Awardee Interviews | Siegfried Hofmann - 2006 Albert Nerken Award - Interview

Siegfried Hofmann

Oral History Interview

Interviewed by Paul Holloway 2006
 
HOLLOWAY: Good afternoon. My name is Paul Holloway. I am a member of the AVS History Committee. I'm here today, the 15th of November, Wednesday, in San Francisco at the 53rd Annual Symposium of the AVS interviewing Dr. Siegfried Hofmann, the 2006 winner of the Albert Nerken Award. The citation for this award reads "for seminal contributions to the quantitative characterization of thin films and interfaces, particularly planar nanostructures by sputtered depth profiling." So Siegfried, it gives me a great deal of personal pleasure to welcome you and congratulate you on this award. To get us started, how about giving us a little bit about your history, something about your education and that sort of thing.

HOFMANN: Well, I am happy to do so, Paul. First of all I would like to emphasize that I am very happy to get the Albert Nerken Award. It's a great honor for me, and in fact it is something which is really valuable and is greatly valued by myself. And with respect to my background, the beginning was back in Munich where I made my doctorate at the Technical University in 1966. This was one of the best universities in Germany, particularly advanced in physics because there was the first nuclear reactor, a research reactor, in Germany after the war. We had excellent professors and I started in the field of nuclear radiation effects in materials and this was the starting point of my work and perseverance in materials science.

HOLLOWAY: You have been interacting particles with metals forever.

HOFMANN: It was a straight line so to speak.

HOLLOWAY: Just change the energy slightly and the character of the particles.

HOFMANN: Yes. but later we added Auger electron spectroscopy and XPS (X-ray photoelectron spectroscopy), quite natural extensions to characterize what is going on at the surface of ion bombarded materials. After my PhD and some not-so-important positions I joined the Max Planck Institute for Metals Research in Stuttgart in 1968, where I started with subjects like recrystallization and the influence of small amounts of impurities, because they strongly influence the recrystallization temperature of metallic materials.

HOLLOWAY: What sort of materials, what metals were you working with?

HOFMANN: With all kinds of metals. Basically we did model studies on copper and gold, because these metals were available in a very pure state. We doped them with only ppm (parts per million) of foreign atoms and studied what was going on in recrystallization. At that point it became clear that we should have a precise method for interfacial characterization, because segregation, i.e. impurity enrichment at interfaces, was thought to be the cause of retardation effects in recrystallization. So I began to find out means how to study grain boundary segregation. At first I turned to SIMS (secondary ion mass spectrometry), but SIMS at that time (1970) was not developed well and was still in a state of infancy. Fortunately, Auger electron spectroscopy was just arising at the end of the '60s, as you well know.

HOLLOWAY: Right.

HOFMANN: I think it was the right step to get into that. In 1972 I succeeded to get funding for an Auger spectrometer, which was the first commercial Auger spectrometer in Germany.

HOLLOWAY: I see.

HOFMANN: I had the first one applied in the materials science field.

HOLLOWAY: Who was the manufacturer? Do you remember?

HOFMANN: Yes, the manufacturer was PHI, Physical Electronics Industries, with Roland Weber and Paul Palmberg who founded the company. I went for training to Minnesota in November 1972, my first time in the United States. At that time the company had about thirty people. During my stay another order from Japan came in and Roland Weber said, "Oh, let's all get together for a cheer," and he showed the order and everybody was happy because for another month their salary was in good shape.

HOLLOWAY: And their employment was ensured for one more additional month.

HOFMANN: Of course; that was a very nice and interesting experience. Since then I always kept good relations with those guys, mainly because the company chiefs were fellow scientists, a situation I frequently met in the United States.

HOLLOWAY: Right.

HOFMANN: And this experience was the beginning of my cooperation with many other people in the United States. During another visit in 1976 I went to IBM, Yorktown Heights, NY, and some other places, and I felt a big difference from Germany where I was always asked, "Who is your boss?" but in the United States I was always asked, "What do you do? Please tell me about your work." By the way, this difference is still true today. For me as a young scientist it was just like feeling free, you know, and from that time onward until today I loved this open attitude in the United States. Furthermore, I found that in my field, a lot of very good work was done within the American Vacuum Society. I became a member and I participated in the Symposia. I think I was at more than 50% of all the Symposia during the past twenty-five years..

HOLLOWAY: That's a remarkable record.

HOFMANN: Yes. But, as you know, many German colleagues were there too, because we always felt that the AVS Symposia are internationally open and we had a very good audience in the applied surface science field, and top science was done there so you could learn a lot. This was very important for my work that started in the '70s. Later I had many chances to come to the United States as a visiting scientist to outstanding laboratories. At first, in 1980/81, I was staying for 6 month with Rick Honig's group at the former David Sarnoff Research Center of RCA Company.

HOLLOWAY: Right, yes.

HOFMANN: I worked with John Thomas III, Charles Magee, Bill Harrington and other excellent colleagues.

HOLLOWAY: Did you do sputtering when you were there?

HOFMANN: Yes, of course we did sputtering. It was exactly why I went there. While in Germany in 1979, Rick Honig visited me. We did not know each other before, but he had read one of my papers and he said, "Please come to my lab and I will introduce you to our work group and implement your work”. And this was why I went to RCA, and I enjoyed the work style and the work place climate very much. We had lots of open discussions about everything, particularly with Charles Magee. I often had discussions about the sputtering process and how it's really going on at the atomic scale. Of course he was in SIMS, but with John Thomas I did sputtering in combination with XPS. For instance, we studied the damage you introduce in silicon dioxide by ion bombardment and sputtering. We found already at that time that silicon dioxide is sputtering congruently, that is with no preferential sputtering of oxygen as compared to many other metal oxides. What you do is damage the bond and therefore you produce a kind of amorphized silicon dioxide which is not like crystalline quartz, and we could detect this by measuring the bombardment induced broadening of the silicon 2p peak which we observed with XPS.

HOLLOWAY: X-ray photoelectron spectroscopy-XPS.?

HOFMANN: XPS, yes. We studied the influence of different sorts of ions, and this research was going rather deep into basic mechanisms. I think for that time it was a very good work. Of course you can do it better now with instruments with better energy and spatial resolution.

HOLLOWAY: They had the benefit of all your preliminary work that showed them how to do this.

HOFMANN: Yes, of course, that's right. Actually this was the starting point of the doctorate thesis of Jose Maria Sanz who is now one of the editors of the journal Surface and Interface Analysis. He is a professor at the Universidad Autonoma (Autonomous University) in Madrid. He was one of my best doctorate students, and he did really excellent work, which is still highly cited today, on the sputtering of oxides and how they were decomposed into different suboxides and metal valence states by preferential removal of oxygen. We could also make a model of the process in order to predict which kind of oxides are particularly prone to reduction and which oxides are not. For example, we could predict that oxides like aluminum oxide or silicon dioxide are almost congruently sputtering, whereas oxides of tantalum, niobium, hafnium or zirconium are terribly susceptible to preferential sputtering of oxygen and are reduced even down to the metal during the sputtering process.

HOLLOWAY: So this was sort of happenstance that you started out with recrystallization and the study of minor impurities and then migrated into surface analysis and into sputter depth profiling.

HOFMANN: That's right, into sputtering applied to depth profiling, that I did mainly with Anton Zalar from Ljubljana, Slovenia. But later we again did work on segregation, for example by looking at the composition of grain boundaries opened by brittle fracture. I was lucky to cooperate with another colleague, Pavel Lejcek from the Czech Academy of Sciences in Prague, Czechia, whose laboratory already had the skills and experience necessary to make oriented bi-crystals of alpha-iron, that is of iron- silicon alloys doped with phosphorus and carbon. We studied these bicrystals extensively with Auger electron spectroscopy until a rather complete misorientation dependence of grain boundary segregation emerged, a very exciting and fascinating work. I think it's still outstanding because we did temperature dependent studies, which means we could establish segregation enthalpy and entropy for silicon, phosphorus and carbon on well characterized grain boundaries. Our results were theoretically confirmed by a PhD student of Profesor David Seidman at Northwestern University.

HOLLOWAY: Yes.

HOFMANN: I think you know him too, he is working with the atom probe mainly to study interfacial segregation.

HOLLOWAY: Right.

HOFMANN: Our results confirm a theoretical model based on the so-called compensation effect, which gives a linear correlation between the segregation enthalpy and entropy. That was proof that our quantification procedure of Auger measurements was correct, because the reliability of grain boundary composition depends very much upon a very detailed and careful quantification.

HOLLOWAY: Right, right.

HOFMANN: And that's where we learned a lot. One of my steady aims was to make surface and interface analysis as quantitative as possible. Therefore I started to make models of sputter depth profiling, models that predict quantitatively how a profile is likely to develop, particularly when you look at it with electron spectroscopy, but also when using SIMS. Because it is obvious that the basic process of ion-surface interactions is the same whether you use SIMS or Auger electron spectroscopy (AES) or any other analysis technique. Of course there are distinct differences between the analysis techniques, particularly with respect to preferential sputtering. For example, SIMS measures what is sputtered away and AES or XPS measure what remains on the surface so there is a complementary difference. Therefore the combination of these techniques is very powerful. I collaborated with Dr. Dae Won Moon from the Korean Research Institute for Standards and Science (KRISS) on that subject, who did SIMS analysis on the same material on which we did AES depth profiling. It was a nanolayer structure of aluminum arsenide in gallium arsenide. We obtained very nice results which basically were the same for SIMS and AES. Typical differences between SIMS and AES were recognized, meaning that SIMS is very good for low concentrations where there are practically no matrix effects, whereas with AES and XPS it's opposite. AES and XPS are very good at higher concentrations because they have generally low matrix effects, but that’s where SIMS has a lot of distortions. With electron spectroscopy, AES and XPS, at low concentrations you end up with a lot of noise and you cannot detect any more the detailed shape of the profile. But for high concentration it's very nice. 

HOLLOWAY: Yeah.

HOFMANN: Whereas SIMS is good for low concentrations, when you get into the 50% region, you know you have huge matrix effects.

HOLLOWAY: Yeah, exactly. So what year was it when you were cooperating with Dr. Moon? What year was that?

HOFMANN: That was actually in the '90s. The paper was published in 1999 . There was a time, you know, I began to develop a model which I have named the MRI model with the three first letters of mixing, roughness and information depth..

HOLLOWAY: MRI model of sputtering.

HOFMANN: Yes, MRI model of sputter depth profiling. That is because I use three parameters to describe the profiles which we got. We tested this very successful model mostly on sputter depth profiles of aluminium arsenide in gallium arsenide but also on nickel-chromium thin film multilayer samples. It was at the end of the '80s when I started with this model. I developed it more and more in the '90s and even today we make more refinements as you know. A little later it was extended because it is too simple to cover everything. For instance, if preferential sputtering occurs, you have to introduce an extra parameter which is the ratio of the sputtering rates. When you go through an interface from A to B and B sputters faster than A, the ratio of the sputtering rate of B and A has to be introduced in a clever way in the model. That’s what we did and it works surprisingly well, even it is simplified in taking the sputtering speed proportional to the composition when you go through the interface. So you start with one sputtering rate and you end up with the other, and in between we just have a smooth transition.

HOLLOWAY: Yes.

HOFMANN: Although we know that this is not the full truth - it's normally nonlinear with composition because the sputter processes are very complicated – it is most often found to be valid. However, when you have sputtering induced compound formation, it can be wrong, and then we are left in the dark with a simple model. But in many cases the MRI model works surprisingly well.

HOLLOWAY: You certainly are the world's leading expert in terms of the quantization of sputter depth profiles.

HOFMANN: Thank you very much, but I am rather one among several colleagues. 

HOLLOWAY: That was a large part, I believe, of why you got the Nerken Award-recognition of that expertise.

HOFMANN: Yes. That is right, but we did a lot of work in that field. We tried really hard to get to that point, and still do so today. Recently one paper was accepted for publication with a study which I did with Jiang Yong Wang from China. He is now at the Max Planck Institute in Stuttgart as a postdoc researcher and he helped me with the mathematical set up. The backscattering effect is a big problem in Auger depth profiling as you know, and it's a bit more complicated to implement it in the MRI model.

HOLLOWAY: Ion backscattering?

HOFMANN: No. Electron backscattering.

HOLLOWAY: Yeah.

HOFMANN: That is what makes quantization of Auger electron spectroscopy so difficult. I learned a lot from your earlier work in the '70s. That was pioneering work, when these effects were shown to exist. We knew already at that time about the magnitude, and that the backscattering effect can go up to more than 50% of the signal strength. So it's a big effect. It's not so easy to be neglected.

HOLLOWAY: Exactly.

HOFMANN: The backscattering effect is what we recently began to tackle. I'm now working on its influence in multilayer profiling which is the next more complicated step, but for simple A/B interface profiles, I think we have solved the problem right now, with some reasonable assumptions which seem to work – again surprisingly because of their simplicity. I think when you have the basic parameters which are decisive for some effect, then you have at least a very good approximation of what is going on, even if reality is more complicated That is my philosophy, so to speak.

HOLLOWAY: Right.

HOFMANN: And in many cases this helps a lot. It is better than looking for complicated multiparameter system where frequently you do not know their exact meaning. I think that the MRI model is successful because it's basically simple and you can –without calculation - already qualitatively predict how a profile will change when you change one of the three parameters.

HOLLOWAY: Right.

HOFMANN: They are described in a way that is simple and you see what is their influence. Some people may not like my philosophy because I know that many theoreticians want to have some exact process description, working with many interrelated parameters, going down to every detail. If you can do this, that's certainly better, but in many cases you are lost because you have to make approximations or use data which are not well known or just guess some quantities, then it does not help.

HOLLOWAY: That's right. So even though you make it more complicated, you can't solve it so you have to simplify it to a point, and that's where you start.

HOFMANN: Yes, right, yeah. Many people who do ab initio calculations or use Monte Carlo calculations and such cannot predict the change of the outcome when you simply change one parameter. That is what you always can do when you have simple analytical relations and solutions where you see how a specific parameter influences a certain shape or intensity of a measured depth profile.

HOLLOWAY: So you have spent quite a large fraction of your professional career looking at sputtering phenomena and the development of the MRI model, but you have done segregation work as well and oxidation work also.

HOFMANN: Yes, oxidation and corrosion work too. Being in a materials science laboratory first of all our goal was always to study appropriate phenomena in the materials science field, like segregation and oxidation which we studied a lot in the '80s. My philosophy always was that the application of a technique, like a tool, can only be as good as you know the properties of that tool. And that is why we have to study fundamental effects in AES, XPS and sputter depth profiling, too. 

HOLLOWAY: Absolutely.

HOFMANN: Only then you can differentiate between what you measure and what is the effect you like to find out, that is what are instrumental effects which are specific to the technique you use. Therefore you have to know your technique; you must know it well enough to make really good and quantitative results for your materials science problem. That approach helped us a lot to get useful data that can be generalized. As I told you before, I think we could show that quantitative AES was the basis to find the correct correlation between segregation enthalpy and entropy. Similar data from other people show some offset which came from a wrong method of quantification of AES. You know the simple old-time quantification of segregation was to use only measured ratios of peaks (ratio of peak-to-peak heights of segregant and matrix elements).

HOLLOWAY: Right.

HOFMANN: But the segregant concentration is confined to the very first surface layer. Setting the ratios proportional to segregant concentration is not correct at least if the concentrations are not very small. As soon as they get in the 20-50% region, then you are wrong when using simply ratios of peaks. Therefore you have to have a model of the layer structure, knowing what element is above another and so on. You have to take this into account, and when you don't do so then it's too simple and therefore wrong. This is what people often do who work with Auger electron spectroscopy, like with a black box: But you have to understand something more. And to understand something more you have to do some model experiments, look at what you really measure and what you really can predict. Of course, in the literature you see what many people are doing while you are doing the most fundamental work. I always prefer data I have obtained myself. Therefore I like to do some model research and make tests on simple substances or phenomena, for example layer structures, things like that, to find out what really is going on and what kind of artefacts occur. For example, one of the questions in sputter depth profiling is always, "How do I know how sharp is the original interface and what kind of broadening do I introduce by sputtering?"

HOLLOWAY: That's right.

HOFMANN: That's very important to really know what is coming from the technique and what was there originally. Tracing back these things was my main goal in the MRI model. What it eventually does is, so to speak, to simulate the sputter depth profiling process by a simple mathematical model and to see how it works, how it broadens the profile and then to come back and tell the profile has had this-and-this sharpness before the sputtering process.

HOLLOWAY: Right.

HOFMANN: The main procedure is to find out from the measured profile the original in-depth distribution in atomic percentage concentrations layer by layer. This is what the MRI model actually can do for you.

HOLLOWAY: Yes. Well, the MRI model you have developed over many years like we discussed already. But I think you are the epitome of somebody who interacts internationally. You have colleagues around the world.

HOFMANN: That's right.

HOLLOWAY: And I wondered if you would like to say how valuable that may have been.

HOFMANN: Yes, of course. First of all, international for me meant always I like to be here in the USA as I told you already, starting with the RCA group in Princeton in 1980. A little later you were so kind to invite me to come to your lab at the University of Florida in Gainesville, and I enjoyed very much the interaction with you and your group, and I could learn a lot. I always tried to sharpen my thinking and my experience and to learn a lot from interactions with everybody, every colleague in the world. I think science is such an international issue, it's really great. And this is why I enjoy so much being a scientist, because the language of science is the same everywhere.

HOLLOWAY: Yes.

HOFMANN: Even when you go to Japan. As you know, I have been in Japan from '96 to '98. I have been in there in a rather high position as a research director. I think it was mentioned in the Nikkei newspaper in Tokyo that I was the first scientist from abroad who held such a position in a national research laboratory.

HOLLOWAY: So you were the standard-setter in that area.

HOFMANN: So to speak.

HOLLOWAY: Has anybody followed you to that level?

HOFMANN: No, not so far. Not that I know. My former Japanese colleagues asked me if I could recommend somebody from Germany, but there was no one that I could find to fit into my footsteps. Obviously my decision was rather special. Actually it had a long history, because it started in '87 with Professor Ryuichi Shimizu from Osaka University, whom you know.

HOLLOWAY: Yes.

HOFMANN: He is one of the, I would say, most international Japanese I know,-. 

HOLLOWAY: Yeah. He certainly reached out.

HOFMANN: Yes. He reached out and got in touch with me. He was formerly at the University of Tuebingen in Germany as a postdoc. He even knows some German. He knew me and he got in touch with me because one of his doctorate students, probably his best one, Shingo Ichimura, who just became Fellow of AVS this year, wanted to come to Stuttgart.

HOLLOWAY: Yes.

HOFMANN: Shingo Ichimura started my collaboration with Japan when he was a Humboldt Fellow for one year cooperating with me in Stuttgart. 

HOLLOWAY: Shimizu?

HOFMANN: That was Ichimura.

HOLLOWAY: Ichimura.

HOFMANN: It was Shingo Ichimura who became now Fellow of AVS.

HOLLOWAY: Yes. But he got the Humboldt Fellowship too.

HOFMANN: Yes, he got the Humboldt Fellowship (a research stipend) in 1988.

HOLLOWAY: I see.

HOFMANN: He was working with me. In '88, that started my interest in Japan – I didn't know much about Japan before. Well, Ichi Shimizu wrote a paper as a comment on one of my papers in 1977, and that was the first time I was aware that somebody was doing ion-surface interactions on the other side of the world, which I didn't expect at that time. But then when Shingo Ichimura was with me, I made a very interesting discovery. I discovered that his thinking was somehow different from mine, and it was so fascinating in the discussion because he had ideas which I never could have myself and I always was wondering, and I thought by myself, "I want to study this culture, this background, and cooperation with such a culture might be very fruitful because it opens your mind and introduces another type of thinking." And so I became very interested in Japan and then the boss of Ichimura invited me to come for three months to the Electrotechnical Laboratory in Tsukuba, Japan. It was my first research stay in Japan. I was cooperating with—

HOLLOWAY: What year?

HOFMANN: That was in 1990.

HOLLOWAY: '90.

HOFMANN: Yeah. And that was my first research stay in Japan. After that it was in '95, I think, when I got the German-Japanese Research Prize from the cooperation between the Humboldt Foundation and the Japanese Society for the Promotion of Science (JSPS). They are equivalent research organizations in their countries and they cooperate. And every year they elect another scientist for the Japanese-German Research Prize, and get a German to Japan and a Japanese to Germany, every year another person. This kind of prize means that you get a Fellowship for up to one year. Actually I spent six months at Osaka University working in the laboratory of Ryuichi Shimizu..

HOLLOWAY: I see.

HOFMANN: After that I didn't think about going abroad for a longer time, but I said to my colleagues, "I would still like to go to another laboratory and do more cooperative research with a Japanese laboratory." And then, Kazuhiro Yoshihara some time later asked me if I were interested in another visit. I think he asked me at some meeting, maybe at an AVS conference. And through him the Director General of NRIM made me the offer to "come for a few years to NRIM." Formerly it was the National Research Institute for Metals, (NRIM), now it's the National Institute for Materials Science (NIMS). It's the same institute, only reorganized and with another name now. I was invited as a senior scientist, but when I was there for three months the colleagues on the directors board decided to get me in a director's position. That was a courageous decision of the Japanese, you know, and I think it was probably because I felt very well adjusted in that surroundings. I could manage to get fairly acquainted with the Japanese culture and habits and with all these kind of things. Because I tried hard to study this and to get more deeply into the ways they are doing the things. And even today, I sometimes am very, very convinced that in some way they are doing things really better than we do it in the rest of the world.

HOLLOWAY: Right.

HOFMANN: For instance finding a consensus. Instead of being too competitive, you just ease out many things and cooperate. And this I learned from them. I really learned it and in fact find it very rewarding in the end.

HOLLOWAY: Yes.

HOFMANN: I think that was one of the reasons why they decided to put me on that position, because the Japanese have a system to look with a high level of scrutiny at the people they promote because the system works like this: once you are in a powerful position, you may screw up the whole thing. So the people have to be very careful to whom they give a certain position. On the other hand I think this kind of trust is really nice and very good in a sense, you know. You get respect and friendship, and I always felt in Japan as if I were in a featherbed. 

HOLLOWAY: They treated you—

HOFMANN: -somehow at ease, you know. And they always find a way to circumvent difficulties and to help you. And this I enjoyed very much I must say.

HOLLOWAY: I remember you telling me the story about them having supplied you with an interpreter so that you would be able to understand what was being discussed in a meeting of the board.

HOFMANN: Of the board, yes. The language difficulty was the toughest thing for me, because if you are not very young it's very difficult to learn the language – different from my younger son, who is now in his thirties. For him it is much easier to learn the language. He is now six or seven years in Japan, by the way. So he can give lectures in Japanese.

HOLLOWAY: So where is he at in Japan? At a university?

HOFMANN: He is now at Hiroshima University as an associate professor of physics. In fact he gives the lectures in Japanese. I think, Japanese pronunciation is not that difficult for us, particularly for Germans, I would say, because pronunciation is very similar, and so it is not a particularly difficult language to speak. But with any language that is different you have to work hard, and the older you get the harder it gets to really achieve a working knowledge. I can shop and know how to express a few things, but I cannot manage a true conversation. That's very difficult.

HOLLOWAY: Well, but you paid careful attention to their language and in particular their culture, and that was very valuable.

HOFMANN: Yes, I think so. And the other thing, now in Japan there is a big movement to open up to the western societies and culture. Anyway scientists all speak English. Therefore language was not a problem in the laboratory. It was more outside and with the administration, it's like in Germany. Those people, they normally cannot speak English. Then you have a problem, but not with the scientists. English is now the international language in the science world. There is no doubt about it. So with the Japanese scientists there is no problem. You can talk about everything in English.

HOLLOWAY: I understand. You told me stories about them using you as an ambassador to some of the governmental administration posts. Could you tell us a little bit about some of your experiences there?

HOFMANN: In Japan, yeah.

HOLLOWAY: As an ambassador to some of the government offices and officials.

HOFMANN: Yes. Because NRIM was a national research institute, the directors frequently, at least once a month, had to go to the Ministry of Research and to give some advice on certain questions. For instance we were discussing the long-term research plans of the Japanese Ministry of Research. All of us were involved, and I got the reports from all the sessions in a written form, with the red stamps on it. It meant secret, you know, not to be disclosed in any way. And I joked and said sometimes to my comrades ”For me it's really secret”, because it was written in Japanese. I almost cannot read Japanese writing. But the Director General was very kind to me, and when I asked him I was given an English-speaking secretary who could translate all the headings at first, and when there was a more interesting things, I asked her to translate them completely for me because otherwise I would have needed months working with a dictionary to learn the contents. The language difficulties were really tough for me, but fortunately two colleagues who were fluent in German were of great help. That was interesting for me, and sometimes they helped me when we had a session and the colleague was sitting in the seat beside me. He told me in German a little bit what was going on, because actually I only could understand as much Japanese as necessary to figure out what was the main topic. It was really tough. And I am still amazed about the patience of the Japanese colleagues. I was on several committees there, and these committees worked with discussions going on. But I felt fully integrated and I was even the chairman of one committee. That was amazing, and I admired their patience with the language problem, just going back and forth and so on. I learned a lot about how decision-making is done in the usual Japanese way, where really the aim is to find the optimum. The chairman of a Japanese committee is quite different as compared to Germany or probably to the USA. In our culture normally the chairman is the strongest person. He is giving the direction.

HOLLOWAY: Yes.

HOFMANN: But not in a Japanese committee. In a Japanese committee the real chairman is like – I use the picture - like a man on a steering wheel of a ship going through a storm, you know. He has to take care that the whole thing is not going astray and he has to find the optimum between the different opinions, and you end up with having no opinion of your own as a chairman. You cannot have that luxury, because you have to find the balance between different opinions. This is the art of leading a committee, I found out, and I had the feeling afterwards that my Japanese colleagues appreciated that. I remember one special occasion that they were very satisfied with the kind of steering I did to find the optimum. The nice thing about committee decisions is that they are not done by an individual, and in the end you say, "Okay, this is the decision of our committee." Everybody agrees and everybody is behind the decision and no personal adverse attitude is left, because it's not a personal decision but that of the committee.

HOLLOWAY: Yes.

HOFMANN: The maybe not-so-good thing is that nobody gets the fame when the result is positive, but in turn when it is negative nobody is the scapegoat. So, if something doesn't work out as you think, this system leads to a lot of personal comfort, and that's very helpful.

HOLLOWAY: Yes.

HOFMANN: A lot of time and money is spent in America and in Germany, I am sure, looking for somebody who was the culprit of this and that thing having gone astray, and work is done on items of the past which does not help for the future. The Japanese are basically free of that drawback because they think of the future, because past is past. Since nobody knows who was the culprit, why should we care about the past. That's gone, so let us look to the future. This is a very good aspect I've found, and it relieves you from many things which are so important in our culture and where you think sometimes why is this issue always going back to the past when we have to make decisions for the future, and better forget about the restrictions of the past. There’s another thing. The Japanese like to plan twenty years in advance. Amazing.

HOLLOWAY: That's a remarkable timeframe.

HOFMANN: Remarkable. Time scale is twenty years. They always asked, in the Ministry of Research, where we will want to be twenty years from now. And it's another thing which I learned, this long-time perspective. In our institute (NRIM) they were running machines which have been set into action more than thirty years ago. For a long time research on fatigue in materials, you know. It's interesting, because in Germany or in the USA we cannot think about setting up an experiment which is going on for thirty years. Everybody would laugh about it, because nobody would know who will be responsible. But in Japan there is continuity. It's very important.

HOLLOWAY: So what do you find most valuable in the marriage between German culture and Japanese culture? Are the two incompatible or do you take the best from both?

HOFMANN: Yes and no. It is difficult to quantify this, but it is really some new kind of impact, because in Japan many of these things I have just mentioned are made in a different way, and this influences your whole point of view and your thinking. There is one thing I also experienced: In Japan you immediately think of how things operate in an optimum way. Not so much concentrating on fundamentals, like the typical German does, maybe even more than the typical American. I believe it is typically German to look at the fundamentals and say, "Why is that operating in this way and not the other?" The Japanese are not so much held up with the question of why is that operating in that way. They say, "What use can I make of this nice effect when I have it?" This is very efficient, this direct thinking going into some useful thing. I think it comes basically from the Japanese culture that is always based on how can we help and make things easier for the people and so on, and what will come out is easily accepted. Whereas in the European and particularly German tradition we are some followers of Kant, the German philosopher. That is “German idealism”, which means we follow certain ideas, and we differentiate between fundamental reason and practical reason, and going deep means going into the fundamentals.

HOLLOWAY: Right, right.

HOFMANN: Therefore you have different aspects looking at science matters in Japan and in Germany. I always felt this. And I think what you can do, of course you mentioned it already, you can try to put together the best of both worlds so to speak to make a fair compromise. And this I think can work very well. You have to see which kind of advantage every aspect might have and whether it may be manageable.

HOLLOWAY: Now you have spent quite a lot of time and studied the culture of Japan. What about the other cultures in that part of the world, Korea and Chinese?

HOFMANN: I do not know much of the other cultures in the world, I must admit, because only with Japanese culture did I have a deep personal encounter. For instance I had also Indian scientists in my group as postdoc fellows, and I was also happy with them, but I did not go that deep into their culture. I simply did not have the chance. You know, to understand a specific culture I think it is essential that you live in the country and you get exposed to the people there for a certain time. Otherwise only reading books or travel will not really help you too much. It gives a kind of acquaintance beforehand, but to work in a country and to live daily with the people there gives you a much better and deeper insight in what is going on. And so I am sorry I can only tell something about Japanese, American and German cultures. Besides, I think you can judge your own culture better when you see it from outside.

HOLLOWAY: Right.

HOFMANN: For instance it's well known, the Japanese people are very polite and they do not want to make you suffer from any kind of things. This is sometimes misunderstood in our western world of not being sincere enough to always tell you the truth. But it is only because they do not want to intimidate you or to make you feel bad, whereas we have no scruples.

HOLLOWAY: We don't have any compunction about that.

HOFMANN: So when I came back from Japan to Germany, I found myself in a situation of what you may call the reverse cultural shock based on misunderstandings. That means that all of a sudden you feel how different the German culture is from what you've come from, and I particularly found the German culture to be very rude. 

HOLLOWAY: Compared to the Japanese.

HOFMANN: Compared to the Japanese culture it's really unbelievably rough and almost brutal, so to speak.

HOLLOWAY: But it's all relative. 

HOFMANN: Of course, relative. But it appears as if in certain human matters we have no culture at all. You must know that Japan is unique in the sense that before World War II, Japan was never occupied by another nation.

HOLLOWAY: Right.

HOFMANN: Still today you feel that makes them very self-sufficient. You know, somehow they have a very good opinion of themselves, so to speak. I would not say they are arrogant or the like. It's sometimes even the contrary. But they have a very good feeling of being naturally proud of their culture, and they have a good culturally based esteem of their ancestors and of tradition. And this eases out many things, because with such an attitude you can be much more generous to other people than if you have an opposite attitude. I wouldn't blame anybody. I'm not a politician, but to the contrary you feel now in the Middle East or other places that many people are suffering from an inferiority complex. That makes life very difficult, and you get easily violent when you are in such a position. But when you are in a position where you know you have a highly valued culture and tradition, you tend to be peaceful.

HOLLOWAY: Right.

HOFMANN: This is something which I like very much in Japan, in Japanese culture .

HOLLOWAY: You participated in a number of different cultures, as you have very well illustrated for us, but you were still employed at the Max Planck Institute.

HOFMANN: Yes, that's right.

HOLLOWAY: And so you had a lot of freedom from that institute.

HOFMANN: Yeah. That's one of the benefits. The Max Planck Institutes are run by the Max Planck Society. The Max Planck Society is like a sports club in principle. But it has a well-defined goal, and the full name is Max Planck Society for the Enhancement of Science.

HOLLOWAY: I see.

HOFMANN: This is the purpose. Our purpose is to do open science for the public, for everybody, for the benefit of everybody and to promote science. This is our goal. And it was that from the beginning when what is now the Max Planck Society was the former Kaiser Wilhelm Society, founded in 1911, and dissolved after World War II because of political implications. Later (1947) it was re-founded and became today's Max Planck Society that still has this goal of being very international. International collaboration is one of our outstanding goals. This was my advantage, so to speak, even when some of my supervisors didn't like me to go abroad. But I could reach out and could do this because it was basically supported by the senate and by the president of the Max Planck Society, and covered by our main goal. International collaboration was always enhanced and looked upon as being important, and this is what I find very nice in the Max Planck Society, among many other things which I don't find so nice. I will not go into more details here, but one thing I don't find so nice is the strict hierarchy and feudal structure which we still have, where ranking is very strict. This is something which I like much better in the United States. The hierarchies are also there, of course, as they are everywhere. You cannot do without. But they are not so rigid. There is really a big difference in the freedom of critical thinking and self-expression. And this is something which I like. This has to do with many other things, as you know. Here in the USA you have democracy for more than two hundred years, whereas in Germany we have it maybe for two generations. We still have traditions which are not very democratic. You always feel some feudal system in society. But that's politics, okay? Anyway, from the point of view of research in the Max Planck Society, I think, still a lot of good work is done. Nevertheless, one of the good things is that we emphasize international cooperation We have many people now in Stuttgart from abroad, and there is always a very open mind about that. I think this influx of many other backgrounds and thinking is very good in terms of new ideas. You know it best, Paul. In science we live from new ideas, and new ideas are always likely to emerge if you have somebody coming from another culture and avoid being inbred in one thinking.

HOLLOWAY: Right. So tell me how many Ph.D. students have you worked with from the Institute?

HOFMANN: With about twenty-five with diploma and Ph.D. students together. Out of these twenty-five, five were very outstanding, and four of them are still around and I still cooperate with them. With some of them even nowadays I have common publications, and from others I have a more indirect support, and we are still in very good contact. Among these are Jose Sanz of whom I have talked before, and who is now professor in Madrid, and Anton Zalar with whom I have lots of publications, as you know.

HOLLOWAY: Yes.

HOFMANN: From Ljubljana. And the third one is Pavel Lejcek from Prague, from the Czech Academy of Sciences there, and the fourth is Joachim Steffen who is now in Mannheim at the University of Applied Science. All are professors and have good positions. A year ago at the ECASIA Conference in Vienna, -as you know I am on the board of the International Steering committee of ECASIA Conferences in Europe.

HOLLOWAY: Yes.

HOFMANN: In Vienna last year at the ECASIA conference, all four of them were there with contributions.

HOLLOWAY: It makes you proud when that happens.

HOFMANN: It makes me very proud. You know, in science you have your “scientific children” around you.

HOLLOWAY: Exactly.

HOFMANN: They are doing well and promote their scientific work. It's nice and it's just wonderful to enjoy it. Yes, that's the way it is, and I enjoy very much their cooperation, I learned a lot from them in steady exchange of ideas and in discussions. That's very important, and I remember many weekends we spent in the laboratory, because it takes a lot of time until you come into a certain level of thinking.

HOLLOWAY: You might say you were already developing the Japanese culture because you were trying to reach consensus on these issues with the students.

HOFMANN: Yes, right. [laughs]

HOLLOWAY: You just didn't understand where it came from.

HOFMANN: Yeah. Maybe.

HOLLOWAY: Well, we covered a lot of territory and you've been very generous in sharing your memories and recollections and details and facts. I wondered if there was anything else you had thought about that you would like to add to the interview.

HOFMANN: Well, first of all I am very grateful that I had not only the chances from the Max Planck Society, but also particularly here in the United States where I feel always somehow at home and very welcome. It's quite natural, because European culture is still around here basically, and so there’s not that much difference. The international cooperation, as I told you, is very valuable, and I always enjoyed being here at the AVS Symposia. I just told my wife, Uta, because even Uta knows many more American people than German people in my research fields. We feel at home here, since colleagues in AVS are very open to international cooperation. I mean that one of the facts you see is that people like me from Germany get such a nice prize. It demonstrates how open you are. This is not so when you look at some – I wouldn't say any name – societies in Germany, because many societies have their peer group movement to focus on the local people.

HOLLOWAY: So, Siegfried, you also spent some time in the USA at the National Institute for Standards and Technology (NIST).

HOFMANN: That was another very positive experience, because I had the chance to stay with Cedric Powell and the late Joe Fine at the National Institute of Standards and Technology in Gaithersburg. And it was again in my old subject, you know, Joe Fine was in sputter depth profiling too, so we were really working closely on practically the same subject. I enjoyed my stay very much, and I also learned a lot from Cedric Powell, about his work and his approach and I enjoyed it for three months in the really cold winter of 1994. 

HOLLOWAY: So you enjoyed the warm camaraderie but not the cold winter, huh?

HOFMANN: Not the cold winter. One day I was fighting my way through meter-high snow to get to the Institute only to find out that it was closed because of the snow.

HOLLOWAY: You thought it was your duty as the visitor to NIST.

HOFMANN: Yes, of course. To show how tough Germans are [laughing]. Anyway, it was a very nice experience I could share there with them. Wherever you are you can learn a lot, that’s part of my philosophy. You never can learn enough, and you may find out something which provides some profit for yourself, and, of course, at the same time you always give something from your side, and both together are very nice. Since we have such a subject as science which is promoted by the input of ideas, it goes always back and forth, and I think that's the reason why we have these conferences and why they are so important for us. Because first of all we learn from each other and we have to present our work to the scientific community, and we get a valid judgment. Normally this is very good and you learn a lot from the critique which you get back, which is beneficial for your own work.

HOLLOWAY: Exactly.

HOFMANN: This is what I enjoyed so much, having had the chance to be here, particularly here in the United States.

HOLLOWAY: Good. Okay. What is the most important trait in research?

HOFMANN: Some people are really apt to take the challenge and see through the task. It is sometimes like an ordeal to move forward in research. And I have the opinion from many collaborations that those people who are really tough are the best in doing science, where endurance is very important. But to get this endurance it is important that they have somebody to discuss with, somebody who encourages them and who is giving them the kind of guidance they may need. I always felt it is very important particularly for senior scientists, for the supervisors and so on, and you know it too, Paul. Everybody who is doing research and coaching students knows how important that is.

HOLLOWAY: Right.

HOFMANN: This is also something else which I learned here in this country in particular, because here I think it's a certain culture. We are talking of the culture of this kind of positive thinking and encouragement which I always felt here. I always came back from America with new and good ideas. Sometimes I think in Europe, in Germany we often suffer from too much pessimism and too little optimism. What I like now to do is to bring a kind of positive feeling to the people which are working at the Max Planck Institute. You know, I am now retired, but nevertheless I am still around and I am very happy to give my advice to the young people there, and I cooperate with some of them very well. Although my projects are going at a slower pace, I'm quite happy with that. It is very tough for me to fully retire because I feel science is my life and was the business I have done all my life. I have never thoroughly learned anything else, and my Japanese friend, Kazuhiro Yoshihara, sometimes told me when we were privately talking about something else, "You are always a scientist." I said to him, "Well, I cannot help I am a scientist." And he told me that everything I’m talking about is going into a scientific kind of thinking. That's what I used to do for many years, and so I cannot help to do so now.

HOLLOWAY: Well, that's an interesting observation on life, and we're grateful for all of the cooperation that you have exhibited with us over the years. While you may have taken a lot of ideas from interactions in the United States, you generated an awful lot of ideas too and so the feeling of admiration for your scientific prowess and your cooperation and abilities are genuine. We're very grateful for the interactions we have had over the years.

HOFMANN: Yeah. Thank you very much, Paul. And I may add just a word of thanks particularly to the award committee that decided to give me the prize. I feel very honored, and I know that this was only possible by the support of you and other colleagues here in the United States who voted positively about my research work. I am sure there are many other people who also deserve such a highly honored award, but I was the lucky guy to get it.

HOLLOWAY: Well, it's very well deserved and we are very pleased. I am very pleased personally, as I said at the beginning, to interview you and record your thoughts on the subject and to congratulate you on the Nerken Award.

HOFMANN: Thank you very much, Paul.

HOLLOWAY: Okay. Thanks.


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