As researchers seek to make computers and electronic devices more efficient, they are looking beyond shrinking components to controlling what happens inside materials at the smallest scales.
Sandhya Susarla, an assistant professor of materials science and engineering in the School for Engineering of Matter, Transport and Energy, part of the Ira A. Fulton Schools of Engineering at Arizona State University, is working to provide scientists with a clearer view of that behavior and to ultimately learn how to control it.
Susarla has received a National Science Foundation Faculty Early Career Development Program (CAREER) Award to study how the structure of two-dimensional quantum materials influences excitons. The CAREER Award is one of the most prestigious honors for early-career faculty awarded by the NSF.
Excitons form when an electron and a positively charged “hole” become bound together within a material. Their behavior can be highly sensitive to their surroundings, including features such as strain and defects in the material’s atomic structure.
Because excitons influence how materials absorb and emit light, understanding and controlling their behavior could support technologies ranging from optoelectronics and sensing to low-power computing.
Many techniques used to characterize excitons examine materials at relatively large scales. Susarla says those measurements can miss nanoscale features such as defects, bends and strain in a material’s atomic structure, even though those features can dramatically change how excitons behave.
“The big problem that we are trying to solve with this project is about understanding the nanoscale landscape of these electron-hole pairs,” Susarla says.
Seeing what happens at smaller scales
Susarla was drawn to ASU in part by the advanced electron microscopy available at the Eyring Materials Center. Those capabilities are central to her project, “Real-Space Topological Control of Excitons in Twisted 2D Semiconductors,” which will examine excitons at the nanoscale and determine how variations in atomic structure affect where they become confined and how they behave.
Her team will focus on twisted two-dimensional semiconductors, materials composed of extremely thin layers positioned at slight angles to one another. Those arrangements can create intricate patterns that influence the material’s electronic properties.
Susarla is particularly interested in how strain and electric fields alter those patterns and, in turn, affect where excitons become confined and how they behave.
Her team will use electron energy loss spectroscopy in an electron microscope to map excitonic behavior at much smaller scales. One part of the project will examine the effects of strain, and another will explore how applying an electrical bias can change the material and its excitonic behavior.
“Electrical biasing of excitons is an upcoming concept,” Susarla says. “Not many people are working on it, and we are quite excited to work on those areas.”
The goal is to move beyond observing unusual properties in quantum materials toward understanding how to deliberately manipulate them.
That understanding could eventually help researchers design materials for technologies that perform computing operations using less energy.
Reaching that point will require more than demonstrating that new materials can work, however.
Reliability is one of the biggest remaining challenges, Susarla says. Materials being considered for low-power computing must perform consistently over long periods and through repeated cycles before they can compete with conventional computing technologies.
Opening pathways into materials science
Over its five-year term, the CAREER Award will fund specialized sample materials, time on advanced electron microscopes and research support for a doctoral student. Susarla sees that continuity as part of her responsibility as an educator, giving students in her group the resources and time they need to develop as researchers.
Anthony M. Waas, a professor and director of the School for Engineering of Matter, Transport and Energy, says Susarla’s CAREER project advances both the school’s research and its student training.
“Sandhya’s work matters because advanced microscopy is essential for connecting a material’s atomic-scale structure and chemistry to its magnetic, electronic and excitonic properties,” Waas says.
The project will also give her students hands-on experience with advanced microscopy, nanoscale spectroscopy and structure-property analysis, among other skills.
“These are highly transferable skills needed in semiconductor manufacturing, quantum materials, microelectronics and national laboratories,” Waas says.
Exposure to the possibilities of materials science starts even earlier. When Susarla talks to middle and high school students, she doesn’t begin with excitons or topology. Instead, she asks them to imagine something much more familiar: What if a computer that currently runs for eight hours on a charge could someday run for 48?
“This would lead to technologies that would enable low-power computing as one of the applications,” Susarla says. “Your computers may become more efficient.”
That connection is important to Susarla because she believes materials science has a visibility problem among younger students. They hear about artificial intelligence and quantum computing, she says, but may not realize the role the field plays in the hardware behind those technologies.
“The heart of all of these technologies is still materials science,” Susarla says.
The CAREER Award project enables Susarla to address that visibility gap through two outreach programs designed to introduce younger students to materials science.
Through Materials Your Mind, Susarla will use visual arts to introduce middle school students to materials and quantum concepts, while Let’s Code Materials will use coding-based projects to engage high school students. She particularly wants to reach middle schoolers who may not yet have formed strong ideas about what they want to study in college.
The goal isn’t simply to teach young students the definitions of concepts such as topology or excitons. Susarla wants them to recognize that materials science offers a way to work on some of the technologies already capturing their imaginations.
Extending the exciton map
By mapping where excitons become confined and how they respond to strain and electric fields, Susarla hopes to establish a foundation other scientists can build on.
The techniques developed through the CAREER project could eventually be applied to more complex two-dimensional structures, including systems that combine semiconducting and magnetic materials.
Susarla is cautious about predicting exactly where the rapidly evolving field will be in five years. But she hopes researchers beyond her laboratory will be able to reproduce the work and extend the mapping approach to questions beyond the original project.
