Interview: Stacey F. Bent
2000 Peter Mark Award Recipient
Interviewed by John Crowell, October 2000
CROWELL: Hello. My name is John Crowell, and I'm from the University of California, at San Diego. I'm a member of the American Vacuum Society. I'm here today with Stacey Bent. She's the Peter Mark Memorial Award winner for the year 2000, and, as part of the Society's history archive series, we're going to talk to her about the research that led up to the award, and about details about Professor Bent.
First, I'd like to explore a little bit, Stacey, about your background. Where did you go for your undergraduate studies?
BENT:: I did my undergraduate work at UC Berkeley, in Chemical Engineering.
CROWELL: What led to the choice of going to UC Berkeley?
BENT:: Oh, there was a bit of a family history there. My father had attended Berkeley when he was a student. Although I grew up in Southern California, the rest of my family all went to UCLA, so it was a little bit breaking with that tradition, but I loved Berkeley. It was a wonderful place to be a student.
CROWELL: Tell us a little bit about where you did your graduate studies.
BENT: After graduating from Berkeley in 1987, I started graduate school at Stanford University, and at that point switched fields, or departments, to chemistry. So I did my graduate work in Chemical Physics.
CROWELL: So did you do research as an undergraduate, and what led to you getting involved in surface science?
BENT:: I did do research for several years as an undergraduate, in the laboratory of Yuan Lee, and that's in fact what got me interested in switching to chemistry at the time, because although I liked chemical engineering, it was such an exciting time to be doing research in chemical dynamics, molecular dynamics, which is what was going on in the Lee group. So I was determined to continue those kinds of studies as a graduate student. But I wasn't doing surface work at the time. I had just decided that interfaces and interface science were really where the future was in chemistry, and that's what I wanted to be involved in.
CROWELL: So who did you do your graduate work with?
BENT:: I did my graduate work with Richard Zare in the chemistry department at Stanford. And so as a graduate student, I was combining molecular beam and dynamic studies with surface studies, and so my research project was looking at the dynamics of the desorption of hydrogen from silicon surfaces.
CROWELL: All right. While you were a graduate student, as well, did you get an opportunity to work elsewhere?
BENT:: Oh, yes. Actually before starting graduate school even, I had been awarded a fellowship through Bell Laboratories, and so, as part of that award, I got to go spend the summer before graduate school out at Bell Labs in Murray Hill. So I did research there for the entire summer, and while I was out there I worked with both John Tully and Mark Cardillo, doing both experiment and calculations of scattering of molecules and atoms from surfaces.
CROWELL: So were you always interested in being a scientist?
BENT:: Well, I always, when I was younger, liked math and science, and I wasn't really sure. I do remember as a young adult, I guess in high school, being in a chemistry class and vowing that the one thing I would never be was a research chemist in a white lab coat. And you know, the career path ultimately has taken me a little bit in that direction. But the reason I didn't want to be a research chemist was my perception of it, which was incorrect. I sort of pictured having to be in the lab all the time, and what I really like to do is interact with people. So I really wanted a career where I could do that. Of course, I've since learned that being on the faculty at a university, one gets to do all those things, including research and interacting with a lot of people. So it worked out, but at the time I was convinced I didn't want to do that.
CROWELL: So were you always interested in being a teacher, as well?
BENT:: No. When I was in college, actually, it was another sort of mental barrier for me to overcome, to go into graduate school, because I always liked to give decisions like that a lot of consideration. There was the expectation that I would just continue on at graduate school, and I wanted to not do what was expected. But at the end, sort of my senior year in college, I decided to go ahead and do that. I was considering both graduate work, which might ultimately lead to teaching and also just taking a job as an engineer at a company.
CROWELL: So since you have industrial experience at Bell Labs, what drove you to decide on an academic career?
BENT: Well, I think the opportunities just arose at the right time for me to do that. I really liked working at Bell Laboratories. I actually worked there two other times after that first summer experience. I went there for a few months one fall while I was a graduate student; I got to work with Alex Harris and a number of other people, and I really loved it. Then I went back again for my post-doctoral work, to Bell Labs. I worked with Bill Wilson. So you know, I thought it was a great amount of fun to work at a place like Bell Labs. But while I was doing my post-doctoral work, different opportunities started arising, to interview for academic positions, and I just followed that path.
CROWELL: So you've been on the faculty at both New York University initially, and then you moved to Stanford University. What aspects of being on the faculty at NYU did you especially like, and how are they different from what you especially like now, being at Stanford?
BENT:: Well, that's a hard question. I enjoyed being on the faculty at both places. When I was at NYU, I was in a chemistry department, and NYU had wonderful students. I had terrific graduate students and really wonderful undergraduates, both in my laboratory doing research, and also in classes there. I had very nice colleagues, and I thought it was a good place to be. And of course, New York City is an exhilarating place to live. Now at Stanford, of course, it's a superb university, and I have lots of great resources and the students are really great, both undergraduate and graduate students. So both experiences have been really good for me. The big shift for me is switching from chemistry to chemical engineering, because after making that switch in graduate school, in my first academic position, I've now switched back to engineering. I'm really enjoying that. I find that keeping a focus on applications, which comes naturally when you're in a school of engineering, has really been a good thing for me as a researcher, and is good. The types of students that I get in an engineering department also are a little bit different from what I had in the science department. So these students keep me on my toes, too, because they're very interested in applications and what's going to be useful for what we're doing. So you really have to answer to a lot of those sorts of questions.
CROWELL: So do you have an appointment in the Chemistry Department at Stanford?
BENT: Yes. At Stanford, I actually have, my main appointment, is in Chemical Engineering, but I have courtesy appointments in the Chemistry Department and also in the Electrical Engineering Department there.
CROWELL: So your research crosses the disciplines between chemistry and chemical engineering?
BENT:: Right. My research is quite interdisciplinary, as are most, or many members here at the American Vacuum Society, because we look at interfaces, which don't necessarily sit only in one department or discipline. But yes, the types of systems I'm interested in are very important in engineering, so semiconductor processing and understanding how semiconductors react and how some of the main processes such as chemical vapor deposition and etching and lithography take place. On the other hand, our focus is on trying to understand the fundamentals of those reactions in that chemistry. So I think our research really bridges the gap between some of the engineering questions and some of the chemistry questions.
CROWELL: In your award, for the Peter Mark Memorial Award, the citation reads, "For seminal studies of Diels-Alder chemistry at semiconductor surfaces and contributions to a fundamental understanding of the reaction processes underlying semiconductor growth and functionalization." Maybe you could briefly describe some of the science that's led to this award, and the nature of the kinds of things involved.
BENT:: Okay, sure. We've been involved over the last few years in some very fun and interesting chemistry of semiconductor surfaces. And the sort of application of this is trying to understand or be able to put organic materials down on semiconductor surfaces, such as silicon. There are lots of applications. We're trying to figure out ways to exploit properties of the organic materials, such as non-linear optical properties, sensing properties, different electronic properties, and the tune-ability that one gets with organics and be able to couple those with standard silicon-based micro-technology. In doing this, what we're focusing on is how to attach the organics in a controlled way to the semiconductor surface. What we have found is that the types of reactions that take place in organic chemistry can also be applied, interestingly enough, to the semiconductor surface because of a unique property of it, that crystal face that we're looking at, which is the (100) 2x1 reconstructed surface. What we've been able to do is show that some classic reactions in organic chemistry, such as the Diels-Alder reaction, take place on top of the surface of silicon, basically, and form the sort of analogous product that you'd expect to see in an organic reaction just of an alkene and a diene. So starting at that point, we've been exploring that analogy for other types of reactions in organic chemistry. So we're now looking at all kinds of functional groups and how we can get a really molecular picture of the silicon surface, in order to understand how to bind organics to semiconductors.
CROWELL Part of your award deals with research that you have done in terms of trying to understand other systems and applying various techniques to try to explore those, so maybe you could describe that work.
BENT:: Right. Yes, we are interested overall in understanding the interfacial chemistry going on in semiconductor processing. So that extends beyond this very nice project of looking at organics on silicon and other semiconductors. We're also interested in taking that same kind of, the same level of detail of understanding of the organics on semiconductors, and extending it to more complicated processes, such as chemical vapor deposition, plasma-enhanced or hot wire-induced chemical vapor deposition. And in order to get sort of molecular-level chemical information on complex systems where one has radicals and ions and lots of collisions at the surface, you need to come up with very creative probes. So one of the things we're looking at is developing or using difficult diagnostics, and they're mainly different spectroscopies, to look at what the surface species and the gas-state species are in one of those complex reactors. We use a lot of infra-red spectroscopy to probe surface species, and we've been looking at different laser-based techniques to probe free radicals in the gas phase. Some of the systems we've been looking at have been involving solar cell materials, such as amorphous silicon and amorphous silicon alloys, for example, with carbon, and looking at the molecular precursors, and how they break apart and what are their reactions that drive the growth of films in those systems.
CROWELL: So in the Diels-Alder chemistry you've been looking at, you've not only shown that you can apply that, using a number of different molecules, but you've shown that it works on other surfaces besides the silicon (100) surface. Maybe if you could, describe a little bit about that.
BENT:: Sure. That's been a real fun part of that research, in seeing just how general that concept is, in using this organic chemistry at the surface. And it turns out that it's not restricted only to the silicon surface. We've also looked at the other Group IV materials, germanium and diamond, and they also have the same important surface structure in those materials. For the (100) crystal face, we've shown that the same reaction occurs. You form the same product of the Diels-Alder system on both germanium and diamond, as well. There are some differences in the chemistry there as you go from diamond to silicon to germanium, and we've been exploring what some of those issues are.
CROWELL: So what are some of the most important differences that exist in some of those systems?
BENT:: I would say that the biggest difference that has jumped out at us is the fact that on the germanium surface, there's a reversibility to that reaction, so you can put down a diene on the surface, put down butadiene and form a nice six-member ring where two of the atoms are germanium atoms from the surface and the other four are your carbon atoms from your butadiene. And if you heat that up a few hundred degrees, the butadiene will come back off the surface reversibly, which is known in organic chemistry as the Retro-Diels-Alder reaction. So that's very nice to see the direct analogy there. In contrast to that, on silicon, and we also believe on diamond, due to the stronger bonds of the absorbate to the surface, that molecular desorption, a reversible process, does not occur, and what happens instead is the decomposition of the molecule.
CROWELL: In exploring these various reactions on semiconductor surfaces, you very nicely coupled your experimental work to theory. Maybe you could describe a little bit about how you got involved in the theory that goes on, that you apply to these systems and how that has helped in your studies.
BENT:: Very well. I should use that as a time to point out that our understanding and the level of understanding that we've been able to obtain on the organic functionalizations would not have been possible without a lot of very good collaborations, and particularly with theoreticians. We initially started because of a very nice theoretical study by Professor Doug Doren at the University of Delaware, where he predicted that we would be able to see a Diels-Alder product on a silicon surface. So I have collaborated with him quite a bit, and more recently have also been collaborating with another theoretical chemist/engineer, Professor Charles Musgrave, at Stanford University, in my department. And one really needs to look at the combination of both experimental techniques, such as spectroscopy, and theoretical calculations, to really be able to understand the bonding of these materials and understand and predict how they would react.
CROWELL: Of the work you've described on diamond surfaces, that, I understand, is a very hard surface to work on. Maybe, if you would, describe how you got involved in those studies.
BENT:: Right. Diamond is, as you mentioned, a very difficult surface to understand how to clean and prepare. And in addition, we were doing an experiment, this infrared spectroscopy through multiple internal reflection, that requires a particular shaped diamond crystal. So we were lucky enough to collaborate with a number of experts in diamond studies on this project; John Russell and Jim Butler at Naval Research Laboratory, Mark D'Evelyn at GE Corporation, and this was a big group effort also with Professor Bob Hamers' group at the University of Wisconsin. So the two of us, the two groups, the Hamers group and my group, were very interested in organics on these semiconductors and we all joined forces to understand how they reacted on diamonds, so it was a real fun experience, and I guess demonstrates the value of collaborative effort.
CROWELL: That seems like your approach, is one where you do whatever it takes to get in there and try the reactions and see what happens. Maybe you could describe a little bit about your philosophy about doing science of this sort.
BENT:: Yes. Well, my philosophy is to just try things. It's actually rather straightforward, if everything's working in the laboratory, to just come up with an idea: "Let's," you know, "what if this molecule, you know, would do that," and just try it. I think it's fun to do research that way, and it actually goes faster, because one can try a lot of things. Of course, as we all know, a lot of them don't pan out. But there is something to be said for just trying it, rather than waiting until you've convinced yourself through whatever types of calculations or thoughts, that it might form a certain product. We're always being surprised when we actually look at things.
CROWELL: What do you think has been the most fun, or the most exciting, in terms of the research you've been looking at?
BENT:: I think for us, in the functionalization reactions, there have been really two aspects of that that I find most interesting. The first is really being able to take these surfaces such as silicon and they're covalent materials, but they're also extended solids, and really be able to think about them in terms of molecules, molecular systems. And the same sorts of reactions that one can do with smaller molecules, you can now think of doing with these covalent solids, the surfaces of these solids. And so just trying to understand some of the fundamental chemistry and coming up with new ways of thinking about the surface chemistry is very interesting to me.
The other aspect of it is I'm very interested in trying to see if we can use this attachment chemistry to try to make devices. So we're interested in trying, for example, to make sensors based on this architecture. To use functionalization reactions in completely different applications, as well, which can range from biological to optical. So I'm also very interested in the possible application.
CROWELL: It sounds like you're in a very good place to accomplish a lot of this work. Maybe you could tell us something about the people that have been involved in the work, in terms of your group.
BENT:: Right. I've had some, as I mentioned, just fantastic graduate students, and undergraduates and collaborators working on this. The initial studies were done at New York University with my first graduate student, Maynard Kong-Moreno, and a post-doc, Andrew Teplycov And they just did some of the first beautiful studies of the Diels-Alder product on the surfaces. At Stanford University, I have some graduate students that are doing wonderful studies of many different types of functional groups and seeing how they bind, and that's George Wang, and Collin Mui, who've been looking at those systems, as well.
CROWELL: So you take an active role in the theory side of things as well, in that you jointly work with grad students and there are joint grad students between you and Charles Musgrave in your department. Is that right?
BENT:: Right. Actually my student, Collin Mui, is a joint graduate student, and it has been extremely productive to work that way. It's difficult and challenging to be a student in that position, to have an advisor who's an experimentalist and an advisor who's a theoretician. Collin handles it beautifully, I should say. But what happens is there is just always discussion going on in my research group about the possible theory that one can do, and then the possible experiments. And so it just becomes part of the lab culture to be thinking in terms of the calculations as well as the experiments, and it's been very productive. It's been a useful way to think about these systems.
CROWELL: I know you were especially pleased to be the recipient of the Peter Mark Memorial Award, and maybe you could describe for us what is so important to you about this particular award.
BENT:: Sure. Well, first of all, the Peter Mark Award is a tremendous honor, and I'm really delighted and grateful to be chosen to win the award this year. The special significance comes from the fact that my late husband, Brian Bent, had been awarded this four years ago, and unfortunately passed away before he was able to pick up the award. So the fact that he had won this and now I've won it really has a special significance that I can't really describe any more than that.
CROWELL: Yes. It seems very, very special. On the more personal level, you're a single mom of two very lovely children, and that seems to me to be just an incredible challenge: trying to balance this remarkable career that you're building, being on the faculty at one of the premiere universities in the country, at Stanford, and trying to balance that with all the responsibilities of being a mother. Maybe you could tell us a little bit about how you manage to pull this off, how you manage to do everything.
BENT:: Well, as you suggested, it is awfully challenging to do that, but I personally think that having my family to take care of gives me a great sense of balance. So I think I am much more productive in my laboratory than I would be, believe it or not, if I didn't have kids. Plus, my life is much more enjoyable, having both aspects. So I have great children, and they are very proud of what I do. I have a very understanding department, which is an important part of that, who understands that I have sometimes other commitments with my children. And obviously, my research group is understanding of that, too. I've just found the balancing of that to be of course, challenging, but quite do-able.
CROWELL: So do you have any advice you would like to share with people who might be thinking of a career in academia or a career in science, and from your experiences.
BENT:: Well, I always tell younger people than myself, to follow their hearts. So if there's something that they really love doing, to really go after that and, you know, hope that it works out. If you really love doing research and science, or engineering, then you should follow that. You should only be doing things as you enjoy them. Another aspect of that, which I do get asked a lot because I do have young children, is you know, "Do you have to make a decision to only have one or the other?" and I hope that it becomes clear more and more, that you can have both a family and also an exciting career in science and engineering. So my advice is to follow you heart, and also not put things off that you really want to be doing now.
CROWELL: Right. Well, I'd like to thank you for giving everyone a chance to learn about the kinds of things you've been doing, and clearly you are very deserving of the Peter Mark Award.
BENT: Well, thank you very much.