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A Study of Transition Metal Dichalcogenides: Synthesis, Catalysis, and Mechanically Induced, Elastic Tuning of Their Optical Properties

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Highly photosensitive, tunable direct band gap materials of subnanometer thickness represent an important path forward in minimization of opto-electronic devices. It is inevitable that the scale of devices will soon move beyond the 2 nm node. With the ever decreasing scale of devices, two dimensional transition metal dichalcogenides (TMDs) offer a promising avenue towards reduced dimensionality and unveil novel direct-indirect band gap shift tuning capabilities by means of thickness, and composition. A primary goal of this work is to investigate bottom-up approaches to fabrication of integrated materials systems using chemical vapor deposition (CVD) grown TMDs. In that vein, this thesis presented examines the methods for growth of the transition metal dichalcogenide materials on a variety of metal oxide terminated substrates, graphene and directly onto an economical photocathode for the hydrogen evolution reaction in water splitting. Where the limits of CVD process preclude bottom-up fabrication, the research presents methods to vertically stack CVD-grown two dimensional materials and deposit them on arbitrary substrates via physical transfer techniques allowing for a single step process to obtain CVD grown TMDs on flexible substrates. Executing physical transfer allows us to reach the final goal of this work, to investigate a third type of optical tuning, that of uniaxial mechanical strain. The thesis probes a mechanical strain induced shift in the optical behavior of the MX2 (M=Mo, W; X=S, Se) materials.

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