Structural investigations on semiconductor nanostructures: wet chemical approaches for the synthesis of novel functional structures

Recently nanotechnology is experiencing a flourishing progress in a variety of arenas from science to engineering and to biology. The fabrication of nanoscale building blocks, understanding their properties, and organizing these building blocks in to devices for various applications are the main objectives of nanotechnology. As an active field in nanotechnology, the work presented in this thesis is mostly focused on the fundamental study about the fabrication of functional semiconductor nanostructures by wet chemical approaches. In particular, the effects of structure-directing agents, which is the core objective of this research are discussed in detail. Zinc oxide is intrinsically an n-type semiconducting materials that finds applications in electronics, optics, and catalysis. ZnO nanowires have been emerged as a potential candidate in various modern devices with enhanced efficiency. Hydrothermal growth is a widely used technique for the synthesis of ZnO nanowires owing to cost effectiveness, simplicity, and easy upscaling. The use of a polymer additive, polyethylene glycol in the reaction medium has a huge effect on the final morphology of the prepared structures. This method is used to grow hexabranched ZnO nanostructures with increased total and polar surface area. The structures have shown enhanced photocatalytic activity than the conventional nanowires. ZnO based heterostructures have attracted research attention in recent years for their novel interface properties. Controlled secondary growth approaches using organic capping agents, in combination with doping, have been intrigued for the preparation of ZnO core-shell nanowires. Thus Sb-doped and Co-doped ZnO core-shell nanowires have been prepared by this method. The Sb-doped ZnO core-shell nanowires have been synthesized using polyethylene glycol-assisted process in aqueous medium. The Co-doped ZnO core-shell nanowires have been prepared in ethylene glycol-assisted process where ethylene glycol acts both as the growth medium and a structure-directing agent. Since both the routes use a secondary growth method, the shell is grown on an already prepared nanowire core; the dopants are selectively distributed in the shell. CuI is intrinsically a p-type semiconductor that is mainly studied for its applications in the fields of solar energy conversion, catalysis, and solid electrolytes. In the later chapters, antisolvent crystallization of CuI nanoparticles and their assembly to form superstructures are discussed. This process also has been tuned using polymer additives to obtain specific morphologies with high porosity. Owing to the chemical flexibility of CuI to convert to other materials, the superstructures have been used as sacrificial templates to fabricate highly convoluted and porous CuO and TiO2 structures. When the CuI superstructures prepared by polymer assisted assembly has been used as adsorbents, they showed a high adsorption capability. As mentioned above, the works presented in this thesis are fundamental study on the synthesis of functional semiconductor nanostructures. In general, this study gives an account on the effect of specific structure- directing agents on the morphology and optimized synthetic routes for the preparation of specific semiconductor nanostructures with desired structures.