Title:

ENERGY TRANSFER IN NANOSCALE ENERGY CONVERSION MATERIALS

Speaker:

Prof. Xianfan Xu

Affiliation:

Purdue University

When:

Thursday, September 30, 2010 at 3:00:00 PM   Add to Calendar

Where:

Love Building, Room 299

Host:

Zhuomin Zhang
zhuomin.zhang@me.gatech.edu
4043854225

Abstract

The demand for energy is projected to more than double in the next couple of decades. The challenge in utilizing solar energy and recovering waste heat by thermoelectric energy conversion is to drastically improve the energy conversion efficiency and reduce cost. Recently, there are renewed interests 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 investigate the fundamentals of energy transfer 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 (10-15 s) to picoseconds (10-12 s). 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 heat. We also probe phonon vibrations of THz (1012 Hz) frequencies in thermoelectric materials, and to understand scattering mechanisms of heat carriers (phonons). In nanoscale thermoelectric materials, interfaces, boundaries, and impurities are engineered to increase phonon scattering, which reduces thermal conductivity and increases thermoelectric efficiency. We work with several materials groups in and outside Purdue on nanomaterials research. This talk will also give a brief discussion on other on-going research projects, including nano-optics and its applications in large-scale nano-manufacturing, enhancing photovoltaic energy conversion, and ultrahigh density data storage.

Biography

Xianfan Xu is a Professor of Mechanical Engineering at Purdue University with a courtesy appointment in Electrical and Computer Engineering. He obtained his B.Eng. degree in Engineering Thermophysics from the University of Science and Technology of China (1989), and M.S. (1991) and Ph.D. (1994) degrees in Mechanical Engineering from the University of California, Berkeley. His current research is focused on ultrafast and nanoscale optics and their applications in energy transfer/conversion studies and nano-materials manufacturing. He is the recipient of the National Science Foundation Faculty CAREER Award and the Office of Naval Research Young Investigator Award, and is the recipient of Purdue University GM Faculty Fellowship, B.F.S. Schaefer Young Faculty Award, and Discovery in Mechanical Engineering Award. He was elected Fellow of the American Society of Mechanical Engineers in 2006 and Fellow of SPIE in 2009.