Interview: Ernst Bauer
1992 Medard W Welch Award Recipient
Interviewed by I.S.T. Tsong, November 12, 1992
TSONG: My name is Ig Tsong. I'm a professor at Arizona State University, and I'm talking to Professor Ernst Bauer, who is the 1992 winner of the Welch Award of the American Vacuum Society. So I'll start by asking Ernst how you got started.
I remember you told me the story that the first vacuum system you built actually included wood as a material!
BAUER: Yes, it was a very important component! Because at the time, steel was very rare in Germany, and so, not only did I have wood in there, I also had a lot of glass in there, and glass was actually a major component. There was a steel plate on the bottom, and everything had to be mounted by glass-blowing. The first experience in building vacuum equipment was a big fire, which I produced due to my highly qualified glass-blowing abilities [chuckles]! But in the following years, slowly, I could afford to buy a complete metal system. It was an interesting period at this time!
TSONG: Were you already working on ultra-high vacuum then?
BAUER: No, this was in the early '50s, and this was a really bad oil vacuum 10-5, 10-6 Torr or so. It was not possible at that time, for example, to work with metal surfaces, simply because they contaminate too easily. We used alkali halide surfaces to deposit our films on. And it was also alkali halide films, barium fluoride and things like that, which are not very sensitive to water vapor, and also didn't show too much oil adsorption. So it was relatively good vacuum.
TSONG: I see. You did your PhD thesis in the University of Munich.
BAUER: Yes, right.
TSONG: Is that what you worked on, the alkali halide films?
BAUER: Actually, yes. It started as a master's thesis, which was on amorphous substrates. My thesis advisor came from the optical industry, and at that time one of the big problems was how to produce good anti-reflection coatings, and so I started simply to study the structure of anti-reflection layers on glass substrates. This was during the master's thesis. And then, during the master's thesis, I discovered that there was a very interesting phenomenon called epitaxy, which was at this time a realm of crystallographers. Nobody in physics understood anything about epitaxy. So, I decided this was an interesting field, and my boss, my thesis advisor, said, "Okay, go ahead." He was very open-minded, and I could work then on epitaxy of fluoride crystal layers on alkali halide, and also fluoride, substrates. So this was the thesis in which I used transmission electron microscopy and diffraction and also reflection electron diffraction.
TSONG: And so I presume that it was in your study of epitaxy that you now came up with the well-known terminologies of thin film growth modes.
BAUER: Yes, there was a big fight at this time amongst the old people with reputation. One said, "No, my theory's right," and the other one said, "My theory's right." So as a young man, you really don't know whom to trust, so I simply sat down and tried to start from elementary considerations, some dynamic considerations, and came to the conclusion that everyone was right in some respect, and this led to this classification. This was an interesting period.
TSONG: I actually have copies of your German papers on these different growth modes, but I don't know how many people still remember it was you who started it.
BAUER: It's interesting. In recent years, it has become known where it came from, actually, but I think that's not important.
TSONG: Okay, but then so after that, did you go to China Lake? Or how did you...?
BAUER: Well, I stayed for a little while at the University of Munich, and a friend of one of my friends at this time started to edit a series of books, and he looked for authors. So he instigated me to write a book on electron diffraction, which occupied me quite a while in my spare time, actually. And after writing this book, I was so exhausted that I just said, "It's time to change the job!" and I looked for possibilities to go to the United States.
So at this time, there was a program of the US Army in which they hired German scientists for the United States, and I got a number of offers, and decided to go to China Lake, because China Lake is on a lake, and there are mountains, and it's a very good climate. So I went to China Lake, because the offer was very generous as far as the possibility of doing research was concerned. It was a good decision.
TSONG: I know that you actually started your LEEM [Low Energy Electron Microscope] while you were there, and I think I even read your first paper on the LEEM, which was actually presented in, I think, maybe the second or third AVS symposium, or one of the first AVS symposiums.
BAUER: Actually, I don't quite remember. I gave a paper in an international electron microscopy conference in '62 in Philadelphia, I think it was, and this was actually a breakthrough with my management that allowed me to build the instrument, which I think was a very courageous decision in many respects, because the mission of China Lake was not to built electron microscopes, but to build missiles and other defense systems. But at this time, we had a very good, very open-minded technical director, Bill McLean, who had developed the sidewinder, for example, without permission from Washington. And so he was very open-minded to new ideas, and he arranged that I could build the microscope.
TSONG: Well, let me backtrack a little bit. I think that how you got into building the microscope was because you had an argument with Germer. Is that right?
BAUER: Yes. Lester Germer at this time had just started his video LEED system, where you could really see the LEED pattern, and he got some very interesting results on oxygen and nickel, which he had interpreted in some way, which I forget, but I disagreed with his interpretation, and we had some discussion about it. It was basically a streak pattern, which I claimed was due to the adsorption on steps, and as a result of this dispute, I told him, "I will show you images." So this started, actually, a desire to build an instrument where you could use slow, reflected electrons for imaging purposes.
TSONG: I see. So I suppose we could go forward a little bit. After China Lake, you returned to Germany to Clausthal-Zellerfeld, right?
BAUER: Yeah, for several reasons. After a few years, of course, management got tired of building an instrument which takes a long development time. Also at this time, management had changed and became more mission-oriented. So this project could not be continued in China Lake, and there was a very attractive position in Germany which was offered to me. It took me a long time to decide, but I was told that, if I ever wanted to possibly go to a German university, I would have to accept this position. So I had hoped that my conditions were set in such a way that a German university administration would not be able to accept it, but after a year or so, conditions had changed in Germany and they could accept the conditions, and then I had to go, basically. But I was allowed to take the LEEM along. This was a very important point. They said I could continue in Clausthal-Zellerfeld. It did not go as I had expected because it was very difficult to find good students who are really interested in building instruments.
TSONG: Of course, in Clausthal-Zellerfeld you continued to expand your work on epitaxy, and then I know that before, you know, the LEEM finally came into operation, you had already developed a whole battery of techniques in your labs - among other things, like ion scattering, doing field ion microscopy, ultra-high vacuum SEM—everything.
BAUER: This was a natural consequence of the conditions in Germany at this time. I was called to Germany because my predecessor was an authority on thin films, and they did not want to continue thin films in the university; they wanted to get started in surface science. In Germany, there were very few people at this time who had already done some work in surface science. My university at this time was the first one which really had the task of doing surface science. It was built up in a rather broad fashion, trying to develop as many techniques as possible.
There were many students at this time. At some period, I had 27 students in my group, and so they all had to do something. There was not enough money to buy instruments, and so everyone had to build some kind of equipment, and this meant all these diverse techniques were built up. LEEM was very slow in developing, because we had first to train students. You find usually at the outset, they're not strong enough to go on for a PhD, until finally a very good student came along. Wolfgang Telieps was his name. He did his master's on the instrument, and also his PhD on the instrument and got it going.
TSONG: So what's the latest? Of course, we've all seen at one time or another your beautiful video tapes of dynamic processes on surfaces using the LEEM. What do you see as the future development?
BAUER: I see a number of future developments there. One is, of course, to not only make use of the charge of the electrons, but also of their spin to do spin polarized LEEM. And this is already running. We already have an instrument which has been modified for this purpose. We already have our first results, and it looks very promising for the study of magnetic materials using spin contrast. The other one is to go in the direction of spectroscopic imaging, because right now, in the instrument as it stands, we can do microstructure studies, and we can do atomic structure studies by LEED, but you would also like to know the chemistry, of course; the composition. So the addition of spectroscopic imaging using Auger electrons or X-ray photoelectrons from undulator sources, this is another development that we're still working on right now.
The thing which I hope will happen in the future is that we will combine efforts and have STM and LEEM in one instrument. So as far as LEEM is concerned, that is specifically what I am thinking of. But one thing which we have done also in operating the LEEM is that it is very difficult or very time-consuming to extract quantitative results, because we have to evaluate a lot of images, and you have to do a lot of statistics. So one thing which I certainly want to continue is to always combine LEEM with some laterally averaging techniques, so to get the statistically significant information simultaneously. LEED, of course, is one of these techniques. Another simpler one is work function change measurements, which can also be done in situ.
TSONG: So what do you think the future sort of availability of the LEEM to other scientific researchers will be? I know now there's one in this country, for example, at IBM. Could you see the widespread use of LEEM at some stage or another?
BAUER: I can see it, but it will take a little while yet because there's still a lot that has to be done to make instruments cheaper. Right now, to build a good instrument, you have to invest a good amount of money. You can build primitive instruments, but the results which you get are very limited. I mean, there are some relatively simple instruments. Our first instrument is relatively simple, of course, but there's a new model which we have developed, one of which will be in Arizona. It's an instrument on the level of commercial transmission electron microscopes with a lot of electronics and a lot of control facilities involved. But when more instruments can be built, it probably can be done cheaper in the long run, and when they are cheaper, they can have more widespread distribution. But right now, LEEM will certainly be limited to a few research centers.
TSONG: Okay. Is there anything else you want to say about your research?
BAUER: Is there anything significant? I think one thing which definitely has to be said, of course, is that an award of this type is always an award, I think, for the co-workers, because they are doing the work, and it's impossible for a single person to really do all this work. But I will say this tomorrow night.
TSONG: So we'll end the interview right here. Thank you.