Quantum transport in nanodevices

Abstract

First-principles simulations of quantum transport in nano-devices are presented in this dissertation. First, the extension of the complex absorbing potential quantum transport framework to the general case of N electrodes is developed. This framework is used with density functional theory to investigate, grids of nanowires, graphene cross junctions and a six terminal carbon nanotube device. Quantum interference between possible paths for electrons was found to have a pronounced effect in multi-terminal systems. The charge transport properties of kinked nanowires, kinked graphene nanoribbons, elongated gold nanowires and a molecular junction with gold electrodes are analyzed with density functional and transport calculations. The simulations show the importance of atomic features and highlight the care needed to create functional devices, particularly in the case of kinked structures. Finally, interfaces between graphene and carbon nanotubes and graphene and MoS2 are studied. In the case of graphene-carbon nanotube junctions the p-type Schottky barrier was found to be low compared to the barrier in standard Palladium-nanotube junctions. Graphene was found to be a favorable electrode material for the injection of electrons into MoS2 due to the low potential barrier and presence of delocalized states near the Fermi energy. In addition to the analysis of these physical systems, a number of advanced computational algorithms were developed.