Fabrication, structural characterization and photoluminescence of Q-1D semiconductor ZnS hierarchical nanostructures

Quasi-one-dimensional semiconductor ZnS hierarchical nanostructures have been fabricated by thermal evaporation of a mixture of ZnS nanopowders and Sn powders. Sn nanoparticles are located at or close to the tips of the nanowires (or nanoneedles) and served as the catalyst for quasi-one-dimensional ZnS nanostructure growth by a vapour-liquid-solid mechanism. The morphology and microstructure of the ZnS hierarchical nanostructures were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The results show that a large number of ZnS nanoneedles were formed on the outer shells of a long and straight ZnS axial nanowire. The ZnS axial nanowires grow along the [001] direction, and ZnS nanoneedles are aligned over the surface of the ZnS nanowire in the radial direction. The room temperature photoluminescence spectrum exhibits a UV weak emission centred at 337?nm and one blue emission centred at 436?nm from the as-synthesized single-crystalline semiconductor ZnS hierarchical nanostructures.     

Brush-shaped ZnO heteronanorods synthesized using thermal-assisted pulsed laser deposition

Brush-shaped ZnO heteronanostructures were synthesized using a newly designed thermal-assisted pulsed laser deposition (T-PLD) system that combines the advantages of pulsed laser deposition (PLD) and a hot furnace system. Branched ZnO nanostructures were successfully grown onto CVD-grown backbone nanowires by T-PLD. Although ZnO growth at 300 °C resulted in core-shell structures, brush-shaped hierarchical nanostructures were formed at 500-600 °C. Materials properties were studied via photoluminescence (PL), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) characterizations. The enhanced photocurrent of a SnO(2)-ZnO heterostructures device by irradiation with 365 nm wavelength ultraviolet (UV) light was also investigated by the current-voltage characteristics.     

Fabrication and optical emission of TiO2-sheathed ZnO nanowires

The ZnO nanowires were synthesized by using vapor-liquid-solid mechanism and then the ZnO nanowires were sheathed with TiO2 by metal organic chemical vapor deposition. The coaxial nanowires were 30-200 nm in diameter and up to 0.2 microm in length. Transmission electron microscopy and X-ray diffraction analysis results showed that the ZnO cores and TiO2 shells of the core-shell nanowires had wurtzite and amorphous structures, respectively. Photoluminescence measurement showed that TiO2 coating increased and decreased the near-band edge (NBE) and deep-level emissions of the ZnO nanowires in intensity, respectively. However, it appeared that subsequent annealing was undesirable since it decreased the NBE emission in intensity.     

Nanostructures of Sn and their enhanced, shape-dependent superconducting properties

A noncatalytic and template-free vapor transport process was developed to make possible simultaneous growth of single-crystalline tin nanowires, nanosquares, nanodisks, and polycrystalline nanoparticles. The formation of such a rich variety of morphologies in a single growth experiment can be attributed to variations in the growth rate among different crystallographic planes when employing the vapor-solid growth mechanism. Structural characterization with high-resolution transmission electron microscopy reveals a preferential growth direction of [100] in Sn nanowires, nanosquares, and nanodisks. Shape-dependent superconducting properties are observed. These four types of Sn nanostructures all show typical diamagnetic behavior in magnetization measurements, with the three anisotropically shaped nanostructures (nanowires, nanosquares, and nanodisks) showing one order of magnitude enhancement in the working magnetic field ranges for superconductivity, compared to bulk Sn and Sn nanoparticles. The magnetic field range is broadest for nanowires, followed by nanodisks, nanosquares, and nanoparticles.     

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.     

Synthesis,characterization and growth mechanism of ZnO nanowires on NiCl<Subscript>2</Subscript>-coated Si substrates

Well-crystallized ZnO nanowires have been successfully synthesized on NiCl₂-coated Si substrates via a carbon thermal reduction deposition process. The pre-deposited Ni nanoparticles by dipping the substrates into NiCl₂ solution can promote the formation of ZnO nuclei. The as-synthesized nanowires were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) spectrum. The results demonstrate that the as-fabricated nanowires with about 60 nm in diameter and several tens of micrometers in length are preferentially arranged along [0001] direction with (0002) as the dominate surface. Room temperature PL spectrum illustrates that the ZnO nanowires exist a UV emission peak and a green emission peak, and the peak centers locate at 387 and 510 nm. Finally, the growth mechanism of the nanowires is briefly discussed.     

Rapid synthesis of aligned zinc oxide nanowires

A solution growth approach for zinc oxide (ZnO) nanowires is highly appealing because of the low growth temperature and possibility for large area synthesis. Reported reaction times for ZnO nanowire synthesis, however, are long, spanning from several hours to days. In this work, we report on the rapid synthesis of ZnO nanowires on various substrates (such as poly(ethylene terephthalate) (PET), silicon and glass) using a commercially available microwave oven. The average growth rate of our nanowires is determined to be as high as 100?nm?min(-1), depending on the microwave power. Transmission electron microscopy analysis revealed a defect-free single-crystalline lattice of the nanowires. A detailed analysis of the growth characteristics of ZnO nanowires as functions of growth time and microwave power is reported. Our work demonstrates the possibility of a fast synthesis route using microwave heating for nanomaterials synthesis.     

In situ observation of size-scale effects on the mechanical properties of ZnO nanowires

In this investigation, the size-scale in mechanical properties of individual [0001] ZnO nanowires and the correlation with atomic-scale arrangements were explored via in situ high-resolution transmission electron microscopy (TEM) equipped with atomic force microscopy (AFM) and nanoindentation (NI) systems. The Young's modulus was determined to be size-scale-dependent for nanowires with diameter, d, in the range of 40 nm ≤ d ≤ 110 nm, and reached the maximum of ～ 249 GPa for d = 40 nm. However, this phenomenon was not observed for nanowires in the range of 200 nm ≤ d ≤ 400 nm, where an average constant Young's modulus of ～ 147.3 GPa was detected, close to the modulus value of bulk ZnO. A size-scale dependence in the failure of nanowires was also observed. The thick ZnO nanowires (d ≥ 200 nm) were brittle, while the thin nanowires (d ≤ 110 nm) were highly flexible. The diameter effect and enhanced Young's modulus observed in thin ZnO nanowires are due to the combined effects of surface relaxation and long-range interactions present in ionic crystals, which leads to much stiffer surfaces than bulk wires. The brittle failure in thicker ZnO wires was initiated from the outermost layer, where the maximum tensile stress operates and propagates along the (0001) planes. After a number of loading and unloading cycles, the highly compressed region of the thinner nanowires was transformed from a crystalline to an amorphous phase, and the region near the neutral zone was converted into a mixture of disordered atomic planes and bent lattice fringes as revealed by high-resolution images.     

Direct growth of oxide nanowires on CuOx thin film

Oxide nanowires were directly grown on a CuO(x) thin film deposited by plasma-enhanced atomic layer deposition without additional metal catalysts. Oxide nanowires would exhibit metal-catalyst-free growth on the CuO(x) thin film with oxide materials diffused on the top. Through a focused ion beam and transmission electron microscopy, we could verify that SnO(2) and ZnO nanowires were grown as single-crystalline structures just above the CuO(x) thin film. Bottom-gate structural SnO(2) and ZnO nanowire transistors exhibited mobilities of 135.2 and 237.6 cm(2) V(-1) s(-1), respectively. We anticipate that a variety of large-area and high-density oxide nanowires can be grown at low cost by using the CuO(x) thin film.     

Electrochemical synthesis of Sn doped ZnO nanowires on zinc foil and their field emission studies

Sn doped ZnO films were obtained by cathodic electrodeposition on Zn foil. The X-ray diffraction analysis revealed formation of the wurtzite phase of ZnO only. The scanning electron microscopic images showed formation of randomly oriented ZnO nanowires having diameter less than 150 nm and lengths of several micrometers. The relative atomic percentage of Sn, estimated from the energy-dispersive spectra, was found to be 0.5 and 2.0 in the post-annealed ZnO films deposited for 10 and 40 min durations, respectively. The field emission characteristics of the Sn doped ZnO nanowires are found to be appreciable in terms of the threshold field and emission current stability.     

Photoluminescence and gas sensing study of nanostructured pure and Sn doped ZnO

The nanostructured pure and Sn doped ZnO have been synthesized by the thermal evaporation technique. The influence of Sn on the morphology and structure is investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analysis techniques. The SEM images indicate change in the growth pattern from nanowires of pure ZnO to tetrapods for Sn doped ZnO. Pure ZnO nanowires exhibit selective response towards acetone vapors while on Sn doping the response decreases. The non-stiochiometry and the morphology of ZnO are probably responsible for such a difference in gas response. However increase in temperature doesn't improve the sensing behavior. The photoluminiscence (PL) studies reveal UV emission in pure ZnO which shifts to green emission on doping of Sn.     

ZnO纳米棒阵列膜的制备及其光电化学性能研究

采用化学溶液沉积法,在ZnO纳米颗粒膜修饰的FTO导电玻璃基底上,制备了ZnO纳米棒阵列。用X射线衍射仪（XRD）、场发射扫描电子显微镜（FESEM）、透射电子显微镜（TEM）对样品进行表征。研究结果表明所制备的ZnO纳米棒为六方纤锌矿相单晶结构,沿c轴择优取向生长,平均直径约为40nm,长度约为900nm;ZnO纳米棒阵列生长致密,取向性较一致。以曙红Y敏化的ZnO纳米棒阵列膜为光阳极制作了染料敏化太阳能电池原型器件,在光照强度为100mW/cm2下,其开路电压为0.418V,短路电流为0.889mA/cm2,总的光电转换效率为0.133%。     

Sn-catalyzed growth of MgO nanowires

We reported the fabrication and characterization of MgO nanowires, which were grown by thermal evaporation of the mixture of MgB2 and Sn powders at 800 degrees C through a vapor-liquid-solid (VLS) process. We characterized as-synthesized MgO nanowires using X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. Sn nanoparticles were located at the tips of the nanowires, serving as catalyst for the growth of MgO nanowires. The produced nanowires were of cubic MgO structures with diameters in the range of 10-170 nm. The PL measurement with a Gaussian fitting exhibited visible light emission bands centered at 403, 576, and 720 nm.     

Characterization of luminescence properties of V2O5-capped ZnSe nanowires

ZnSe-core/V2O5-shell nanowires were synthesized by the thermal evaporation of ZnSe powders on gold-coated Si (100) substrates followed by the sputter depositon of V2O5. Scanning electron microscopic images showed that the core-shell nanowires were a few tens to a few hundreds of nanometers in diameter and a few hundreds of micrometers in length. Transmission electron microscopy and X-ray diffraction analyses revealed that the core and shell of the core-shell nanowires were single crystal wurtzite-structured ZnSe and amorphous V2O5, respectively. Photoluminescence measurement showed that the core-shell nanowires as-synthesized or annealed in an oxidative atmosphere had a green emission band centered at around 520 nm whereas the as-synthesized ZnSe nanowires and the ZnSe-core/V2O5-shell nanowires annealed in a reducing atmosphere had a yellow emission band centered at around 590 nm. Our results also showed that V2O5 capping with an optimal thickness and subsequent annealing in a reducing atmosphere could significantly enhance the emission intensity of the ZnSe nanowires. In addition, the origins of the enhancement in intensity and the blue shift of the major emission by V2O5 capping are discussed.     

Zn(1-x)Mg(x)Te nanowires grown by solid source molecular beam epitaxy

This paper reports on the epitaxial growth of single-crystalline ternary Zn(1-x)Mg(x)Te nanowires covering a broad compositional range of molar fraction 0≤x≤0.75. The nanowires were grown on (100), (110), and (111) GaAs substrates using a vapor-liquid-solid mechanism. Solid source molecular beam epitaxy and an Au-based nanocatalyst were used for these purposes. The composition of nanowires can be adjusted by changing the ratio of Mg to Zn molecular beam fluxes. Electron microscopy images show that the nanowires are smooth and slightly tapered. The diameters of the obtained nanowires are from?30 to 70?nm and their length is around 1?μm. X-ray diffraction analysis and transmission electron microscopy reveal that the nanowires have a zinc-blende structure throughout the whole range of obtained compositions, and have a [Formula: see text] growth axis. The Raman measurements reveal both the expected splitting and shift of phonon lines with increasing Mg content, thus proving the substitutional incorporation of Mg into metallic sites of the ZnTe lattice.     

Synthesis and characterization of ZnO nanowires for nanosensor applications

In this paper we report the synthesis of ZnO nanowires via chemical vapor deposition (CVD) at 650 °C. It will be shown that these nanowires are suitable for sensing applications. ZnO nanowires were grown with diameters ranging from 50 to 200 nm depending on the substrate position in a CVD synthesis reactor and the growth regimes. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), and Raman spectroscopy (RS) have been used to characterize the ZnO nanowires. To investigate the suitability of the CVD synthesized ZnO nanowires for gas sensing applications, a single ZnO nanowire device (50 nm in diameter) was fabricated using a focused ion beam (FIB). The response to H₂ of a gas nanosensor based on an individual ZnO nanowire is also reported.     

Synthesis and photocatalytic property of metal@SnO2 core-shell structure nanocomposites

A simple soft-chemical technique for processing of metal@SnO2 nanocomposites with core-shell morphology is reported. In the present technique metal nanoparticles are prepared by chemical reduction technique followed by deposition of tin dioxide. Thus a core-shell type structure is produced. The phase and morphology has been investigated by X-ray diffraction technique (XRD) and transmission electron microscopy (TEM). As prepared Au@SnO2 and Ag@SnO2 core-shell nanocomposites have shown distinct surface Plasmon band in the UV-visible spectrum at 540 nm and 400 nm respectively. The core-shell morphology is confirmed from the TEM images. XRD patterns have suggested the presence of noble metal and tin dioxide in the Cassiterite form. These metal@SnO2 nanocomposites have been successfully used for the photocatalytic oxidation of acetaldehyde. Our investigations suggest that presence of noble metal core in contact with tin dioxide shell enhances the photocatalytic activity of the material.     

Novel diode-shaped ZnO nanocrystals

We have synthesized novel diode-shape ZnO nanocrystals via a simple solid–vapor approach. This new nanostructure is constructed by two basic parts: a hexagonal nanorod and ultra-long nanowires on the two tips of the nanorod. The whole structure is a perfect single crystal along the [0001] growth direction with the length of a few 10 mm. This configuration is a new member in the family of ZnO nanostructures. Based on our XRD and electron microscopy study, the new effect of Sn in the growing process is discussed.     

Vertical single-crystal ZnO nanowires grown on ZnO:Ga/glass templates

Vertical single-crystal ZnO nanowires with uniform diameter and uniform length were selectively grown on ZnO:Ga/glass templates at 600/spl deg/C by a self-catalyzed vapor-liquid-solid process without any metal catalyst. It was found that the ZnO nanowires are grown preferred oriented in the [002] direction with a small X-ray diffraction full-width half-maximum. Photoluminescence, field-emission scanning electron microscopy, and high-resolution transmission electron microscopy measurements also confirmed good crystal quality of our ZnO nanowires. Field emitters using these ZnO nanowires were also fabricated. It was found that threshold field of the fabricated field emitters was 14 V//spl mu/m. With an applied electric field of 24 V//spl mu/m, it was found that the emission current density was around 0.1 mA/cm/sup 2/.     

Fabrication of single-crystalline gallium nitride nanowires by using alginate as template

Hexagonal gallium nitride nanowires were synthesized successfully by solvothermal method with alginate as template. The microstructure, morphologies and compositions of the as-prepared product were characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), high resolution transmission electron microscopy (HRTEM), and energy dispersive X-ray (EDX). Results suggested that the rod-like nanowires were hexagonal single-crystalline GaN growing along [001] direction. The photoluminescence spectra (PL) of the GaN revealed that the as-synthesized sample possesses excellent optical properties.