Fabrication, morphology and structural characterization of ordered single-crystal Ag nanowires

Highly aligned Ag nanowires have been synthesized by dc electrodeposition within a hexagonal close-packed nanochannel anodic aluminum oxide template. The pore diameter varies from 20 nm to 50 nm depending on the anodization voltage and temperature for the two types of aqueous solutions, sulphuric and oxalic acids, respectively. The size and morphology of the Ag nanowire arrays were measured by scanning electron microscopy and transmission electron microscopy. The images indicate that the highly aligned Ag nanowires grow in the uniform nanochannels of the anodic alumina template and that the size of the nanowires depends on the size of the nanochannels. X-ray diffraction, selected area electron diffraction pattern and high-resolution transmission electron microscopy images show that the Ag nanowires are single-crystal. The temperature coefficient of resistivity (temperature range from 4.2 K to 300 K) of the Ag nanowire arrays decreases with decreasing diameter of the nanowires. Received: 5 November 2001 / Revised version: 12 March 2002 / Published online: 6 June 2002     

Catalytic growth and characterization of Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanowires

β-Ga₂O₃ nanowires have been synthesized using Ga metal and H₂O vapor at 800 °C in the presence of Ni catalyst on the substrate. Remarkable reduction of the diameter and increase of the length of the Ga₂O₃ nanowires are achieved by separation of Ga metal and H₂O vapor before they reach the substrate. Transmission electron microscopy analyses indicate that the β-Ga₂O₃ nanowires possess a single-crystalline structure. Photoluminescence measurements show two broad emission bands centered at 290 nm and 390 nm at room temperature. Received: 27 June 2002 / Accepted: 7 October 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +886-6/234-4496, E-mail: wujj@mail.ncku.edu.tw     

Novel technique for hetero-epitaxial diamond film growth on cubic boron nitride from iron carbide at high temperature and high pressure

Cubic boron nitride (c-BN) crystals about 0.1–0.3 mmin dimension were treated with iron carbide powders (high purity 99%) with size of 80–100 mesh at a high temperature of 1620 K and a high pressure of 5.2 GPa. It was found that hetero-epitaxial diamond films have been grown on the c-BN from iron carbide. The formation of dia-mond films on the cubic boron nitride can be confirmed by laser Raman spectra, face scan of elements and reflective high-energy electron diffraction. It was suggested that diamond films could be epitaxially formed on the c-BN through decomposition of iron carbide. This approach provides a possible and very effective way to realize hetero-epitaxial growth of homogeneous and large-area diamond films on c-BN, which is different from the conventional technique using a chemical vapor deposition method. Received: 20 December 2000 / Accepted: 9 January 2001 / Published online: 28 February 2001     

Fabrication and characterization of In2O3 nanowires

In₂O₃ nanowires were successfully fabricated through a simple gas-reaction route in argon atmosphere. These nanowires have diameters ranging from 20 nm to 50 nm and lengths up to tens of micrometers. High-resolution transmission electron microscopy observations and the electron-diffraction (ED) pattern reveal that the In₂O₃ nanowires are formed by the stacking of (2) planes along the [1] direction, which is parallel to the wire axis. A strong and wide ultraviolet (UV) emission band centered at around 392 nm is observed for the first time in the room-temperature photoluminescence measurement in addition to the usual blue emission (468 nm). Moreover, five discrete fine peaks (372 nm, 383 nm, 406 nm, 392 nm and 413 nm) are further identified in this broad UV band. Received: 10 April 2002 / Accepted: 12 April 2002 / Published online: 19 July 2002     

Direct synthesis of beta gallium oxide nanowires, nanobelts, nanosheets and nanograsses by microwave plasma

In this study, beta-gallium oxide (β-Ga₂O₃) nanowires, nanobelts, nanosheets, and nanograsses were synthesized through microwave plasma of liquid phase gallium containing H₂O in Ar atmosphere using silicon as the substrate. The nanowires with diameters of about 20-30 nm were several tens of microns long and the nanobelts with thickness of about 20-30 nm were tens to hundreds of microns long. The morphology and structure of products were analyzed by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM) and X-ray diffraction (XRD). These results showed that multiple nucleation and growth of β-Ga₂O₃ nanostructures could easily occur directly out of liquid gallium exposed to appropriate H₂O and Ar in the gas phase. The growth process of β-Ga₂O₃ nanostructures may be dominated by VS (vapor-solid) mechanism.     

Structure, catalysis and atomic reactions on the nano-scale: a systematic approach to metal hydrides for hydrogen storage

We show how reducing structure, catalysis and atomic reactions to the nano-scale may be used in a systematic way to substantially enhance the hydrogenation properties of metal hydrides. We examine, with examples from a wide range of hydrides, the direct impact of nano-scale structure, subsequent improvements in kinetics through nano-scale solid state catalysis, the special properties of nano-composites, and the role played by nano-scale reactions. Received: 25 August 2000 / Accepted: 14 November 2000 / Published online: 9 February 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     

Nanophotonics: a new multidisciplinary frontier

Nanophotonics, defined as nanoscale optical science and technology, is a new multidisciplinary frontier. This article presents our studies on nanoscale matter–radiation interactions utilizing nanoscale confinement of radiation as well as on nanoscale photochemical transformations, particularly nanoscale nonlinear optical interactions. The selected examples of our studies include nanoscopic optical harmonic generation, multiphoton fluorescence, transient absorption dynamics, surface-plasmon-enhanced two-photon fluorescence, and nonlinear optical information storage. Received: 12 December 2001 / Published online: 11 June 2002     

Large-scale synthesis of GaN nanorods and their photoluminescence

Large quantities of gallium nitride (GaN) nanorods have been synthesized via direct reaction of metallic gallium vapor with flowing ammonia at 970 °C in a quartz tube. The nanorods have been confirmed as crystalline wurzite GaN by powder X-ray diffraction, selected-area electron diffraction and X-ray photoelectron spectrometry. Transmission electron microscopy and scanning electron microscopy reveal that the nanorods are straight and uniform, with diameters ranging from 40 nm to 150 nm and lengths up to hundreds of micrometers. The growth mechanism is discussed briefly. Photoluminescence measurements on bulk GaN nanorods at room temperature show two strong peaks at 377 nm (3.28 eV) and 360 nm (3.44 eV) attributed to the zero-phonon donor-acceptor pair transition and the donor-bound exciton, respectively. Received: 19 April 2001 / Accepted: 10 May 2001 / Published online: 20 June 2001     

Synthesis and optical properties of CuS nanoplate-based architectures by a solvothermal method

The controlled synthesis of copper sulfide (CuS) nanoplate-based architectures in different solvents has been realized at low cost by simply reaction of Cu(NO₃)₂·3H₂O and S under solvothermal conditions without the use of any template. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-vis spectrometer and fluorescence measurement were used to characterize the products. The products were all in hexagonal phase with high crystallinity and the morphology was significantly influenced by the solvents. The CuS products synthesized in dimethylformamide (DMF) were nanoplates and the samples prepared in ethanol were flower-like morphology composed of large numbers of nanoplates, but those synthesized in ethylene glycol (EG) were CuS architectures with high symmetry made up of several nanoplates arranged in a certain mode. The optical properties were investigated and the growth mechanisms of these CuS crystals were also proposed.     

Characterization of PbS with different morphologies produced using a cyclic microwave radiation

PbS was produced from different lead (Pb(CH₃COO)₂·H₂O, PbCl₂·2.5H₂O, Pb(NO₃)₂) and sulfur (CH₃CSNH₂, CH₅N₃S, NH₂CSNH₂) sources in propylene glycol using a cyclic microwave radiation at different powers and prolonged times. PbS (cubic) was detected using X-ray diffraction (XRD) and selected area electron diffraction (SAED) techniques. The interpreted and simulated patterns are in good accord. Raman spectrometer revealed the presence of vibrations at 138, 273 and 439 cm⁻¹. Different morphologies (nano-sized particles, hexapods, cubes, ferns and magic squares) were characterized using a scanning electron microscope (SEM) and a transmission electron microscope (TEM). The product morphologies were influenced by the starting agents, microwave powers and prolonged times.     

Single-crystalline Zn2SnO4 hexangular microprisms: Fabrication, characterization and optical properties

Large-scale Zn₂SnO₄ hexangular microprisms were successfully synthesized through a simple thermal evaporation method by heating metal Zn and Sn powders under varying temperatures. The synthesized microprisms are single-crystalline, tens of micrometers in length. And their surfaces have many nano-scale skewed steps along the axial direction. Structurally, we supposed that the hexangular prism could be described as a row of inlaid octahedron of Zn₂SnO₄ crystals. A broad asymmetrical emission band was observed in the PL spectrum of these Zn₂SnO₄ microprisms, which was discussed in detail in the paper.     

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     

Novel W-shaped and straight porous ZnO nanobelts

Novel W-shaped porous ZnO nanobelt with the periodical junction angles of about 118° and straight porous ZnO nanobelt have been successfully synthesized. The W-shaped structure growth changes from [0 0 0 1] to periodically. The straight nanobelt grows along [0 0 0 1] direction. Both of the structures have smooth surfaces with high porous density. Based on our X-ray diffraction (XRD), electron microscopy and photoluminescence (PL) spectrum study, the growth mechanism of the special ZnO nanostructures is discussed, emphasizing the effect of alteration of the reactant concentration for two different morphologies.     

Deposition of mass-selected cluster ions using a pulsed arc cluster-ion source

A PACIS (pulsed arc cluster-ion source) developed for high average cluster-ion currents is presented. The performance of the PACIS at different operational modes is described, and the suitability for cluster-deposition experiments is discussed in comparison with other cluster-ion sources. Maximum currents of mass-selected cluster ions of 3–6 nA of small Si_n ^- (n=4–10) clusters and 0.3–0.5 nA of large Al_n ^+/- (n=20–70) clusters are achieved. The mass-selected cluster ions are soft-landed on a substrate at residual kinetic energies lower than 1 eV/atom, and the samples are characterized by X-ray photoelectron spectroscopy and scanning tunneling microscopy. First results on the soft landing of “magic” Si₄ ^- clusters on graphite are presented. Received: 30 May 2001 / Accepted: 14 June 2001 / Published online: 2 October 2001     

A relation between a metallic film covering on diamond formed during growth and nanosized inclusions in HPHT as-grown diamond single crystals

One of the most important characteristics and basic phenomena during diamond growth from liquid metal catalyst solutions saturated with carbon at high temperature–high pressure (HPHT) is that there exists a thin metallic film covering on the growing diamond, through which carbon-atom clusters are delivered to the surface of the growing diamond by diffusion. A study of microstructures of such a metallic film and a relation between the thin metallic film and the inclusions trapped in HPHT as-grown diamond single crystals may be helpful to obtain high-purity diamond single crystals. It was found that both the metallic film and the HPHT as-grown diamond single crystals contain some nanostructured regions. Examination by transmission electron microscopy suggests that the microstructure of the thin metallic film is in accordance with nanosized particles contained in HPHT as-grown diamond single crystals. The nanosized particles with several to several tens of nanometers in dimension distribute homogeneously in the metallic film and in the diamond matrix. Generally, the size of the particles in the thin metallic film is relatively larger than that within the diamond matrix. Selected area electron diffraction patterns suggest that the nanosized particles in the metallic film and nanometer inclusions within the diamond are mainly composed of f.c.c. (FeNi)₂₃C₆, hexagonal graphite and cubic γ-(FeNi). The formation of the nanosized inclusions within the diamond single crystals is thought not only to relate to the growth process and rapid quenching from high temperature after diamond synthesis, but also to be associated with large amounts of defects in the diamond, because the free energy in these defect areas is very high. The critical size of carbide, γ-(FeNi)and graphite particles within the diamond matrix should decrease and not increase according to thermodynamic theory during quenching from HPHT to room temperature and ambient pressure. Received: 13 September 2001 / Accepted: 12 June 2002 / Published online: 17 December 2002 RID="*" ID="*"Corresponding author. Fax: +86-0531/295-5081; E-mail: yinlw@sdu.edu.cn     

Microstructural properties of bulk nanocrystalline Ag–Ni alloy prepared by hot pressing of mechanically pre-alloyed powders

A bulk nanocrystallined Ag50Ni alloy has been prepared by hot-pressing the mechanically pre-alloyed powders at 620 °C under a normal pressure of 58 MPa in vacuum. The microstructural characteristics of the alloy were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results of the precise determination of the lattice parameters of the phases in the powders and in the alloy by XRD show that, after mechanical alloying for 200 h, the solid solubility of Ag in Ni reaches 4.85±0.21 at %, while that of Ni in Ag reaches 0.84±0.30 at %. After hot pressing, the Ag- and Ni-rich phases in the alloy still show a certain degree of supersaturation, with a solid solubility of 0.45±0.11 at % of Ag in Ni. After further annealing of the alloy at 700 °C for 24 h, the solubility decreases to a value of 0.21±0.11 at % for Ag in Ni and to less than 0.1 at % for Ni in Ag. The grain size of the mechanically alloyed powders was of ca 6 nm. After hot pressing, the grain size of the alloy increased to 40–60 nm and then grew further to 100–110 nm after annealing. The influence of the variation of the grain size and the internal stress on the line breadth of the X-ray diffraction peaks has been evaluated in detail. Finally, the role of the nanocrystalline structure in the fast densification process of the powders is also discussed. Received: 12 September 2001 / Accepted: 18 Febraury 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-24/2389-3624, E-mail: wwt@icpm.syb.ac.cn     

Effects of temperature and pressure on CVD diamond growth from the C-H-O system

Received: 28 August 1997/Accepted: 18 November 1997     

Synthesis and morphology of boron nitride nanotubes and nanohorns

Boron nitride (BN) nanotubes have been synthesized by evaporating a mixture of boron and gallium oxide in the presence of ammonia gas. The synthesized BN nanotubes exhibit a well-crystallized concentric structure with diameters less than 30 nm, and no carbon contamination or defects could be observed, while the BN nanotubes with large diameters usually show a number of defects. Some BN nanohorn structures could also be observed in the product. The carbon-free growth of BN nanotubes was explained based on the vapor–liquid–solid growth mechanism, and the catalytic activity of liquid gallium for BN one-dimensional growth was also demonstrated. Received: 16 April 2002 / Accepted: 25 May 2002 / Published online: 19 July 2002     

Synthesizing of ZnO Micro/Nanostructures at Low Temperature with New Reducing Agents

Instead of the conventional graphite, new additional reducing agents （diamond, silicon, metal elements, etc.） have been mixed with zinc oxide （ZnO） powder to fabricate ZnO micro/nanostructures by a thermal vapour transport method. Due to the strong reducibility for those additions, the corresponding heating temperature is decreased by 100 500℃ compared to the case of graphite, which subsequently decreases the corresponding growth temperature for the products. Being placed separately for the powder sources of ZnO and addition, a vapour-vapour reduction-oxidation reaction mechanism between the sources is proposed as an important channel to fabricate ZnO. Photoluminescence and magnetic examinations indicate that the ZnO products synthesized have strong ultraviolet （visible） emissions and are room-temperature ferromagnetic, meaning that the products are available for applications.