The “What If?” Whiz

Mildred Dresselhaus was summoned to the Oval Office last May for what was to have been a five-minute audience with the president. But after Obama congratulated her and a fellow physicist for winning the Enrico Fermi prize, which is awarded for outstanding contributions to energy science, they got talking about global warming and the importance of basic science. Before they knew it, a half-hour had sped by. “He let his whole schedule go to pot,” she says. In September, she traveled to Oslo to dine with Norway’s King Harald and receive the $1 million Kavli Prize in nanoscience.

“All these awards that I’ve gotten recently … it’s made me think, ‘Oh, I’ll just keep going for another few years,’” says ­Dresselhaus, 82, who authored or coauthored 39 papers in 2012. “I’ve been retiring for a long time. I’m officially retired now. But I’m not actually retired.” In fact, seven days a week, the Institute Professor emerita of physics and electrical engineering is in her Building 13 office by 6:30 a.m.; until recently, she and her husband, retired physics professor Gene Dresselhaus, arrived each morning at 5:30. She likes to stay on top of the 100-plus daily e-mails from colleagues and former students—invitations to events, updates on careers and personal lives, and requests for input on their research. Colleagues consider her the go-to person when they’ve made an interesting discovery but aren’t sure what to do with it.

She brushes off the volume of her correspondence as “typical” of an MIT professor. But there’s not much typical about Millie, as nearly everyone calls her.

A pioneer of nanoscience, Dresselhaus was one of the first scientists to imagine that it was possible to make carbon nanotubes, which are remarkably strong and conduct heat and electricity better than carbon typically does. She was the first to exploit the thermoelectric effect at the nanoscale to efficiently harvest energy from temperature differences in materials that conduct electricity. “Millie’s contributions are vast,” says James Tour, a leading nanotech researcher and a professor at Rice University. “She is responsible for much of what we know about the methods to define and characterize carbon materials including graphite, graphene, and carbon nanotubes.”

Along the way, Dresselhaus also served as director of the Office of Science at the U.S. Department of Energy, treasurer of the National Academy of Sciences, and president of both the American Association for the Advancement of Science and the American Physical Society, to name just a few of her extracurricular appointments. Winner of the National Medal of Science and the recipient of 28 honorary doctorates, she helped shape modern physics even as she shepherded more than 60 PhD students through MIT and raised four children in an era when mothers were often expected to stay at home.

The Benefits of Adversity
When Dresselhaus was starting out, women were often actively discouraged from pursuing scientific careers. She says Andrew Lawson, her PhD advisor at the University of Chicago, believed women had no place in science and didn’t even know what she was working on until two weeks before she turned in her thesis. But she was no stranger to adversity, having grown up in a poor neighborhood in the Bronx during the Depression. Dresselhaus excelled at music and academics; by six she was taking the subway to violin lessons by herself. At Hunter College, physics professor (and future Nobel laureate) Rosalyn Yalow recognized and encouraged her gift for science.

After attending the University of Cambridge on a Fulbright and earning a master’s at Radcliffe, Dresselhaus headed to the University of Chicago in 1953. There, as a first-year PhD student, she frequently found herself walking to campus alongside the great physicist Enrico Fermi in the last year of his life. (“We talked about what he wanted to talk about,” she says. “I was a very shy youngster and wouldn’t think of suggesting the topic to Enrico Fermi.”) That year of conversations helped shape ­Dresselhaus as a scientist. “He was always ready to tackle the unknown,” she recalls. “He would always ask questions about ‘What if this and this and this were true? What if we could make this—would it be interesting, and what could we learn?’”

Abandoned by her advisor, Dresselhaus sought out other students and faculty as sounding boards for such questions as she developed her thesis on magnetism and superconductivity, repurposing salvaged equipment to conduct her experiments. “I did my thesis very independently, so when I finished, I was a kind of more independent creature than average,” she says. “I believe that adversity can lead to benefits.”

The Lure of Carbon
Dresselhaus married Gene, a fellow University of Chicago physicist, in 1958 and went with him to Cornell, where he was on the faculty and she was a postdoc. Their daughter, Marianne ’81, was born there in 1959. At the time, only two places in the country would hire a pair of married scientists—IBM and MIT. So in 1960 they both went to work at Lincoln Laboratory’s Solid State Division, which researched the physics of solids and potential solid-state applications for the military. Division director Ben Lax, PhD ’49, thought a recent theory of superconductivity left no further mysteries to be solved, so he asked Dresselhaus to research something else.

Forced to switch gears, Dresselhaus decided to focus on carbon, and especially on the electronic structure of graphite, the soft, electricity-conducting form of carbon that fills pencils. Her goal: to explore how it acts at “the most fundamental level.”

She became one of the first scientists to use lasers to observe how electrons behave in high magnetic fields. Such work was considered difficult, and graphite’s electronic structure was then seen as very complex. So she essentially had the field to herself. “There were three papers per year in the world, and I think they were almost all mine,” she recalls. By 1964, she had four children under the age of six, so the lack of competitive pressure proved useful as she juggled the demands of research and motherhood.

In 1967, Dresselhaus was invited to serve for a year as a visiting professor at MIT. Philanthropist Abby Rockefeller Mauzé had established a fund to support a female professor in a subject in which women were underrepresented; women in the physical sciences were extremely rare, so Dresselhaus was a shoo-in. She was soon hired full time, she says, because no one else was willing to teach physics to engineering students. She was—even though a senior faculty member at Cornell had told her that women can’t teach engineers. Dresselhaus developed a course that focused on the physics of practical, real-world engineering problems. The courses she started—the modern version of 6.732 (Physics of Solids) and what turned into 6.730 (Physics for Solid State Applications)—are still taught today, and they’re still based largely on her original notes.

She also continued her carbon research, and in the 1970s, she looked more deeply at graphite. It is a layered material whose planes are very weakly bonded, and Dresselhaus wanted to know more about the properties of those individual layers. She and her students essentially pried the layers apart by putting different molecules between them and then measured such things as their electrical and magnetic properties. That work proved so fertile that Dresselhaus’s lab drew students from five different departments long before interdisciplinary research became popular. It resulted in about two dozen theses through the 1980s, and it helped lay the groundwork for research happening today on graphene—single-atom-thick sheets of graphite that could serve as a strong and highly efficient conducting material.

“Her early work on graphite contained most of what is now rediscovered in the case of graphene,” says Phaedon Avouris, an IBM Fellow and manager of nanometer-scale science and technology at the Thomas J. Watson Research Center in Yorktown Heights, New York.

The Bottom Falls Out of the Ship
Nearly all the work that had Dresselhaus’s lab humming required the use of MIT’s high-magnetic-field lab, which was funded by the National Science Foundation. But in 1990 the NSF shifted its funding to Florida State University—and Dresselhaus had no interest in heading south.

Although she doesn’t advocate seeking out adversity, it’s critical to learn how to function when “the bottom falls out of the ship you’re on and you have to move to a different one,” she says. “Reëxamination of who you are and what you want to do is very valuable. Every 20 years or so, it’s probably the best thing that can happen.” When it happened to Dresselhaus in 1990, she fell back on her earlier conversations with Fermi to figure out what to do next. “You keep a little bit of what you know as your safety position,” she says. “But then you put 90 percent of your effort into starting the new thing that you don’t know.”

She knew a lot about carbon. But by continuing to ask “what if” questions about it, she went in uncharted directions. In 1990, at a Department of Defense workshop on carbon materials research, she and Rice physicist Richard Smalley were discussing how adding a ring of 10 carbon atoms to a buckyball (the soccer-ball-shaped C₆₀ molecule) transforms it into C₇₀, an elongated ball. That led to the idea of further stretching such balls into what would be known as single-wall carbon nanotubes, rolled-up cylinders of carbon one atom thick. In 1992, Dresselhaus wrote a paper with her husband and colleagues Riichiro Saito and ­Mitsutaka Fujita positing that it would be possible to make either semiconducting or metallic carbon nanotubes—which would have very different properties—simply by altering their geometry very slightly. This idea was startling, but ultimately correct. By 1994, she was researching nanotube properties in her lab. “It was a major step forward,” she says. “Nanotubes were kind of the first really nano thing.”

In 1992, Dresselhaus started another research effort when the U.S. Navy asked for help in figuring out how to generate power quietly and invisibly—without combustion, exhaust, or bubbles—to propel submarines in stealth mode. That request got her thinking about the thermoelectric effect, a phenomenon that converts temperature differences to voltage in certain materials. Harvesting that energy had always proved tricky because it requires low thermal conductivity (to maintain the temperature difference) and high electrical conductivity (so the voltage generated by the temperature difference can flow). But increasing electrical conductivity typically increases thermal conductivity, while lowering thermal conductivity also lowers electrical conductivity. By designing the conducting material at the nanoscale, she found a way to control thermal and electrical conductivity much more independently, giving rise to the new field of nanothermoelectricity. Thermoelectric devices can harness a temperature gradient (perhaps caused by waste heat or sunlight) to generate electricity, or use electricity to heat or cool without moving parts. So the potential importance of such devices is huge. Today, Dresselhaus collaborates with Gang Chen, who heads MIT’s Solid-State Solar-Thermal Energy Conversion Center, on research to enhance the efficiency of thermoelectric materials.

Though it “seemed a little bit traumatic” to her students when she had to shift her research focus, both new directions paid off. “The most fruitful thing is to change,” she says.

“Some Days It’s Not So Easy”
Dresselhaus dealt with the trauma of having to switch directions in her research with minimal fuss. But throughout her career, she also had to deal with the challenge of simply being a woman in a field dominated by men. When she arrived at Lincoln Laboratory, Dresselhaus’s daughter was a baby; having three more children within the next five years did not endear her to her boss, who she says considered four children “excessive.” For the births of her three sons, Dresselhaus took a total of five days’ maternity leave. (One was born on a long weekend, she recalls; another arrived on a snow day.) Armed with a thick cushion for driving, she went right back to work.

When she began teaching at MIT in 1967, only 4 percent of MIT students were women (45 percent are now), and the percentage of female faculty members was even lower. “When you’re so outnumbered and you just don’t see other women professors, you wonder yourself if you have a chance, whether you belong there,” she says. “Some days it’s not so easy to keep going. Some days you could be quite discouraged about it.”

But her husband encouraged her to persist. She also had a reliable babysitter. (“I was her ticket to college education for her children,” she says. “We had a good collaboration.”) Her persistence not only led to remarkable research but also helped change attitudes about women in science. In fact, she says, her PhD advisor eventually apologized for having ignored her, and invited her to give a distinguished lecture at his university. “People change,” she says. “And so it’s important for us to keep going, because we do have a good influence. It wasn’t that hard to change him.”

At MIT, Dresselhaus used part of the stipend that came with her Abby Rockefeller Mauzé Chair to fund events to support women. For about 45 years, she met almost daily with small groups of women to discuss problematic situations they faced at MIT. When she served in the Department of Energy’s Office of Science under President Clinton, she flew home every weekend to meet with her PhD students. Today, she still gives regular workshops to bolster students’ presentation skills and confidence.

Stories of how she helped students are legion. When Course VI major Marcie Black ’95, MNG ’05, PhD ’03, was struggling with Dresselhaus’s Advanced Solid State Physics class as a PhD student, Dresselhaus announced that she would hold an optional recitation before class at 8 a.m. (“That’s like the middle of the night to an MIT student,” says Black, who suspects ­Dresselhaus knew she’d be the only one who would come at that hour.) Likewise, when Sandra Brown, PhD ‘00, was floundering in the early days of her PhD work and thinking of leaving MIT, a single meeting with ­Dresselhaus convinced her to stay. “Millie changed my life,” she says.

Today, although Dresselhaus makes sure, as she always has, to play chamber music regularly with her family, she is not the least bit tempted to actually retire—to go sit on a beach and relax. “I’m not really good at that,” she confesses. “It’s funny, I believe that this is true of most MIT professors: we enjoy our work so much that coming to work is not a sacrifice, it’s something we really like doing. If we didn’t have it, we wouldn’t be too happy.”