Search

The mass preparation of SnO2 nanobelts and nanowires has been achieved by carrying out the reaction of SnO2 powder and graphite at 1150°C. A metallic catalyst and vacuum conditions are not necessary. The temperature of the substrates and the concentration of oxide vapour were the critical experimental parameters for the formation of different morphologies of SnO2 nanostructures. The as-synthesized SnO2 nanobelts formed in region II are single crystalline with a [101] growth axis, with widths ranging from 50 to 500 nm, width-to-thickness ratios of 5–10, and lengths up to a few millimetres. [ABSTRACT FROM AUTHOR]

This article describes both electrochemical deposition and electrophoretic deposition of high-density tellurium (Te) nanowire arrays with wire diameters of 60 nm and lengths of 15-20 µm in the nanochannels of anodic aluminum oxide (AAO) templates. The Te nanowires synthesized via electrochemical deposition (ECD) are generally single crystalline in nature with the wire longitudinal axis along the [001] direction, whereas those synthesized via electrophoretic deposition (EPD) show polycrystalline structures with numerous tiny Te crystallites packed randomly in the wires. The single-crystalline Te nanowires produced by the ECD route are believed to form under a near chemical equilibrium condition; however, the imposed transport and the rapid packing of Te nanocrystallites in the nanochannels of AAO template in external fields lead to polycrystalline Te nanowires in the EPD process. This comparative study of the Te nanowire formation in the nanochannels of AAO template will facilitate the tailoring of the growth of other inorganic nanowires of high quality. [ABSTRACT FROM AUTHOR]

The colloidal, highly crystalline, and size-controlled ZnS nanorods have been prepared through a thermal decomposition of single-source-precursor approach in oleylamine solution. The length and width of nanorods can be controlled simply by varying the molar ratio of zinc 2-mercaptobenzothiazole complex and oleylamine or prolonging the anneal duration. Optical and electrochemical properties of different sizes of ZnS nanorods are discussed and size-dependent optical and electrochemical band gaps are evidently observed, which show a direct correlation between the electronic spectra and electrochemical band gap. [ABSTRACT FROM AUTHOR]

ZnS nanowires with periodically alternating twins along the growth direction of wires have been synthesized via a thermal evaporation method. Structural characterizations reveal that both sphalerite (cubic) and wurtzite (hexagonal) phases coexist in the synthesized nanowires. The periodically twinned ZnS nanowires are formed through the vapor-solid mechanism. High quality of the nanowires is confirmed by the optical absorption and the photoluminescence observations combined with large ratio surface and interfaces induced by the twin modulations. The perfect crystal structure indicates their potential applications in nanoscience and nanotechnology. [ABSTRACT FROM AUTHOR]

The lattice parameter of bismuth nanowires has been measured using the in situ high-temperature x-ray diffraction method. Single-crystalline Bi nanowire arrays with the diameters from 10 nm to 250 nm have been fabricated within the porous anodic alumina membranes by a pulsed electrodeposition technique. Different temperature dependencies of lattice parameter and thermal expansion coefficient were found for Bi nanowires with different diameters, and there is a transition from positive thermal expansion coefficient at low temperature to negative one at high temperature, and the transition temperature shifts to high temperature with the increase in the diameter of Bi nanowires. [ABSTRACT FROM AUTHOR]

Large-scale synthesis of amorphous silica nanowires was achieved by using simple physical evaporation of a mixture of Si and Al2O3 powders. Scanning electron microscopy observations showed that the silica nanowires have lengths of several mm and diameters of 20-100 nm. X-ray photoelectron spectroscopy revealed that these nanowires consisted of Si and O elements in an atomic ratio of approximately 1:2, consistent with the stoichiometric formula SiO2. Photoluminescence measurements showed a blue luminescence band in the wavelength range of 400-500 nm with three peaks at 420 nm, 440 nm, and 470 nm, respectively, which also differs from the previous reports of the photoluminescence for oxygen-deficient silica nanowires. This may suggest that the fully oxidized silica nanowires still have many structural defects that contribute to the photoluminescence. [ABSTRACT FROM AUTHOR]

Alumina nanowire arrays standing on the surface of a porous anodic alumina membrane have been achieved by first forming a porous anodic alumina membrane with parallel Y-branched nanochannels by reducing the applied anodizing voltage by a factor of [inline image] in the anodization process of high-purity Al foil, and then chemically etching the Y-branched nanochannel alumina membrane in an aqueous phosphoric acid solution. The novel nanostructures may be used for two-dimensional photonic bandgap structural materials. [ABSTRACT FROM AUTHOR]

S-doped ZnO nanowires with an average diameter of 80 nm and length up to several tens of micrometers were produced through a simple physical evaporation approach. The nanowires had a single-crystal hexagonal structure and grew along the [102] direction. Photoluminescence (PL) measurements showed that the doping of sulfur shifted the PL spectrum peak towards short wavelengths, and the doping quantity was found responsible for the different characteristics. [ABSTRACT FROM AUTHOR]

Monoclinic gallium oxide (β-Ga[sub 2]O[sub 3]) nanowires were synthesized by heat treating a composite material of GaAs and pre-evaporated Au at 1240 °C in dry oxygen atmosphere. The catalytic Au metal generated liquid nanoclusters that serve as reactive sites confining and directing the growth of β-Ga[sub 2]O[sub 3] nanowires during the vapor-liquid-solid growth process. The β-Ga[sub 2]O[sub 3] nanowires have diameters ranging from 20 to 50 nm and lengths of several micrometers. Photoluminescence measurement under excitation at 250 nm shows that the bulk β-Ga[sub 2]O[sub 3] nanowires have a stable blue emission at 475 nm and an ultraviolet emission at 330 nm, which may be related to the defects such as the oxygen vacancy and the gallium-oxygen vacancy pair. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Highly ordered TiO[sub 2] nanowire (TN) arrays were prepared in anodic alumina membranes (AAMs) by a sol-gel method. The TNs are single crystalline anatase phase with uniform diameters around 60 nm. At room temperature, photoluminescence (PL) measurements of the TN arrays show a visible broadband with three peaks, which are located at about 425, 465, and 525 nm that are attributed to self-trapped excitons, F, and F[sup +] centers, respectively. A model is also presented to explain the PL intensity drop-down of the TN arrays embedded in AAMs: the blue PL band of AAMs arises from the F[sup +] centers on the pore walls, and the TNs first form in the center area of the pores and then extend to the pore walls. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Large-scale of crystalline GaN nanowires (diameter∼50 nm) have been fabricated through chemical-vapor deposition in the nanochannels of the anodic alumina template. X-ray diffraction and selected area electron diffraction pattern investigations indicate that the nanowires are single crystal with hexagonal wurtzite structure. A typical scanning electron microscopy image and the energy dispersive x-ray spectroscopy results indicate that indium nanoparticles only act as catalyst in GaN nanowires growth. At room temperature, photoluminescence spectrum of the GaN nanowire arrays shows a visible broadband with three peaks, which are located at about 363, 442, and 544 nm. The light emission may be attributed to GaN band-edge emission, the existence of defects or surface states, and the interaction between the ordered GaN nanowires and anodic alumina membrane. The growth mechanism of crystalline GaN nanowires is discussed. The method makes it possible to synthesize other nitride nanowire arrays. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Single-crystalline Bi nanowires with diameters ranging from 20 to 70 nm were prepared by electrodeposition using nanoporous aluminum oxide membranes rather than the more usual track-etched polycarbonate membranes. X-ray diffraction and selected area electron diffraction investigations revealed that the nanowires are essentially single crystalline and highly oriented. The temperature dependence of zero-field resistance of different diameter nanowires indicated that these Bi nanowires undergo a semimetal-semiconductor transition due to two-dimensional quantum confinement effects. The resistance maximum was observed at 50 K in zero magnetic field for 20 nm Bi nanowires, while the resistance minimum at 258 K for 50 nm Bi nanowires, due to the quantum size effect. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ordered semiconductor In[sub 2]O[sub 3] nanowire arrays are uniformly assembled into hexagonally ordered nanochannels of anodic alumina membranes (AAMs) by electrodeposition and oxidizing methods. Their microstructures were characterized by x-ray diffraction, scanning electron microscopy, and transmission electron microscopy. A blue-green photoluminescence (PL) band in the wavelength range of 300–650 nm was observed in the In[sub 2]O[sub 3]/AAM assembly system. The PL intensity and peak position depend on the annealing temperature, which is mainly attributed to the singly ionized oxygen vacancy in the In[sub 2]O[sub 3] nanowire array system. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We propose that quantum cables can be used as a kind of transport spectroscope to obtain directly the quasi-one-dimensional (Q1D) density of states (DOS) of cylindrical quantum wires. By simultaneously measuring the direct current through the cylindrical quantum wire and the leaky tunneling current into its neighboring wire at desirable temperatures, one can obtain detailed information about the Q1D DOS and subband structure of the cylindrical quantum wire. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Ordered semiconductor ZnO nanowire arrays embedded in anodic alumina membranes (AAM) were fabricated by generating alumina templates with nanochannels, electrodepositing Zn in them, and then oxidizing the Zn nanowire arrays. The polycrystalline ZnO nanowires with the diameters ranging from 15 to 90 nm were uniformly assembled into the hexagonally ordered nanochannels of the AAM. Photoluminescence (PL) measurements show a blue PL band in the wavelength range of 450-650 nm caused by the singly ionized oxygen vacancy in ZnO nanowires. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

This article focuses on a study related to direct electrodeposition of highly dense Bi/Sb superlattice nanowire arrays. Heterostructure formation in one-dimensional nanostructures is equally important for their unique physics properties and has produced much interesting research. Theoretical study indicated that superlattice nanowires are promising systems for the thermoelectric applications, because this structure is believed to be better in reducing phonon transport and keeping high electron mobility. The electrodeposition process is stopped when the wires emerge from the anodic alumina membranes surface.