Characterization of scanning gate technique and transport in nanostructured graphene
13 June 2017
Campus Groenenborger, U0.24 - Groenenborgerlaan 171 - 2020 Antwerpen (route: UAntwerpen, Campus Groenenborger
Organization / co-organization:
Department of Physics
PhD defence Marko Petrovic - Faculty of Science, Department of Physics
This thesis deals with electron transport in a two-dimensional electron gas formed in semiconductor heterostructures and in graphene. One of the main goals of this work is to simulate and understand what is measured in scanning gate microscopy (SGM) experiments. These experiments present a novel way to probe electron transport at the nanoscale. A typical SGM experiment uses a charged tip of the atomic force microscope (AFM) to perturb electron motion. The measured tip-dependent conductance is then used to characterize electron transport.
We investigate and interpret previous experiments theoretically, by using the Landauer-Büttiker approach to calculate electron conductances. We obtain electron transmissions from two distinct numerical methods: the wave packet propagation method, and the wave function method (as implemented in the KWANT software package).
Transport characteristics of several nanosized devices, with different geometries, are studied with these two methods. In a classical 2D electron gas, we focus on scanning gate microscopy of small Aharonov-Bohm rings, while in graphene, we investigate microscopy of electron focusing devices. Beside scanning gate microscopy, we are also interested in general graphene transport properties, particularly on the influence of vacancy disorder and edge potentials.
We show that in quantum rings, the SGM tip is imaging interferences caused by electron backscattering, while in graphene (for sufficiently large systems) the tip is blocking the current and imaging classical electron trajectories. Regarding the effects of edge potentials and vacancy disorder, edge potentials can lead to electron guiding in graphene, while vacancy disorder induces new states in the relativistic Landau spectrum.