Atomic, electronic, and transport properties of quantum point contacts on graphite surface

Abstract

In this thesis, the variation of conductance through a contact formed by a hard STM tip pressing on a graphite substrate is investigated. Our study involves the molecular dynamics simulations to reveal the evolution of the atomic structure during the growth of the contact, and ab initio electronic structure calculations of graphite that is under expansive and compressive strain along the [0001] axis. Combining the results obtained from these calculations, we propose a mechanism to explain the peculiar variation of the conductance. Owing to the layered structure of graphite, the variation of conductance exhibits dramatic differences from that of normal metals. It is predicted that in graphite, the conductance first increases, and then drops to a lower value with the puncture of the atomic plane. This phenomenon repeats quasi-periodically as the tip continues to press on the surface.