“Energy Transfer in Nanoscale Energy Conversion Materials”
Dr. Xianfan Xu, Purdue University
The demand for energy is projected to more than double in coming decades. The challenge in using solar energy and recovering waste heat by thermoelectric energy conversion is to drastically improve efficiency and reduce cost. Recently there is renewed interest in photovoltaic and thermoelectric materials research due to the discovery of much-improved energy conversion efficiency in nanomaterials such as quantum dots, nanowires and superlattices. In our laboratory we carry out energy transfer studies in nanoscale energy conversion materials. From a microscopic viewpoint, energy conversion efficiency is determined by interactions among basic energy carriers (photons, electrons, excitons and phonons), often occurring at a time scale of femtoseconds to picoseconds. We develop advanced optical measurement techniques with high temporal (~ fs) and high spatial (~ nm) resolutions. These techniques are used to investigate interaction dynamics among the energy carriers, with the aim of discovering new energy coupling channels to facilitate photovoltaic energy conversion and minimize waste heat generation. In nanomaterials it is possible that quantized phonon vibration states lead to a decrease in interactions between electrons and phonons, therefore increasing the probability for harvesting energy from electrons before it is converted to waste heat. We also probe phonon vibrations of THz (1012 Hz) frequencies in thermoelectric materials to understand the scattering mechanisms of heat carriers (phonons). In nanoscale thermoelectric materials, interfaces, boundaries and even impurities are purposely engineered to drastically increase phonon scattering, which reduces thermal conductivity and increases thermoelectric efficiency. We work with several materials groups at Purdue and elsewhere on nanomaterials research. This talk will also give a brief discussion on other ongoing projects, including nano-optics and its applications in large-scale nano-manufacturing and ultrahigh density data storage.
Xianfan Xu is a professor of mechanical engineering at Purdue with a courtesy appointment in electrical and computer engineering. He obtained his bachelor’s degree in engineering thermophysics from the University of Science and Technology of China (1989) and his M.S. (1991) and Ph.D. (1994) in mechanical engineering from UC Berkeley. His research is focused on ultrafast and nanoscale optics and their applications in energy transfer/conversion studies and nanomaterials manufacturing. He is a recipient of a National Science Foundation Faculty CAREER Award and an Office of Naval Research Young Investigator Award. He was elected a fellow of the American Society of Mechanical Engineers in 2006 and a fellow of SPIE in 2009.