The ongoing miniaturization, power reduction, and performance improvements of nanoscale electronics continues to fuel research and developmental efforts into new materials, synthesis techniques, and fabrication methods. Bottom-up assemblies of nanowire structures, grown catalytically and non-catalytically, have the potential to significantly contribute to complex architectures leading to new applications and higher device performance. Here, the implementation of various reaction and thermochemical models in predicting suitable nanowire growth conditions is presented using the framework of chemical vapor deposition (CVD) and vapor transport (VT) nanowire growths. Investigating novel bottom-up structures in group IV nanowires, germanium nanowire growths are performed using CVD, where the introduction of a controlled quantity of oxygen forms an oxide which selectively rejects the adsorption of precursor species on the nanowire sidewall, limiting sidewall deposition and radial growth. The catalytic nature of the oxide formation permits the oxide sheath to be switched on and off controllably, leading to the ability to produce segments that are oxide-stabilized alongside regions where sidewall deposition is allowed, resulting in large controllable radial discontinuities along the nanowire. VT is a powerful alternative to CVD and allows for new avenues for materials synthesis and nanowire growth that cannot be achieved by CVD alone. VT growth of ZnO, Se, Ge, GeO_x, and binary chalcogenides is investigated, particularly tellurium, which is an ideal candidate for VT growths due to its highly anisotropic crystalline structure which readily lends itself to the formation of high aspect-ratio nanostructures. Growth mechanism studies on tellurium guide an understanding of the energetic landscape of nanowire growths and provide effective activation energies consistent with the reaction modeling, allowing for the controlled growth of tellurium mesh nanowire networks of tailorable porosity. Additional VT growths of thermoelectrically relevant group V-VI nanowires guided by thermochemical modeling are shown to be successful in producing core-shell structures and axial transitions. Precise modeling of the growth space and the necessary modifications for catalytic and non-catalytic growths are determined for Bi_2Se_3 and Bi_2Te_3 nanowire growths, the characterization of which illustrates the importance and utility of pairing predictive thermochemical modeling with reactor design and nanowire growth.Ph.D., Materials Science and Engineering -- Drexel University, 201
