Physical Chemistry Seminar: Dr. Scott Cushing, UC Berkeley (Host: Tom Markland)
"The Electronic-Structural Barrier to Higher Photoconversion Efficiency in Semiconductors"
About the Seminar
Converting light to power, whether by photovoltaics or photocatalysis, is primarily associated with electronic dynamics. Higher device efficiencies are sought by absorbing more light or prolonging the lifetimes of the photoexcited carriers. In this talk, I will discuss the role that structural dynamics play in limiting the photoconversion efficiency of semiconductors. These findings are enabled by the development of transient extreme ultraviolet (XUV) spectroscopy. Similar to a synchrotron, transient XUV spectroscopy uses core level absorption spectra to measure electronic occupations and structural distortions. Unlike a synchrotron, a pulsed laser is used to create the low energy x-rays, allowing femtosecond temporal resolution of core level dynamics in a table-top package. I will first discuss how local structural distortions, known as polarons, trap photoexcited carriers on a femtosecond time scale in α-Fe2O3, limiting its photoconversion efficiency to one-third of its electronically predicted maximum. Second, I will discuss how electron scattering with lattice vibrations (phonons) can be controlled in Si nanostructures to prevent the loss of optically-absorbed energy to heat. Finally, I will demonstrate the element-specific measurement of photoexcited charge transfer, carrier relaxation, and heat flow in a metal-insulator-semiconductor junction (Ni-TiO2-Si) such as relevant to photoelectrochemical water splitting.
About the Speaker
Scott Cushing received his B.S. and Ph.D. from West Virginia University where he studied materials science under Prof. Nick Wu and ultrafast optics under Prof. Alan Bristow. He is currently a DOE EERE Postdoctoral Fellow at the University of California, Berkeley working under Prof. Stephen Leone on ultrafast x-ray spectroscopy. Scott’s research involves studying next-generation solar energy conversion technologies through photonics and materials approaches, as well as the development of advanced characterization techniques. For his work, Scott has been awarded a Goldwater Scholarship, the top graduate student awards for the ECS and SPIE societies, and the Council of Graduate Schools’ top thesis award.