EFRC Researchers in Focus

Tom Mason

In this video excerpt, Dr. Thomas O. Mason, a principal investigator in the Center for Inverse Design, explains the approach and benefits of this Energy Frontier Research Center (EFRC) for materials science research and for students and postdocs. Mason is a professor in Materials Science and Engineering at Northwestern University.

"One of the reasons as an experimentalist that I'm so excited about being involved with the Center for Inverse Design—as are the students and postdocs—is the opportunity to reverse the paradigm. In conventional materials science, we stumble on to new materials, and then we have the theorists tell us what the band structure is, and we've already developed the properties. But these may or may not be the optimal materials. In the Center for Inverse Design, we are working backwards, where we are targeting functionality and then together deciding on classes of materials to study. And then the theorists are leading us in a rapid search of phase space in order to identify in the opposite direction the materials that we indeed should characterize—we should synthesize first, but then characterize—and prove that indeed we have developed new materials. A second important value added—at least to the students involved with the Center for Inverse Design—is to be immersed in an environment that is so different, as opposed to conventional research where we stumble on to new materials and the theorists then tell us what the structures are. We are working in reverse, where the theorists are telling us—based upon band structure calculations targeting the properties we want to obtain—what materials, what doping levels. And so, for the students, this is an opportunity to be involved, to be immersed, in a completely new paradigm. The other thing that's value-added as far as the students are concerned, who will be future practitioners in the materials field, is to be involved with interdisciplinary research—not only crossing disciplines within institutions but across the institutions—our students and postdocs getting opportunity to visit other sites and actually see how things are done both theoretically and experimentally."

Alex Zunger

In this video excerpt, Dr. Alex Zunger, Chief Scientist for Theory in the Center for Inverse Design, explains the background in modern physics that has led to inverse design. Zunger is a professor at the University of Colorado, Boulder.

"Solid-state theory as we know it today was basically constructed by the earlier days of quantum mechanics by people such as in the 1940s and 50s, Enrico Fermi in the 1930s, 40s, and 50s, and Walter Kohn in the 1950s and 60s. That Landau-Fermi-Kohn basis of solid-state theory really involved to a large extent existence theorems and modern Hamiltonians that gave us the basic ideas but didn't tell us how to do and how to actually predict the properties. For instance, that theory could explain after-the-fact why a given thing happened but really couldn't tell you which material would have a given property. That was not possible. So after the Landau-Kohn era, there are three other eras. We're now in the third era that really makes this EFRC possible. The first era after Landau and Kohn was the era of actually putting some realism into the earlier theories of Landau and Kohn. This was the era of the late 1970s and early 1980s where we have developed pseudo-potentials, developed methods for calculating total energy, we developed those unknown functionals for theory and so on. The second era after Landau was really the era of the 1980s and 90s where all of the developments from the 1970s and 80s were actually applied. And they were applied to understand the physics of alloys, the physics of defects, high-pressure, and many other effects related to photovoltaics. The third era after Landau is the era we are now in. And that is the era where we now have the theoretical basis, we know how to compute those quantities, and now it is time for us to ask the reverse question, the inverse question, this is, given a particular property that you want, which system will have that property? And that is really how modern solid-state theory of the third era is going to be used in the future."

Alex Zunger

In this video, Dr. Alex Zunger, Chief Scientist for Theory in the Center for Inverse Design, explains the essential aspects of inverse design. Zunger is a professor at the University of Colorado, Boulder.

"The new inverse design is to first declare the functionality that you need. Let's say that you want a different absorber, different band gap, a given mobility, a given effective mass. And you know that is what you need for a given application. Why beat around the bush? Why not start by declaring what the functionality that you need is, and then inverting the problem and finding the material that has that functionality. And the way that we're going to do that is to take the developments of solid-state physics that were done in the first, second, and third eras after Landau and Kohn, combined them with biologically inspired methods like genetic algorithms, which permit you to search astronomic spaces of possibilities and for each of them to predict the physical properties. The net result is very much like Jeopardy. You first state the answer—for instance, this is the property I need—and then you find the question. The question is, which material has that property? This work is going to be done in very close collaboration with experimentalists. In fact, this is the critical aspect, the close interaction between theory and experiment. To some extent it's a little bit like ping-pong. The theorists are going to predict the material, and the experimentalists are going to keep us honest and test it to see if it's right. And then we're going to exchange ideas and see how we can converge on the right answer. Actually, we call it innovation without borders."

Doug Keszler

In this video excerpt, Dr. Doug Keszler, a principal investigator in the Center for Inverse Design, discusses Oregon State University's role in inverse design research. Keszler is a professor at Oregon State University.

"This is a very exciting opportunity to be part of the Center for inverse design. We have a great group of students pushing forward on the project. We've been primarily interested in using the inverse design concept to develop and study new types of solar absorber materials. Our specific emphasis is really on developing new materials that have very high absorption cross sections. We think that that can provide new opportunities to produce much higher efficiency thin film solar cells than currently exist. And we feel that this collaboration with theoreticians combining their efforts with the experimental approach is allowing us to identify and develop whole new families of solar absorbers. So we are very much looking forward to continuing the effort and actually being able to make significant breakthroughs in science and technology."

Mike Toney

In this video excerpt, Dr. Mike Toney, a principal investigator in the Center for Inverse Design, discusses the role of the SLAC National Accelerator Laboratory in inverse design research. Keszler is a scientist at SLAC and is joined in this discussion by SLAC post-doctoral researcher Dr. Johanna Bettinger and Stanford graduate students Yezhou Shi and Linda Lim.

"Hi, my name is Mike Toney. I'm here at the Stanford Synchrotron Radiation Light Source as part of the SLAC National Accelerator Lab. This is beamline 7-2 which we use for x-ray diffraction to look at so-called best-in-the-class materials that are made as part of the Energy Frontier Research Center, Center for Inverse Design. So here we basically test structures that are made by our collaborators. This is my postdoc Joanna Bettinger who will tell you more about what we do.

Hi, my name is Joanna Bettinger. I have been a postdoc here at SSRL/SLAC for a year, year and a half and this is really a great project to be working on, the Center for Inverse Design. Here at SSRL we do a lot of the experimental characterization and we work really closely with the other experimentalists who synthesize the samples. Also interestingly, we work with the theorists who predict what material properties these materials have and we're focusing on novel solar energy materials. Here, I'd like to introduce a grad student, Yezhou Shi who is a second-year grad student at Stanford.

My name is Yezhou Shi and I'm a second-year graduate student in the Material Science Department at Stanford. I joined this project last summer. What is most exciting and interesting to me about this project is that we have a chance to talk to our collaborators from various different institutions and every time I go to those meetings with our collaborators it's so great a learning opportunity. And in fact just two weeks ago one of our collaborators came here and we worked together at this particular beamline and I really enjoyed the experience. The next we move on to Linda, another graduate student.

Hi, my name is Linda. I'm a first-year graduate student at Stanford University. I joined this project two months ago and I'm really looking forward to working on this project—in the near future, working on this beamline and characterizing samples for solar applications.

Mike Toney: As part of the Center for Inverse Design, we work with the theorists who are able to guide us to predict what kind of structures we should look at to achieve favorable properties for solar energy, for power generation from the sun. This then allows us to bypass much of the materials science which has been Edisonian or trial and error. As a consequence we are able to more efficiently and effectively develop materials that can be used for solar energy.

Johanna Bettinger: In the Center for Inverse Design we work really closely with theorists, more closely than I've worked in any previous research projects I've done. And they really feed us information about what materials we should be looking at, they tell us if we want a certain band gap, a certain conductivity, these are materials to focus on. It really helps to narrow down the experimentalists' search for materials. So it's really an interesting and unique way to do novel research.

Mike Toney: This concept of inverse design has the potential to revolutionize materials science and largely bypass some of the more time-consuming processes that are part of developing new materials. So are all very excited to be able to participate in this groundbreaking Energy Frontier Research Center."

Yezhou Shi

In this video excerpt, Yezhou Shi, a second-year graduate student at Stanford University who is participating in the Center for Inverse Design, discusses a graduate student's perspective of the Center for Inverse Design and its research. He is working with Dr. Mike Toney at the SLAC National Accelerator Laboratory.

"…from my perspective. So when I was an undergrad, I worked in a wet chemistry lab where we need to do this trial and error. So we start with the material system, we work on a specific material system that doesn't work, try something else, change the composition, change some parameter, and try again until you get a very nice material. But this experience is very different. We start with the help of theories and a very targeted material. We test their properties and see if they match them well with the theories, then we know how to move on. And I think that's very exciting and saves a lot of effort and time for graduate students, at least from my perspective."