Thermal Transport in carbon nanostructures

Abstract

Graphene has recently become the focus of scientific community due to its unique electronic, phononic and optical properties, and it has great potential to become the mainstream semiconductor material in future devices. The Nobel Prize in Physics for 2010 is awarded to Andre Geim and Konstantin Novoselov ?for groundbreaking experiments regarding the two-dimensional material graphene?. This breakthrough has revealed plenty of new physics and potential applications of graphene. Prior to the discovery of graphene, carbon nanotubes are also found to have unusual properties, which are valuable for nanotechnology, electronics, optics and other fields of materials science and technology. In particular, owing to their extraordinary thermal and electrical properties, carbon nanotubes may find applications as building blocks being incorporated into future circuits. Moreover, graphene nanoribbons (GNR), which are patterned as thin strips of graphene (sometimes thought of as unrolled single-walled carbon nanotubes), are also known to display diverse transport properties compared to the infinite sheet, as GNR has electronic properties that range from metallic to semiconducting. This is due to the possibility of manipulating different ribbon width as well as the possibility of controlling via the atomic configuration at the edges in the GNRs. Furthermore, one obtains bilayer graphene nanoribbons by stacking monolayer graphene nanoribbons, which exhibits quite different properties in terms of energy gaps, electronic conductance, and edge states etc. In this case, the room for manipulation and as a result, obtain diverse properties in carbon derivatives has made carbon nanostructures based nanoelectronics a widely regarded alternative to silicon-based devices for the future.

On the other hand, as the size of devices shrinks to the nano-regime, heat dissipation becomes one of the key topics for nanotechnology. At the same time, phononic (thermal) devices have been brought forward theoretically, in which the phonon is used as information carrier. Both topics drive us to further study the thermal transport properties in nanostructures. On the first part of this thesis, it is proposed that classical molecular dynamics along with quantum thermal baths (quantum molecular dynamics) can be implemented to study the thermal transport properties of carbon derivatives. This method is capable of numerically predicting the quantum effect in heat conduction. Followed by the second part, the question of minimizing thermal conductivity in carbon derivatives is addressed to meet the requirement of maximizing electricity conversion efficiency in thermoelectric application. On the third part, interesting topics in thermal transport applications, like thermoelectric and thermal rectification effects are further studied in carbon nanostructures, which opens broader room for applications of carbon derivatives in energy management.