Development and Electronic Characterization of Graphene-Based Hall Effect Devices

Abstract

Graphene is a two-dimensional carbon material with a unique honeycomb lattice structure and exceptional electronic properties. Its band structure confines carriers to a single plane, allowing them to act like relativistic massless particles at low carrier densities. This has made graphene a focal point in condensed matter physics, particularly following the groundbreaking discovery of the first topological state using a graphene lattice. Research into graphene's potential as a platform for quantum topological computing has surged. In addition to its distinct band interactions, graphene is also being studied as a potential standard for electrical resistance. However, progress in its isolation since its initial synthesis in 2004 has been limited.

This thesis focuses on the synthesis of single-layer graphene (SLG) through low-pressure chemical vapor deposition (LPCVD) on copper films at temperatures above 1000 °C. The graphene films are transferred using a wet transfer technique and characterized with atomic force microscopy (AFM) and Raman spectroscopy. Hall devices for electrical transport studies are patterned using maskless alignment photolithography, with palladium as ohmic contacts. Electronic transport measurements are conducted at cryogenic temperatures up to a magnetic field of 5T using 4-terminal measurement techniques.

Moreover, this work explores electronic transport in twisted bilayer graphene (TBG) - tungsten diselenide WSe2 Hall devices. This structure facilitates the study of strongly correlated electronic states enhanced by spin-orbit coupling induced by WSe2. Preliminary experiments to detect unconventional Hall states in similar devices are carried out at millikelvin temperatures and in magnetic fields up to 18 Teslas.