Growth and morphologies of large-scale SnO2 nanowires, nanobelts and nanodendrites

Single-crystalline SnO₂ nanowires, nanobelts and nanodendrites were synthesized by a simple gas-reaction route on a large scale at 900 °C. They were characterized by means of X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM) and selected-area electron diffraction (SAED). FE-SEM images showed that the products consisted of nanowires, nanobelts and nanodendrites that represent a novel morphology reported for the first time. XRD, SAED and EDS indicated that they were single-crystalline tetragonal SnO₂. The influence of experimental conditions on the morphologies of the products is discussed. Received: 3 June 2002 / Accepted: 10 June 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: 86-10/82649531, E-mail: xlchen@aphy.iphy.ac.cn     

Electroless synthesis of large scale Co-Zn-P nanowire arrays and the magnetic behaviour

Co-Zn-P nanowire arrays have been synthesized by electroless deposition in an anodic alumina membrane (AAM). The images of Co-Zn-P nanowire arrays and single nanowires are obtained by both scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that Co-Zn-P nanowire arrays are amorphous in structure. The hysteresis loops characterized by a vibrating sample magnetometer (VSM) show that the easily magnetized direction of Co-Zn-P nanowire arrays is parallel to the nanowire arrays and that there exhibits clearly a magnetic anisotropy as a result of the shape anisotropy.     

Autocatalytic redox fabrication and magnetic studies of Co-Ni-P alloy nanowire arrays

Uniform and large-scale Co-Ni-P alloy nanowire arrays have been fabricated by autocatalytic redox reaction in an anodic alumina membrane (AAM). The images of Co-Ni-P alloy nanowire arrays and single nanowires are obtained by scanning electron microscope (SEM) and transmission electron microscope (TEM), respectively. Selected area electron diffraction (SAED), X-ray diffraction (XRD) and energy dispersive spectra (EDS) are employed to study the morphology and chemical composition of the nanowires. The results indicate that the Co-Ni-P nanowire arrays are amorphous in structure. The magnetic property of Co-Ni-P nanowire arrays is characterized using a vibrating sample magnetometer (VSM). The hysteresis loops show that the easily magnetized direction of Co-Ni-P nanowire arrays is parallel to the nanowire arrays and that it has obvious magnetic anisotropy as a result of the shape anisotropy.     

Large-scale synthesis of SnO2 nanobelts

Tin dioxide (SnO₂) nanobelts have been successfully synthesized in bulk quantity by a simple and low-cost process based on the thermal evaporation of tin powders at 800 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations reveal that the nanobelts are uniform, with lengths from several-hundred micrometers to a few millimeters, widths of 60 to 250 nm and thicknesses of 10 to 30 nm. X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX) and selected-area electron diffraction analysis (SAED) indicate that the nanobelts are tetragonal rutile structure of SnO₂. The SnO₂ nanobelts grow via a vapor–solid (VS) process. Received: 3 June 2002 / Accepted: 10 June 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-551/559-1434, E-mail: gwmeng@mail.issp.ac.cn     

Synthesis of aligned GaN nanorods on Si (111) by molecular beam epitaxy

Straight and well-aligned GaN nanorods have been successfully synthesized by molecular beam epitaxy (MBE) method. The GaN nanorods have been characterized by field-emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). SEM images show that GaN nanorods are constituted with two parts of which shapes are different from each other. The upper part of the nanorod is very thin and its lower part is relatively thick. The XRD and EDS analysis have identified that the nanorods are pure hexagonal GaN with single crystalline wurtzite structure. The TEM images indicate that the nanorods are well crystallized and nearly free from defects. The XRD, HRTEM, and SAED pattern reveal that the growth direction of GaN nanorods is 〈0001〉. The photoluminescence (PL) spectra indicate the good emission property for the nanorods. Finally, we have demonstrated about the two-step growth of the nanorods. PACS 81.07.Bc; 81.05.Ea; 81.15.Hi     

Fabrication of bamboo-shaped GaN nanorods

Bamboo-shaped GaN nanorods were formed through a simple sublimation method. They were characterized by means of X-ray powder diffraction (XRD), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM) and selected-area electron diffraction (SAED). The TEM image showed that the nanorods were bamboo-like. XRD, HRTEM and SAED patterns indicated that the nanorods were single-crystal wurtzite GaN. Received: 8 January 2001 / Accepted: 28 April 2001 / Published online: 20 December 2001     

Sol–gel electrophoretic deposition and optical properties of Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowire arrays

Ordered Fe₂O₃ nanowire arrays embedded in anodic alumina membranes have been fabricated by Sol–gel electrophoretic deposition. After annealing at 600 °C, the Fe₂O₃ nanowire arrays were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected-area electron diffraction (SAED) and X-ray diffraction (XRD). SEM and TEM images show that these nanowires are dense, continuous and arranged roughly parallel to one another. XRD and SAED analysis together indicate that these Fe₂O₃ nanowires crystallize with a polycrystalline corundum structure. The optical absorption band edge of Fe₂O₃ nanowire arrays exhibits a blue shift with respect of that of the bulk Fe₂O₃ owing to the quantum size effect. PACS 78.67.Lt; 81.05.Je; 81.07.Vb     

High-quality GaN nanowires synthesized using a CVD approach

High-quality GaN nanowires were synthesized on a large-area Si substrate by direct reaction of gallium with ammonia using InCl₃ as a catalyst. The morphology and microstructure of the resulting products were characterized using a field-emission scanning electron microscope (SEM), a high-resolution transmission electron microscope, and X-ray diffraction (XRD). XRD and electron diffraction revealed that the nanowires are of a hexagonal GaN phase with the wurtzite structure. The SEM study showed that the nanowires are straight and have a smooth morphology with lengths up to 500 μm. The present results reveal that InCl₃ is an optimal catalyst in GaN nanowire production. Received: 2 April 2002 / Accepted: 12 April 2002 / Published online: 19 July 2002     

Electrochemical synthesis of ordered CdTe nanowire arrays

Semiconductor CdTe nanowire arrays embedded in the nanochannels of the porous anodic alumina (PAA) template have been prepared by using a potentiostatic electrochemical deposition method. The morphology and structure of the CdTe nanowire arrays have been characterized by X-ray powder diffraction, transmission electron microscopy, and high-resolution transmission electron microscopy. It is found that the CdTe nanowires with diameters and lengths of about 60 nm are single-crystalline with cubic phase structure, uniformly and continuously embedded in the nanochannels of the PAA template. X-ray energy-dispersion analysis and X-ray photoelectron spectroscopy analysis indicate that stoichiometric CdTe was formed. The growth mechanism of the CdTe nanowires is also discussed. Received: 11 June 2002 / Accepted: 2 July 2002 / Published online: 8 January 2003 RID="*" ID="*"Corresponding author. Fax: +86-551/559-1434, E-mail: aiwuzhao@yahoo.com.cn     

Synthesis, morphologies and Raman-scattering spectra of crystalline stannic oxide nanowires

SnO₂ nanowires were synthesized using a direct gas reaction route and were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), selected-area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM) and Raman-scattering spectroscopy. XRD, SEM, SAED and HRTEM indicated that the products were tetragonal SnO₂ nanowires with diameters of 10–50 nm. The nanowires were single crystal and solid inside. Dendritic nanowires were observed for the first time. Three vibrational modes were observed in the Raman spectra of the samples. Received: 7 January 2002 / Accepted: 11 April 2002 / Published online: 19 July 2002     

Copper nanowire arrays for infrared polarizer

A micropolarizer of copper nanowire arrays within anodic alumina membrane (AAM) was fabricated by anodization of pure Al foil and electrodeposition of Cu, respectively. X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations reveal that the ordered Cu nanowires are essentially single crystal, and have an average diameter of 90 nm. Spectrophotometer measurements show that the copper nanowire arrays embedded in AAM can only transmit polarized light vertical to the wires. An extinction ratio of 24 to 32 dB and an average insertion loss of 0.5 dB in the wavelength range of 1 to 2.2 μm were obtained, respectively. Therefore Cu nanowire/AAM can be used as a wire grid type micropolarizer. Received: 28 January 2002 / Accepted:17 May 2002 / Published online: 22 November 2002 RID="*" ID="*"Corresponding author. Fax: +86-551/559-1434, E-mail: ytpang@263.net     

Synthesis and magnetic properties of spinel CoFe2O4 nanowire arrays

Spinel CoFe₂O₄ nanowire arrays were synthesized in nanopores of anodic aluminum oxide (AAO) template using aqueous solution of cobalt and iron nitrates as precursor. The precursor was filled into the nanopores by vacuum impregnation. After heat treatment, it transformed to spinel CoFe₂O₄ nanowires. The structure, morphology and magnetic properties of the sample were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and vibrating sample magnetometer (VSM). The results indicate that the nanowire arrays are compact. And the individual nanowires have a high aspect ratio, which are about 80 nm in diameter and 10 μm in length. The nanowires are polycrystalline spinel phase. Magnetic measurements indicate that the nanowire arrays are nearly magnetic isotropic. The reason is briefly discussed. Moreover, the temperature dependence of the coercive force of the nanowire arrays was studied.     

Synthesis of aligned gallium nitride nanowire quasi-arrays

Self-aligned GaN nanowire quasi-arrays were synthesized on MgO crystal through a simple gas reaction method. They were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray (EDX) spectroscopy and high-resolution transmission electron microscopy (HRTEM). FE-SEMimages showed that the product consisted of quasi-arrays of nanowires. XRD, EDX and HRTEM indicated that the nanowires were wurtzite GaN single crystals. Received: 19 June 2000 / Accepted: 21 June 2000 / Published online: 9 August 2000     

Studies on nanocrystalline (Sr,Pb)TiO3 solid solutions prepared via a facile self-propagating combustion method

Macroporous nanocrystalline (Sr,Pb)TiO₃ solid solutions were prepared by a facile self-propagating combustion method. The samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), selected area electron diffraction (SAED), energy dispersive X-ray spectrum (EDS) and X-ray photoelectron spectroscopy (XPS). (Sr,Pb)TiO₃ solid solutions showed enhanced photocatalytic activity for the degradation of methyl orange (MO) than pure SrTiO₃ and an optimum performance was observed for Sr_29/32Pb_3/32TiO₃. The possible mechanism for the enhanced photocatalytic activity on (Sr,Pb)TiO₃ solid solutions was proposed.     

Catalytic synthesis of single-crystalline gallium nitride nanobelts

Single-crystalline gallium nitride nanobelts have been synthesized through the reaction of gallium vapor with flowing ammonia using nickel as a catalyst. The as-synthesized products were characterized using X-ray powder diffraction (XRD), scanning electron microscopy, energy-dispersive X-ray spectroscopy, transmission electron microscopy, and selected-area electron diffraction (SAED). XRD and SAED results revealed that the products are pure, single-crystalline GaN with hexagonal structure. The widths and thickness of the nanobelts ranged from 80 to 200 nm, and 10 to 30 nm, respectively. The lengths were up to several tens of micrometers. The nanobelts had smooth surface with no amorphous sheath, and a sharp-tip end. The growth mechanism of nanobelts was discussed.     

Fabrication of well-aligned CdS nanotubes by CVD-template method

Well-aligned CdS nanotubes have been synthesized within the nanochannels of the porous anodic alumina (PAA) membranes by pyrolyzing cadmium bis(diethyldithiocarbamate) [Cd(S₂CNEt₂)₂] at 400 °C. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) show that the CdS nanotubes are highly ordered with uniform diameter in range of 80-150 nm and the length up to tens of microns. X-ray diffraction (XRD), Raman spectrum, energy-dispersive spectroscopy (EDS) and selected-area electron diffraction (SAED) demonstrate that the nanotubes are composed of pure hexagonal phase polycrystalline CdS. The synthetic route can, in principle, be extended to fabricate other nanotubes of a wide range of semiconductors.     

Template synthesis of single-crystal Cu nanowire arrays by electrodeposition

Cu nanowire arrays have been synthesized using potentiostatic electrodeposition within the confined nanochannels of a porous anodic alumina membrane. The Cu nanowire arrays and the individual nanowires have been characterized using SEM, TEM, SAED, HREM and XRD. Investigation results reveal that the Cu nanowire arrays having high wire packing densities are highly ordered over large areas. The individual Cu nanowires (diameter ∼60 nm) were single-crystal and found to be dense and continuous with uniform diameters throughout their entire length. An optimum ECD condition (at lower overpotentials) for the synthesis of single-crystal Cu nanowires was also discussed. Received: 19 April 2001 / Accepted: 28 April 2001 / Published online: 20 June 2001     

A simple wet-chemical synthesis and characterization of CuO nanorods

Using a simple wet-chemical route, we synthesized CuO nanorods with diameters of ca. 5–15 nm and lengths of up to 400 nm. The purity, crystallinity, morphology, structure features, and chemical composition of the as-prepared CuO nanorods were investigated by powder X-ray diffraction, transmission electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and Raman spectroscopy. Received: 22 March 2002 / Accepted: 12 June 2002 / Published online: 28 October 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: wangqun@nju.edu.cn     

Synthesis and photoluminescence of aligned SiO<Subscript>x</Subscript> nanowire arrays

Aligned SiO_x nanowire arrays standing on a Si substrate were successfully synthesized using a simple method by heating a single-crystalline Si slice covered with SiO₂ nanoparticles at 1000 °C in a flowing Ar atmosphere. The SiO_x nanowire arrays were characterized by scanning electron microscopy and transmission electron microscopy. The SiO_x nanowires become progressively thinner from bottom to top. The formation process of the SiO_x nanowire arrays is closely related to a vapor–solid mechanism. Room-temperature photoluminescence measurements under excitation at 260 nm showed that the SiO_x nanowire arrays had a strong blue–green emission at 500 nm (about 2.5 eV), which may be related to oxygen defects. Received: 29 April 2002 / Accepted: 30 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-551-559-1434, E-mail: gwmeng@mail.issp.ac.cn     

Growth and characterization of high-quality GaN nanowires by ammonification technique

GaN nanowires were successfully synthesized at high quality and large yield on Si (1 1 1) substrate through ammoniating Ga₂O₃/BN films deposited by radio frequency (RF) magnetron sputtering system. X-ray diffraction (XRD), Fourier transformed infrared spectra (FTIR) and selected-area electron diffraction (SAED) confirm that the as-synthesized nanowires are of a hexagonal GaN with wurtzite structure. Scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) reveal that the nanowires have a straight and smooth curved structure with extremely uniform diameter of about 60 nm, which is helpful to the application of GaN nanowires. The present results demonstrate that the BN is a very important intermedium in the growth of GaN nanowires by this method.