Synthesis of ZnS nanorods by annealing precursor ZnS nanoparticles in NaCl flux

ZnS nanorods were fabricated by annealing precursor ZnS nanoparticles, which were prepared by one-step, solid-state reaction of ZnCl₂ and Na₂S through grinding by hand at ambient temperature, in NaCl flux. The as-prepared ZnS nanorods have diameters of 40-80 nm, and lengths up to several micrometers. The structural features and chemical composition of the nanorods were investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HRTEM), and Raman spectra.     

Preparation and spectroscopic properties of Nb2O5 nanorods

Nb₂O₅ nanorods have been prepared using water/ethanol media. The samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), UV-visible absorption and photoluminescence spectroscopy. The as-prepared Nb₂O₅ nanorods appeared to be single pseudohexagonal (TT-Nb₂O₅) phase. From the photoluminescence spectrum, two emission bands at 407 and 496 nm, respectively, were observed. The origin of the luminescence was discussed in detail.     

Structural and optical properties of ZnO nanorods grown on MgxZn1−xO buffer layers

ZnO nanorod arrays were synthesized by chemical-liquid deposition techniques on Mg_xZn_1−xO (x = 0, 0.07 and 0.15) buffer layers. It is found that varying the Mg concentration could control the diameter, vertical alignment, crystallization, and density of the ZnO nanorods. The X-ray diffraction (XRD), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) data show the ZnO nanorods prefer to grow in the (0 0 2) c-axis direction better with a larger Mg concentration. The photoluminescence (PL) spectra of ZnO nanorods exhibit that the ultraviolet (UV) emission becomes stronger and the defect emission becomes weaker by increasing the Mg concentration in Mg_xZn_1−xO buffer layers.     

Synthesis and characterization of β-Ga2O3 nanorods

A novel method was applied to prepare β-Ga₂O₃ nanorods. In this method, β-Ga₂O₃ nanorods have been successfully synthesized on Si(1 1 1) substrates through annealing sputtered Ga₂O₃/Mo films under flowing ammonia at 950 °C in a quartz tube. The as-synthesized nanorods are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and Fourier transform infrared spectroscopy (FTIR). The results show that the nanorod is single-crystalline Ga₂O₃ with monoclinic structure. The β-Ga₂O₃ nanorods are straight and smooth with diameters in the range of 200-300 nm and lengths typically up to several micrometers. The growth process of the β-Ga₂O₃ nanorods is probably dominated by conventional vapor-solid (VS) mechanism.     

Preparation and optical properties of Cu2O hollow microsphere film and hollow nanosphere powder via a simple liquid reduction approach

In this work, we report a simple liquid reduction approach to prepare Cu₂O hollow microsphere film and hollow nanosphere powder with Cu(OH)₂ nanorods as precursor and ascorbic acid as the reductant at 60 °C. When Cu(OH)₂ nanorod array film grown on a copper foil is used as the precursor, Cu₂O thin film made up of hollow microspheres with average diameter of 1.2 μm is successfully prepared. When the Cu(OH)₂ nanorods are scraped from the copper foil and then used as the precursor, Cu₂O hollow nanosphere powder with the average diameter of 270 nm is obtained. The samples are characterized by X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and ultraviolet-vis light (UV-vis) absorption spectra. A possible formation mechanism of Cu₂O hollow spheres is discussed.     

Growth mechanism and photoluminescence of the SnO2 nanotwists on thin film and the SnO2 short nanowires on nanorods

SnO2 nanotwists on thin film and SnO2 short nanowires on nanorods have been grown on single silicon substrates by using Au-Ag alloying catalyst assisted carbothermal evaporation of SnO2 and active carbon powders.The morphology and the structure of the prepared nanostructures are determined on the basis of field-emission scanning electron microscopy(FESEM),transmission electron microscopy(TEM),selected area electronic diffraction(SAED),high-resolution transmission electron microscopy(HRTEM),x-ray diffraction(XRD),Raman and photoluminescence(PL) spectra analysis.The new peaks at 356,450,and 489 nm in the measured PL spectra of two kinds of SnO2 nanostructures are observed,implying that more luminescence centres exist in these SnO2 nanostructures due to nanocrystals and defects.The growth mechanism of these nanostructures belongs to the vapour-liquid-solid(VLS) mechanism.     

Synthesis and characterization of single crystalline SnO<Subscript>2</Subscript> nanorods by high-pressure pulsed laser deposition

Tin oxide (SnO₂) nanorods were grown by high-pressure pulsed laser deposition (PLD). The nanorods were grown without the use of a catalyst but required high background pressure growth in order to realize small grain columnar growth and nanorod formation, with nanorod formation most favored on non-epitaxial substrates. The structures and morphology were characterized by field emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM). X-ray diffraction and HRTEM analysis indicate that the as-grown SnO₂ nanorods are single crystals with a rutile structure. The nanorods are approximately 50–90 nm in diameters and 1.5 μm in length. This method provides an approach for large area synthesis of one dimensional SnO₂ nanostructure materials. PACS 81.16.Mk; 61.46.-w; 81.07.-b     

Fabrication, morphology, and photoluminescence properties of GaN nanowires and nanorods by ammoniating Ga2O3/V films on Si(1 1 1)

GaN nanowires and nanorods have been successfully synthesized on Si(1 1 1) substrates by magnetron sputtering through ammoniating Ga₂O₃/V films at 900 °C in a quartz tube. X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectrum were carried out to characterize the structure, morphology, and photoluminescence properties of GaN sample. The results show that the GaN nanowires and nanorods with pure hexagonal wurtzite structure have good emission properties. The growth direction of nanostructures is perpendicular to the fringes of (1 0 1) plane. The growth mechanism is also briefly discussed.     

Influence of SnO2 coating and thermal annealing on the structure and luminescence properties of CuO nanorods

CuO-core/ SnO₂-shell one-dimensional nanostructures have been fabricated by thermal oxidation of a copper foil and then atomic layer deposition of SnO₂. The structure and optical properties of the nanostructures have been investigated by using scanning electron microscopy, transmission electron microscopy, X-ray diffraction, photoluminescence (PL) spectroscopy, and energy-dispersive X-ray analysis techniques. The nanostructures are found to have the form of nanorods, with the diameter of the CuO cores being in the range from a few tens to a few hundreds of nanometers, the thickness of the SnO₂ shells being ～15 nm, and with a length of a few tens of micrometers. The CuO cores and the SnO₂ shells of the as-synthesized nanorods have crystalline monoclinic CuO and amorphous SnO₂ structures, respectively, but the SnO₂ shells are found to crystallize to tetragonal SnO₂ on thermal annealing. The PL emission intensity of the CuO nanorods has been slightly increased by SnO₂ coating. The PL emission of the SnO₂-coated CuO nanorods is somewhat increased and the emission peak position is red-shifted from 550 to 580 nm by annealing in a reducing atmosphere. On the other hand, the PL emission is significantly increased and the emission peak position is shifted from 550 nm further to around 595 nm by annealing in an oxidative atmosphere. In addition, the origins of the PL enhancements in the nanorods by coating and annealing are discussed.     

Raman spectroscopic and photoluminescence study of single-crystalline SnO2 nanowires

Single-crystalline SnO₂ nanowires with sizes of 4-14 nm in diameter and 100-500 nm in length were produced in a molten salt approach by using hydrothermal synthesized precursor. Structural characters of the nanowires were examined by X-ray diffraction and high-resolution electron transmission microscopy. Raman, photoluminescence and X-ray photoelectron spectra of the samples were examined under heat treatments. Three new Raman modes at 691, 514 and 358 cm⁻¹ were recorded and assigned. The former two are attributed to activation of original Raman-forbidden A_2uLO mode and the third is attributed to defects in small-sized nanowires. A strong photoluminescence is observed at about 600 nm, the temperature effects is examined and the origin of the PL process is discussed via X-ray photoelectron spectra.     

Effect of zinc nitrate concentration on the structural and the optical properties of ZnO nanostructures

ZnO nanorods and nanodisks were formed on indium-tin-oxide-coated glass substrates by using an electrochemical deposition method. Scanning electron microscopy images showed that the ZnO nanorods were transformed into nanodisks with increasing Zn(NO₃)₂ concentration. X-ray diffraction patterns showed that the ZnO nanostructures had wurzite structures. The full widths at half maxima of the near band-edge emission peak of photoluminescence spectra at 300 K for ZnO nanorods were small, indicative of the high quality of the nanorods. These results indicate that the structural and the optical properties of ZnO nanostructures vary by changing Zn(NO₃)₂ concentration.     

Synthesis of GaN nanowires by Tb catalysis

Rare earth metal seed Tb was employed as catalyst for the growth of GaN wires. GaN nanowires were synthesized successfully through ammoniating Ga₂O₃/Tb films sputtered on Si(1 1 1) substrates. The samples characterization by X-ray diffraction and Fourier transform infrared indicated that the nanowires are constituted of hexagonal wurtzite GaN. Scanning electron microscopy, transmission electron microscopy, and high-resolution transmission electron microscopy showed that the samples are single-crystal GaN nanowire structures. The growth mechanism of the GaN nanowires is discussed.     

Fabrication of bismuth telluride nanotubes via a simple solvothermal process

The unique Bi₂Te₃ tubes were obtained via a simple solvothermal reaction in the presence of ethylenediaminetetraacetic acid disodium salt. The product was characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. Bi₂Te₃ nanosheets are vertically grown off the tube wall to form Bi₂Te₃ tubes. A possible formation mechanism is proposed.     

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     

Porous SnO2 nanoflakes with loose-packed structure: Morphology conserved transformation from SnS2 precursor and application in lithium ion batteries and gas sensors

Porous SnO₂ nanoflakes with loose-packed structure were synthesized by calcination of SnS₂ precursors that were obtained through solvothermal method at low temperature. The as-obtained SnO₂ product had a three-dimensional porous structure with relatively high specific surface area. It was found that the SnO₂ nanoflakes inherited the morphology of precursor while numerous pores were formed after the annealing process. The combined techniques of X-ray diffraction, energy-dispersive spectrum, field emission scanning electron microscopy, and (high-resolution) transmission electron microscopy were used for characterization of the as-prepared SnO₂ product. Moreover, the porous SnO₂ nanoflakes with loose-packed structure could be used as gas sensors for detecting ethanol and acted as anode for lithium ion batteries. Our study shows that the as-prepared SnO₂ nanoflakes not only exhibit good response and reversibility to ethanol gas but also display enhanced Li-ion storage capability.     

Luminescence properties of hierarchical CaMoO4 microspheres derived by ionic liquid-assisted process

Hierarchical calcium molybdate (CaMoO₄) nanostructured microspheres were synthesized via a facile room-temperature route assisted by an ionic liquid, 1-n-butyl-3-methylimidazolium chloride. The product was characterized by means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that micro-scaled CaMoO₄ powders were assembled by nanoparticles with diameters ranging from 10 to 20 nm. The optical absorbance, photoluminescence emission (PL), and luminescence excitation (PLE) were investigated. The PL spectra excited at 273 nm have a strong green emission band maximum at 511 nm, which is attributed to the charge-transfer transitions within the MoO₄²⁻ complex, and the luminescence intensity indicated a good luminescence quality of the CaMoO₄ materials. By varying the amount of this assisted agent, we found that the ionic liquid played a crucial role as a surfactant in the formation of CaMoO₄ materials with uniform hierarchical structure, which may be beneficial to the luminescence performance. This study presented a promising preparation strategy towards other luminescent materials.     

Studies on the structural and electrical properties of spray deposited SnO2:Sb thin films as a function of substrate temperature

Thin films of antimony doped tin oxide (SnO₂:Sb) were prepared by spray pyrolysis technique using SnCl₂ as precursor with the various antimony doping levels ranging from 1 to 4 wt%. The XRD analysis showed that the undoped SnO₂ films grow in (211) preferred orientation whereas the Sb doped films grow in (200) plane. Scanning electron microscopy studies indicated that the surface of the films prepared with lower doping level (1 wt%) consists of larger grains whereas those prepared with higher doping levels (>1 wt%) consist of smaller grains. The sheet resistance has been found to be reduced considerably (2.17 Ω/□) for Sb doped films. To the best of our knowledge this is the lowest sheet resistance obtained for Sb doped SnO₂ thin films.     

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.     

Preparation and characterization of SrSnO3 nanorods

Perovskite strontium stannate (SrSnO₃) nanorods were prepared by annealing the precursor SnSr(OH)₆ nanorods at 600 °C for 3 h. The precursor nanorods were hydrothermally synthesized at 160 °C for 16 h using Sr(NO₃)₂ and SnCl₄·5H₂O as starting materials in the presence of surfactant cetyltrimethyl ammonium bromide (CTAB). As-prepared samples were characterized by X-ray diffraction (XRD), thermogravimetric-differential thermal analysis (TG-DTA), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and infrared ray spectroscopy (IR). The results show that the as-synthesized powders are made of SrSnO₃ one-dimensional nanorods of about 0.2-1 μm length and 100-150 nm diameter. Possible formation mechanism of SrSnO₃ with nanorod structure under certain conditions was preliminarily analyzed, in which it was thought that CTAB played an important role in the formation process of the nanorod structure. Electrochemical performance of the samples versus Li metal was also evaluated for possible use in lithium-ion batteries.     

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