Nanomaterials for chemical and biological applications: Inorganic nanoparticles, nanotubules, and nanowires

A new method to produce epitaxial single-crystal cobalt silicides using isolated cobalt nanoparticles on silicon will be discussed in chapter 2. The nanostructures are produced by reacting cobalt nanoparticles with a silicon substrate. The dimensions of these silicide nanostructures are smaller than those made using lithography, and the orientation of the nanostructures is controlled by the silicon substrate. In addition to characterization using transmission and scanning electron microscopies, energy dispersive x-ray spectroscopy, atomic force microscopy, and electron diffraction, the silicides were studied with grazing incidence x-ray absorption spectroscopy (GI-XAS). Analysis of the extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge spectroscopy (XANES) data obtained from these measurements, as well as theoretical calculations of the spectra using Feff8 conclusively identified the nanostructures as single-crystalline cobalt silicide. The GI-XAS measurements and the results of the simulated spectra will be discussed in chapter 3.; In chapter 4, a high-yield synthesis of silica nanowires in a CVD-type mechanism will be discussed. These nanowires are grown directly from silicon wafers at high temperatures in the presence of cobalt nanoparticles and hydrogen gas. All three ingredients are critical to the growth of silica nanowires, which can be heavily coiled or straight and range between 5 and 60 nm in diameter and mum to mm long. Experimental evidence suggests that the source of silicon for the nanowire growth is in the gas phase, indicating a classical CVD-type mechanism.; Chapter 5 describes the synthesis and characterization of two types of nanomaterials with potential as radiation sensitizers in cancer treatment. One of these nanomaterials is a DNA-targeting nanoparticle functionalized with an ethidium-type intercalating ligand, while the other material is a tubular gold nanoshell surrounding a silica nanowire template. These nanomaterials work as DNA sensitizers via two different mechanisms that will be discussed in chapter 6. The x-ray radiation enhancement mechanisms were derived using simulation, and experimentally verified using supercoiled DNA as a biological target.