Transport studies of two-dimensional materials for nanoelectronics applications
Abstract
The success of the physical isolation of graphene in 2005 has sparked intense research into two-dimensional materials in the years since. Graphene's honeycomb crystal structure prohibits direct backscattering of carriers in graphene, leading to large phase coherence lengths. Taking advantage of graphene's long phase coherence lengths, experiments revealing snake orbits at pn and pp+ junctions in graphene via the Aharonov-Bohm effect are presented. Graphene also exhibits the unique half-integer quantum Hall effect. This dissertation will present detailed studies of the half-integer quantum Hall effect on epitaxial graphene on SiC, confirming that graphene grown on SiC exhibits the same physics as graphene exfoliated from graphite. The scaling of the plateau to plateau transition follows a single parameter scaling theory, where the phase coherence length plays the role of the size system. Additionally, this exam presents studies of spin transport in epitaxial graphene via spin valve measurements to explore epitaxial graphene's use in spintronics applications. Motivated by the success of graphene research, interest has renewed in the transition metal dichalcogenides, a family of two-dimensional materials which includes insulators, semiconductors, and metals. Graphene's lack of a bandgap limits its usefulness in field effect transistors, focusing recent interest on the semiconducting transition metal dichalcogenides, particularly MoS2. However, recent experiments on MoS2 have also demonstrated superconductivity and valley polarization, pointing to MoS 2's potential for novel device applications beyond the FET. Using the phase coherent effect of weak localization, this dissertation presents studies of the phase coherence length and spin-orbit scattering length in MoS 2, further motiving the study of MoS2 for use in spintronics and other novel device applications. In addition to semiconducting transition metal dichalcogenides, metallic transition metal dichalcogenides also exhibit many interesting properties, including superconductivity and charge density waves. Recent calculations have revealed the important role of strong spin-orbit coupling in understanding the bandstructure of the metallic transition metal dichalcogenide TaSe2. With that motivation, this dissertation determines the spin-orbit scatting length of TaSe2 via studies of phase coherent weak anti-localization, pointing to its potential for use in spintronics devices based on the spin Hall effect.
Degree
Ph.D.
Advisors
Ye, Purdue University.
Subject Area
Electrical engineering|Condensed matter physics|Nanotechnology
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