lin Guo

Preparation and characterization of CdS nanowire arrays by dc electrodeposit in porous anodic aluminum oxide templates

Abstract Aligned CdS nanowires have been prepared by dc electrodeposition in porous anodic aluminum oxide template from dimethylsulfoxide solution containing cadmium chloride and elemental sulfur. These nanowires have uniform diameters of about 20 and 100 nm, which correspond to the pore sizes of the templates used, and lengths are up to tens of micrometers. HREM investigations demonstrate that these nanowires have a uniform crystalline structure of hexagonal CdS single crystal. It was proposed that the steady diffusing process of ions probably plays an important role in the growth of the nanowire by dc electrodeposition.

Controlling growth and field emission property of aligned carbon nanotubes on porous silicon substrates

An aligned and well-distributed carbon nanotubes array was produced by pyrolysis of hydrocarbons catalyzed by nickel nanoparticles embedded in porous silicon (PS) substrates. Scanning electron microscope images show that the nanotubes form an aligned array approximately perpendicular to the surface of the PS substrate and the diameters of most of the tubes within the array are 10–30 nm. High-magnification transmission electron microscopy images confirmed that the nanotubes are well graphitized and typically consist of about 15 concentric shells of carbon sheets. Furthermore, the strong field emission from the aligned carbon nanotubes emitter by pyrolysis of hydrocarbons was observed.

Preparation of II-VI group semiconductor nanowire arrays by dc electrochemical deposition in porous aluminum oxide templates

II-VI group compound semiconductors such as CdS, CdSe, and CdTe nanowire arrays have been prepared by direct current electrodeposition in porous anodic aluminum oxide template from nonaqueous electrolyte. SEM and TEM results show that these nanowires have a highly anisotropic structure of aligned nanowires with diameters of 15-200 nm, which are consistent with the diameters of the templates used. Electron diffraction and HREM investigations demonstrate that the crystalline structures of these nanowires are uniform hexagonal single crystal. This approach can be used to fabricate single crystal nanowire arrays of a wide range of semiconductors and other materials.

Hydrolysis and silanization of the hydrosilicon surface of freshly prepared porous silicon by an amine catalytic reaction

A novel catalytic reaction using a trace of organic amine as the catalyst enables hydrolysis of the silicon–hydrogen groups on the fresh prepared porous silicon (PS), generating the hydroxyl-terminated surfaces without extensive oxidation of the Si–Si backbonds. The reactivity of the hydroxyl-terminated surfaces with various silanization reagents was investigated, which proceeds by abstraction of the surface –OH to form an organic monolayer of Si–O–Si–C bonds and importantly retains the intrinsic structural properties of the PS layers. Furthermore, an in situ silanization modification of the silicon–hydrogen surfaces has been established. Stability testing shows that the resulting organic monolayers are densely packed and are shown to be highly stable under a variety of conditions including hot water, hot organic solvent, acid, and base, but can be removed by a HF rinse.

Silver telluride nanowires prepared by dc electrodeposition in porous anodic alumina templates

Silver telluride nanowire arrays were synthesized by cathodic electrolysis into porous anodic alumina membranes from dimethyl sulfoxide (DMSO) solutions containing 0.1 M NaNO3, 5.0 mM AgNO3 and 6.0 mM TeCl4. XRD and SAED patterns of the nanowires were indexed to be a monoclinic structure of Ag2Te. TEM images show that the nanowires have smooth surfaces with uniform diameters. Near stoichiometric Ag2Te nanowires were obtained for potentials between −0.55 and −0.65 V vs. Ag/AgCl. Furthermore, the composition of the nanowires can be controlled continuously from Ag-rich to Te-rich mainly by changing the concentration of TeCl4 in the solutions.

Preparation of Ag2Se and Ag2Se1-xTex nanowires by electrodeposition from DMSO baths

We have developed a novel electrochemical route to fabricate highly ordered stoichiometric Ag2Se nanowire arrays by electrodeposition from non-aqueous dimethyl sulfoxide (DMSO) solutions. Cyclic voltammetry technique was used to study this cathodic deposition process. X-ray energy dispersion analysis shows that stoichiometric; Ag2Se nanowires can be obtained in a wide range of deposition condition. X-ray diffraction and electron diffraction patterns demonstrate that the as-deposited nanowires are [002] oriented orthorhombic beta-Ag2Se. Furthermore, ternary Ag2Se1-xTex nanowires have been electrodeposited in mixed SeCl4-TeCl4 DMSO solutions

Electrodeposition of silver selenide thin films from aqueous solutions

Silver selenide thin films have been electrodeposited potentiostatically from aqueous acid solutions containing silver ions complexed with SCN− and selenium dioxide at room temperature. The electrodeposition reactions were studied by cyclic voltammetry. The deposited films were characterized by X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectra (XPS) and scanning electron microscopy (SEM). The influence of deposition parameters such as potential, electrolyte composition and pH-value on the chemical composition and crystallinity of the films is discussed. The compositions of silver selenide films were controlled continuously from Ag-rich to near stoichiometry by adjusting the bath concentration and deposition potential. After annealing and slowly cooling in argon atmosphere, the films are highly (002) oriented. Furthermore, the excess Ag in the films transformed into Ag2Se by annealing in Se vapor at 230 °C for 4–5 h.

Electrochemical fabrication of one-dimensional silica nanostructures

Electrochemically induced sol–gel deposition has been used to generate one-dimensional silica nanostructures, such as nanotube, “bamboo-like” structure and nanowire. The deposition was carried out in the pores of the anodic alumina membrane from a mixed tetraethoxysilane (TEOS), ethanol and 0.3 M KNO3 aqueous solution in a potential range between −0.95 and −1.25 V. We demonstrated that the growth of these nanostructures is strongly dominated by the electrochemical process.

Silver Selenide Nanowires by Electrodeposition

Silver selenide nanowires were synthesized by potentiostatic electrodeposition into porous anodic alumina membranes from an aqueous acid electrolyte containing silver ion complexed with SCN and selenium dioxide at room temperature. Electron microscopy results showed that the lengths, diameters, and growth directions of the nanowires are quite uniform. X-ray energy dispersion analysis indicated that the nanowires are composed of Ag and Se with an atomic ratio of Ag/Se = 2.08, which is close to stoichiometric Ag 2 Se. X-ray diffraction patterns showed that the as-deposited nanowires are polycrystalline orthorhombic β-Ag 2 Se, and the annealed nanowires are highly [002] oriented. Furthermore, the selected area electron diffraction pattern and the high-resolution transmission electron microscopy image demonstrated that after annealing the nanowires have a uniform crystalline structure of orthorhombic β-Ag 2 Se, which are (002) oriented along the direction vertical to the wire axes.

Intense and stable blue-violet emission from porous silicon modified with alkyls

An intense blue-violet band, centered at 3.0 eV, has been observed besides the red-orange band of the photoluminescence (PL) from the chemically modified porous silicon (PS) samples. The PS samples were formed on 30–50 Ω cm p-type (100) Si wafers by anodic etching at large current densities and then treated with 5-cyano-1-pentynes in toluene solution at 110–120 °C. The intensities of the blue-violet lights increase with the increasing of the etching current densities, while the peak energies are hardly changed. The Fourier transform infrared spectra of the modified samples show that the alkyls have been bonded to the surfaces of the nanometer crystallite silicon particles. The decays of the blue-violet emission with a lifetime about 0.5 μs are different from the nanosecond lifetimes of the blue emissions in the oxidized PS samples reported before, and the 20 μs lifetimes of the concomitant orange PL bands. A carbon-compounds-related luminescence center has been proposed as the origin of this blue-violet P...