一维纳米氧化锌的场发射性能和光学性能研究

采用真空热蒸发法在不同的制备温度下,制备出了准阵列状和阵列状一维纳米ZnO结构。并利用X射线衍射、扫描电子显微镜、场发射测试仪、光致发光谱对ZnO纳米材料的结晶质量、形貌及场发射性能进行了分析研究。阵列状纳米氧化锌有较明显的择优生长取向。准阵列状纳米氧化锌的场发射性能优于阵列状纳米氧化锌。并通过对PL谱的对比分析得出,准阵列状纳米结构的结晶质量较好,阵列状纳米结构中存在的缺陷较多。     

Synthesis and field-emission properties of In2O3 nanostructures

Large-scale indium oxide nano/microstructures have been successfully synthesized by chemical vapor deposition. Scanning electron microscopy shows that the synthesized two kinds of products display two-section awls (the shape of synthesized products is like the awl which consists of a short-thick section and a long-thin section) and microcube morphologies. The as-synthesized products, characterized by XRD and TEM, are pure, structurally uniform and single crystalline. Field-emission measurements of these nano/microstructures showed low turn-on field of 3.2 V μm^− 1 and 4.1 V μm^− 1. The results showed that the two-section awl-like structure which has nanometer tips has better field-emission properties than the cube, which makes indium oxide structures promising candidates for further applications in field-emission microelectronic devices.     

Optical and field-emission properties of ZnO nanostructures deposited using high-pressure pulsed laser deposition

ZnO nanostructures were deposited on GaN (0001), Al2O3 (0001), and Si (100) substrates using a high-pressure pulsed laser deposition (PLD) method. Vertically aligned hexagonal-pyramidal ZnO nanorods were obtained on the Al2O3 and Si substrates whereas interlinked ZnO nanowalls were obtained on the GaN substrates. A growth mechanism has been proposed for the formation of ZnO nanowalls based on different growth rates of ZnO polar and nonpolar planes. Both ZnO nanorods and nanowalls exhibit a strong E2H vibration mode in the micro-Raman spectra. The corresponding fluorescence spectra of ZnO nanorods and nanowalls showed near band emission at 3.28 eV. The ZnO nanorods grown on the Si substrates exhibited better crystalline and optical properties compared with the ZnO structures grown on the GaN and Al2O3 substrates. The high aspect ratio, good vertical alignment, and better crystallinity of the ZnO nanorods with tapered tips exhibited promising field emission performance with a low turn-on field of 2 V/μm, a high current density of 7.7 mA/cm2, and a large field enhancement factor.     

Thermochromic VO2 nanorods and other vanadium oxides nanostructures

Thermochromic VO₂ nanorods were prepared via thermal conversion of the metastable VO₂–B phase synthesized by hydrothermal methods. We observe an increased thermochromic transition temperature to ∼75–80 °C by variable-temperature infrared spectroscopy. Nano- and sub-micron structures of other vanadium oxides (V₃O₇, (NH₄)_0.5V₂O₅, and V₂O₅) were obtained simply by varying the starting materials in the hydrothermal synthesis. We also obtained nanostructures of the high temperature tetragonal rutile phase of VO₂ by thermolysis of single-source vanadium (IV) precursors.     

二氧化钒制备与应用的新进展

二氧化钒是一种性能优异的金属-半导体相变材料,其相变温度接近于室温,因此具有良好的应用前景.综述了二氧化钒粉体与薄膜的制备方法,系统地介绍了二氧化钒薄膜在各领域的研究进展,并展望了二氧化钒的研究前景.     

Fabrication, microstructure, and mechanical properties of tin nanostructures

Vertically aligned, cylindrical tin nanopillars have been fabricated via an electron beam lithography and electroplating method. Characterization by a non-destructive synchrotron X-ray microdiffraction (μSXRD) technique revealed that the tin nanostructures are body-centered tetragonal and are likely single-crystalline, or consist of a few large grains. The mechanical properties of tin nanopillars with average diameters of 920 nm, 560 nm, and 350 nm were studied by uniaxial compression in a nanoindenter outfitted with a flat punch diamond tip. The results of compression tests reveal strain rate sensitivity for nanoscale tin deformation, which matches closely to the previously reported bulk tin values. However, unlike bulk, tin nanopillars exhibit size-dependent flow stresses where smaller diameter specimens exhibit greater attained strengths. The observed size-dependence matches closely to that previously reported for single-crystalline face centered cubic metals at the nanoscale. μSXRD data was used to compare the dislocation density between as-fabricated and deformed tin nanopillars. Results of this comparison suggest that there is no measurable accumulation of dislocations within deformed tin nanopillars.     

Beaklike SnO2 nanorods with strong photoluminescent and field-emission properties

Beaklike SnO2 nanorods were synthesized by a vapor-liquid-solid approach using Au as a catalyst. The nanorods grow along the [10 1] direction and the beak is formed by switching the growth direction to [1 12] through controlling the growth conditions at the end of the synthesis. The photoluminescence (PL) spectrum of the nanorods exhibits visible light emission with a peak at 602 nm. The field-emission (FE) properties of the nanorods have been measured to exhibit a turn-on field of 5.8 V microm(-1). A comparative study of FE measurements between SnO2 nanorods with uniform diameters and these beaklike nanorods suggests that the shape and curved tips are important factors in determining the FE properties.     

Low-dimensional SiC nanostructures: Fabrication, luminescence, and electrical properties

Nanostructured silicon carbide has unique properties that make it useful in microelectronics, optoelectronics, and biomedical engineering. In this paper, the fabrication methods as well as optical and electrical characteristics of silicon carbide nanocrystals, nanowires, nanotubes, and nanosized films are reviewed. Silicon carbide nanocrystals are generally produced using two techniques, electrochemical etching of bulk materials to form porous SiC or embedding SiC crystallites in a matrix such as Si. Luminescence from SiC crystallites prepared by these two methods is generally believed to stem from surface or defect states. Stable colloidal 3C-SiC nanocrystals which exhibit intense visible photoluminescence arising from the quantum confinement effects have recently be produced. The field electron emission and photoluminescence characteristics of silicon carbide nanostructures as well as theoretical studies of the structural and electronic properties of the materials are described.     

Fabrication and optical properties of spear-like ZnO nanostructures by chemical vapor deposition

Novel spear-like ZnO nanowires with a length of 2 μm and a width of 0.26 μm were synthesized on p-Si (100) substrates by chemical vapor deposition (CVD) method without catalysts. The crystal structures and morphographies of the products were characterized by X-ray powder diffraction (XRD) and high resolution field emission scanning electron microscope (FE-SEM). Energy dispersive X-ray spectrum (EDS) demonstrated that the spear-like microstuctures consist of element Zn and O. It indicated that the shapes of the products strongly depend on the growth conditions. The optical properties of spear-like ZnO nanostructures were investigated by temperature-depended photoluminescence (PL) measurements and all of the observed emission lines were well fitted by the Varshni formula.     

Controlled growth and field-emission properties of NbSe2 micro/nanostructured films

Single-crystalline NbSe2 nanobelt, nanorod (containing nanotube), and microplate films were grown on Nb substrates by a surface-assisted chemical-vapor-transport (CVT), respectively. The nanobelts have a rectangular section of 50 x 250 to 300 x 4500 nm2, and a length up to 330 microm. The nanorods have a hexagonal section with a diameter of about 0.1-0.5 microm, and a length up to 15 microm. The nanotubes have rectangular, pentagonal or round sections with a diameter of about 0.4-0.5 microm, a tube-wall thickness of about 45 nm, and a length up to several microns. The microplates have a hexagonal section with a diameter of about 0.05-10 microm and a thickness of about 100 to 600 nm. Field-emission experiments using the films as cold electron cathodes showed that they had notable emission currents and low turn-on fields, suggesting their potential applications in field emission devices.     

Structural transformation, photocatalytic, and field-emission properties of ridged TiO2 nanotubes

Self-organized, freestanding TiO(2) nanotube arrays with ridged structures have been fabricated using a one-step anodic oxidation method. Their structural, photocatalytic, and field-emission (FE) properties have systematically been investigated. The as-synthesized nanostructures have been characterized using XRD, Raman spectroscopy, SEM, and HRTEM. The experimental results show that after an annealing process, the starting amorphous nanotubes have been turned into anatase phase structures, and the tube walls have been decorated with nanoparticles, different from the original ridged nanotubes. Furthermore, the anatase phase nanotubes have demonstrated better photocatalytic properties than their amorphous counterparts, which is caused by the larger surface area and improved crystallinity. With respect to FE properties, the as-grown nanotubes have the lower turn-on field E(to) and the higher field enhancement factor β compared to the annealed nanotubes. The relationship between E(to), β, and the tube arrangements and morphologies has also been discussed.     

Synthesis and photocatalytic properties of TiO2 nanostructures

TiO₂ particles, rods, flowers and sheets were prepared by hydrothermal method via adjusting the temperature, the pressure and the concentration of TiCl₄. The as-prepared TiO₂ powders were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflectance spectra and N₂ adsorption–desorption measurements. It was found that pressure is the most important factor influencing the morphology of TiO₂. The photocatalytic activity of the products was evaluated by the photodegradation of aqueous brilliant red X-3B solution under UV light. Among the as-prepared nanostructures, the flower-like TiO₂ exhibited the highest photocatalytic activity.     

Preparation and optical properties of phase-change VO2 thin films

In this work, VO₂ thin films were prepared on three kinds of substrates by the sol-gel dipcoating method followed by heat treatment under vacuum. These thin films were analysed by x-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. The infrared and ultraviolet-visible spectra of the VO₂ thin films were also recorded during heating and cooling between room temperature and 100°C. The experimental results show that VO₂ thin films thus prepared exhibit thermally induced reversible phase transition, and the largest changes in transmittance and reflectivity are approximately 58 and 25%, respectively, in the case of vacuum heat treatment at 400°C and silica glass substrates. The refractive index (n) decreases and the absorption coefficient (k) increases when heating these thin films from room temperature to 100°C, and vice versa for cooling. The reasons why the optical constants and infrared absorption spectra change so remarkably are discussed.     

热致变色VO2薄膜的制备及光学性能研究

利用等离子体发射光谱监测系统(PEM)控制钒的等离子强度,在石英基底上磁控溅射制备了VO2薄膜。采用XRD、XPS、SEM、紫外-可见-近红外分光光度计及傅立叶红外分光光度计研究薄膜的结构、光学及相变特性。结果表明,所制备的VO2薄膜具有(011)取向,VO2薄膜的热滞回线宽度为25℃,可见光透过率和太阳光调节率分别可达Tlum,l=34.1%、Tlum,h=35.3%和ΔTsol=6.8%,相变前后,红外光区的反射率变化最大值可达44.4%。     

Fabrication and structure characterization of te butterfly nanostructures

Te nanowires and butterfly nanostructures have been fabricated by template-free electrodeposition (TFED) in aqueous solution. By high-resolution transmission electron microscopy (HRTEM) study, the favored growth directions of the nanowires and the wings of the butterfly nanostructures were determined to be along the [0001] direction of trigonal Te, and the twinning plane of the butterfly nanostructures was (11-22). The cathodoluminescence measurements carried out at different positions of the butterfly nanostructure indicated that the twin boundaries influenced the photoemission efficiency.     

Fabrication and morphological control of ion-induced zinc nanostructures

An efficient method for the fabrication of zinc (Zn) nanostructures (nanoneedles and nanofibers) of controllable density and morphology without any catalyst, hazardous chemicals or external heat supply has been investigated. By varying the ion irradiation time and the ion current density, morphological control and the density of Zn nanostructures were successfully achieved using a fast and viable ion irradiation technique. Scanning (SEM) and transmission electron microscopy (TEM) results revealed that the sputtered surface was almost entirely covered with densely distributed conical and needle-like protrusions with linear shaped (sometimes curved) nanostructures (such as nanoneedles and nanofibers) with diameters and lengths of about 20-50 nm and several hundred nanometers, respectively. Detailed analysis of selected area electron diffraction (SAED) patterns with TEM analysis indicates that the Zn nanofibers were polycrystalline in nature. A possible mechanism of the formation of Zn nanostructures is briefly discussed. These aligned arrays of Zn nanoneedles/nanofibers could be a promising material for the fabrication of zinc oxide nanostructures by subsequent oxidation of Zn nanostructures and their future application in nanodevices. Thus, it is believed that this ion irradiation technique could open up a new approach for the fabrication of many kinds of nanomaterials of controllable density.     

Fabrication and characteristics of three-dimensional flower-like titanate nanostructures

A novel and facile approach has been developed to fabricate three-dimension (3D) flower-like titanate nanostructures from Ti powders. The synthesized flower-like titanate nanostructures were composed of many thin nanoribbons and have an ultrahigh specific surface area of 572.3 m2/g. After high temperature heat treatment, the flower-like titanate nanostructures were totally transformed into corresponding anatase TiO2 nanostructures without destroying their 3D hierarchical structural motif. The flower-like TiO2 nanostructures exhibited high photocatalytic activity for photodecomposition of methyl blue, and they could possibly be further used in photovoltaic cell, sensors, Li-ion batteries, and so on.     

Fabrication of high-aspect-ratio metallic nanostructures using nanoskiving

This communication describes the fabrication of gold structures (for example, rings) with wall thickness of 40 nm, and with high aspect ratios up to 25. This technique combines thin-film deposition of metal on a topographically patterned epoxy substrate, with nanometer-scale sectioning using a microtome in a plane parallel to the patterned substrate. The dimensions of the metal structures are determined by the thickness of the metal film and the thickness of the epoxy sections. The shape of the resulting nanostructure is defined by the cross section of the original template.     

Fabrication and mechanical properties of suspended one-dimensional polymer nanostructures: polypyrrole nanotube and helical polyacetylene nanofibre

Mechanical properties of suspended quasi-one-dimensional polymer nanostructures were investigated using atomic force microscopy (AFM). A recently developed new acid-free etch method combined with electron beam lithography was used to fabricate suspended polypyrrole (PPy) nanotubes and helical polyacetylene (HPA) nanofibres. The elastic modulus of each suspended structure was obtained by AFM force-distance measurements. The estimated modulus value of the PPy nanotube (HPA nanofibre) was 0.96?GPa (0.5?GPa). Using this acid-free method, all-organic flexible NEMS devices can be fabricated in the future.