2012 Kavli Prize in Nanoscience: A Discussion with Mildred Dresselhaus
MILDRED DRESSELHAUS, this year's recipient of the Kavli Prize in Nanoscience (and the first sole recipient of a Kavli Prize) has had a long and illustrious career in physics. Dubbed "The Queen of Carbon" by her peers, she was instrumental in unlocking the secrets of carbon's electronic structure and the mysterious forms it takes on in nature.
For example, Dresselhaus contributed to the discovery of fullerenes – very large molecules of carbon that resemble Buckminster Fuller’s geodesic domes. She also predicted the existence of carbon nanotubes – single-atom-thick cylinders of carbon that could be used in everything from stronger materials, ultrastrong cables, and hydrogen storage to advanced electronics, solar cells, and batteries. And she remains a leader in the science of nanoscale carbon structures, which are thousands of times smaller than the diameter of a human hair, exploring their electronic behavior and how they convert heat into electricity.
Physics was not an obvious choice for Dresselhaus. She grew up poor in New York City, and enrolled in Hunter College in 1948. She planned to become a teacher, one of the few professional careers open to women at the time. Instead, she took a physics class with Rosalyn Yalow, a future Nobel Prize winner, who encouraged her to study physics. She eventually received a doctorate at University of Chicago, where she was further mentored by Enrico Fermi, also a Nobel Prize winner. In 1960, she joined Lincoln Laboratory, which the Massachusetts Institute for Technology (MIT) operated for the U.S. Department of Defense, and after seven years, moved to MIT itself.
Dresselhaus remains an Institute Professor of electrical engineering and physics at MIT. Among her many honors and memberships: she is a fellow of such leading scientific societies as the American Academy of Arts and Sciences, American Physical Society (APS), IEEE, and the American Association for the Advancement of Science (AAAS), and a member of the U.S. National Academy of Sciences (NAS). Her long list of awards includes the U.S. National Medal of Science, and she is the recipient of 28 honorary doctorates. She has also played an active role in the public sphere, and has served as president of the AAAS and the APS, treasurer of the NAS, and chair of the governing board of the American Institute of Physics.
THE KAVLI FOUNDATION (TKF): At the start of your career, you were mentored by two outstanding physicists. One was Rosalyn Yalow, who won a Nobel Prize for developing a way to measure biological substances in blood and other fluids using radioactivity. Could you tell us about her?
MILDRED DRESSELHAUS: Rosalyn Yalow was my physics professor in my second year at Hunter College. Hunter did not have much of a physics department. After the introductory first-year courses, the classes were minuscule, maybe three or four students and Rosalyn taught there for only one semester. I was the student she was interested in, and she encouraged me to go on to graduate studies.
Rosalyn was quite a domineering person. She just gave orders, and I pretty much did what she said. She continued to take an interest in my career and was there to advise me over the years.
TKF: Graduate studies took you to the University of Chicago, where you met Enrico Fermi, who had won a Nobel Prize in 1938 and then went on to build the first nuclear reactor in a squash court under the university’s football stadium in 1942. Although he died after your first year as a graduate student, you spent many early mornings walking with him to the laboratory, and you have said that he had a profound effect on your life. How so?
DRESSELHAUS: I really did not know much physics before I arrived at Chicago. Fermi had a system for teaching that required graduate students to understand many different aspects of physics. This is because you had to generate your own thesis problems and you couldn't possibly do that in a vacuum. It was very good training; that and talking with the other graduate students. Some also had advisors who were interested in their work.
TKF: Your advisor was not?
DRESSELHAUS: My advisor didn't know what I was working on until two weeks before I submitted my Ph.D. thesis. He never talked with me because he didn't think women should be in science. When I sought him out, he essentially told me to get lost. That actually helped me. I began to learn from other physicists. One was Clyde Hutchinson, a pioneer in using magnets and microwaves to study molecules. We had lots of surplus government equipment, including microwave equipment, at Stagg Field waiting to be salvaged, so I salvaged some it and built my experimental devices. That was common procedure then, and all the graduate students did some of that.
So I already knew something about the topic when Brian Pippard came to work at University of Chicago for a year. He was a leader in using the reflection and absorption of microwaves on surfaces to understand material behavior, and he taught me many things.
TKF: What was your thesis about?
DRESSELHAUS: Superconductor behavior in magnetic fields. I was working on this project in 1957, the same year Bardeen, Cooper and Schrieffer proposed the BCS theory, which explained the fundamental behavior of superconductors. They later received a Nobel Prize for this discovery. But I had observed that a magnetic field could enhance superconductivity under some conditions, an effect no one could explain. For some reason, John Bardeen, one of the architects of the BCS theory, was in the audience at a conference when I presented my findings, and he invited me to University of Illinois to give a colloquium. My experiment was repeated with variations many times over the years. It turned out we were seeing something related to electromagnetism and not fundamental superconductivity, but it took many years before that became apparent.
TKF: So there you were, a freshly minted Ph.D. who had just participated in your first major colloquium. What happened next?
DRESSELHAUS: Between 1958 and 1960 I didn't do too much in science. I married Gene Dresselhaus, a theoretical physicist, in 1958 and we moved to Cornell University. In 1959, my daughter was born.
TKF: You also had three sons, but by then you and your husband had moved to the Department of Defense’s Lincoln Labs, where you began your study of carbon and graphite. Why not continue with superconductors?
DRESSELHAUS: Ben Lax, a very influential physicist in condensed matter physics, headed the Lab’s Solid State Division. He thought superconductivity had been studied intensively, and it was not where the next breakthrough would occur. He was more interested in taking advantage of masers and lasers, which just had been invented, to study the properties of semiconductors. He was right; lasers became very important in research. I decided to see what lasers could do for magneto-optics. The idea was to induce a magnetic field and use lasers to see how the electrons behaved in high magnetic fields.
Many researchers were all studying semiconductors, but I was drawn to carbon and especially graphite. Those materials were hardly known at the time, and the field was wide open. Carbon materials were attractive because they had small effective masses and widely spaced energy levels that electrons could inhabit, and it only took a small amount of energy to bump the electrons up and down between levels. We had a specialized facility, the MIT Magnet Lab, to generate fields that could do that.
TKF: You continued to explore carbon properties for decades. Why so long?
DRESSELHAUS: We were measuring many properties at the same time and examining many different carbon-related materials. We needed many different techniques to try to understand what we were seeing, and it took intensive study to understand what the data told us.
TKF: Your previous work in superconductivity enabled you to pick up quickly on intercalation, where researchers slip atoms into the spaces between graphite sheets. One found that doing this with certain types of metals could produce superconductors from materials that were not superconducting. Could you tell us a bit about that?
DRESSELHAUS: That was a real harvest. Intercalation allowed us to isolate individual layers of graphene and to do some very interesting physics. We discovered many interesting electrical and thermal properties. People don't know much about this research, but it could become important for future applications of graphene, carbon layers that are only one atom thick and have many potentially useful applications. We are now writing a review article on this early work.
TKF: Of course, when you were doing this, no one was thinking about applications. It was pure science, right?
DRESSELHAUS: We did this because it was interesting. The funding agencies were very supportive. Our monitor at the Department of Defense let us do almost anything we wanted to do with our grants -- as long as we came back with interesting results.
We enjoyed the freedom of discovery. At that time, so many things were open but not understood. As long as we made new discoveries and produced good students who got jobs when they graduated, everybody was happy with the outcomes.
TKF: Given your experience with your graduate advisor, did you ever feel that you had to go further to prove yourself because you were a woman?
DRESSELHAUS: I was so happy to have chance to do research in a good place, under good conditions and get good results. I had no trouble raising money from the National Science Foundation to fund my research. I had wonderful students and they were happy, so all was good. MIT needed someone to teach physics and computation to engineering students. This was the heyday of semiconductor research, and the industry was growing rapidly. No one could anticipate the sort of skills our students would need to invent the next generation of semiconductor devices, so a broad background in the Fermi tradition was very much desired. Many of our students proved very successful at using physics to create new devices of commercial significance. I was hired as a full professor, and was the first woman tenured in the engineering school. They were not prejudiced. In fact, the department head loved what I was doing, and I became the associate department head not long afterwards.
Incidentally, after 25 years, my former thesis advisor at the University of Chicago contacted me and apologized for his attitude towards me as a graduate student. It was a very gracious thing to do, something he did not have to do.
TKF: When many of us hear that a scientist has won a major prize, we want to hear about his or her grand theory. Yet much of your work involved measurements of graphite properties. Could you talk about that?
DRESSELHAUS: I do small science. There is no one big thing, just many small things. Some of my biggest breakthroughs came in the early 1990's, after MIT had lost the Magnet Lab to University of Florida. Since I headed the Magnet Lab's largest group, I needed to change research directions. That's when I started looking at nanocarbons. My new interests came about through conversations with people thinking about things to do. That is the way science moved forward for me. It was not always planned. I followed what was in the air.
TKF: Could you tell us a bit more about fullerenes and nanotubes?
DRESSELHAUS: It started in the 1980s, when we were using a laser to knock atoms off a carbon rod. When we did the calculations, we found that we were not knocking off clusters of two or three atoms, which is what we thought at first, but clusters that consisted of up to 100 atoms. We shared our results with Exxon's corporate research laboratory in New Jersey, which was also looking at carbon clusters, and this led to talking with Richard Smalley of Rice University. Smalley was an expert on large clusters. He did the key experiments on these clusters, and later won the Nobel Prize for his discovery of fullerenes.
TKF: I remember when Smalley unveiled his results. Scientists were startled at what they saw. It looked like someone had welded together two of Buckminster Fuller’s domes. Technically, this was called a truncated icosahedron. Were you surprised at what you saw?
DRESSELHAUS: Not really. I taught a class on symmetry at MIT and gave my students a homework exercise where they had to calculate the vibrations of carbon atoms on a regular icosahedron, which resembles a fullerene. I thought it was interesting. My class was mad at me because I didn't publish the solution to this problem as a paper in Physical Review.
The discovery of fullerenes and nanotubes was in the air. Several groups were working on clusters, and clusters led to fullerenes. As we learned more about fullerenes and also carbon fibers, Smalley and I predicted the possibility of elongated fullerenes, which are nanotubes.
Smalley worked on how to make them. In our lab, we developed an understanding of their electronic properties. When we look back at that time, we each say, "If I hadn't met you, I wouldn't have done all these things." We stimulated each other by asking what-if questions.
TKF: We got on this strand when discussing grand theories. That was a hallmark of what many call the "Golden Age of American Physics." The United States invested in expensive particle smashers, space observatories, supercomputers and the like. Today, many believe the U.S. government wants to scale down those investments. Is our golden age of research ending?
DRESSELHAUS: My perspective is that science expanded and grew in the United States during World War II and afterwards, while the rest of the world was still recovering from the war. Then other countries caught up. This was inevitable. It should and did happen. Now, every country is funding good research. When you think about our excellent universities and research laboratories, we're still competing with rest of the world. Not leading, but competing. As long as we're still competing, I'm not upset. If we're not competing, then I'm worried because this is going to impact our economy.
TKF: Can we continue to compete?
DRESSELHAUS: In the United States, our pre-college education system is not as good as it ought to be. Other countries are providing our graduate schools with scientific talent that we might have developed ourselves. Here, our brightest young people are going to Wall Street, where the money is, and not where the most interesting science is. Their parents support that. With college education so expensive, parents expect their kids to have a good return on their educational investment.
TKF: Have you seen this among your students?
DRESSELHAUS: I was always excited about my work as a scientist, and I lived as well as I would ever care to live. Most of my students feel this way too. Some tried Wall Street, and it was exciting for the first few years. They had the big income, the fancy home, and the like. But when they considered what they were doing every day, it was not that interesting after a while. The reality is that once they go down that road, it's irreversible. They can do a more mundane sort of job in science that's semi-interesting, but it's not what they trained for. Science is moving so fast that it's hard to keep up. If you miss two or three years, you're out of it.
TKF: Yet you took a few years off when you first got married. Are you saying you could not do that now?
DRESSELHAUS: In 1960, it was not like this. If we go back even 20 years ago, it was easy to come up with an idea that nobody had developed before. Nowadays, there are just so many more people working in the field and sharing information online that it is hard to find ideas that other people haven't already had. It's hard to be first all the time, so students have to stay much closer to the field than in the past.
TKF: Yet you have that rare ability to jump on new discoveries. Why is that?
DRESSELHAUS: I have an open door here at MIT. When people see things that they don't understand, or they start something and cannot see clearly how to take advantage of it, they come to me. The most exciting ideas come from people with results they don't understand.
TKF: You have mentored many graduate students, including more than 60 Ph.D.'s. Many went on to distinguished careers. What type of skills and lessons do you impart to your own students?
DRESSELHAUS: Fermi is the key to the whole story. What I learned from him was the importance of having a very broad understanding of science, so you can take advantage of new science opportunities so that you can really serve society.
Fermi really knew how to frame a problem so it could be solved and to come up with an approach worth trying. In teaching, his classes ended with a problem that sounded easy, like why does the sun emit a spectrum or why is the sky blue. These were things we observe every day in nature. When you solve them, you learn some new physics, and it was highly instructive to learn about these broad fields.
He contributed to the forefront of every known area of physics. From him, I learned that we don't have to be leaders in every field, but we can use our understanding to see connections that others might miss. Because of this training, when I headed up the Department of Energy's Office of Science, I felt comfortable asking substantive questions to people conducting research outside my own research field.
TKF: How has this played into your own mentoring?
DRESSELHAUS: I try to impart the same type of broad knowledge, but the most important thing that young people need is the confidence that they can succeed. That's what I work on. When I have students, I make sure they are able to formulate and solve their own problems. I will help them, if they come in and talk with me. And I make sure they receive training for their next job. I always felt Fermi and Rosalyn [Yalow] were interested in my career, and I try to show the same concern for my students. More than almost anything else, I learned from them how to train students.
TKF: You've lived through one of the great ages of physics, and have worked with scores of eminent scientists. This gives you an interesting perspective on the next generation of physicists. What do you think?
DRESSELHAUS: There are so many talented young people. I'm an advisor to the Packard Fellowships for Science and Engineering, which funds the research of promising faculty early in their career. It takes more than an hour to read what each of the 100 annual applicants are doing. Compared with when I studied with Fermi, the amount of knowledge researchers must know is so many orders of magnitude greater than it used to be. If you are in condensed matter physics, you can't even know all of that single field of research. But a large number of Packard Fellowships are awarded to people who are doing work at the intersection of different research areas. If there is a general theme to the awards, it is that they go to people who combine breadth and depth in their research.
The things they are doing are amazing, and research today remains exciting.
- August 2012