Interview: Dr. Stan Veprek
2005 John Thornton Award Recipient
November 2005
HOLLOWAY: Good afternoon. I'm Paul Holloway a member of the AVS History Committee. As part of the Society's Historical Archives Series today I will be talking with Dr. Stan Veprek from the Technical University of Munich, who is this year's John Thornton Award winner. It is November 2, 2005, and we are at the 52nd AVS Symposium in Boston, Massachusetts.
So Stan, thank you very much for taking time, and congratulations on the John Thornton Award, very well deserved.
VEPREK: Thank you.
HOLLOWAY: You're quite welcome. Could you give us a little bit of information about your background, how you got started in the field, and your education, and that sort of thing?
VEPREK: Well first I studied for high school teacher, and after finishing this I studied physics at the Charles University in Prague. And then I was working in glow discharge physics, spectroscopy, instabilities until I get rid of it and started with plasma CVD, the chemical transport of solids in the glow discharge plasma. This was the first paper on nanocrystalline silicon published in 1968. This is nowadays used in thin film transistors for flat panel displays and such things. Then I have to leave Czechoslovakia because of the communists and the Red Army which came on August 1, 1968. So, I was in Germany for a while, as a visiting scientist at the University of Munster, (Holloway: Uhm-hmm.) and then Professor Oswald invited me to Zurich, so I went to Zurich. And at that time I was already working between physics and chemistry, so I got my PhD in inorganic chemistry there in 1972, and then I was, I worked for the habilitation. (Holloway: Right.) It's something like Ph.D.
(A Stan's remark in the proofs: Here we confused it: I got the Ph D in 1972. The "habilitation" was another independent scientific work and Thesis which, after acceptance by the Faculty, gave me the approval to teach at the University. The official Title is "Privatdozent", you may compare it to the "Reader" in the British system. I received it in 1975 or 1976, cannot remember exactly.)
HOLLOWAY: So, what year was the habilitation?
VEPREK: Oh, about plasma CVD and etching. It was 1972.
HOLLOWAY: 1972? So, you said that you worked early on in nanocrystalline silicon?
VEPREK: Yeah.
HOLLOWAY: What do you call nanocrystalline? What size?
VEPREK: Well, anything below a hundred nanometers.
HOLLOWAY: Below a hundred nanometers? Yeah. So, is that the same as some people call polysilicon? (Veprek: Yeah.) Or, is it different?
VEPREK: Yeah. Well, polysilicon can have larger crystallized size, (Holloway: Yeah.) but you don't want it. (Holloway: Right.) Even in some production steps you want to oxidize, etcetera, etcetera, etcetera, you want to keep the crystallite size small. (Holloway: Uhm-hmm.) So, most of the early stuff, dependeding on the deposition temperature, is in the range of not more than a few hundred nanometers.
HOLLOWAY: Well, that goes along with your citation for the Thornton Award, and I would like to read it into the record. "For the generic description and generic design concepts of strong and hard materials as well as their deposition as thin films by plasma-assisted techniques." And so, you were using plasma-assisted techniques to do the nanocrystalline silicon?
VEPREK: Yeah. It was chemical transport in hydrogen plasma.
HOLLOWAY: Uhm-hmm. Yeah.
VEPREK: Which, it gives you the single phase of a crystalline silicon without amorphous tissue.
HOLLOWAY: So, what were you using for a source for your silicon? Was it a silicon wafer?
VEPREK: No, just powder.
HOLLOWAY: Just powder?
VEPREK: Yeah. You want to have a large area, surface area, to achieve large etch rates for the production of the silane in situ.
HOLLOWAY: So, what sort of vacuum system did you use to handle that?
VEPREK: [Laugh] Handmade.
HOLLOWAY: Handmade?
VEPREK: I have learned glass blowing. [Laugh] But, you know, that's what we figured out later on, to make it work and you really need the total oxygen impurity level in the plasma less than ten parts per millions. So, at the time it was just a question of getting good vacuum, which was not so easy; 10 to the minus eight millibar in 1965, was not every day.
HOLLOWAY: Yeah, it was more difficult in those days because of the different techniques, and the understanding was not there in terms of vacuum system performance?
VEPREK: Well, yes and no. The disadvantage was as you said, but you know, it was also an advantage that we had to learn.
HOLLOWAY: Yes. The exciting part was learning (Veprek: Yeah.) all the time. Yeah. So, what sort of pumps did you use? Did you use diffusion pumps?
VEPREK: Diffusion pumps made of glass. We designed them and the glassblower made them.
HOLLOWAY: The fluid was mercury?
VEPREK: Mercury, and later on oil. But the first was mercury.
HOLLOWAY: Yeah. That was a dangerous time. We didn't really appreciate it probably as much.
VEPREK: Yeah. (Holloway: Yeah.) If I would have known how dangerous mercury is, when I was purifying it by distillation, [Laugh] but I survived. And I can tell you another funny story. It was at Charles University. There were no dry forepumps back then. So, for my prediploma-work, which was supposed to be work of four or five weeks, I was asked to study the absorption properties of charcoal.
HOLLOWAY: Oh, is that right?
VEPREK: So, I got it from the gas masks, German Wehrmacht (Stan's remark in proof: Wehrmacht = the Nazi's Army) [Laugh] (Holloway: Yeah.) and we didn't have liquid nitrogen. We had only liquid air. And I fortunately went into laboratory and read about what happens when liquid air comes into contact with charcoal. And then we had not pyrex. It was the soft glass. So, I was extremely careful whenever I was putting the dewar with the liquid air, on the glass containing maybe that much of the charcoal. When I finished the study, and I started with a summary of the explosion properties of this combination. The supervisor, when he read it, came to the lab and shouted, "Are you making jokes?"
HOLLOWAY: [Laugh] Did you ever have an explosion in reality?
VEPREK: No.
HOLLOWAY: Oh, thank goodness.
VEPREK: No, I was, I was very careful. We had once an explosion when the liquid air came into contact with the hot oil in the diffusion pump. And, the lab was "very clean" afterwards. (Stan's remark in proofs: I wanted to say that everything was destroyed in that lab)
HOLLOWAY: [Laugh] Well, there are lots of interesting stories that I know a lot of us could tell about those sorts of things in the lab but it sounds like you had some good experience. Let's see. Once you finished your degree, what did you do then? Did you go to another university?
VEPREK: No. I was at Zurich for a long time, because I had kids there, (Holloway: Yeah.) so, I could not leave so well until they were sufficiently grown up.
HOLLOWAY: Uhm-hmm. So, when did you leave Zurich then?
VEPREK: 1989.
HOLLOWAY: And, where did you go then?
VEPREK: To Munich.
HOLLOWAY: Ah yes. And, what department were you in Munich?
VEPREK: Chemistry Department.
HOLLOWAY: So, did you teach and do research there?
VEPREK: Ya. Ya. Ya. I'm still teaching and still having my smaller group, although I'm officially retired since more than one year.
HOLLOWAY: So, you what sort of research did you do when you first went to Munich? Was it plasma interaction still?
VEPREK: Well, most of my work in the work is somehow related to plasma.
HOLLOWAY: Yeah. Uhm-hmm.
VEPREK: When I moved to Munich. Also I was doing a lot of silicon, amorphous and nanocrystalline. We developed a new method for the restoration and conservation of metallic archaeological artifact. (Holloway: Uhm-hmm.) I still... it was just a time when I was finished in my activity in the plasma-wall interactions and devices for controlling nuclear fusion. (Holloway: Uhm-hmm.) We developed the so-called boronization.
HOLLOWAY: Tell me about boronization for fusion reactor containment.
VEPREK: Well, this was a program when the Soviet Union developed the Tokomak which stabilized the plasma, and the plasma became hotter. At the higher temperature, one problem is the release of the impurities from the first wall. And, this was particularly dangerous for metallic impurities because if they get stripped of electrons at 10 or 11 keV, already the Bremstrahllung is sufficient to prevent the Tokomak from reaching ignition. So, there was concern what to do. And so, I suggested in 1975 to use boron carbide because it has very good properties on that point. (Holloway: Right.) We use only light elements, and it took more than ten years to show it until we did an experiment in the TEXTOR Tokamak in Julich, Germany, and it was for the first time that when the people operating the machine applied auxiliary heating, the temperature went up and not down. (Holloway: Ah.) It was up till that time the auxiliary heating released more impurities from the wall so that the effective Z of the plasma increased, the losses increased, and the temperature went down. (Holloway: Yeah.) So, it has been used afterwards for, or it is still being used in Tokomaks.
HOLLOWAY: So, what precursor do you use for the boron carbide deposition?
VEPREK: Diborane.
HOLLOWAY: Diborane?
VEPREK: It's the simplest way.
HOLLOWAY: So what's the composition of diborane?
VEPREK: B2H6.
HOLLOWAY: And where do you get the carbon from then, for the boron carbide?
VEPREK: From methane.
HOLLOWAY: From methane? So, you mix the diborane and the methane?
VEPREK: That's the simplest way, because in the big machines you cannot use the chlorides, for example. (Holloway: Uhm-hmm.) So, the people at Julich told me too, of their concern about diborane because it's quite a nasty gas. (Holloway: Uhm-hmm.) So, they used later organometallic compounds.
HOLLOWAY: How thick of a layer must you deposit of the boron carbide in order to passivate the wall?
VEPREK: Quite thin. A few hundred nanometers was enough.
HOLLOWAY: Is that right?
VEPREK: Yeah. A few hundred nanometers on the weekend and then they could keep shooting for the whole week.
HOLLOWAY: Is that right?
VEPREK: Yeah.
HOLLOWAY: But, on a weekly basis you would replenish that layer then, (Veprek: Yeah.) and the diffusion rate would come back? (Veprek: Yeah.) I see.
VEPREK: But, this is no solution for the reactor, but there are other problems with the controlled fusion that I don't think is going to work.
HOLLOWAY: Is that -- yeah,
VEPREK: As an energy source.
HOLLOWAY: I was going to ask your opinion on that. So, your opinion is that it's not going to be feasible in the final analysis?
VEPREK: Just one example, yeah. (Holloway: Yeah.) The plasma for the controlled fusion has a very low power density. (Holloway: Yeah.) A factor of 200 and more lower than conventional fission reactors. (Holloway: Uhm-hmm.) So, you have to make it big, and that's the problem of costs. (Holloway: Yeah.) The other most serious problem is that the fast neutrons which have to leave through the first wall of the vessel to get into the blanket to breed tritium, have 14.5 MeV, I think, and they cause something like thirty to fifty-atom displacement of atoms per year, (Holloway: Yeah.) in the first wall. Can you imagine a material, which can survive it for twenty years?
HOLLOWAY: No. I'm not even sure I can imagine with fifty-atom displacements a material that would last for a year even. [Laugh]
VEPREK: And there are also studies back to 1970s which show that, because of this lower power density and large amount of material you need to build such reactors, there would be probably not enough beryllium, not enough copper. You would need maybe forty percent of the worldwide production of steel, at the level of the year seventy-five, to build it , etc., etc. So, I don't see a possible scenario in which it should really work, but who knows.
HOLLOWAY: There's a lot of challenges and some challenges that you wouldn't expect to able to overcome have been overcome. But sometimes there's too many challenges.
VEPREK: Yeah. But this is a very fundamental problem (Holloway: Yeah.) for displacements.
HOLLOWAY: So now, you're working still in the area of nanocomposite materials and nanostructured materials?
VEPREK: So, this, so called nanocomposites, it's been developed in the last ten years, (Holloway: Yeah.) the so-called, so to say my last field which I started.
HOLLOWAY: Now, in your talk on Monday you talked about the composition of the inntergranular spaces, for lack of a better term. The region between, the interfaces between the nanocrystalline crystallites. Could you tell us a little bit about that? What's your understanding of those interfaces?
VEPREK: Well, it's, this is some interesting still quite new things in which I think we still do not fully understand. When we did the first nanocomposites, titanium nitride - silicon nitride, and characterized them, I realized it is really fully segregated, and the silicon nitride must be somewhere around the titanium nitride nanocrystals, and I estimated how thick the interfacial layers should be. And, I was surprised when I found one monolayer. And so, we were looking into many other systems just to verify whether this principle was universal, and it was coming out all the time the same. And, after enough thinking about what could be the reason behind it. I thought it might be somehow related to quantum confinement phenomena at the interface, which means in simple chemical terms, the bond strength increases as well. (Holloway: Yeah. Right.) But then, we didn't know how to verify how to prove it. And now in the last year, on one hand, the friends from the University of Linkoping did heterostructures and found exactly the maximum at one monolayer, and the maximum hardness 33 gigaPascals is limited by impurities. That's what we know for sure because I did the measurements of the oxygen impurities for them. And, on the other hand, Professor Catherine Stampfl from the University of Sydney, who did nice calculations, theoretical calculation of the stabilization of cubic aluminum nitride by titanium nitride. I asked her a few years ago if she could do that calculations for the titanium nitride/silicon nitride system, and she got exactly that the most stable configuration is the one monolayer of silicon nitride between the titanium nitride, and there is indeed a negative charge on silicon. So it seems to be some universal principle. It seems to be valid also for other systems, but it's too early now to generalize.
HOLLOWAY: So, I still don't understand what you think is magic about one monolayer. So, it's the strength of the bond? And, what is the composition of the one monolayer?
VEPREK: Well, it is stoichiometric silicon nitride.
HOLLOWAY: It's stoichiometric?
VEPREK: And well, as far as I believe, or understand it now, that when you have less than a monolayer of silicon nitride, you have titanium nitride to touch titanium nitride, (Holloway: I see.) this is the normal grain boundary defects, which is always the weakest point in any polycrystalline material. (Holloway: Uhm-hmm.) When you have the monolayer then you get this strengthening. (Holloway: Right.) It avoids any diffusion, or movement of dislocation, well, there are not dislocations anyhow in 3-4 nm small crystallines. But when it is getting thicker and thicker, because you have some lattice mismatch, (Holloway: I see.) the strain energy of this thicker layer is increasing, and also the stabilization due to quantum confinement is decreasing. (Holloway: Uhm-hmm.) So, this is logically a combination of two reasons why one monolayer should be the strongest configuration.
HOLLOWAY: Yeah. So, is it an amorphous material, or is it . . .
VEPREK: Well, we call it x-ray amorphous because you don't see it in the XRD. (Holloway: Yeah.) But, if you have a planar interface, then it heteroepitaxial. There's a little bit tensile strain in the silicon nitride. And, in the experiments of the Linkoping group, the one monolayer is cubic. But in a three-dimensional nanocomposite, you don't know because crystallites seem to be regular in the high resolution TEM, but you can never image the grain boundaries because you lose contrast there. (Holloway: Uhm-hmm.) So, it will be somehow polyhedra. (Holloway: Yeah.) But, it must be somehow ordered on the surface of titanium nitride. But we call it amorphous because it is x-ray amorphous. One monolayer doesn't have three-dimensional periodicity.
HOLLOWAY: Now, you believe that the one monolayer at the interface is produced by spinodal decomposition?
VEPREK: Yeah. Because the computations are clear. Even when the sublattice model is not quite exact, the difference between the chemical demixing energy of almost three hundred kilojoules at these conditions, and the destabilizing strain energy, is of two orders of magnitude. And so, it cannot kill it. However, there is a metastable cubic phase frequently reported in the silicon-titanium nitride, (Holloway: Uhm-hmm. Yeah. Uhm-hmm.) It is not quite clear. It happens when films are deposited far from equilibrium. But, it is there. So, probably you get the deposition with the mixed phase from the top of the deposited films, (Holloway: Uhm-hmm.) which then, on a timescale of several hundred to a few hundred of seconds decomposes, but that's a long way to go to really understand these things. (Holloway: Yeah.) But, you know, if I would have the time, it is a unique and a good goal [Laugh] to do these experiments.
HOLLOWAY: Well, you have a lot of collaborators that you work with around the world on that project, plus other projects. Would you like to talk a little bit about those collaborators?
VEPREK: Well, those are good friends that I always learn something from them. [Laugh]
HOLLOWAY: Yes. [Laugh] Good friends.
VEPREK: For example, for example, Professor Ali Argon from MIT. He's well known in the field of fracture physics and fracture mechanics. He did a lot of work on mechanical properties of metallic glasses and polymers, etcetera. And, when we met on the shuttle bus from the Denver airport to the hotel I started talking to him. He admitted later on that he believed that I am off by at least an order of magnitude. [Laugh] But, he was interested so we spent a lot of time in discussion, and started collaborating, and I learned a lot from him.
HOLLOWAY: Good. (Veprek: Yeah.) What about other collaborators?
VEPREK: Well, my old friend, Professor Li Shizhi, who had actually started that field (Holloway: Uhm-hmm.), we are good friends and collaborators. Not continuously, but since 1985. (Holloway: Yes.) The last work which we did jointly is the internal friction measurements, where we looked into the processes going on in the grain boundaries of these nanocomposites. (Holloway: Uhm-hmm.). Because, it turned out that, when we studied the thermal stability by annealing and measuring of the crystallite size, hardness and things like that, in the PVD coatings, you don't see any changes like in the CVD coatings when you deposit them correctly at high temperature. But if you look into the internal friction, you still see a friction peak which vanishes when you heat to 700-750 centigrade. (Holloway: Uhm-hmm.) So, it again shows that during the sputtering, you don't have so fast diffusion and phase segregation as you have during the plasma CVD. This is another interesting problem I'd like to solve, if I can, in the next time, because it's important for the clarifications. (Holloway: Uhm-hmm.) And, my friends from industry. That's a very nice story. It was a small company in the Czech Republic. They started in 1993, 1994, something like that. (Holloway: Uhm-hmm.) Just two of them. And, when we met, the company had six or seven people.
HOLLOWAY: That's SHM?
VEPREK: SHM. Yeah.
HOLLOWAY: Yeah.
VEPREK: And now they have two companies, all together more than probably one hundred people.
HOLLOWAY: Wow. That's quite a spectacular growth.
VEPREK: Yeah. Very nice, new buildings.
HOLLOWAY: And so now you're affiliated at least part time with Singapore?
VEPREK: Yeah.
HOLLOWAY: Is that, is that accurate?
VEPREK: Yeah. That's the Singapore Institute of Manufacturing Technology, which belongs to this A-STAR agency, the founding Agency for Science Technology And Research. As I mentioned before, they wanted me to go there for full time but I cannot go there because of my family. (Holloway: Uhm-hmm.) So, we shall see how it is going to work.
HOLLOWAY: So, do you consult with them in terms of process for hard coatings?
VEPREK: Ya. Ya.
HOLLOWAY: Teach courses there as well?
VEPREK: Well, I'm teaching courses at the National University of Singapore (NSU). SIMTech is not associated with the University. It is under on the campus of NTU, Nanyang Technological University, but has nothing to do with the University. (Holloway: Uhm-hmm.) Yeah. So, for example, the students must formally be students of the University, (Holloway: Right.) even if they are working at SIMTech.
HOLLOWAY: Right. Now, at the beginning of your talk on Monday you mentioned, you showed a picture of John Thornton. Did you interact any with John Thornton?
VEPREK: Well, I had the good luck that in 1984 when Soren Berg invited me to the International Conference at Thin Films at Stockholm. After my talk John came to me and was interested in our work. So, we were discussing particularly the nanocrystalline silicon. And, it was a quite interesting experience then because he knew a lot and he was really a very, very nice person.
HOLLOWAY: Yeah. He was a wonderful person.
VEPREK: Yeah. Yeah. Very patient. Patient? (Holloway: Yeah.) My English is not so good. [Laugh]
HOLLOWAY: Yeah, patient.
VEPREK: Yeah? Patient and I had very good feelings from that discussion.
HOLLOWAY: Good.
VEPREK: But, I didn't see him often. At least I don't remember.
HOLLOWAY: So, that was one encounter that you remember?
VEPREK: Yeah.
HOLLOWAY: Yeah.
VEPREK: It may be we met afterwards sometime, somewhere again but I don't remember. I remember this because I was, you know, surprised.
HOLLOWAY: So, you were relatively young when you met him?
VEPREK: Well, I think we were not so different in age.
HOLLOWAY: I see.
VEPREK: Because if I'm now sixty-six, (Holloway: Uhm-hmm.) and he was relatively young when he died.
HOLLOWAY: He was.
VEPREK: By any chance do you know when he was born?
HOLLOWAY: I'm sorry, I don't remember. I'm not sure that I've ever heard, but I certainly don't remember if I've heard. So. But, what I was thinking about was, what advice would you give to young people who are just getting started in the field in how to have a career as successful as your career?
VEPREK: Well, I don't know if my career was so successful, but I would tell them what I told my son who, when he was finishing the gymnasium and didn't know what to do, and I told him, "Well, then go and study physics, because when you get a good background and then you finish with a diploma in physics you can start in many different fields from chemistry, to biology, or whatever." And he is now doing very well. (Stan's remark in proof: Please include it because otherwise one can get the wrong feeling that my son is not interested in fundamental. This were not fair to him, because he is doing very good basic research; thanks for understanding) This is what I am a little bit missing nowadays by many young people. They don't really want to study the fundamentals to understand, just to get the degree. And, you find that they're not, even with PhD students, etc, that they are superficial. No deep understanding. (Holloway: Yeah.) So, my recommendation was, "Don't think of career. As long as you are a student, enjoy learning, enjoy discovery." You know, there's a story of how I got interested in physics. [Laugh] A lady, I don't remember her name, who interviewed me for the AVS newspaper, or newsletter, asked me this question then. It was very simple. I learned, I was interested in and a studied of nature. (Holloway: Uhm-hmm.) And somehow I got a book, and I learned, somehow that the sun was getting energy from burning hydrogen. And, I asked my uncle who was a teacher at grammar school, "How is it?" "Yes. Yes. It is so." I said, "Is it burning oxygen and hydrogen?" Because I didn't know any other way how hydrogen could burn. He said "Yes," and I could not believe it because of when I did that calculation it took me about two or three hours in the night. I don't remember now what would be the lifetime of the sun, but very short. And, he was suggesting that it is so. So, I started looking for more information and found the hydrogen cycle (Stan's remark in proof: I meant the Bethe-Weisszecker cycle), which I didn't understand of course, so I had to learn something about nuclear physics. So, I got interested in physics.
HOLLOWAY: So, you sort of were following a self-interested, (Veprek: Yeah.) self-directed path. And, that's something that you would encourage the young people (Veprek: Yeah.) to think about doing? Yeah. Explore your interests?
VEPREK: Yeah.
HOLLOWAY: Ask questions?
VEPREK: Yeah.
HOLLOWAY: Yeah.
VEPREK: Particularly during the study, including the Ph.D. because if they are free to learn, they are not obliged to work for a company or whatever, (Holloway: Yeah.), or, that's, this is the best time to learn and really learn from their mentors. It's what I always was telling to students, "What you've understood you can never forget. What you just learned you forget three weeks after the exam." [Laugh] (Holloway: Yeah.) This is something really important. On average, in the examiner, you find very, very few such people nowadays. Maybe it was the same forty years ago. [Laugh] But this is my perspective.
HOLLOWAY: [Laugh] Well, I've often asked the question how students today compare to students yesterday? And, I tell them "The good are as good as they were yesterday, the bad are as bad as they were yesterday, and the in-between I think are about the same." [Laugh] So, but it's a different world. There's a different set of knowledge, and they're starting from a different point in their careers and knowledge base than we were. Different experiences, so it's difficult to give a very accurate comments and answers.
VEPREK: Yeah but, I think you would agree. If a student learns whatever (Holloway: Yes.) learns really fundamentals, (Holloway: The fundamentals.) then he or she is very flexible later on in their life to learn and extend the knowledge in other fields, etcetera. (Holloway: Right.) But, if somebody learn only superficially without understanding, (Holloway: Right.) then he will never learn.
HOLLOWAY: I agree with that completely. If they memorize only and don't understand why this is true, then they soon forget it. They soon lose that. Memory just doesn't last that long, but the fundamentals do last. I agree with you a hundred percent there. So.
Well, I wonder if there was anything else you'd like to cover today for the interview for the Historical Archives?
VEPREK: Not that I know. Well, I had a lot of fun when we developed metals for the restoration of our archeological artifacts.
HOLLOWAY: Oh, I was going to ask you about that.
VEPREK: Yeah? Because I learned a lot of people from the archeology, and made new friends there. It was really fascinating because it was a completely new experience to learn about history which I never had time to. Particularly this gentleman, his name was Elmer, from the National Museum in Zurich. It was really a very nice friendship. And, all together we treated something like twenty, or twenty-one thousand objects in my office in Zurich, and later on in Munich.
HOLLOWAY: So, how did you treat them or how did . . .
VEPREK: Well, the problem is that if something made of, for example, iron, (Holloway: Yes.) was buried in the soil for 2,000 years then it's stabilized somehow. But, due to the electrochemical corrosion, the iron diffused and formed an encrustation with the soil, which is harder than the iron object underneath. (Holloway: Uhm-hmm.) So, when the restorator was polishing it, he could not recognize the transition between the encrustation and the original surface. (Holloway: Yes.) So, what we did was to treat it in our hydrogen and methane plasma to reduce partially this encrustation so that it became brittle. And then you could, using a scalpel, remove it, and uncover the original surface. And we have many, many examples, for example, where you see the traces of the file from the finishing of the object 2000 and more years ago.
HOLLOWAY: Is that right?
VEPREK: Yeah. And then the other problem is that this object could be stable in the solid for 2000, two and a half thousand years. After the excavation, it would then corrode completely after 20-30 years, (Holloway: Yeah.) when exposed to air. So, we also solved this problem of the conservation, so it could be relatively easily redone. It was a very nice time. And, last but not least, I also enjoy working with my wife. She's also scientist, she has a PhD in physics.
HOLLOWAY: Ah yes.
VEPREK: And so when you see her name on papers, then she really contributes to the whole. [Laughter]
HOLLOWAY: I believe you acknowledged her at your talk on Monday. Yes, I remember that.
VEPREK: Well, without her support I would never be able to do what I did in the last years.
HOLLOWAY: Yes. Well, we all have support from our families and they contribute a lot to our lives. So, anything else you would like to share with us?
VEPREK: I don't know. I don't think, I don't find anything too interesting. [Laughter]
HOLLOWAY: Well, Stan, thank you very much for interviewing for the archives for the AVS and again, congratulations on the Thornton Award.
VEPREK: Well, thanks as well, and I shall mention this evening, many thanks to all the people who are involved, who have selected me, because I didn't expect it. And, when I was phoned a few months ago, and told that I'm going to receive this award, I was just speechless. [Laughter]
HOLLOWAY: Well, it's very well deserved. So, again congratulations.
VEPREK: Thanks.