is that because you are now more involved in the bio-side, or because the field in general has moved towards bio.

JA : I don't think the field in general has moved towards bio. The prime investigations are still made in superstructures and under-potential deposition, which is mono-layer studies, because in situ STM is the only technique where you can obtain atomic resolution. Subatomic resolution can be obtained even with other techniques than in situ STM. Some groups may consider imaging of proteins as subatomic. It's not really atomic resolution. Superatomic I'd say, not really at a higher resolution but at a lower resolution than atomic resolution. And they don't consider this very interesting because you get some difficulties in STM theory : how does it work when you see a protein ? People are a little anxious that they may be studying artifacts rather than real molecules.

AH : Yes of course.

JA : There are a number of artifacts in STM, it's known for artifacts.

AH : Can we back up a little ? I have difficulties imagining just how you would scan something like a protein where you don't have a surface, right ? You have something more unwieldy - how does it work ?

JA : It's a little surprising when you try to study large features with STM because the tunneling distance is some 10 Ångstroms, and a protein is at least 40 Ångstroms in diameter. Obviously, the tunneling current itself ought to deform the protein completely. And something like the deformation of a protein is observed : it's flattened considerably. The measured thickness of a protein is approximately 20 Ångstroms so it's probably flattened while in scanning. But it needs to be immobilized at a surface, otherwise you cannot get the image.

AH : How do you do that ?

JA : We choose specific enzymes and proteins where you have a sulfide bridge to a gold surface. If you react sulfides or thiols with gold you form a covalent bond that is relatively strong. Sulfides react readily with gold surfaces, and our problem in the first instance was to show that we were able to image proteins that were immobilized properly and the question was : Is one sulfide bridge from the protein to the gold surface sufficient linkage for imaging ? And it turned out it was adequate. There was just one molecular bond to the gold surface from the protein, through this sulfide bridge.

AH : Thank you !

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Pour citer l'entretien :

« Entretien avec Jens E.T. Andersen », par Arne Hessenbruch, 6 mars 2001, Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article4.

Lieu : Danish Technical University, Lyngby, Danemark.

Support : enregistrement cassette.

Transcription : Arne Hessenbruch.

Édition en ligne : Sacha Loeve

GAUTHIER Sébastien, 2006-11-16

2009-12-15T15:58:16Z

Sébastien Gauthier, né en 1956, est physicien, directeur de recherche CNRS. Il soutient sa thèse en 1981 à l'Université de Paris Diderot. Elle porte sur une étude quantitative de la spectroscopie tunnel. Il travaille ensuite au Groupe de physique des solides de Paris Jussieu (Universités Paris 6 et 7 - CNRS). Il contribue à y développer la microscopie à effet tunnel pour l'étude des surfaces cristallines. Puis il intégre l'équipe « STM, AFM, NFOM, nanomanipulation, surface » du Groupe Nanosciences (GNS), coordonné par Christian Joachim au Centre d'élaboration des matériaux et d'études structurales (CEMES). Ses recherches au CEMES concernent l'instrumentation associée à la microscopie en champ proche, les nanosciences et l'électronique moléculaire.


Autorisation de diffusion

SACHA LOEVE (SL) : Pourriez-vous nous dire où vous avez été formé au STM ?

SÉBASTIEN GAUTHIER (SG) : Où j'ai été formé ? Et bien... nulle part ! Quand on a démarré, on partait de pas grand-chose. Je suis allé à Zürich, là où a été construit le premier STM. J'ai vu Rohrer, qui m'a reçu. Il m'a expliqué un certain nombre de trucs. Il m'a donné une photo de son appareil, et avec ça, je me suis débrouillé ! J'avais des questions à lui poser, et il m'a expliqué. Il m'a montré un certain nombre de choses, voilà... et puis j'en ai fabriqué un.

XAVIER GUCHET (XG) : Et le STM que vous aviez fabriqué, il était différent de celui de Rorher ?

SG : Oui, un peu différent. Je suis quand même parti de ce qu'il m'avait montré, après, ça a évolué de manière assez différente.

XG : Et il y avait beaucoup de physiciens qui, comme vous, s'intéressaient déjà à cet époque à cet instrument, qui en fabriquaient ou essayaient d'en fabriquer ?

SG : Oui, enfin, en France, il y avait quatre ou cinq groupes qui s'y sont mis à la même époque.

XG : Il y avait beaucoup d'échanges entre les groupes ?

SG : Au début, oui. On était tous dans le même bateau.

XG : Peut-on dire qu'à cette époque, une petite communauté STM s'était constituée ?

SG : Oui, je pense. Il y avait cinq labos qui avaient démarré simultanément, avec pas mal d'échanges.

XG : Et aujourd'hui ?

SG : Aujourd'hui, le problème, c'est que le STM sert à tellement de choses différentes que ce sont des communautés différentes. Même si il y a des recouvrements, les thématiques sont très variées. Et l'instrument en lui-même ne suffit pas à souder les gens... C'est vrai que je connais personnellement beaucoup de gens qui font du STM sur des sujets très différents, c'est sûr ; mais je n'ai pas forcément d'interactions avec eux sur le plan scientifique, même si j'en ai sur le plan technique. Sur le plan technique oui, un peu, mais pas sur le plan scientifique.

XG : D'après ce qu'on avait cru comprendre, le STM, c'est quand même un instrument manipulé par des physiciens, pensé par des physiciens, mais qui commence à se diffuser dans des communautés qui ne sont pas celles des physiciens, mais des chimistes, des biologistes, d'autres communautés qui commencent à l'utiliser. Est-ce que c'est quelque chose que vous constatez ?

SG : Oui, mais c'est le cas depuis le début. En particulier, il y a eu les biologistes, beaucoup de biologistes... Disons que le STM a suscité pas mal d'espoir pour certaines recherches en biologie ; et donc, il y a des labos de biologie qui se sont équipés dès le début... et il faut bien dire que ça n'a pas été un franc succès. Parce que cet instrument, il n'est pas comme un microscope optique : je veux dire que faire des images avec, ce n'est pas tout à fait simple ; interpréter des images, ça n'est pas simple non plus, alors bon... je ne veux pas dire que le STM, c'est l'exclusivité des physiciens, mais que ce n'est pas un appareil que l'on peut utiliser en routine de façon habituelle. Enfin après, tout dépend ce que l'on veut faire avec, mais souvent, il y a beaucoup d'artefacts. Maintenant, les gens sont spécialisés. Il y a des gens qui travaillent pour les biologistes, mais en général ce sont des physiciens qui sont allés vers la biologie quand les biologistes sont allés vers la physique. Ce sont des physiciens, mais qui ont une espèce de double compétence. Ce ne sont pas des appareils que l'on peut utiliser comme ça. Ce n'est pas routinisé.

XG : Et ces biologistes qui se sont équipés : ils ont acheté des STMs, ou ils ont fait venir des physiciens dans leur labos ?

SG : Il y eu les deux. Certains ont seulement acheté des appareils ; et il y a des physiciens qui sont venus dans la biologie avec l'instrument.

SL : Ce qui implique, pour les recherches en biologie, qu'ils n'utilisent pas le STM en ultravide ?

SG : Oui, en pratique pour les biologistes, la plupart du temps c'est même en milieu liquide qu'ils font tourner le STM.

SL : Alors ces labos de bio qui se sont équipés en STM, vous disiez que ce n'était pas un franc succès. Bref, comment vous voyez ces travaux ?

SG : Alors en effet, il y a des labos qui ont acheté un STM. Ils ont constaté qu'ils n'y arrivaient pas et ils ont laissé tomber. Il y a des labos qui se sont dit « il faut que j'y arrive » : ils se sont mis à fond là-dessus et il y a des cas où ça marche, justement, en milieu liquide. Il y a des physiciens qui sont allés vers la biologie parce que ça les intéressait. Il y a eu un peu tous les cas de figure. Mais ça demande une compétence... oui, une compétence de physicien que les biologistes peuvent acquérir, bien sûr, mais néanmoins, le biologiste, il faut bien dire qu'il n'est plus tout à fait exclusivement biologiste quand il commence à travailler avec cet outil. Inversement, il y a eu des physiciens qui ont voulu s'intéresser à des problèmes de biologie et qui sont tombés complètement à côté. Ils qui ont fait des choses qui, finalement, n'avaient aucun intérêt du point de vue de la biologie. Il obtenaient peut-être des belles images au niveau de la physique sur des objets biologiques, mais bon, c'était limité.

XG : Vous avez un exemple de ce cas de figure ?

SG : Je n'ai pas tellement d'exemple très précis là-dessus mais je sais qu'il y a eu pas mal de scepticisme chez les biologistes quand à ce qu'apportaient ces travaux. Ceci dit, ce n'est pas dû au STM, c'est un peu général... il faut dire que la façon dont les physiciens abordent les problèmes des biologistes se fait par une approche de physicien et non pas de biologiste... et il y a des biologistes qui trouvent que cela n'a pas d'intérêt.

XG : Est-ce que vous continuez à essayer de perfectionner le STM ?

SG : Oui. Tout le temps oui. C'est quelque chose de permanent. Perfectionner, modifier, adapter l'instrument à de nouvelles choses.

SL : Quelle est la proportion, au CEMES, entre les instruments qui sont achetés tout faits, ceux qui sont construits « maison », et ceux qui sont moitié commercial, moitié construits ?

SG : Oh, la tendance est clairement à acheter, maintenant.

SL : Et ça a changé beaucoup de choses ?

SG : Oui. Enfin pour ce qui concerne la microscopie en champ proche, oui, ça a été un changement. Mais ceci dit, il y a encore des gens qui fabriquent, ce n'est pas exclu. Mais il y a eu pas mal de changements à ce niveau là, oui.

SL : Pour quelle raison fabrique-t-on et pour quelle raison achète-t-on un STM ?

SG : Et bien au début, on fabriquait parce il n'existait pas d'appareil standard. On ne pouvait pas acheter un STM. Maintenant, on achète parce que finalement, développer coûte aussi cher que d'acheter parce que cela prend beaucoup de temps pour des résultats qui sont parfois meilleurs d'ailleurs... enfin cela dépend... c'est pour cela qu'on trouve des labos où on en fabrique encore et d'autres où on achète. Pour nous, en ce qui concerne les choses récentes, on a plutôt acheté.

SL : Qu'est-ce qui fait que l'on peut avoir un meilleur résultat quand on a un microscope qui est construit ?

SG : Pour un microscope à effet tunnel, ce qui est important c'est la stabilité. La température à laquelle on travaille est aussi très importante. Après, il y a beaucoup de choses autour. C'est rare que l'on fasse que du STM. Il y a plein d'autres techniques, un ensemble de choses disposées autour (figure 1) et qui varie d'une expérience à l'autre. Par exemple, il faut transférer l'échantillon. C'est toujours une opération un peu compliquée, plus ou moins facile ou difficile. Enfin, il y a toutes sortes de commodités annexes qui sont importantes dans l'utilisation quotidienne. Il y a des appareils beaucoup plus lourds à utiliser que d'autres. Cet aspect est important aussi.

Figure 1. Le STM et ses dispositifs périphériques.

XG : Vous voulez dire que le STM est devenu un instrument parmi d'autres ?

SG : Non pas tout à fait. Pour nous, c'est l'instrument central, en général, dans les manips' que l'on fait. Ce qu'il va y avoir autour, au niveau instrumentation, dépend un peu du type de physique qu'on fait avec le STM. Par exemple, le problème avec les molécules, c'est que le dépôt est important. Il faut donc pouvoir déposer les molécules sur les surfaces comme on aimerait qu'elles le fassent, ce qui n'est pas toujours très simple. Il faut donc aménager des dispositifs pour le faire.

SL : On peut vouloir faire des choses très différentes avec le STM. On comprend bien que les possibilités sont très larges. Mais encore faut-il que les instruments le permettent. Les instruments commerciaux ont-ils toujours toute cette variété de fonctionnalités ?

SG : Si, et ils l'ont mêmes plutôt davantage que les instruments construits, mais il y a des cas où, si on développe un instrument pour une utilisation spécifique, il sera peut-être plus simple et peut-être plus performant pour cette application-là que l'instrument commercial, qui lui peut tout faire, mais... un peu moins bien. C'est souvent le cas de figure. Et puis aussi, l'intérêt d'un appareil qu'on a fait soi-même, c'est que c'est quand même plus facile à réparer qu'un appareil commercial. Et les budgets de maintenance il ne sont pas négligeables. C'est aussi à prendre en compte.

XG : Oui d'accord, évidement, un appareil qui a été fabriqué par vous il...

SG : il est plus réparable mais pas forcément plus simple... Enfin au moins, on ne dépend pas d'un service après-vente !

SL : Une fois qu'on l'a monté on sait comment le démonter...

SG : Oui.

SL : Et vous qui avez construit ce type de microscope, est-ce que vous vous occupiez aussi du soft, de l'électronique ?

SG : Ah oui, c'est pareil pour les softs. Au début, on faisait les softs du STM, maintenant, on les fait beaucoup moins.

SL : Et les logiciels développés par le labo, ESQC et STM Virtuel ?

SG : Le logiciel ESQC c'est un logiciel de calcul d'image, l'autre, de simulation. Mais ce n'est pas le logiciel qui pilote l'appareil. ESQC c'est du calcul d'image, le STM Virtuel c'est un peu différent. Il utilise l' ESQC mais c'est une sorte de superstructure qu'il y a autour.

SL : D'accord. Mais pour le traitement des images, j'imagine qu'il y a eu des standards, des normes à adopter dans la conception de l'électronique, pour stabiliser les images ?

SG : Des standards ? non. Et c'est pour ça qu'il y a tellement de types de microscopes, de microscopes à effet tunnel. Il n'y a pas une proportion très standardisée, non je ne pense pas.

XG : D'accord c'est-à-dire que le STM qui est utilisé ici, ça ne va pas forcément être le même que chez le voisin ?

SG : oui, sauf que celui qu'on utilise maintenant est commercial, donc il y a un standard qui est imposé par l'entreprise qui le fabrique. Sinon, pour les appareils fabriqués il n'y a pas forcément de standard.

XG : Et l'offre commerciale, elle est très importante pour ces outils là, ou alors est-ce qu'il y a très peu de modèles, finalement, à choisir ?

SG : Par exemple, pour ce qui est du STM en ultravide, des fabricants sérieux, il y en a peut-être cinq sur la planète. Entre cinq et dix, mais je dirais plutôt cinq que dix. Chacun propose deux ou trois modèles différents. Vous voyez donc que ce n'est pas gigantesque.

XG : Et la différence des images obtenues, peut-elle être très importante d'un modèle à l'autre ?

SG : Non. Parce que la qualité des images dépend quand même beaucoup du savoir-faire de la personne qui manipule ce truc là ; ça dépend des échantillons ; de la préparation de la surface ; ça dépend de tellement de choses qui ne sont pas liées à l'instrument qu'on a beaucoup de mal à isoler la contribution de l'instrument dans le résultat.

XG : Et ça représente un changement par rapport au tout début de cette aventure ?

SG : Au début, il y avait effectivement des choses pas très fiables... mais bon il y a encore des bons et des mauvais instruments, c'est clair ; mais ça dépend de ce qu'on veut voir. Pour un certain type d'expérience, c'est clair qu'il faut avoir l'instrument adapté. A partir de ce moment là, les différences sont davantage liées au savoir-faire des gens qu'il y a autour que des instruments, très souvent. Bon, il y a aussi des instruments qui marchent bien mais qui sont beaucoup plus lourds à utiliser. Ce qui fait que les gens seront un peu moins productifs avec ce type-là d'instrument. Mais sinon, en termes de résultat, c'est difficile de montrer ce qui marche le mieux. C'est difficile à montrer. Il y a des groupes qui ont une grosse tradition de STM et d'autres qui l'ont moins, et c'est à ce niveau là qu'on voit la différence, c'est pas tellement au niveau de l'instrument lui-même.

XG : Vous, avec le recul, vous préférez travailler avec un instrument que vous avez acheté, ou que vous avez fabriqué, ou alors cela vous est indifférent ?

SG : Dans l'absolu, je préférerais travailler avec un instrument que j'ai fabriqué. Après, en pratique, si l'instrument marche bien, alors je n'ai pas de position de principe... Peut-être avec un exemple... tiens, le problème avec l'instrument que j'ai maintenant c'est que le soft il ne fait pas tout ce que je voudrais qu'il fasse. Et aller mettre le nez dans le soft actuellement c'est impossible parce qu'on n'a pas les sources. Alors là, on est complètement dépendant des gens qui vendent le logiciel. Et donc, qu'est-ce qu'on peut faire ? Soit on refait un logiciel complet, soit on est coincé. Mais si on a pas les sources c'est vraiment... Alors que sur un instrument fabriqué, moyennant le temps... si on suppose qu'on a le temps de développer le logiciel, on a toujours la possibilité de le faire, alors que là, par principe, on ne peut pas le faire.

SL : Vous ne pouvez pas faire appel au constructeur ?

SG : Pour les constructeurs, si il y a vingt groupes différents qui demandent la même chose, ils le feront. Si il y a un groupe qui demande quelque chose, il ne le feront pas. C'est la logique commerciale. Ils ne vont pas faire quelque chose comme ça à l'échelle d'un groupe. Ou alors, ils vont faire payer le service tellement cher que ce ne sera pas intéressant.

XG : Et quand vous dites « je ne peux pas faire ce que je veux avec le soft », cela va évidemment influer, j'imagine, sur les rapports que vous avez avec les chimistes qui synthétisent les molécules que vous manipulez et les autres physiciens qui aident à la conception ?

SG : Oh... un petit peu... certainement...un petit peu oui...

XG : Vous pouvez être plus précis ?

SG : Oui, par exemple, cette histoire de molécules qu'on peut déplacer avec la pointe du STM, il se trouve que c'est pas facile à faire. C'est compliqué quoi, on ne peut pas tout faire. Donc, si on a une idée de projet où il faut absolument manipuler une molécule de manière sophistiquée, on va avoir tendance à dire « non on peut pas le faire » ; l'idée, on va l'écarter tout de suite, on va se censurer là-dessus. On va plutôt essayer de faire des choses qu'on sait faire. Et donc l'instrument, ce qu'on sait faire avec lui, ça conditionne les choses. Ceci dit, comme il y a beaucoup de choses à faire, ce n'est pas une limitation majeure pour l'instant. Le jour où on aura une idée de projet où on considérera qu'il faut absolument faire une manip' compliquée, alors soit on trouvera un moyen de la faire, soit on sera effectivement coincé.

XG : Là, il n'y aura pas d'autre solution que de racheter un autre appareil ?

SG : Oui ou, enfin, de refaire un logiciel ou de faire... une astuce. Ou alors, d'aller voir le fabricant pour essayer de le convaincre... et il faut avoir les moyens. C'est sur ces limitations que cela se joue.

XG : Vous connaissez des collègues qui continuent de fabriquer eux-mêmes leurs instruments ?

SG : Oui. J'en connais même un certain nombre. Je connais quelqu'un à Paris, Dimitri Roditchev. Il travaille à l'INSP [Institut des NanoSciences de Paris] à Paris, mon ancien laboratoire. Lui, il continue en partie à construire. Il y a des choses qu'il achète et des choses qu'il fait... c'est un peu l'école russe.

XG : Donc cette logique, celle d'abandonner la fabrication des instruments et de se mettre à acheter, elle n'est pas inexorable, finalement ?

SG : Elle n'est pas inexorable en effet, mais après, tout dépend des moyens qu'on a sur le plan technique. Pour faire du développement, il faut des gens, il faut des mécaniciens et, éventuellement, des électroniciens. Il faut tout ce monde-là, et cela prend du temps. Donc soit on a du temps, soit on a de l'argent, et si on a les deux, alors c'est parfait. Mais nous, ici, on a plutôt de l'argent mais pas beaucoup de bras, et donc ça dicte forcément une logique : celle d'acheter de l'appareil commercial. Si on a avait moins d'argent et plus de bras, peut-être qu'on construirait encore. Et puis les appareils commerciaux ont fait beaucoup de progrès aussi. Ça dépend un peu de tout ça.

XG : Est-ce que vous pensez qu'il est envisageable, si jamais vous bloquez un jour sur des limites liées au soft, d'envoyer les molécules, pour les faire traiter par des instruments fabriqués qui, eux, n'auraient pas cette limitation ?

SG : Bien sûr. Ça on le fait, oui. Parce qu'on est dans des réseaux européens, avec un certain nombre de gens qui font du STM. Et en fait, la répartition du travail se fait souvent sur ces bases-là. On peut très bien faire une molécule ici, faire une partie du travail dessus, et puis l'envoyer pour que ce soit repris par un autre groupe qui lui, peut très bien faire autre chose. C'est assez courant en fait.

SL : Et vous utilisez beaucoup l'AFM, également, au CEMES ?

SG : Globalement l'AFM est beaucoup plus utilisé que le STM, mais pas pour ce qu'on fait nous, parce qu'on travaille dans l'ultravide. Le problème avec l'AFM, c'est que sa résolution n'est pas au niveau du STM. Voir des molécules isolées, comme on le fait nous, c'est quelque chose qui n'est pas du tout routinier, et donc pour l'instant, il se trouve qu'on fait de l'AFM, mais que dans le contexte « molécule unique » c'est encore quelque chose qui n'est pas très... disons qu'à ce moment-là, imager la molécule à l'AFM est une fin en soi, alors que ce n'est plus le cas en STM. En STM, imager la molécule, c'est la première étape. En général, on veut aller beaucoup plus loin ensuite. En AFM, si on arrive à imager une molécule, on est déjà assez content. On essaiera peut-être de passer au-delà mais disons que ce qui, avec le STM, ne nous satisferait pas est suffisant en AFM pour l'instant. La résolution n'est pas du même niveau.

XG : Les chercheurs en matériaux utilisent davantage l'AFM ?

SG : Oh et bien l'AFM, c'est un instrument qui sert à tellement de choses... il sert au gens qui font des polymères, il sert à des biologistes...

XG : Je voulais dire dans le cadre du CEMES...

SG : Au CEMES, oui. L'AFM sert un peu au gens qui font du matériau, pour caractériser en surface la rugosité, la texture et des choses de ce genre. Mais là, c'est utilisé plutôt comme un appareil de routine parmi toute une palette de techniques. Il n'est pas du tout central pour eux comme le STM l'est pour nous.

SL : Et du microscope optique en champ proche, où la pointe est, si je comprend bien, une fibre optique ?

SG : La pointe est une fibre optique qui vient capter les photons près de la surface et qui utilise cela comme information pour faire de l'imagerie.

XG : Et c'est un appareil acheté ?

SG : Non, fabriqué.

XG : C'est vous qui l'avez fabriqué ?

SG : Non, c'est quelqu'un qui s'appelle Renaud Péchou. il a fabriqué ça il y a un petit moment.

SL : Il y a beaucoup de types de microscopes en champ proche aujourd'hui, non ? C'est tellement diversifié, spécifié...

SG : Ah oui, aujourd'hui, c'est tout un catalogue. Selon le type de sonde qu'on utilise, il y a vraiment pas mal de choses différentes.

SL : Elle s'est diffusée relativement vite quand même, la microscopie en champ proche ? Si on la compare par exemple avec la spectroscopie, on a l'impression que ça a pris très vite.

SG : Oui ça a pris assez vite. L'AFM c'est 1986, le STM c'est 1982. Après, je ne sais pas trop à quoi il faut comparer. Mais oui, ça a été vite. Surtout l'AFM, je dirais. L'AFM est beaucoup plus utilisé que le STM maintenant mais surtout en air, et comme appareil plutôt accessoire... il est dans un coin du labo, l'AFM, et puis, on y passe un échantillon de temps en temps.

XG : J'aimerais savoir une chose : être surpris par ce que fait la molécule que vous manipulez, par rapport à ce qui était prévu, ça arrive souvent ?

SG : Cela arrive souvent oui.

XG : Vous avez un exemple en tête ?

SG : Je n'ai pas d'exemple très précis. Je sais qu'il y a certaines molécules, comme celles qu'a fait André Gourdon et qui s'appellent les « landers », qui ont été développées pour une application bien précise, et qui se sont retrouvées servir à une multitude d'autres choses.

SL : Et il y a le cas des roues de la brouette non ? C'était des dimères, et puis on a aussi trouvé des trimères et d'autres fragments ?

SG : Oui, les brouettes, c'est un projet où pour l'instant, le gros problème, c'est déjà de mettre la molécule à peu près intacte sur la surface , ce qui n'est pas évident. Disons que elle n'a pas fait quelque chose de très inattendu, pour l'instant, cette molécule. Bon, c'est un projet ambitieux qui requiert pas mal d'étapes... pour l'instant, disons qu'il n'y a pas eu beaucoup de choses inattendues.

XG : Qu'est-ce qui a motivé, en 1997, votre arrivée au laboratoire. Pourquoi avait-on besoin, à ce moment là, d'un spécialiste du STM ?

SG : Et bien parce qu'au laboratoire, ici, il y a avait les chimistes de synthèse qui étaient déjà là, et il y avait la partie théorique où il y avait du calcul d'image. Mais il n'y avait pas de partie expérimentale STM. Il y avait un trou.

XG : Avant 97, il n'y avait pas de STM du tout au CEMES ?

SG : Non, pas dans la partie qui s'appelle GNS, ou « électronique moléculaire ».

SL : C'est quand Christian Joachim a commencé à vouloir faire de la molécule unique que sont arrivés les STMs ?

SG : Pour la chronologie, je ne sais plus très bien à vrai dire. Oui, disons que c'est à peu près à cette époque-là. Christian [Joachim] et André Gourdon étaient déjà ici. Ils travaillaient déjà avec le labo d'IBM à Zürich par exemple... donc il y avait visiblement un trou ici, parce qu'en effet, pourquoi aller faire à Zürich ce qu'on pouvait faire ici ? Et c'est comme cela que je suis venu. Effectivement, il était déjà question de molécule unique, oui.

XG : Vous êtes combien, vous, les physiciens, à vous occuper des instruments, type STM, AFM ?

SG : Pour la partie électronique on est deux CNRS, un prof et trois thésards.

XG : Et concrètement, les thésards, c'est quoi leur travail ici ? Ils contribuent à améliorer les instruments ?

SG : Non, leur travail, c'est de faire des manips', de faire fonctionner les instruments, éventuellement de les modifier si il y a besoin oui, de les modifier pour quelque chose, d'interpréter les résultats, d'essayer de faire des calculs ; leur travail, c'est tout le spectre : de la clef de douze à l'ordinateur. C'est assez varié.

Fin de l'enregistrement.

Pour citer l'entretien :

« Entretien avec Sébastien Gauthier », par Xavier Guchet et Sacha Loeve, 16 novembre 2006, Sciences : histoire orale, /spip.php ?article2.

Pour citer l'entretien :

« Entretien avec Sébastien Gauthier », par Xavier Guchet et Sacha Loeve, 16 novembre 2006, Sciences : histoire orale, https://sho.spip.espci.fr/spip.php?article2.

Lieu : bureau de Sébastien Gauthier, CEMES, Toulouse, France.

Support : enregistrement numérique.

Transcription et édition en ligne : Sacha Loeve.