Advances in Science and Technology Vol. 51

Abstract: A simple technique to synthesis crystalline Tungsten Oxide nanowires is presented. Using a standard thermal hotplate, a pure 99.9% tungsten foil is annealed to 484 ± 5 oC under ambient condition to generate vapor deposition of the heated materials on a piece of 150μm thick glass cover slide pressing on the tungsten foil. Tungsten oxide nanowires are found to deposit on the cover slide facing the heated tungsten foil. These tungsten oxide nanowires were characterized with SEM, TEM, EDX, micro-Raman and XRD. The crystalline nanowires were found to be straight and clean with a diameter of 10-300nm and a length of a few tens of micrometers.

Abstract: Using appropriate electrodeposition conditions, it is shown that the structural and magnetic properties of arrays of Co and CoCu/Co nanowires can be controlled. The hcp c axis orientation can be oriented parallel or perpendicular to the wire axis simply by changing the pH of the electrolytic solution and/or deposition rate. This selected orientation of the c axis leads to a drastic change in overall magnetic anisotropy and is promising for the fabrication of spin valves structures by electrodeposition.

Abstract: Dynamic study of the growth of TiSi2 nanorods on Si bicrystal was conducted in an ultrahigh vacuum transmission electron microscope. The growth of the nanorods was affected by the underlying dislocation grids significantly. The dislocation grids confined the shape of the nanoclusters and nanorods. Compared to the time of the nanorod remaining at the same length, the elongating time is relatively short. The dislocation network confined the nanorod to match the dislocation interspacing and the step-wise growth of the nanorod was found. The growth mechanism is attributed to the compliant effect. The observation was constructive to the basic understanding of the stress effect on the initial stage of the reaction of metals on Si.

Abstract: Nanocrystalline TiO2 (anatase) has attracted considerable interest for applications in photoelectrochemical solar cells. This device is based on charge injection from photoexcited organometallic dye which is adsorbed on the TiO2 surface. Titanium dioxide can electrochemically accommodate Li+ which is useful for a design of new Li-ion batteries. Whereas the charge storage in anatase or rutile is based on the Li-insertion into the bulk crystal, the monoclinic TiO2(B) exhibits an unusual pseudocapacitive Li-storage mechanism. The photoelectrochemical and Liinsertion activity of mesoscopic TiO2 depend significantly on the electrode morphology.

Abstract: Interfacing of biomolecules to inorganic frameworks is essential for fabricating robust, functionally integrated biocomposites that may prove useful in a wide range of technologies including biocatalysis, biosensors or protein-based devices. Our work is directed at developing means to integrate biomolecules into mesostructured inorganics. These frameworks serve to both improve the mechanical stability of the proteins and to facilitate communication with them. Toward that end, we have synthesized and characterized mesoporous silicas and conductive metallic frameworks and have examined the encapsulation of both soluble (cytochrome c) and membrane proteins (bacteriorhodpsin) within them.

Abstract: Vertically aligned ZnO nanorods have been synthesized on a-plane sapphire via a metal catalyzed vapor phase transport and condensation process in a two-zone vacuum furnace. Planar-tip ZnO nanorods were synthesized using commercial ZnO and graphite powder as the source of Zn vapor controlled by a simple vapor-liquid-solid (VLS) process. On the other hand, tapered-tip ZnO nanorods were synthesized from pure ZnO powder governed by both VLS and vapor-solid processes. From room temperature cathodoluminescence measurements, planar-tip ZnO nanorods are applicable for room temperature UV nanolasers.

Abstract: Self-assembled low-resistivity NiSi nanowire arrays have been grown on relaxed epitaxial Si0.7Ge0.3 on (001)Si. The formation of the one-dimensional ordered structure is attributed to the nucleation of NiSi nanodots on the surface undulations induced by step bunching on the surface of SiGe film owing to the miscut of the wafers from normal to the (001)Si direction. Furthermore, the nanodots were connected along individual arrays and turned into nanowires with increasing amount of Ni and a-Si. Since the periodicity of surface bunching can be tuned with appropriate vicinality and misfit, the undulated templates promise to facilitate the growth of ordered, catalyst-free NiSi nanowires with selected periodicity and size for utilization in high-speed Si-Ge nanodevices.

Abstract: Quasi-vertical ZnS nanostructures with different Ga doping level ( ZnS:Ga nanowalls ) have been synthesized in high yield from the mixed powders in the vacuum furnace at 1150 oC. ZnS:Ga nanowalls were grown vertically on the substrate with the size in the range of several microns and the thickness down to 15 nm and have very rough edges. The possible growth mechanism of nanowalls is likely governed by a vapor-solid (VS) growth mechanism. Room-temperature cathodoluminescence spectra of ZnS : Ga nanowalls show two emission peaks at approximately 443 nm and 578 nm. The emission mechanisms are discussed.