Thermal Transport Control in Nanocarbon Composites and Thin Films

Abstract

The continuous trend of integrated and smart devices requires materials to have superior mechanical/physical properties and potential to be used under extreme conditions. Nanostructured two-dimensional (2D) or thin-film materials have been widely used and tailored for nanoelectronics and energy-related applications such as thermal management of high-performance power electronics, thermoelectric and solar cells. To better understand and control the thermal transport within nanostructures, this dissertation is a collection of research projects about thermal engineering methods in nanocarbon composites and thin films.In this dissertation, for phonon transport in nanocarbons, composite films consisting of reduced graphene oxides (rGOs) and single-wall carbon nanotubes (SWCNTs) are experimentally studied for their in-plane thermal conductivities (k_∥) and reported with a rare amorphous solid-like thermal behavior, i.e. k_∥ following the trend of phonon specific heat. In understanding the phonon transport in polycrystalline thin-film materials, a simple analytical model is proposed to predict the in-plane thermal conductivity of columnar-grained thin films with independent treatments of phonon specularity at film boundaries and phonon transmissivity across grain boundaries. The experimental and theoretical works provide rich experience in the phonon engineering method to tailor the thermal transport in nanocarbon composites and thin films. Along another line, strain-dependent thermal studies have been carried out on Si thin films by a homemade vacuum-compatible holder with accurate strain control, providing important guidance to “elastic strain engineering” for thermal properties.