Crystalline boron nanowires

Ideal nanowire interconnects for nanoelectronics will be refractory, covalently bonded, and highly conductive, irrespective of crystallographic orientation. Theoretical studies suggest that boron nanotubes should be stable and exhibit higher electrical conductivities than those of carbon nanotubes. We describe CVD growth of elemental boron nanowires, which are found to be dense nanowhiskers rather than nanotubes. Conductivity measurements establish that they are semiconducting, with electrical properties consistent with those of elemental boron. High conductivities should be achievable through doping.     

Needlelike bicrystalline GaN nanowires with excellent field emission properties

Large-yield and crystalline GaN nanowires have been synthesized on a Si substrate via a simple thermal evaporation process. The majority of the GaN nanowires has bicrystalline structures with a needlelike shape, a triangular prism morphology, and a uniform diameter of approximately 100 nm. Field-emission measurements show that the bicrystalline GaN nanowires with sharp tips have a lower turn-on field of approximately 7.5 V/microm and are good candidates for low-cost and large-area electron emitters. It is believed that the excellent filed emission property is attributed to the bicrystalline structure defects and sharp tips.     

Electrogenerated upconverted emission from doped organic nanowires

The electrogenerated upconversion was achieved in the uniformly doped organic nanowires based on triplet energy transfer from tris(2,2'-bipyridyl)ruthenium(II) to 9,10-diphenylanthracene.     

Field emission properties of large-area nanowires of organic charge-transfer complexes

In this contribution, large-area organic charge-transfer complex (AgTCNQ and CuTCNQ) nanowires were synthesized by organic vapor-solid-phase reaction at mild experimental conditions. These nanowires were facilitated on the surface of Cu and Ag foils or different kinds of substrates coated with a layer of silver and copper on a large scale. The excellent field emission properties were observed in the as-grown AgTCNQ and CuTCNQ nanowires. They should have great potential in vacuum device applications.     

Optical and field emission properties of thin single-crystalline GaN nanowires

Thin high-quality gallium nitride (GaN) nanowires were synthesized by a catalytic chemical vapor deposition method. The synthesized GaN nanowires with hexagonal single-crystalline structure had thin diameters of 10-50 nm and lengths of tens of micrometers. The thin GaN nanowires revealed UV bands at 3.481 and 3.285 eV in low-temperature PL measurements due to the recombination of donor-bound excitons and donor-acceptor pairs, respectively. The blue shifts of UV bands in the low-temperature PL measurement were observed, indicating quantum confinement effects in the thin GaN nanowires which have smaller diameters than the exciton Bohr radius, 11 nm. For field emission properties of GaN nanowires, the turn-on field of GaN nanowires was 8.5 V/microm and the current density was about 0.2 mA/cm(2) at 17.5 V/microm, which is sufficient for the applications of field emission displays and vacuum microelectronic devices. Moreover, the GaN nanowires indicated stronger emission stability compared with carbon nanotubes.     

Hydrogels with Crystalline or Liquid Crystalline Structure

The formation of ordered structure in hydrogels derived from copolymers of hydrophilic and hydrophobic monomers with crystalline or liquid‐crystalline moieties is reviewed. The role of water in the formation of ordered structure and its influence on the thermal and mechanical properties of hydrogels are clarified. For example, by inducing a certain amount of water, an amorphous to crystalline transition occurs in gels of acrylic acid/alkyl acrylate copolymers. On the other hand, water induces a liquid‐crystalline (SmA) to liquid‐crystalline (SmI) transition in copolymers consisting of acrylic acid and 11‐(4′‐cyanobiphenyloxy)undecyl acrylate. These specific features regarding the formation of ordered structures in hydrogels might shed some light on the formation of ordered structure in biological tissues.     

Enhanced ultraviolet emission from ZnS-coated ZnO nanowires fabricated by self-assembling method

A simple chemical route for ZnS-coated ZnO nanowires with preferential (002) orientation is reported. Sodium sulfide and zinc nitrate were employed to supply S and Zn atoms at 60 degrees C to form ZnS-coated ZnO nanowires structures. Electron diffraction measurement shows that the ZnO/ZnS core-shell nanostructure is single crystalline. Interesting features are found in the photoluminescence (PL) spectra of ZnS-coated ZnO nanostructures. After coating, the UV emission of nanorods is dramatically enhanced at the expense of the green emission. The core/shell structure with higher band gap shell material and reduced surface states should be responsible for this PL enhancement.     

Characterization and field emission properties of ZnMgO nanowires fabricated by thermal evaporation process

In this paper, we investigate the roles of gold catalyst using modified thermal evaporation set-up in the growth process of ZnMgO nanowires. ZnMgO nanowires are fabricated on silicon substrates using different thickness of gold catalyst. A simple horizontal double-tube system along with chemical vapor diffusion of the precursors, based on Fick’s first law, is used to grow the ZnMgO nanowires. Field emission scanning electron microscopy images show that the ZnMgO nanowires are tapered. The optical properties of the ZnMgO nanowires are characterized by room temperature photoluminescence (PL) measurements. The PL studies demonstrate that the ZnMgO nanowires grown using this method have good crystallinity with excellent optical properties and have a larger band-gap in comparison to the pure ZnO nanowires. Field emission characterization shows that the turn-on field for the nanowires grown on the thinner gold film is lower than those grown on the thicker gold film.     

Non-catalytic and template-free growth of aligned CdS nanowires exhibiting high field emission current densities

Various CdS nanostructures, including nanoparticle film, bundles of quasi-aligned and well-aligned nanowires, were fabricated with a non-catalytic and template-free MOCVD process. The well-aligned CdS nanowires exhibit unusually high field emission current densities of 225 mA cm(-2) at the applied electric field of 20 V microm(-1).     

Accelerating electrochemistry with metal nanowires

Scalable, solution-phase syntheses of metal nanowires are enabling their increased use in electrochemical processes. This review highlights recent results demonstrating how metal nanowires can exhibit better durability and higher activity than traditional metal nanoparticle electrocatalysts on carbon supports. Metal nanowires can also form interconnected two-dimensional and three-dimensional (3D) networks that eliminate the need for a carbon support, thus eliminating the detrimental effects of carbon corrosion. Porous 3D networks of nanowires can be used as flow-through electrodes with the highest specific surface areas and mass transport coefficients obtained to date, enabling dramatic increases in the productivity of electrochemical reactions. Nanowire networks are also serving as 3D current collectors that improve the capacity of batteries. The tunable surface structure and dimensions of metal nanowires offer researchers a new opportunity to create electrodes that are tailored from the atomic scale to the microscale to improve electrochemical performance.     

Reagents with a Crystalline Coat

Tetrakis(dimethoxyphenyl)adamantane (TDA) readily forms crystalline inclusion complexes with reactive, toxic, or malodorous reagents, such as benzoyl chloride, acetyl chloride, cyclohexyl isocyanide, phosphorus trichloride, and trimethylsilyl chloride. The crystals are stable and largely free of the problematic properties of the free reagents. When exposed to solvents such as DMSO or MeOH, the reagents react, and a large portion of the TDA precipitates. The TDA‐coated reagents may lead to a safer way of storing, handling, and delivering reagents, and ultimately to synthetic protocols that do not require fume hoods.     

Review: the multicolored coordination chemistry of violurate anions

This review provides a comprehensive overview on the coordination chemistry of violuric acid, C₄H₃N₃O₄ (= H₃Vio), and its derivatives (e.g. 1,3-diorganovioluric acids and thiovioluric acid). The most remarkable property of these colorless compounds is the formation of brightly colored (pantochromic/polychromic) salts with colorless cations such as alkali metal and alkaline earth metal ions and organoammonium ions. These magnificent colors have fascinated chemists for more than a century. Only in recent years it has been fully recognized that the structural chemistry of violurates is rather interesting and diverse. Violurate anions are excellent building blocks for new supramolecular assemblies in the crystalline state. Various organoammonium violurates and transition metal violurate complexes have been structurally characterized through single-crystal X-ray diffraction. Highly characteristic for these structures is the formation of 1D, 2D, or 3D hydrogen-bonded assemblies in the crystalline state. This review provides a comprehensive overview on the multicolored coordination chemistry of violurate anions, with the focus being on structurally characterized species.     

Temperature and pH influences on the structural and the emission properties of electrodeposited CdSe nanowires

Cadmium selenite (CdSe) nanowires have been electrodeposited by potentiostatic method using polycarbonate membranes as template. For the same potential value, the pH modification of the solution or the temperature variation of the substrate leads to drastic differences of the CdSe composition. A meticulous study of the influence of both temperature and pH value on the stoichiometry of electrodeposited CdSe nanowires has been done and several combinations of temperature/pH leading to the 50–50 CdSe composition have been found. The as-electrodeposited CdSe nanowires under these specific conditions reveal a good crystallinity with a <111> preferred growth orientation exhibiting a luminescence band in the visible range corresponding to the CdSe gap.     

Fabrication of polydiacetylene nanowires by associated self-polymerization and self-assembly processes for efficient field emission properties

The paper described here concerns a challenge of general interest for producing a novel structure of a polymer aggregate, the achievement of nanowires with controlled diameters. We provide a strategy for fabricating a supramolecular polymer, in which ordered polydiacetylene nanowires can be obtained by associated self-polymerization and self-assembly processes. The polymer nanowire film shows excellent field emission properties with the turn-on field of 8.2 V/mum at 10 muA/cm2 and the maximum current density of 5 mA/cm2 at an applied field of 15 V/mum.     

具有结晶孔壁介孔镁锌氧复合物(英文)

以介孔碳为硬模板经过二次填充制备了介孔镁锌氧复合物.采用X射线衍射(XRD),透射电镜(TEM),扫描电镜(SEM),N2吸附脱附等手段对材料的结构及形貌进行了表征.结果表明,所制备的材料在具有高有序介孔结构的同时还具有结晶的孔壁.孔径尺寸均为4.0nm,比表面积均为114.5m2.g-1.广角XRD结果初步表明,材料中氧化镁和氧化锌复合形成了固溶体.该材料作为一种半导体材料有望在光学器件领域获得新的应用价值.     

液晶离聚物--液晶行为的研究

综述了液晶离聚物中离子的种类,位置、在链中浓度对液晶性能的影响,无论是主链还是侧链液晶离聚物,离子的种类,位置对中介区间的宽度有影响,但对中介相类型基本没有影响,当离子浓度增大到一定值时,液晶性能消失。     

Anisotropic and passivation-dependent quantum confinement effects in germanium nanowires: a comparison with silicon nanowires

Electronic structures of hydrogen-passivated germanium nanowires (GeNWs) along the [100], [110], [111], and [112] directions are studied by using the density functional theory within the generalized gradient approximation. The band gaps of the fully relaxed GeNWs along the [100], [110], and [111] directions are all direct at the smaller sizes, while those of the wires along the [112] direction remain indirect. The magnitude of the band gaps of the GeNWs for a given size approximately follows the order of E(g)[100] > E(g)[111] > E(g)[112] > E(g)[110]. Compared with silicon nanowires, GeNWs exhibit stronger quantum confinement effects. Replacement of H by the more stable ethine group is found to lead to a weakening of the quantum confinement effects of GeNWs.     

Bamboo-shaped Ag-doped TiO2 nanowires with heterojunctions

Bamboo-shaped Ag-doped TiO2 nanowires with heterojunctions were synthesized by a simple solvothermal method. The diameter of the nanowires was about 50-100 nm, and they had a length of up to a few millimeters. The detailed structure of the heterojunction in the nanowire was also characterized.