Emily Carter wrestles with a world so tiny that if you were to hold it in your hand you could not feel it or see it. Yet the type of work she does, as a professor of mechanical and aerospace engineering, has the potential for large-scale transformations.
“In contrast to traditional mechanical engineering, which tends to focus on the macroscopic world, Emily’s interest is more in the microscopic world, which is a new trend that will influence the future of engineering in a big way,” said Weinan E, professor of mathematics at Princeton and a collaborator of Carter’s.
Beyond exploring new technical frontiers, she is shaping the future of her field through close interactions with students, who credit Carter with nurturing their careers.
In her research, Carter creates state-of-the-art computer simulations that model complex phenomena in chemistry and materials science. The ultimate practical goal of such work is to engineer new nanomaterials — materials designed on an atom-by-atom level — that perform better than existing materials or replace them altogether.
While Carter uses many theoretical tools — among them molecular dynamics, kinetic Monte Carlo methods and continuum methods — her main instrument is quantum mechanics, a fundamental theory of physics that describes the behavior of objects that are about a billion times smaller than the average speck of dust.
“We design materials on the computer so that ultimately you have to do fewer physical tests and you get a solution faster,” said Carter.
Among Carter’s most tangible research efforts are her quests to build an impenetrable, lightweight ceramic armor for soldiers as well as durable ceramic thermal-barrier coatings that keep parts of jet engines cool despite tremendous surrounding temperatures.
In the March issue of Nano Letters, published by the American Chemical Society, Carter has co-written a paper with Emily Jarvis, a former student who is now a research scientist at the National Institute of Standards and Technology. The paper outlines their research into the “fatigue” of ceramics. While fatigue — the tendency of a material to break under repeated stress — is well-studied in metals, less attention has been paid to a corollary phenomenon in ceramics.
In this paper, based on research funded by the Air Force Office of Scientific Research, Carter and Jarvis explore how ceramics fatigue takes place at the microscopic, rather than the macroscopic, level. This atomic-scale fatigue poses a significant challenge to designing thermal barrier coatings that withstand the cycling of extreme temperatures in a jet engine while continuing to adhere to the engine parts as they are supposed to.
The thermal-coating research highlights one hallmark of Carter’s approach, which is to focus not so much on how materials work but, rather, on how they fail. “Our philosophical approach to materials design is: Let’s first understand how materials fail and then turn that on its head,” she said. Knowing what causes the failure, Carter said, helps guide her intuition as she figures out how to build a material that will not fail.
While Carter’s work may seem very theoretical, the kind of research she is doing has broad applicability to real technological problems. Her research uncovering the atom-by-atom culprits responsible for corrosion of metals — a multibillion dollar per year expense — could help design corrosion-resistant cars, ships and airplanes. Her numerical simulations of combustion may help optimize clean-burning and efficient alternative fuels for cars.
Carter came to Princeton in 2004 from the University of California-Los Angeles, where she was a professor of chemistry. Given her background in chemistry (she earned her Ph.D. in chemistry from the California Institute of Technology in 1987), it may seem surprising to other physical chemists that Carter’s lab is based in the Department of Mechanical and Aerospace Engineering. But it makes sense to Carter.
“The work that I do — developing quantum mechanics-based software for predictive materials modeling — was recognized by MAE as having the potential of great impact for solving aerospace and mechanical engineering problems,” she said.
Moreover, Carter’s work is so interdisciplinary it could sensibly live in a number of different departments.
“Emily’s research lies at the intersection of chemistry, material science, applied physics and applied mathematics,” Professor E points out. The size of Carter’s lab — which is supported by seven different grants and includes 10 graduate students and three postdoctoral researchers — also reflects the broad reach and impact of her work.
Jarvis, who was a graduate student of Carter’s at UCLA, said she appreciated the cross-pollination resulting from this interdisciplinary approach. “We had people from different fields in our group meetings — physicists, chemists, mathematicians,” said Jarvis. “Something that may have been obvious to someone with a given background was not so obvious to someone with a different background. It was invaluable.”
In addition to the breadth of work in the engineering school, Carter said she was drawn to the larger Princeton community because of its commitment to scholarship and the work going on in the Princeton Institute for the Science and Technology of Materials and the Program in Applied and Computational Mathematics.
“Princeton was very attractive because of all the people involved with materials theory,” Carter said. “The work that I do is synergistic with the work going on here in materials and applied mathematics.”
Although much of what she does today relates to applied mathematics — the branch of mathematics that tackles specific problems in science, engineering and society — Carter said she never heard of applied math as an undergraduate at the University of California-Berkeley.
“When I got to upper division math it was too abstract for me and I lost interest,” she recalled. So she returned to chemistry, which her father, a physicist, had encouraged her to take in high school. Soon she was captivated. “I love chemistry. It’s complex and quantitative but it’s not abstract or reductionist in the way that pure mathematics often is. You’re not always in the ‘picture-a-spherical-cow’ mode,” Carter said, referring to the frequent mathematical technique of reducing messy physical reality to simpler models.
Since those early days as a chemistry major, Carter has been passionate about spreading her enthusiasm for science. She takes an active role in encouraging girls who are interested in science by participating in numerous outreach programs over the course of her career. She recently accompanied a group of Princeton students, other faculty and the dean of engineering on a trip to New York City to talk with girls about careers in science and engineering, and she has spoken to high school groups in New Jersey.
“I was a girl nerd, I guess,” mused Carter. She was a member of the chess club and a study hound. But she also did a lot of community theater and even thought seriously about pursuing a career as an actress.
Despite his own career choice, Carter’s father never pressured her to go into the sciences, she said.
“I try to emulate that approach with my own child,” she said of her 11-year-old son. “I tell him and my students, ‘You just have to find something you love doing that contributes to the world. You can’t just be taking up space on the planet. But this is hard work. You should only do it if you really love doing it.’”
Carter also has found that she serves as a role model without meaning to.
Last year friends and colleagues e-mailed her a feature in the Boston Globe on Debrah Rud, a graduate student in biology at Harvard. Rud, who was an undergraduate at UCLA recalled how she signed up for a chemistry class taught by “E.A. Carter,” and was surprised when a “stylish” woman professor appeared on the first day. “I could identify with her, as opposed to the scientist in the lab coat with goggles and exploding beakers,” Rud told the Globe.
Carter said she had not been in touch with Rud and had no idea the Globe article would be appearing. “It’s so nice to see you had a positive effect on someone without realizing it,” Carter said.
Rud told the Globe she was doubly impressed when she found out Carter was a mother, and indeed Carter has been an outspoken advocate of reforms that would make academic science and engineering more hospitable not just to women but to women who are mothers.
Those who work closely with her say that Carter puts her ideals into practice in her daily life. “She is committed to her family and works hard to balance being a much-in-demand scientist, researcher, scholar and teacher and still raise a family,” said Laurie Hebditch, an administrative assistant in MAE. “She is keenly aware of other women in that same position.”
Though she is a couple of decades removed from her own college career, Carter is still very in tune with the profound effect a professor’s interest and encouragement can have on a student. As a first-term freshman at Berkeley, she was one of only two students out of 350 in a math class on differential equations who got an A+ in the course. She still warmly recalls how the professor invited her and the other student to tea as a reward for their efforts.
Carter says she is especially keen that her lab be a nurturing, career-enhancing environment. “My goal is to get my grad students and postdocs to become full-fledged independent scientists,” Carter said. “When a student is able to define a research project of his or her own, carry it out and analyze it properly, present a coherent talk on it and write it up clearly, then I know that the student is ready to leave the nest and fly.”
Jarvis, Carter’s co-author and erstwhile grad student, praised her former professor for giving her graduate students autonomy and responsibility and for holding them to high expectations.
“She makes sure they have the opportunity to attend the right conferences and write small grants of their own and not be stuck in a niche of research while she gets to do all the big thinking,” Jarvis said. “It’s something you don’t often find with professors who are as established as she is. She is very good at making sure her graduate students and postdocs realize their dreams.”