| Nanocrystals are fundamental to modern science and technology. Mastery over the shape of nanocrystals provides a feasible and unique way to control their collective properties and enhance their applications. The objective of this dissertation is to develop reliable synthetic strategies for preparing high-quality functional nanocrystals in organic solution with both uniform size and shape. As an extensive investigation, study of the shape evolution mechanism, and exploration of potential applications in optical, electronic, electrocatalytic aspects, and packing of self-assembled supercrystals are also involved.;As a model system, preparation of ZnTe nanocrystals in three different morphologies, that is, quasi-spheres, tetrahedra, and nanorods, were first demonstrated. These nanocrystals were synthesized by tuning both the thermodynamic and kinetic parameters. In this system, the reduction process is believed to be the key step in shape determination. Following the understanding of this growth mechanism, one-dimensional ZnTe nanobelts were successfully synthesized as well. The electronic behaviors of these single-crystal ZnTe nanobelts, as Field-Effect Transistors, were also studied.;On the next level, high-quality, large-yield PbTe nanocubes were prepared. Assemblies of these cubic building-blocks into both two-dimensional square-array patterns and three-dimensional simple cubic supercrystals were, for the first time, demonstrated. The influence of reducing agent in the nanocrystal synthesis and core/shell formation through an anion-exchange mechanism was also studied. The simple cubic supercrystals together with two-dimensional assembly patterns containing PbTe nanocubes and their core/shell building blocks were well-characterized using TEM, SEM, AFM, XRD, SAXS and FTIR.;By extending the shape-control strategy from semiconductor to the territory of metal and alloys, a novel and reliable approach of preparing Pt3M (M = Co, Ni) nanopolyhedra was successfully developed. The mechanism governing the shape evolution process has also been proposed. As one of significant applications, collective electrocatalytic activities of these monodisperse nanopolyhedra, on oxygen reduction and methanol oxidation, were evaluated, respectively. It was determined that the electrocatalytic activities of these nanocrystals were greatly dependent on their morphologies (i.e. nanocubes and nanoctahedra), creating an alternative avenue for enhancing the catalytic performance of nanomaterials used in fuel cells.;The fundamental insights gained in this study would enable the preparation of a large range of nanomaterials with both size- and shape-control. The size- as well as shape-monodisperse nanocrystals, as promising building blocks, are potentially important in urgent and high-impacted applications such as microelectronics, nanophotonics, electrocatalysis, high-density information storage, bio-imaging, and telecommunication. |
