Two-dimensional (2D) transition metal dichalcogenides (TMDCs) are atomically thin, layered materials with unique physical and electronic properties relative to their bulk forms. Due to these properties, 2D TMDCs show promise for many applications, including catalysis, nanoelectronics, optoelectronics, and spin- and valleytronics. To utilize TMDCs for these applications, they must first be reproducibly isolated. Much previous work in this area has resulted in material batches with low yield, small crystal sizes, and little control over the crystal morphology and orientation. Here, I present the reproducible chemical vapor deposition (CVD) growth of a wide array of 2D TMDCs, including MoS2, WS2, MoTe2, NbS2, and WSe2. Control of the growth of these materials is achieved through the optimization of many parameters, including substrate surface chemistry and synthetic growth parameters. Through the optimization of these parameters, I demonstrate control over the resulting material thickness, phase, and morphology. These high-quality TMDCs are subsequently used to grow many relevant heterostructures, including MoS2/WS2 lateral and vertical heterostructures, MoO2/MoS2 core/shell plates, 2H-1T´ MoTe2 few-layer homojunctions, and WS2/NbS2 lateral heterostructures, and the utility of these heterostructures is assessed. MoS2/WS2 heterostructures show promise as a semiconductor-semiconductor heterostructure in which the nature of the alignment is controlled by the initial MoS2 seed crystal. MoO2/MoS2 core/shell plates are freestanding and show epitaxial alignment with the underlying crystal substrate, with potential applications in catalysis. 2H-1T´ MoTe2 few-layer homojunctions are grown using a patternable phase engineering procedure, and devices fabricated from these homojunctions show reduced contact resistance relative to 2H MoTe2 devices with noble metal contacts. Finally, WS2/NbS2 lateral heterostructures show promise as an alternative metal-semiconductor heterostructure system for creating 2D TMDC devices with low contact resistance. The controlled CVD growth of these materials and heterostructures bolsters their future use for relevant applications.
University of Minnesota Ph.D. dissertation. August 2018. Major: Chemistry. Advisor: James Johns. 1 computer file (PDF); xvii, 172 pages.
Chemical Vapor Deposition Growth of Two-Dimensional Transition Metal Dichalcogenides and Related Heterostructures.
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