Study On Preparation, Microstructure And Formation Mechanism Of Low Dimensional Semiconductor Nanomaterials

In this thesis, the preparation methods and microstructures of low-dimensional semiconductor nanomaterials, especially zero-dimensional germanium nanocrystals(Ge-ncs) and one-dimensional indium phosphide nanowires(InP NWs), have been systematically studied by high-resolution transmission electron microscopy(HRTEM). Based on HRTEM characterization, the growth mechanisms of low-dimensional semiconductor nanomaterials are clarified, which could be beneficial to the study and applications of low-dimensional semiconductor nanomaterials.The thesis consists of four chapters.In chapter 1, the basic characteristics, preparation methods, characterization methods and applications of low-dimensional semiconductor nanomaterials are reviewed.In chapter 2, Ge-ncs were prepared by implantation of 74Ge+ into an SiO2 film on(100) Si, followed by high-temperature annealing from 700 °C to 1100 °C. Transmission electron microscopy(TEM) studies show that the average size of Ge-ncs increases with the annealing temperature. HRTEM investigations reveal the presence of planar and linear defects in the formed Ge-ncs and different changing trends of defects with the annealing temperature are discussed.In chapter 3, InP NWs were prepared by solid-source chemical vapor deposition method and the morphologies and microstructures of kinked InP NWs were examined by electron microscopy. Four different kinds of kinks are dominant in the grown InP NWs with a bending angle of approximately 70°, 90°, 110°, and 170°, respectively. Their formation mechanisms are discussed. Specifically, the existence of kinks with bending angles of approximately 70° and 110° are mainly attributed to the occurrence of stacking faults and nanotwins in the NWs, which could easily form by the glide of {111} planes, while approximately 90° kinks result from the local amorphorization of InP NWs. Also, approximately 170° kinks are mainly caused by small-angle boundaries, where the insertion of extra atomic planes could make the NWs slightly bent.In chapter 4, alternating twin defects have been observed along the <111> growth direction of the zinc-blende InP NWs using HRTEM. It is observed that the twin density increases with the nanowire(NW) diameters. A simple model has been proposed to explain this trend, in which the degree of indium supersaturation in Au catalysts induced by the size of catalysts might play an important role.