CBET Award Achievements
Notable Accomplishments from CBET Awards

CAREER: Thermal Transport and Thermoelectric Measurements of Nanotransistors, Nanowires, and Superlattices

Li Shi - University of Texas at Austin

Background: With increasing miniaturization in microelectronics, one of the challenges to maintaining device performance is the management of excess heat. A researcher at the University of Texas at Austin has developed unique experimental tools to identify potentially promising new materials for addressing this problem. His findings may have broad applications in electronics and energy conversion.

Results: The researcher developed a device to characterize the crystal structure and chemical composition of nanowires and single wall carbon nanotubes. He also used a specialized microscope that he had developed previously under the award to characterize how nanowires respond to different temperatures and their ability to conduct heat and be thermoelectic. Thermoelectric materials pump heat across a temperature jump when an electric current passes through them and generate electric currents when heat is applied. These properties are important in a wide range of applications from cooling of high power chips, power conversion, and chemical sensing.

He identified one type of bismuth telluride nanowire with high thermoelectric properties that may provide the basis for energy-efficient on-chip spot cooling of electronic devices. He also found single-wall carbon nanotubes to have high thermal conductivity--higher than diamonds, which are one of the best conductors. This suggests that single-wall carbon nanotubes might be used in thermal interface materials in electronic packaging to enhance the efficiency of microchips in a variety of applications.

A powerful new design of a device for nanowire characterization was developed in this project. The new device can be used to characterize the crystal structure and the chemical composition of the nanowire together with the thermal and thermoelectric properties so as to establish the structure-property relationship of nanowire materials. The new device for nanowire characterization and the Scanning Thermoelectric Microscope that was developed earlier as a result of this award constitute a set of unique tools for thermal and thermoelectric characterization of nanomaterials for electronic and energy applications.

Li Shi Image 1
(a-b) A micro-device for characterization of structure-thermal/thermoelectric
property relationships of nanotubes and nanowires

Credit:  Li Shi, University of Texas at Austin

Li Shi Image 2
(c) The measurement results of the thermal conductance of a single-wall carbon nanotube (SWCNT)
is very close to the calculated ballistic thermal conductance of a 1-nm-diameter SWCNT;
(d-e) Schematic showing two opposite phonon flows at different temperatures transported
ballistically in a SWCNT

Credit:  Li Shi, University of Texas at Austin

Broader Impacts: For the past year, one Hispanic-American graduate student and one female undergraduate student have been supported to participate in this research, and an experimental module based on a miniaturized thermoelectric cooler was demonstrated in the 'Introduce a Girl to Engineering Day'. For the past three years, two Ph.D. and five B.S. students supported in part by this award have graduated. One of the two graduated Ph.D. students is continuing post-doctoral study at Lawrence Berkeley National Lab, and the other has joined Applied Materials, Inc. One of the B.S. students graduated with highest honor, while three of the other four B.S. students are continuing graduate study at UT Austin and two of them have received M.S. degree under the P.I.?s supervision.

This work is notable because this work has resulted in a set of unique experimental methods for measuring thermal and thermoelectric properties of nanoelectronic devices and nanostructured materials, as well as the first measurement results of thermal conductance of single-wall carbon nanotubes, thermoelectric figure of merit of bismuth telluride nanowires, and local thermopower profile in p-n junctions and thin film superlattices.

This work involves multidisciplinary research. This work impacts the fields of thermal sciences, electronic devices, and nanomaterials.

Program Officer:   Patrick Phelan
NSF Award Number:   0239179
Award Title:   CAREER: Thermal Transport and Thermoelectric Measurements of Nanotransistors, Nanowires, and Superlattices
PI Names:   Li Shi
Institution Name:   University of Texas at Austin
Program Element:   1406

Top of Page

This Nugget was Updated on 30 July 2008.