Degree Type

Dissertation

Date of Award

2013

Degree Name

Doctor of Philosophy

Department

Mechanical Engineering

First Advisor

Xinwei Wang

Abstract

Graphene is a two-dimensional (2D) material that exhibits exceptional electric and optical properties. The high electron mobility and thermal conductivity of graphene are of great interest for interconnects, electronic devices and radio frequency devices. In spite of the extensive experimental and theoretical studies on single layer graphene (SLG), its thermal properties have not yet been fully addressed and vast work need to be done to reveal the phonon transport mechanism within this micro/nanoscale material.

A transient molecular dynamics technique is developed to characterize the thermophysical properties of two-dimensional graphene nanoribbons (GNRs). By directly tracking the thermal relaxation history of GNR that is heated by a thermal impulse, we are able to determine its thermal diffusivity fast and accurate. In the right-angle bended GNR system, three peculiar features about the phonon energy transport have been observed for the first time. An energy inversion phenomenon has been observed during the transient thermal transport in GNR system. Phonon energy coupling among different phonon modes are investigated and it is found that both dynamic and static heat sources can evoke the energy inversion in GNR. The unique thermal properties of GNR enable it to support a bi-directional heat transfer in the system. And when the bi-directional heat conduction reaches steady state, a single thermal conductivity cannot be used to reflect the relation between the heat flux and the temperature gradient. The calculated thermal conductivities are dependent on the net heat fluxes and the app of graphene are calculated at positive, negative, zero and infinite values, depending on the proportions of each phonon mode energy added/subtracted to/from the heating/cooling areas. The dynamic response of graphene to a thermal impulse is investigated and the interfacial thermal resistance between graphene and Si is evaluated. A transient pump-probe method is designed for interfacial thermal resistance characterization.

Copyright Owner

Jingchao Zhang

Language

en

File Format

application/pdf

File Size

154 pages

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