Synthesis and characterization of nanostructured materials

In addition to technological motivations, nanomaterials are interesting for basic scientific investigation because their properties reside in the largely unexplored realm between molecules and bulk solids. The controlled synthesis of these materials, by methods that permit their assembly into functional nanoscale structures, lies at the core of nanoscience and nanotechnology. Here, controlled synthesis refers to a process of collective nanostructure growth where the pertinent attributes such as location, size, orientation, and composition as well as the electrical, mechanical, and chemical properties of the individual elements can be predetermined by the choice of the growth conditions and the preparation of the growth substrate. This dissertation work furthers the understanding of the mechanisms by which synthesis conditions affect the morphology, composition, and crystal structure of nanostructured materials with the objective of achieving greater control over the synthesis process. Three types of systems are investigated in depth: vertically aligned carbon nanofibers (grown by plasma-enhanced chemical vapor deposition), catalytic alloy nanoparticles (sputter-deposited, carbon-encapsulated), and tungsten nanowires (grown by electron-beam-induced deposition). The effects of growth parameters on the resulting nanostructure properties are characterized by methods including high-resolution transmission electron microscopy, electron diffraction, and chemical spectroscopy.