Date of Award
Doctor of Philosophy (PhD)
Physics & Astronomy
Topological insulators and two-dimensional ferromagnetic materials are novel phases with wideranging applications including quantum computing, spintronics, and other advanced electronic devices with the potential for ultrathin and ultralow-power wearables. TEM, AFM, EDS, Ramanspectroscopy, and low-temperature transport measurement are used to characterize an unusual superconducting alloy formed between palladium and bismuth selenide under low-temperature annealing. TEM, AFM, and EDS are used to perform a materials study of metallic nickel and niobium annealed with Bi2Se3 under similar conditions, with the conclusion that Ni reacts to form a diffuse layer within Bi2Se3 flakes that travels along edges and line defects, and Nb does not react at all. Detailed materials analysis of Bi2Se3 flakes nanosculpted with a gallium focused ion beam and with a TEM beam is also presented, with the result that FIB ablation causes the formation of a debris field alongside the edges of a cut region, but electron-beam ablation does not. Finally, a materials, defect, and degradation study of electrochemically exfoliated ultrathin vanadium selenide nanoflakes is presented, in which the VSe2 is characterized by Raman spectroscopy and a newly-invented MFM technique inforporating torsional resonance oscillation, as well as time studies of AFM, MFM, and low-temperature TEM to investigate the effects of both air and electrolyte exposure. It is found that propylene carbonate exposure causes the breakdown of VSe2 into its elemental constituents and that passivation with dilute perfluorodecane thiol confers a concentration-dependent protective effect. This research lays the groundwork for exciting future studies into the nature and properties of Group X alloys of Bi2Se3 and potentially novel spin textures and transport characteristics of VSe2 heterostructures.
Friedensen, Sarah, "A Materials Study Of Topological Insulators And Two-Dimensional Ferromagnets" (2022). Publicly Accessible Penn Dissertations. 5612.