ZnO/Zn2SnO4纳米电缆结构表征与发光特性

ZnO、Zn2SnO4均为直接带隙宽禁带氧化物半导体,是优异的功能材料.以ZnO、SnO2为原料,通过共热蒸发法,合成了ZnO/Zn2SnO4纳米电缆结构.该纳米电缆结构为以ZnO为芯,Zn2SnO4为鞘,直径为50~100nm,长度可达上百微米.通过TEM分析手段,发现该纳米电缆结构中,ZnO的生长方向为<0001>方向,ZnO芯与Zn2SnO4鞘之间形成晶格外延关系.室温下光致发光谱结果显示,该纳米电缆结构在紫外区域(380.58nm附近处)存在很强的带边发光,而在可见光区域没有明显的发光带,这一结果表明:Zn2SnO4鞘层的存在能有效抑制ZnO表面的缺陷发光.ZnO/Zn2SnO4纳米电缆结构可以抑制电子-空穴的复合,在染料敏化太阳能电池等方面有一定的应用潜力.     

Three-dimensional structure of helical and zigzagged nanowires using electron tomography

Electron tomography and high-resolution transmission electron microscopy were used to characterize the unique three-dimensional structures of helical or zigzagged GaN, ZnGa2O4, and Zn2SnO4 nanowires. The GaN nanowires adopt a helical structure that consists of six equivalent <011> growth directions with the axial [0001] direction. We also confirmed that the ZnGa2O4 nanosprings have four equivalent <011> growth directions with the [001] axial direction. The zigzagged Zn2SnO4 nanowires consisted of linked rhombohedrons having the side edges matched to the <110> direction and the [111] axial direction.     

Optical properties of zigzag twinned geometry of Zn2SnO4 nanowires

High-density single-crystalline Zn2SnO4 nanowires have been successfully synthesized by using a simple thermal evaporation method by heating a mixture of ZnO and SnO2 nano powders. The products in general contain various geometries of wires, with an average diameter of 80-100 nm. These nanowires are ultra-long, up to 100 microns. The transmission electron microscopy study showed that these nanowires exhibited zigzag twinned geometry, and grow along the (111) direction. Low-temperature photoluminescence properties of the nanowires were measured, showing a strong green emission band at about 515 nm and a weak peak corresponding to UV emission at about 378 nm, which have not been reported before.     

Novel fabrication of an SnO(2) nanowire gas sensor with high sensitivity

We fabricated a nanowire-based gas sensor using a simple method of growing SnO(2) nanowires bridging the gap between two pre-patterned Au catalysts, in which the electrical contacts to the nanowires are self-assembled during the synthesis of the nanowires. The gas sensing capability of this network-structured gas sensor was demonstrated using a diluted NO(2). The sensitivity, as a function of temperature, was highest at 200?°C and was determined to be 18 and 180 when the NO(2) concentration was 0.5 and 5?ppm, respectively. Our sensor showed higher sensitivity compared to different types of sensors including SnO(2) powder-based thin films, SnO(2) coating on carbon nanotubes or single/multiple SnO(2) nanobelts. The enhanced sensitivity was attributed to the additional modulation of the sensor resistance due to the potential barrier at nanowire/nanowire junctions as well as the surface depletion region of each nanowire.     

Synthesis, characterization and opto-electrical properties of ternary Zn2SnO4 nanowires

Ternary oxides have the potential to display better electrical and optical properties than the commonly fabricated binary oxides. In our experiments, Zn(2)SnO(4) (ZTO) nanowires were synthesized via thermal evaporation and vapor phase transport. The opto-electrical performance of the nanowires was investigated. An individual ZTO nanowire field-effect transistor was successfully fabricated for the first time and shows an on-off ratio of 10(4) and transconductance of 20.6 nS, which demonstrates the promising electronic performance of ZTO nanowire in an electrical device. Field emission experiments on ZTO nanowire film also indicate their potential application as a field emission electron source.     

Selective synthesis and superconductivity of In-Sn intermetallic nanowires sheathed in carbon nanotubes

We demonstrate a simple and reproducible technique to synthesize crystalline and superconducting In-Sn intermetallic nanowires sheathed in carbon nanotubes (CNTs). The method is based on the catalytic reaction of C(2)H(2) over a mixture of both SnO(2) and In(2)O(3) particles. Importantly, tetragonal β-In(3)Sn and hexagonal γ-InSn(4) nanowires with diameters of less than 100?nm are selectively synthesized at different SnO(2) to In(2)O(3) weight ratios. CNTs may serve as cylindrical nanocontainers for continuous growth of liquid-phased In(1-x)Sn(x) nanowires during growth process as well as for their solidification into In-Sn intermetallic nanowires during the cooling process. Microscopic and spectroscopic analyses clearly reveal evidence of a core-shell structure of the CNT-sheathed In-Sn intermetallic nanowires. Magnetization measurements show that the superconducting In-Sn nanowires have a critical magnetic field higher than the value of their bulk intermetallic compounds. Our method can be adopted to the nanofabrication of analogous binary and ternary alloys.     

The structure and photoluminescence properties of Bi2O3-core/SnO2-shell nanowires

Bi2O3-core/SnO2-shell nanowires have been prepared by using a two-step process: thermal evaporation of Bi2O3 powders and sputtering of SnO2. The crystalline nature of the Bi2O3-core/SnO2-shell nanowires has been revealed by high resolution transmission electron microscopy (HRTEM) and selected area electron diffraction (SAED). TEM analysis and X-ray diffraction (XRD) results indicate that the Bi2O3-core/SnO2-shell nanowires consist of pure tetragonal alpha-Bi2O3-phase momocrystalline cores and tetragonal SnO2-phase polycrystalline shells. The photoluminescence (PL) measurements show that Bi2O3 nanowires have a broad emission band centered at around 560 nm in the yellow-green region. On the other hand, the Bi2O3-core/SnO2-shell coaxial nanowires with the sputtering times of 4 and 8 min have a blue emission band centered at around 450 nm. In contrast, those with a sputtering time of 10 min have a broad emission band centered at approximately 550 nm again. The origin of this yellow-green emission from the core/shell nanowires, however, quite differs from that from Bi2O3 nanowires, i.e., it is not from the Bi2O3 cores but from the SnO2 shells.     

Metal organic chemical vapour deposition of vertically aligned ZnO nanowires using oxygen donor adducts

Vertically aligned zinc oxide (ZnO) nanowires (NWs) have been grown by liquid injection Metal Organic Chemical Vapour Deposition, using oxygen donor adducts of Me2Zn. The growth and characterisation of the nanowires grown using [Me2Zn(L)] where L = monodentate ethers, tetrahydrofuran (C4H8O) (1), tetrahydropyran (C5H10O) (2), furan (C4H4O) (3) and the bidentate ethers, 1,2-dimethoxyethane (C4H12O2,) (4) 1,4-dioxane (C4H8O2) (5) and 1,4-thioxane (C4H8SO) (6) is discussed. Single crystal X-ray structures of (4), (5), (6) have been established and are included here. The ZnO NWs were deposited in the absence of a seed catalyst on Si(111) and F-doped SnO2/glass substrates over the temperature range 350-600 degrees C. X-ray diffraction (XRD) data shows that the nanowires grown from all adduct precursors were deposited in the wurtzitic phase.     

The template-free synthesis of square-shaped SnO(2) nanowires: the temperature effect and acetone gas sensors

Square-shaped single-crystalline SnO(2) nanowires and their sphere-like hierarchical structures were synthesized successfully with a template-free hydrothermal approach. It was found that an intermediate phase-Na(2)Sn(OH)(6)-is first produced because it is slow to dissolve in ethanol/water media. The intermediate phase gradually decomposes and converts into SnO(2) at temperatures higher than 200?°C. The reaction temperature also affects the microstructure of SnO(2) nanomaterials. Uniform square-shaped SnO(2) nanowires, which form sphere-like hierarchical structures in 100% structure yield, can be produced at 285?°C on a large scale. The diameter of the nanowires shows a decrease accompanying the increase of the reaction temperature. The temperature effect could be a result of the faster and oriented growth of SnO(2) nanowires along their [Formula: see text] direction at higher temperature. Chemical sensors constructed with square-shaped SnO(2) nanowires exhibit excellent stability, good sensitivity and selectivity, as well as a quick response and short recovery times under exposure to acetone gas in practical applications.     

Functionalization of selectively grown networked SnO2 nanowires with Pd nanodots by γ-ray radiolysis

γ-ray radiolysis is applied to synthesizing Pd nanodots on networked SnO(2) nanowires. The growth behavior of Pd nanodots is systematically investigated as a function of the precursor concentration, illumination intensity, and exposure time of the γ-rays. These factors greatly influence the growth behavior of the Pd nanodots. Selectively grown networked SnO(2) nanowires are uniformly functionalized with Pd nanodots by the radiolysis process. The NO(2) sensing characteristics of the Pd-functionalized SnO(2) nanowires are compared with those of bare SnO(2) nanowires. The results indicate that γ-ray radiolysis is an attractive means of functionalizing the surface of oxide nanowires with catalytic Pd nanodots. Moreover, the Pd-functionalization greatly enhances the sensitivity and response time in SnO(2) nanowire-based gas sensors.     

Ordered array of linear and spherical nanomaterials in a film formation via self assembly

Convective force driven self-assembled colloidal templates worked to confine one dimensional Au nanorods and carbon nanotubes in parallel mode around the spherical colloidal templates. Au nanorods showed different array density depending on the Au nanorod concentration (ca. 0.03-0.09 wt%). It was found that the flexural property of CNTs allowed the formation of ordered, two dimensional CNT networks. This ordering was successfully observed for both polystyrene and silica colloidal templates. The resulting CNT network order was kept after the colloidal templates were etched away. In contrast, a similar procedure to produce ordered nanowires of SnO2 indicated that the rigidity of the SnO2 nanowires did not allow the arraying along the surface of the colloidal template particles but instead induced local disorder in the colloidal array.     

Preparation of SnO2 nanowires by solvent-free method using mesoporous silica template and their gas sensitive properties

In this paper, a facile method was presented to synthesize tin dioxide (SnO2) nanowires by solvent-free method using SnCl2 x 2H2O as precursor and mesoporous silica SBA-15 as the hard template. No solvent was used in the processing. The products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS) and N2 adsorption/desorption isotherms. The results indicated that SnO2 nanowires fabricated by this method have a diameter of about 8 nm and a relatively high surface area 73.0 m2/g. The gas sensing properties of SnO2 nanowires were measured. The response and recovery time of this sensor were 6 s and 12 s, respectively. With the concentration of toluene increasing, the response of the sensor doubled increase. Compared with bulk SnO2, SnO2 nanowires showed much higher response to toluene.     

Zn-Sn-O系统透明导电薄膜的制备及其性能

本文采用溶胶-凝胶(Sol-Gel)过程和旋涂技术,通过高温烧结,得到了Zn-Sn-O系统的薄膜。结合干凝胶的差示扫描热分析(TG-DSC)和薄膜的X射线衍射分析(XRD),研究了干凝胶在烧结过程中发生的反应。通过控制溶胶的组成和薄膜烧结温度,得到了较纯净的Zn2SnO4晶相薄膜和ZnSnO3晶相薄膜。ZnSnO3晶体薄膜的电阻率显著低于Zn2SnO4晶体薄膜;N2气氛热处理后,ZnSnO3薄膜的电阻率升高而Zn2SnO4薄膜的电阻率大幅降低;当[Zn]/[Zn+Sn]=50.3at%时,薄膜的晶相仍为ZnSnO3,其电阻率较[Zn]/[Zn+Sn]=50.0at%的薄膜降低,约为8.0×102Ω.cm-1。通过上述两种晶相薄膜的X射线光电子能谱分析(XPS),探讨了这两种晶体不同的导电机理:Zn2SnO4晶体通过其中的氧空位导电,而ZnSnO3晶体则以间隙阳离子导电。紫外-可见光透过率(UV-Vis)分析表明:Zn2SnO4和ZnSnO3晶体薄膜在400~900nm的可见光波段的透过率可达80%以上。     

Ferromagnetism driven by oxygen vacancies in SnO2 nanowires

Room temperature ferromagnetism has been observed in SnO2 nanowires synthesized by a chemical vapor deposition using Au layers as catalyst. The nanowires are homogeneous and single-crystalline grown along the [101] direction, with diameters ranging from 25 to 100 nm and length greater than 20 microm. The special magnetization reaches 0.114 emu/g for the nanowires with diameter of approximately 25 nm and reduces with increasing diameters. Branched SnO2 nanowires were prepared via a two-step vapor-liquid-solid approach, and an enhanced magnetization was obtained. To the contrary, the nanowires annealed at 1300 degrees C in air were completely transformed into the particles and exhibit weakened magnetization. These results demonstrate that the ferromagnetic properties of the samples depend on the surface-to-volume ratio of nanowires. With a combined study of photoluminescence, our results reveal that the oxygen vacancies at the surface of nanowires contribute to the ferromagnetism of SnO2 nanowires. This argument is further confirmed by a sequential annealing in a rich-oxygen atmosphere, then in a low vacuum condition.     

Flexible Zn2SnO4/MnO2 core/shell nanocable-carbon microfiber hybrid composites for high-performance supercapacitor electrodes

We demonstrate the design and fabrication of a novel flexible nanoarchitecture by facile coating ultrathin (several nanometers thick) films of MnO2 to highly electrical conductive Zn2SnO4 (ZTO) nanowires grown radially on carbon microfibers (CMFs) to achieve high specific capacitance, high-energy density, high-power density, and long-term life for supercapacitor electrode applications. The crystalline ZTO nanowires grown on CMFs were uniquely served as highly conductive cores to support a highly electrolytic accessible surface area of redox active MnO2 shells and also provide reliable electrical connections to the MnO2 shells. The maximum specific capacitances of 621.6 F/g (based on pristine MnO2) by cyclic voltammetry (CV) at a scan rate of 2 mV/s and 642.4 F/g by chronopotentiometry at a current density of 1 A/g were achieved in 1 M Na2SO4 aqueous solution. The hybrid MnO2/ZTO/CMF hybrid composite also exhibited excellent rate capability with specific energy of 36.8 Wh/kg and specific power of 32 kW/kg at current density of 40 A/g, respectively, and good long-term cycling stability (only 1.2% loss of its initial specific capacitance after 1000 cycles). These results suggest that such MnO2/ZTO/CF hybrid composite architecture is very promising for next generation high-performance supercapacitors.     

Fabrication of reliable semiconductor nanowires by controlling crystalline structure

One-dimensional SnO(2) nanomaterials with wide bandgap characteristics are attractive for flexible and/or transparent displays and high-performance nano-electronics. In this study, the crystallinity of SnO(2) nanowires was regulated by controlling their growth temperatures. Moreover, the correlation of the crystallinity of nanowires with optical and electrical characteristics was analyzed. When SnO(2) nanowires were grown at temperatures below 900?°C, they showed various growth directions and abnormal discontinuity in their crystal structures. On the other hand, most nanowires grown at 950?°C exhibited a regular growth trend in the direction of [100]. In addition, the low temperature photoluminescence measurement revealed that the higher growth temperatures of nanowires gradually decreased the 500 nm peak rather than the 620 nm peak. The former peak is derived from the surface defect related to the shallow energy level and affects nanowire surface states. Owing to crystallinity and defects, the threshold voltage range (maximum-minimum) of SnO(2) nanowire transistors was 1.5 V at 850?°C, 1.1 V at 900?°C, and 0.5 V at 950?°C, with dispersion characteristics dramatically decreased. This study successfully demonstrated the effects of nanowire crystallinity on optical and electrical characteristics. It also suggested that the optical and electrical characteristics of nanowire transistors could be regulated by controlling their growth temperatures in the course of producing SnO(2) nanowires.     

ZnO nanocone arrays on self-assembled Zn2SnO4 base: synthesis, structure, growth mechanism and optical property

ZnO nanocone arrays on self-assembled Zn2SnO4 base were successfully synthesized via a thermal evaporation method of two-step temperature-rising. The as-prepared ZnO nanocone products had a well crystalline wurzite structure with symmetry about the growth direction along [0001]. Based on the calculation of the lattice misfit between different families of crystal planes of ZnO and Zn2SnO4, Stranski-Krastanow growth mode of ZnO nanocones was proposed in which the ZnO relaxing layer plays an important role. The orientation relationship of nanocone and base was also investigated. For the optical property of this nanocones-base system, a strong green fluorescence-emission at 523 nm was detected while the Zn2SnO4 base provides a defect peak at 486 nm which broadens the green emission band.     

Improvement in sensing properties of SnO2 nanowires by functionalizing with Pt nanodots synthesized by gamma-ray radiolysis

Selectively-grown networked SnO2 nanowires were functionalized with Pt nanodots by the radiolysis process. NO2 sensing characteristics of Pt-functionalized SnO2 nanowires were compared with those of bare SnO2 nanowires. The results demonstrate that the Pt functionalization greatly enhances the sensitivity and response time in SnO2 nanowire-based gas sensors. The enhancement is likely to be associated with the spillover effect and/or easy dissociation of NO2 into more active chemical species by the catalytic effect of Pt.     

Investigation of substrate influence on tin dioxide nanostructures synthesized using horizontal furnace

SnO2 nanostructures were directly synthesised by chemical vapour transport on different substrates in a horizontal furnace. The influence of substrate on the morphology of these nanostructures was investigated by changing the substrate type, coating, and temperature. The SnO2 nanowires and nanorods were one dimensional (1D) structures with widths and lengths of 50-200 nm and several micrometers respectively. Scanning electron microscope (SEM) images show formation of short nanorods with lengths of less than 1 microm on indium-tin oxide (ITO) substrates. The effect of substrate temperature on growth was studied. SnO2 nanowires were obtained using silicon substrate, and the effect of Au coating on the size and morphology of these structures was proposed. By coating the Si wafer with a thin layer of Au, the size of the nanostructure was reduced and the length increased. The differences in size and morphology are shown by transmission electron microscopy (TEM). X-ray diffraction (XRD) spectra show tetragonal structures for both substrates.     

Rutile structured SnO2 nanowires synthesized with metal catalyst by thermal evaporation method

One-dimensional (1-D) nanostructures such as tubes, rods, wires, and belts have attracted considerable research activities owing to their strong application potential as components for nanosize electronic or optoelectronic devices utilizing superior optical and electrical properties. Characterizing the mechanical properties of nanostructure is of great importance for their applications in electronics, optoelectronics, sensors, actuators. Wide-bandgap SnO2 semiconducting material (Eg = 3.6 eV at room temperature) is one of the attractive candidates for optoelectronic devices operating at room temperature, gas sensors, and transparent conducting electrodes. The synthesis and gas sensing properties of semiconducting SnO2 nanomaterials have became one of important research issues since the first synthesis of SnO2 nanobelts. Considering the important application of SnO2 in sensors, these structures are not only ideal systems for fundamental understanding at the nanoscale level, but they also have potential applications as nanoscale sensors, resonator, and transducers. The structured SnO2 nanorods have been grown on silicon substrates with Au catalytic layer by thermal evporation process over 800 degrees C. The resulting sample is characterized and analyzed by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), and energy-dispersive X-ray spectroscopy (EDS). The morphology and structural properties of SnO2 nanowires were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The mean diameter of the SnO2 nanorods grown on Au coated silicon (100) substrate is approximately 80 nm. In addition, X-ray diffraction measurements show that SnO2 nanorods have a rutile structure. The formation of SnO2 nanowires has been attributed to the vapor-liquid-solid (VLS) growth mechanisms depending on the processing conditions. We investigated the growth behavior of the SnO2 nanowires by variation of the growth conditions such as gas partial pressure and temperature.