Electronic Thermal Transport in Nanoscale Conductors

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0933454ShiThe Wiedemann-Franz (W-F) law describing thermal transport by electrons is a hallmark of success of the Sommerfeld theory. For electrons confined in one- or two-dimensional nanostructures, however, several intriguing phenomena can lead to the breakdown of the W-F law. These phenomena include strong correlation effects associated with increased electron-electron interaction, as well as electron localization. Intellectual Merit. This experimental study addresses a fundamental question regarding whether the Wiedemann-Franz Law is valid in low dimensional conductors. The scientific question being addressed is of a very fundamental nature, and one that will impact multiple disciplines. The experimental study examines electronic thermal transport in copper nanowires, quasi one-dimensional polyacetylene nanofibers, and two-dimensional graphene nanoribbons. The thermal conductivity, electrical conductivity, and Seebeck coefficient of these nanostructures are measured using nanofabricated suspended measurement devices at various temperatures. Chemical doping, electrical field effects, and the thermal Hall effect are employed to tune and determine the electronic thermal conductivity and isolate the lattice contribution. The validity of the W-F law is examined by analyzing the measured Lorenz number and its temperature dependence, and comparing the measurement results with the predictions of different transport theories. Broader Impacts. The nanostructures of interest are being considered for nanoelectronics, sensors, energy conversion, and thermal management applications, all of which will benefit from a better understanding of electronic thermal transport in these nanostructures. The research provides interdisciplinary education opportunities for graduate and undergraduate students. New example materials for a graduate and an undergraduate course in thermal science are being produced, as are new materials for three K-12 outreach activities designed to attract young girls to engineering professions, and to expose public school students and teachers in Texas to engineering principles.