Local transport properties in graphene for electronic applications

Abstract

In view of possible applications in electrostatically tunable two-dimensional field-effect devices, this thesis is aimed at discussing electronic properties in substrate-supported graphene. Original methods based on various variants of Scanning Probe Microscopy techniques are utilized to analyze graphene exfoliated- and-deposited (DG) on SiO2 /Si, SiC(0001) and high-k dielectric substrate (Strontium Titanate) as well as graphene grown epitaxially (EG) on SiC(0001). Scanning Capacitance Spectroscopy is discussed as a probe to evaluate the electrostatic properties (quantum capacitance, local density of states) and transport properties (local electron mean free path) in graphene. Furthermore, based on this method two important issues adversely affecting room temperature charge transport in graphene are addressed to elucidate the role of: 1. Lattice defects in graphene introduced by ion irradiation and 2. Charged impurities and Surface Polar Phonon scattering at the graphene/substrate interface. Moreover, a comparative investigation of current transport across EG/SiC(0001) and DG/SiC(0001) interface by Scanning Current Spectroscopy and Torsion Resonance Conductive Atomic Force Microscopy is discussed to explain electrical properties of the so-called 'buffer layer' commonly observed at the interface of EG/SiC(0001). This study also clarifies the local workfunction variation in EG due to electrically active buffer layer.