Woodruff School of Mechanical Engineering
Faculty Candidate Seminar
Thermal and Thermoelectric Transport in Low-Dimensional Carbon and Topological Insulator Materials
Dr. Michael Pettes
University of Texas at Austin
Thursday, February 7, 2013 at 11:00:00 AM
MRDC Building, Room 4211
Dr. Zhuomin Zhang
Nearly 60 % of the energy generated globally is lost as unused heat. With well publicized requirements for a sustainable path to the growth in global demand for energy, the development of fundamental knowledge of transport phenomena in materials for the management, conversion, and storage of thermal energy is needed. The engineering of materials at the nanoscale to take advantage of non-traditionally paired properties, such as light weight and high conductivity, can offer radical solutions to current energy management limitations in addition to the transformation of numerous technological fields. In this talk I will discuss our recent experimental investigations of two material systems near the extremes of the thermal conductivity spectrum, sp2-bonded carbons for thermal management and energy storage and topologically insulating bismuth chalcogenides for thermal to electrical energy conversion. Thermal transport in carbon nanotubes (CNTs) and graphene has been an active area of investigation for more than a decade due to interest in fundamental low-dimensional phonon transport phenomena and their potential for thermal management and thermal energy storage applications. Among several factors including agglomeration, structural deformation, defects, and support or medium interaction, one critical issue that has prevented these CNT- and graphene-based networks to reach their full potential is the thermal contact resistance at their interface with both the medium and adjacent nanostructures. I will discuss our recent experiments demonstrating how these problems can be overcome by macroscopic ultra-thin graphite-based foam structures because internal contact thermal resistance may be greatly reduced or eliminated in these continuous, three-dimensional architectures of covalently-bonded building blocks. Secondly, observation of topologically protected metallic electronic energy states on the surface of semiconducting bismuth telluride bulk crystals has given hope that this material system, already the standard for near room temperature thermoelectric applications, will allow for significant increases in thermoelectric figure of merit as it is scaled to the two dimensional limit. In these materials, surface states can show orders of magnitude increase in electrical conductivity owing to unallowed backscattering of electrons. Additionally, the much stronger reduction of the thermal conductivity than the electrical conductivity in nearly two-dimensional Bi2Te3 single crystals when compared to the bulk is very promising for thermoelectric applications, an observation which could be attributed to two metallic surfaces that have not yet hybridized to form the band gap suggested in theoretical reports.
Michael Thompson Pettes attended Duke University in Durham, North Carolina, receiving a Bachelor of Science in Mechanical Engineering in May, 2001. He was commissioned as a second lieutenant in the United States Marine Corps and served as an infantry officer with the 1st Marine Division. In June 2005, he joined the University of Texas at Austinís Nano Materials and Thermo-Fluids Lab, under the guidance of Professor Li Shi. Michael is the recipient of fellowships from the National Science Foundation Graduate Research Fellowship Program, the Donald D. and Sybil B. Harrington Foundation, and the University of Texas at Austin, where he earned a Ph.D. in May 2011 and is conducting postdoctoral research.
Refreshments will be served.