Computational study of geometry induced effect on the phonon transport in nanostructure

Abstract

Technological advancement have made manufacturing of various nanostructures possible. Thermal transport in such nanostructures is fundamentally different from macroscale. Initial studies have indicated that thermal properties of these nanostructures also depends on its geometry. Hence, it is possible to tailor nanostructure geometry to achieve targeted thermal properties. In the present work, finite volume method based code has been developed to solve the gray phonon Boltzmann transport equation in the relaxation time approximation. This code is used to study thermal transport in (a) constricted thin films and (b) constricted nanowires for a wide range of constriction ratio. We show in this thesis that by varying the degree of constriction thermal conductivity of thin films and nanowires can be altered significantly. Thin films and nanowires are found to respond differently to constriction. Secondly, Phonon transport through the constriction formed by probe and substrate is also studied. It is observed that thermal spreading in substrate increases with increase in degree of constriction. The magnitudes of total, substrate and constricted tip-interface resistance are established for range of constriction ratio. The combined thermal resistance of tip and interface (as predicted by BTE) is found to be much higher than the total resistance predicted by fourier law. Also, interface is found to offer significantly higher resistance to phonons in axisymmetric model as compared to the 2-D model.