Formation of well-aligned ZnGa(2)O(4) nanowires from Ga(2)O(3)/ZnO core-shell nanowires via a Ga(2)O(3)/ZnGa(2)O(4) epitaxial relationship

Formation of well-aligned and single-crystalline ZnGa(2)O(4) nanowires on sapphire (0001) substrates has been achieved via annealing of the Ga(2)O(3)/ZnO core-shell nanowires. Ga(2)O(3)/ZnO core-shell nanowires were prepared using a two-step method. The thickness of the original ZnO shell and the thermal budget of the annealing process play crucial roles for preparing single-crystalline ZnGa(2)O(4) nanowires. Structural analyses of the annealed nanowires reveal the existence of an epitaxial relationship between ZnGa(2)O(4) and Ga(2)O(3) phases during the solid-state reaction. A strong CL emission band centered at 360 nm and a small tail at 680 nm are obtained at room temperature from the single-crystalline ZnGa(2)O(4) nanowires.     

Synthesis of blue-light-emitting ZnGa2O4 nanowires using chemical vapor deposition

A high-density array of vertically aligned ZnGa(2)O(4) nanowires has been synthesized on Si substrates via CVD of ZnO-Ga at 1000 degrees C consisting of a single-crystalline cubic spinel structure grown in a [111] direction and exhibiting strong photoluminescence and cathodoluminescence in the blue wavelength region.     

Dielectrophoretic growth of platinum nanowires: concentration and temperature dependence of the growth velocity

The growth velocity of platinum nanowires in an aqueous solution of K(2)PtCl(4) is investigated as a function of the metal complex concentration and temperature. The solution is specially prepared to provide mainly the neutral complex cis-[PtCl(2)(H(2)O)(2)] for growing nanowires by dielectrophoresis. The measured growth velocities indicate diffusion-limited nanowire growth at low concentration and high temperature in qualitative agreement with a theoretical analysis that includes the diffusion of metal complexes and the dielectrophoretic force on the complexes. At concentrations greater than 100 μM and low temperature, different behavior is observed, suggesting the growth rate to be limited by the deposition reaction of platinum at the nanowire tip. The enhancement of the K(+) concentration is found to support nanowire growth. Possible reasons for a rate limitation and for the difference between observed and calculated nanowire growth velocities are discussed.     

Novel Zn1-xMnxSe (x = 0.1-0.4) one-dimensional nanostructures: nanowires, zigzagged nanobelts, and toothed nanosaws

Novel Zn1-xMnxSe one-dimensional nanostructures-straight nanowires (x = 0.1 and 0.3), zigzagged nanobelts (x = 0.4), and toothed nanosaws (x = 0.4)-were synthesized using the chemical vapor deposition method. They all consisted of single-crystalline wurtzite ZnSe crystals, irrespective of the Mn content. In particular, the nanosaws have a unique structure in which double-sided teeth are rooted in the nanowire core and bent so as to align as two parallel rows. The long axis is parallel to the [010] direction, and all of the teeth have the [0001] growth direction. The X-ray diffraction pattern confirms the formation of wurtzite ZnSe crystal and the decrease of the lattice constant owing to Mn doping. The Mn2+ emission at 2.1 eV (appeared below 100 K), originating from the d-d (4T1 --> 6A1) transition, proves the effective substitution of Mn2+ ions at the tetrahedral coordinate sites.     

Polymorph-tuned synthesis of α- and β-Bi2O3 nanowires and determination of their growth direction from polarized Raman single nanowire microscopy

We report polymorph-tuned synthesis of α- and β-Bi(2)O(3) nanowires and their single nanowire micro-Raman study. The single crystalline Bi(2)O(3) nanowires in different phases (α and β) were selectively synthesized by adjusting the heating temperature of Bi precursor in a vapor transport process. No catalyst was employed. Furthermore, at an identical precursor evaporation temperature, α- and β- phase Bi(2)O(3) nanowires were simultaneously synthesized along the temperature gradient at a substrate. The growth direction of α-Bi(2)O(3) nanowires was revealed by polarized Raman single nanowire spectra. For thin β-Bi(2)O(3) nanowires with a very small diameter, the polarized Raman single nanowire spectrum was strongly influenced by the shape effect.     

Single-crystalline ZnGa2O4 spinel phosphor via a single-source inorganic precursor route

The synthesis of single-crystalline ZnGa 2O 4 spinel phosphor with intense ultraviolet-emitting properties through a novel single-source inorganic precursor route is reported. This synthetic approach involves the calcination of a Zn-Ga layered double hydroxide precursor followed by selective leaching of the self-generated zinc oxide. Material characterization has been presented by chemical analysis, X-ray diffraction analysis, thermogravimetric-differential thermal analysis, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, electron paramagnetic resonance, nuclear magnetic resonance, extended X-ray absorption fine structure analysis, UV-vis, and photoluminescence measurements. The results indicate that a single-crystalline ZnGa 2O 4 spinel with an average particle size of around 150 nm has been obtained at a lower calcination temperature and shorter calcination time compared with that with the high-temperature solid-state reaction method, based on the fact that the large amount of highly dispersed ZnO particles generated during the high-temperature calcination of the single-source inorganic precursor has a remarkable segregation and inhibition effect on the growth of ZnGa 2O 4 spinel. Furthermore, it has been confirmed that that Ga (3+) ions locate not only on the octahedral sites but also on the tetrahedral sites in the matrix of the ZnGa 2O 4 spinel structure, and the Ga-O coordination environment has a great influence on the photoluminescence of ZnGa 2O 4 phosphors.     

Synthesis, assembly, and optical properties of shape- and phase-controlled ZnSe nanostructures

Shape-, size-, and phase-controlled ZnSe nanostructures were synthesized by thermolysis of zinc acetate and selenourea using liganding solvents of octadecylamine (ODA) and trioctylphosphineoxide (TOPO) at different molar ratios. Materials synthesized in pure ODA resulted in uniform ultranarrow nanorods and nanowires of 1.3 nm in diameter. Morphological change from nanowire to spherical particle of larger diameter occurs with increasing TOPO/ODA ratio. Variation of the TOPO content in the mixed solvent also allows control of the crystallographic phase of ZnSe (wurtzite or zinc blende). The conditions and mechanisms of shape and phase control are discussed. Ultra-high-density networks of the ordered wires are achieved using the Langmuir-Blodgett technique in a single step as an essential stage on the route to ultra-high-density semiconductor nanocircuit fabrication.     

Epitaxial heterostructures: side-to-side Si-ZnS, Si-ZnSe biaxial nanowires, and sandwichlike ZnS-Si-ZnS triaxial nanowires

Epitaxial semiconducting heterostructures: side-to-side Si-ZnS, Si-ZnSe biaxial nanowires, and sandwichlike ZnS-Si-ZnS triaxial nanowires were grown via a simple two-stage thermal evaporation of mixed SiO and ZnS or SiO and ZnSe powders under a precise temperature control. Each nanowire had a uniform diameter of 40-120 nm and length ranging from several to several tens of micrometers. Subnanowires of Si, ZnS, and ZnSe within them had a diameter of 20-50, 40-60, and 20-50 nm, respectively. The optical property (nanoscale cathodoluminescence) was also investigated from these new structures. It is proposed that the Si nanowires formed through disproportionation of SiO to Si in the first evaporation stage and then served as one-dimensional nanoscale substrates (or templates) for an epitaxial growth of ZnS or ZnSe nanowires in the following thermal evaporation of ZnS or ZnSe powders. The present results suggest that the simple method might be useful for the synthesis of many other heterostructures containing Si and II-VI or III-V semiconducting composite nanowires to meet the growing demands of nanoscale science and technology.     

Synthesis of porous zinc gallate prisms composed of highly oriented nanoparticles by an in situ conversion reaction

Porous ZnGa(2)O(4) prisms assembled by highly oriented nanoparticles have been fabricated by an in situ chemical conversion approach. We report, for the first time, that a solid α-Ga(2)O(3) precursor can be directly converted into ZnGa(2)O(4) rather than through the intermediate GaOOH. Based on a detailed study of the evolution of ZnGa(2)O(4) prisms, a growth mechanism is proposed for the in situ conversion reaction. During this conversion process, the precursor morphology can be highly retained, which is attributed to the similar atomic arrangements of the Ga and O atoms and excellent matching of the lattice spacing between the α-Ga(2)O(3) and ZnGa(2)O(4) prisms. The direct reaction between the precursor α-Ga(2)O(3) and Zn(2+) ions is more efficient than that between the byproduct GaOOH and Zn(2+) ions. Moreover, the photoluminescent color of the ZnGa(2)O(4) phosphor can be tuned by doping with Mn(2+) ions. Efficient energy transfer (ET) from the host lattice to the Mn(2+) centers is observed, whereas ET from the defects to the Mn(2+) ions is prohibited. The fabricated ZnGa(2)O(4) products have potential in the field of display applications.     

三维分级结构ZnO的制备及光催化性能

以聚乙烯醇/醋酸锌复合纳米纤维为模板, 采用模板辅助共沉积技术制备了三维尖晶石型ZnO纳米线/纳米纤维分级结构, 并采用SEM, XRD对其形貌和晶型结构进行了表征. 在光催化降解乙醛性能实验中, 三维分级结构ZnO表现出比纳米粒子和纤维更好的光催化性能. 这主要归因于ZnO纳米线的次级结构和开放的三维网络结构更有利于乙醛分子和氧分子的扩散和传输, 从而提高了乙醛的光降解速率.     

Synthesis and characterization of indium-doped ZnO nanowires with periodical single-twin structures

In-doped ZnO (IZO) nanowires have been synthesized by a thermal evaporation method. The morphology and microstructure of the IZO nanowires have been extensively investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM). The products in general contain several kinds of nanowires. In this work, a remarkable type of IZO zigzag nanowire with a periodical twinning structure has been investigated by transmission electron microscopy (TEM). HRTEM observation reveals that this type of IZO nanowire has an uncommonly observed zinc blend crystal structure. These nanowires, with a diameter about 100 nm, grow along the [111] direction with a well-defined twinning relationship and a well-coherent lattice across the boundary. In addition, an IZO nanodendrite structure was also observed in our work. A growth model based on the vapor-liquid-solid mechanism is proposed for interpreting the growth of zigzag nanowires in our work. Due to the heavy doping of In, the emission peak in photoluminescence spectra has red-shifted as well as broadened seriously.     

Synthesis of CdS and ZnS nanowires using single-source molecular precursors

Single-source molecular precursors were used to synthesize II-VI compound semiconductor nanowires for the first time. Cadmium sulfide and zinc sulfide nanowires were prepared using cadmium diethyldithiocarbamate, Cd(S2CNEt2)2, and zinc diethyldithiocarbamate, Zn(S2CNEt2)2, respectively, as precursors in a gold nanocluster-catalyzed vapor-liquid-solid growth process. High-resolution transmission electron microscopy studies show that the CdS and ZnS nanowires are single-crystal wurtzite structures with stoichiometric compositions. In addition, photoluminescence measurements demonstrate that these nanowires exhibit high-quality optical properties. The applicability of our approach to the synthesis of other compound and alloy semiconductors nanowires as well as nanowire heterostructures of these materials is discussed.     

Metal dicarboxylates as thermal stabilizers for PVC

Different metal dicarboxylates such as calcium glutarate, zinc glutarate, calcium sebacate and zinc sebacate were investigated in this paper as thermal stabilizers (without and with calcium stearate and pentaerythritol as costabilizers) of poly(vinyl chloride) (PVC). The thermal stability of the PVC films was determined by two different methods which are visual color comparison and measurement of HCl release from heated pellets. Both zinc dicarboxylates and calcium dicarboxylates exhibited good thermal stability. With respect to stabilizing performance, zinc glutarate (ZnGa) was more effective than zinc sebacate (ZnSe), particularly in the presence of a large amount of pentaerythritol. Similarly, calcium glutarate (CaGa) was more effective than calcium sebacate (CaSe). And the relative order of stabilizing effectiveness of metal dicarboxylates was as follows: CaGa > CaSe > ZnGa > ZnSe. Moreover, the Ca-Zn complex thermal stabilizer and the Pe-Zn complex thermal stabilizer were also studied. It was found that no more than 20% of the zinc compound exhibited better stabilizing performance.     

Cr掺杂镓铟酸锌长余辉纳米粒子的制备及生物传感应用

通过水热法合成了不同含量In离子掺杂的ZnGa_1.99-xIn_xO₄∶Cr_{0. 01}³⁺长余辉纳米粒子(PLNPs)。通过In掺杂和改变反应pH条件,PLNPs的余辉强度和时长明显改善,近红外余辉时间超过96h,平均粒径为15.36nm。实验结果表明,PLNPs的余辉强度被多巴胺猝灭,PLNPs的相对余辉强度(F₀-F)/F₀与多巴胺浓度在0.005～20μmol/L范围内呈良好的线性关系,线性回归线方程为y=0.1789x+0.4427,相关系数R²=0.9974,对多巴胺的检出限为0.0024μmol/L,其在生物传感领域有应用潜力。     

Molten gallium as a catalyst for the large-scale growth of highly aligned silica nanowires

The vapor-liquid-solid (VLS) process is a fundamental mechanism for the growth of nanowires, in which a small size (5-100 nm in diameter), high melting point metal (such as gold and iron) catalyst particle directs the nanowire's growth direction and defines the diameter of the crystalline nanowire. In this article, we show that the large size (5-50 microm in diameter), low melting point gallium droplets can be used as an effective catalyst for the large-scale growth of highly aligned, closely packed silica nanowire bunches. Unlike any previously observed results using gold or iron as catalyst, the gallium-catalyzed VLS growth exhibits many amazing growth phenomena. The silica nanowires tend to grow batch by batch. For each batch, numerous nanowires simultaneously nucleate, grow at nearly the same rate and direction, and simultaneously stop growing. The force between the batches periodically lifts the gallium catalyst upward, forming two different kinds of products on a silicon wafer and alumina substrate. On the silicon wafer, carrot-shaped tubes whose walls are composed of highly aligned silica nanowires with diameters of 15-30 nm and length of 10-40 microm were obtained. On the alumina substrate, cometlike structures composed of highly oriented silica nanowires with diameters of 50-100 nm and length of 10-50 microm were formed. A growth model was proposed. The experimental results expand the VLS mechanism to a broader range.     

Si nanowire semisphere-like ensembles as field emitters

Silicon nanowires assembled in micro-sized semispheres were synthesized through simple thermal evaporation without using any templates and metal particle catalysts; electron microscopy revealed that the nanowires within semisphere ensembles are well-aligned and evenly distributed; a typical nanowire array density was of approximately 4 x 10(9) cm(-2); field-emitting characteristics of the arrays were analyzed.     

Controlled growth of large-area, uniform, vertically aligned arrays of alpha-Fe2O3 nanobelts and nanowires

Vertically aligned iron oxide nanobelt and nanowire arrays have been synthesized on a large-area surface by direct thermal oxidation of iron substrates under the flow of O(2). The effects of reactive gas pressure, composition, and temperature have been systematically studied. It was found that nanobelts (width, tens of nanometers; thickness, a few nanometers) are produced in the low-temperature region (approximately 700 degrees C) whereas cylindrical nanowires tens of nanometers thick are formed at relatively higher temperatures (approximately 800 degrees C). Both nanobelts and nanowires are mostly bicrystallites with a length of tens of micrometers which grow uniquely along the [110] direction. The growth habits of the nanobelts and nanowires in the two temperature regions indicate the role of growth rate anisotropy and surface energy in dictating the ultimate nanomorphologies.     

Low-temperature synthesis of single crystalline Ag2S nanowires on silver substrates

We report on the successful synthesis of silver sulfide (Ag(2)S) nanowires by a simple and mild gas-solid reaction approach. For the nanowire synthesis, a preoxidized silver substrate is exposed to an atmosphere of an O(2)/H(2)S mixture at room temperature or slightly above. The resulting Ag(2)S nanowires are phase pure with a monoclinic crystal structure and have diameters of a few tens of nanometers and lengths up to 100 mum. The influence of reaction conditions on the diameter, length, and morphology of the Ag(2)S nanowires has been studied by a number of structural and spectroscopic techniques. The nanowire growth mechanism on the Ag substrate has been discussed, which is likely characterized by continuous deposition at the tip. Additionally, we demonstrate thinning and cutting of individual Ag(2)S nanowires with electron beams and laser beams, which are potentially useful for nanowire manipulation and engineering.     

Control of the ZnO nanowires nucleation site using microfluidic channels

We report on the growth of uniquely shaped ZnO nanowires with high surface area and patterned over large areas by using a poly(dimethylsiloxane) (PDMS) microfluidic channel technique. The synthesis uses first a patterned seed template fabricated by zinc acetate solution flowing though a microfluidic channel and then growth of ZnO nanowire at the seed using thermal chemical vapor deposition on a silicon substrate. Variations the ZnO nanowire by seed pattern formed within the microfluidic channel were also observed for different substrates and concentrations of the zinc acetate solution. The photocurrent properties of the patterned ZnO nanowires with high surface area, due to their unique shape, were also investigated. These specialized shapes and patterning technique increase the possibility of realizing one-dimensional nanostructure devices such as sensors and optoelectric devices.     

泡沫镍负载的NiCo2O4纳米线阵列电极的超级电容性能

采用无模板自然生长法制备了泡沫镍支撑的NiCo₂O₄纳米线阵列电极, 利用扫描电镜(SEM)和透射电镜(TEM)观测了纳米线的表面形貌, 利用X射线衍射(XRD)分析了纳米线的结构, 通过循环伏安、恒流充放电和交流阻抗测试了电极的超级电容性能. 结果表明: NiCo₂O₄纳米线直径约为500-1000 nm、长度约为10 μm, 垂直且密集地生长在泡沫镍骨架上. 纳米线阵列电极的放电比容量高达741 F·g^-1, 循环420次后比容量仍保持在655 F·g^-1, 电化学阻抗测试其电荷传递电阻仅为0.33 Ω, 420次循环后电荷传递电阻仅增加0.06 Ω.