Fabrication and magnetotransport properties of graphene nanostructures.

摘要

Graphene have attracted considerable interest for fundamental studies and potential applications because of their unique electronic properties. However, its application in logic circuits is limited due to the lack of bandgap. It has been demonstrated that a conduction band gap can be achieved in graphene nanostructures, such as nanoribbons (GNRs), due to size confinement and edge effect, making it a very interesting electronic materials for circuits application. Theoretical studies have also suggested interesting magneto-electronic properties in GNRs originated from the magnetic edge states or the Hall-edge states under a perpendicular magnetic field, with very large magnetoresistance (MR) predicted. On the other hand, a GNRs device with width down to sub-10 nm is required to show large enough bandgap or spin coupling in order to operate under ambient condition, which remain significant challenging to state of art fabrication techniques.;In this dissertation, I will present my research studies on rational fabrication of GNRs with sub-10 nm width by employing nanowire as etch mask. Taking a step further, I will demonstrate a new graphene nanostructure-graphene nanomesh as a mimic of GNR network. This nanomesh structure introduces finite size effect into a large sheet of graphene while retaining the two-dimensional nature, and therefore may be advantageous in practical device fabrication and integration. Based on the advance of our fabrication method, I will show the first experimental observation of a dramatic enhancement of the conductance in a GNR field-effect transistor by a perpendicular magnetic field. Very large negative MR of nearly 100% with conductance enhanced over 10,000 times was observed at low temperatures; and more than 50% remained at room temperature. Similar magnetotransport behavior was also observed in graphene nanomesh device. The observed large MR was attributed to the complex interplay between edge roughness, quantum confinement and the formation of cyclotron orbits. These findings demonstrate interesting magnetotransport properties in graphene nanostructures, and can open up exciting new opportunities for a new generation of magneto-electronic devices.