Transport in graphene tunnel junctions

Abstract

It has been predicted that gold, aluminum, and copper do not fundamentally change the graphene band structure when they are in close proximity to graphene, but merely increase the doping. My data confirms this prediction, as well as explores other consequences of the metal/graphene interface. First, I present a technique to fabricate thin oxide barriers between graphene and aluminum and copper to create tunnel junctions and directly probe graphene in close proximity to a metal. I map the differential conductance of the junctions versus tunnel probe and back gate voltage, and observe mesoscopic fluctuations in the conductance that are directly related to the graphene density of states. I develop a simple theory of tunneling into graphene to extract experimental numbers, such as the doping level of the graphene, and take into account the electrostatic gating of graphene by the tunneling probe. Next, results of measurements in magnetic fields will also be discussed, including evidence for incompressible states in the Quantum Hall regime wherein an electron is forced to tunnel between a localized state and an extended state that is connected to the lead. The physics of this system is similar to that encountered in Single Electron Transistors, and some work in this area will be reviewed. Finally, another possible method of understanding the interface between a metal and graphene through transport is presented. By depositing disconnected gold islands on graphene, I am able to measure resonances in the bias dependent differential resistance, that I connect to interactions between the graphene and gold islands.