ABSTRACT: Recently discovered or synthesized 2-dimensional materials promise new applications in electronics, photonics, and even thermal management. In this talk we will discuss studies on emerging 2D materials including van der Waals layered black phosphorous, Se, and Te single element 2D materials and topological insulators. Detailed discussions will be given on the recent work on topological insulators. Topological insulators (TIs) have gained immense interest due to their novel fundamental properties such as suppression of electron backscattering, spin-momentum locking, and spin-split Dirac cones with possible applications in spintronics and quantum computing. These properties appear only on the surface of these materials, with the bulk behaving as usual semiconductor. Hence it is important to study the surface state energy landscape. We discovered exceptionally large, room temperature in-plane thermal (and electrical) transport in Bi2Te2Se TI thin films caused by the spin-momentum locked surface state electrons. Correspondingly, the Lorenz number of these films are found to be exceptionally large, more than ten times of the Sommerfeld value. Computations were carried out to analyze the charge and thermal transport of the surface states. Moreover, we utilize infrared femtosecond pump-probe laser spectroscopy to isolate the surface state dynamics and study their contributions to transport. Detailed electron-phonon coupling in the Dirac cone, recombination time after excitation of charge and spin, and Dirac cone-bulk state coupling are studied to provide a fundamental understanding of the enhanced transport processes.
BIOSKETCH: Prof. Xianfan Xu is James J. and Carol L. Shuttleworth Professor of Mechanical Engineering at Purdue University. He obtained his B.S. degree from the University of Science and Technology of China in 1989, and M.S. and Ph.D. degrees in Mechanical Engineering in 1991 and 1994, both from the University of California, Berkeley. His research interests include developing novel laser processing techniques for laser micro- and nanoscale manufacturing, fundamental studies of laser-matter interactions, thermal transport in nanoscale materials, and near field nano-optics and its applications. He has given over 100 invited talks in academic institutes, technical conferences, government laboratories, and industry, and has published over 180 papers in archival journals. He is a fellow of the American Society of Mechanical Engineers (ASME), SPIE, and the Optical Society of America (OSA). He received the ASME Heat Transfer Memorial Award in 2014.
Date(s) - Jun 05, 2018
11:00 am - 12:00 pm