Katherine Harmon, a fellow at the U.S. Department of Energy’s (DOE) Argonne National Laboratory, studies the atomic and nanoscale structure of silicon carbide, a material used in car brakes, light-emitting diodes, steel production, semiconductor electronic devices and in nascent quantum information science applications. While pursuing her Ph.D. in applied physics at Northwestern University, Harmon had an opportunity to work with Argonne’s X-ray tools. The powerful resources at Argonne and ability to shape her own research program inspired her to apply for the Maria Goeppert Mayer Fellowship.

The Maria Goeppert Mayer Fellowship is an international award given to outstanding doctoral scientists and engineers to help them develop their careers in Argonne’s high-impact research environment. The fellowship honors Maria Goeppert Mayer, a theoretical physicist who earned the Nobel Prize in Physics in 1963 for her work at Argonne proposing a mathematical model for the structure of nuclear shells of the atomic nucleus. The fellowship provides early-career scientists the opportunity to pursue their own research interests, with the support of a sponsor and up to three years of funding. Fellows may also be offered long-term positions at Argonne after completing their fellowships. Harmon began her Maria Goeppert Mayer fellowship in February 2021. Here, she describes her research program and how the fellowship has contributed to her career development.

“Our X-ray-compatible silicon carbide synthesis chamber is the first of its kind, and people have shown a lot of excitement about what we’ll be able to do with it.” — Katherine Harmon, Maria Goeppert Mayer fellow

Q: Tell us about your research at Argonne

A. I’m a materials scientist who uses X-ray beams to study the atomic to nanoscale structure of materials. I use the Advanced Photon Source (APS) at Argonne, a DOE Office of Science user facility, to characterize the synthesis of silicon carbide, which is a material used in high power electronics and quantum information science. Silicon carbide can have point defects, such as a missing atom or pair of atoms in the crystal structure, that are also called color centers and can be quite useful. The material is also prone to structural defects, such as 2D planar defects that can occur in crystalline materials, that influence the color center properties.

In general, defects have traditionally been thought of as negative because they interfere with the properties of materials and devices. We’re turning that notion on its head by asking how to exploit those defects instead of trying to just get rid of them. We’ve learned over the past couple decades that certain color centers can be useful for quantum applications, and the question then is how we can design the material platform better to optimize color center performance.

My research at Argonne uses X-ray beams to study how some of the structural defects enter silicon carbide materials during synthesis and how we might be able to use them to our advantage to control color centers. I’ve spent most of my time here designing and building a growth chamber to synthesize silicon carbide and characterize this process using X-ray beams in real time.

Q. What are some broader impacts of your work? 

A. Because some point defects emit light and are incredibly sensitive to their surrounding environments, they could be used to make powerful quantum sensors that detect small changes in temperature, chemical environment or magnetic fields. Silicon carbide is also very robust to harsh environments, so we might be able to use this material to create sensors that operate in environments with extreme temperatures or high radiation. There’s been a lot of research over the last couple decades to study different kinds of point defects, but there’s still a lot unknown about how defects are created, and we’ve only just scratched the surface as to how we can control them at the level of precision needed in technological applications. We’re really just at the ground floor of discovering what we can actually do with these defects.

Q. What inspired you to apply for this fellowship? 

A. I wanted to pursue my own ideas and continue using the APS after finishing my PhD. Before applying to the fellowship, I reached out to my current supervisor because I liked the research that he was doing using coherent diffraction X-ray tools, which I think will revolutionize material science. X-ray beams allow us to understand atomic to nanoscale structures, and as we always say in materials science, structure drives functionality. The fellowship is also named after a famous female scientist who won a Nobel Prize. Getting this award and following in her footsteps is very inspiring.

Q. How did the fellowship contribute to your career growth? 

A. The funding has been pivotal for me developing an independent research program. The silicon carbide growth chamber was partially built by the time I started my fellowship, but getting it operational and optimized for this new characterization capability took a lot of time and money. I’ve been able to start going to more conferences this year, where I can share my research with the community. Our X-ray-compatible silicon carbide synthesis chamber is the first of its kind, and people have shown a lot of excitement about what we’ll be able to do with it. The network aspect of the fellowship is also really valuable. I’ve learned about really cool science being done by the other named fellows at Argonne and their research groups, which gives me ideas for collaboration. It would be harder to form those connections if I wasn’t part of the fellowship.