Characterization and synthesis of nanoscale materials

This dissertation focuses on the systematic study of techniques for characterization and synthesis of nanoscale materials. We have achieved several goals. Firstly, high number density uniform zinc oxide nanostructure growth has been achieved using thermal evaporation, through control of experimental parameters that include source material temperature, substrate temperature, substrate material, gas flow rate, and choice of catalyst. Aligned zinc oxide nanowires, randomly oriented zinc oxide nanowires, zinc oxide container-shaped structures, and zinc oxide nanobelts have been synthesized with high yield. Secondly, using a one parameter family of lattice fringe geometry curves, we show how to examine the epitaxial relationship between catalyst particles and a cylindrical support. Using digital darkfield techniques, this investigation can be automated. Thirdly, the structure relationship between catalyst particles and zinc oxide nanowires has been investigated using scanning and high resolution scanning transmission electron microscopes. A vapor-solid-solid growth model involving a hexagonal array of aligned growth regions is proposed in zinc oxide nanowire formation. Evidence indicates in particular that gold catalyst particles remain solid during ZnO nanowire growth. Finally, the effect of tin catalyst thickness on nanostructure formation has been investigated. The catalyst abundance on the substrate has a direct impact on its ability to absorb ZnO. The thicker coated substrates can absorb more source vapor, and form larger structures, than can thinner coated substrates --Abstract, page iv