Investigation on High-Mobility Graphene Hexagon Boron Nitride Heterostructure Nano-Devices Using Low Temperature Scanning Probe Microscopy
This thesis presents several experiments, generally aiming at visualising the ballistic and topological transport on the high-mobility graphene/boron nitride heterostructure using the scanning gate microscope.
For the first experiment, we use the scanning gate microscopy to map out the trajectories of ballistic carriers in high-mobility graphene encapsulated by hexagonal boron nitride and in a weak perpendicular magnetic field. We employ a magnetic focusing transport configuration to image carriers that emerge ballistically from an injector, follow a cyclotron path due to the Lorentz force from an applied magnetic field, and land on an adjacent collector probe. The local potential generated by the scanning tip in the vicinity of the carriers deflects their trajectories, modifying the proportion of carriers focused into the collector. By measuring the voltage at the collector while scanning the tip, we are able to obtain images with arcs that are consistent with the expected cyclotron motion. We also demonstrate that the tip can be used to redirect misaligned carriers back to the collector.
For the second experiment, we investigate the graphene van der Waals structures formed by aligning monolayer graphene with insulating layers of hexagonal boron nitride which exhibit a moir