Fabrication and measurement of graphene devices

Wilkes, Ian and Ponomarenko, Leonid (2020) Fabrication and measurement of graphene devices. Masters thesis, Lancaster University.

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Abstract

Graphene, an allotrope of carbon, has been prepared by mechanical exfoliation and Chemical Vapour Deposition. The graphene so produced has been micro manipulated using polymer membranes and optical microscopy and so placed on silicon wafer. In addition, individual graphene fragments were micro manipulated and placed on pre-prepared hexagonal boron nitride flakes to aid in the fabrication of devices for testing. Graphene devices were prepared by sequential lithography, metalisation and plasma treatment to make field effect multi terminal Hall bar test pieces. The Hall bar geometry test pieces were examined at a variety of magnetic field strengths between 11 Tesla and zero magnetic field. By careful control of the gate voltage, temperature the I-V characteristics of the Hall bar test pieces were measured. Analysis of the I-V characteristics as a function of gate voltage and magnetic field strength was undertaken to determine the location of Dirac cones. Simple analysis of resistance change with gate voltage and magnetic field strength resulted in identification of the first parts of the Hofstadter energy spectrum. To help fabricate multilayer mesas of graphene and hexagonal boron nitride a micromanipulator workstation and simple UV microscope were constructed.