Gold-catalyzed low-temperature growth of cadmium oxide nanowires by vapor transport

Ultralong cadmium oxide nanowires were synthesized in high yield on gold-coated silicon substrates by using a vapor transport process. Cadmium vapor generated by the carbothermal reduction of CdO powder in a tube furnace heated to 500 degrees C was carried to the substrate zone by an argon flow with a trace amount of oxygen. The CdO nanowires grew via a vapor-liquid-solid growth mechanism. The diameters of the nanowires are approximately 40-80 nm, and can reach lengths of 30-50 mum. Because the nanowire formation was gold particle catalyzed, patterned nanowire growth on substrates can be achieved. These nanowires grew along the [111] direction and have slightly rough surfaces due to the presence of crystalline CdO shells formed via a physical vapor deposition process. Interesting CdO nanowires with a necklace-like morphology were also observed in a small region of the substrate, where the oxygen supply may be ample to facilitate the lateral growth of rhombohedron-shaped crystals over the straight wires. Electron diffraction and high-resolution TEM results suggest that these side crystals should grow epitaxially on the wire surfaces. The band gap of the CdO nanowires with smoother surfaces was determined to be approximately 2.53 eV. These nanowires exhibit a relatively weak emission band centered at approximately 550 nm.     

大长径比ZnS纳米线的制备、结构和生长机理

通过碳热辅助化学气相沉积法, 以Au作为催化剂, 在较低温度(800 益)制备了ZnS纳米线, 其尺寸均匀, 表面光滑, 直径约为40 nm, 具有很大的长径比, 是典型的单晶纤锌矿六方结构. 高分辨透射电镜和选区电子衍射分析表明, 纳米线的生长方向为[1100], 与已报道的生长方向不同. 纳米线的生长是由气-液-固(vapor-liquid-solid)机理控制的.     

Low-temperature growth of ZnO nanorods by chemical bath deposition

Aligned ZnO nanorod arrays were synthesized using a chemical bath deposition method at normal atmospheric pressure without any metal catalyst. A simple two-step process was developed for growing ZnO nanorods on a PET substrate at 90-95 degrees C. The ZnO seed precursor was prepared by a sol-gel reaction. ZnO nanorod arrays were fabricated on ZnO-seed-coated substrate. The ZnO seeds were indispensable for the aligned growth of ZnO nanorods. The ZnO nanorods had a length of 400-500 nm and a diameter of 25-50 nm. HR-TEM and XRD analysis confirmed that the ZnO nanorod is a single crystal with a wurtzite structure and its growth direction is [0001] (the c-axis). Photoluminescence measurements of ZnO nanorods revealed an intense ultraviolet peak at 378.3 nm (3.27 eV) at room temperature.     

Synthesis of sodium tantalate nanorods by alkalide reduction

NaTaO3 nanorods were synthesized with high (>90%) yield by reduction of TaCl5 with THF solutions of the alkalide K+(15C5)2Na-, followed by product annealing under dynamic vacuum at 250 and 600 degrees C. In addition to the nanorods, the product is comprised of 5-10% approximately 10-nm diameter spheroidal NaTaO3 nanocrystals. The nanorods are generally longer than 500 nm, with some exceeding 1 mum, and 10-100 nm wide, with aspect ratios that vary between 10 and 20:1. Select area electron diffraction patterns of individual nanorods indicate that each nanorod is a single crystal with its axis oriented in the [010] direction.     

Direct synthesis of aligned silicon carbide nanowires from the silicon substrates

Aligned silicon carbide nanowires were synthesized directly from the silicon substrates via a novel catalytic reaction with a methane-hydrogen mixture at 1,100 degrees C, with a mean diameter of 40 nm and length of 500 microm; they consist of a single-crystalline zinc blende structure crystal in the [111] growth direction; X-ray diffraction, Raman, and infrared spectroscopy confirm the synthesis of high-purity silicon carbide nanowires.     

Temperature-triggered self-assembly of ZnO: from nanocrystals to nanorods to tablets

ZnO nanocrystals, nanorods, and tablets were prepared at 110, 140, and 180 degrees C in a water-ethanol system. Nanorods (~2 x 40 nm) arranged in serpentine morphologies formed by the oriented coalescence of anhedral ZnO nanocrystals (~3.5 nm diameter), while tabular ZnO grew by [1210] textural attachment of the nanorods. The development of these crystal habits is believed to proceed via a dissolution and growth mechanism mediated by a transient amorphous phase. Materials synthesized at intermediate temperatures (125 and 160 degrees C) possessed microstructures containing mixed crystal forms in the expected orientation relationship. Photoluminescent spectra of the nanocrystals and nanorods showed blue shifts of 0.16 and 0.13 eV with respect to the bulk ZnO band gap (3.26 eV) due to quantum confinement, with the narrow emission peaks typical of particles possessing uniform size and shape. The larger tablets displayed a less energetic emission (3.10 eV) ascribed to exciton-exciton collisions.     

Electron microscopy study of exotic nanostructures of cadmium sulfide.

In this article, two simple methods, evaporation-condensation and catalytic thermal evaporation, were used to investigate the synthesis of CdS nanostructures for nanoscale optoelectronic applications. To understand their growth mechanisms, various electron microscopy and microanalysis techniques were utilized in characterizing their morphologies, internal structures, growth directions and elemental compositions. The electron microscopy study reveals that when using the evaporation-condensation method, branched CdS nanorods and self-assembled arrays of CdS nanorods were synthesized at 800 degrees C and 1000 degrees C, respectively. Instead of morphological differences, both types of CdS nanorods grew along the [0001] direction. However, when using the catalytic thermal evaporation method (Au as the catalyst), patterned CdS nanowires and nanobelts were formed at the temperature region of 500-600 degrees C and 600-750 degrees C, respectively. Their growth direction was along the direction [1010] instead of [0001]. Based on the microscopy and microanalysis results, we propose some growth mechanisms in relation to the growth processes of those exotic CdS nanostructures.     

Aqueous solution route to high-aspect-ratio zinc oxide nanostructures on indium tin oxide substrates

High-aspect-ratio ZnO nanowires and nanotubes are formed on indium tin oxide (ITO) substrates using a three-step route at low temperatures. The three steps, including successive ionic layer absorption and reaction (SILAR) deposition of the ZnO seed layer, hydrothermal annealing of the seed layer, and chemical bath deposition (CBD) of the one-dimensional (1D) ZnO nanostructures, are all conducted in aqueous solutions at temperatures below 120 degrees C. Both the hydrothermal annealing of the SILAR seed layer and the low-concentration precursor solution employed in the CBD process are crucial in order to synthesize the uniform and high-aspect-ratio ZnO nanostructures on the ITO substrate. TEM analyses reveal that both the nanowire and the nanotube possess the single-crystal structure and are grown along [001] direction. Room-temperature cathodoluminescence spectrum of the 1D ZnO nanostructures shows a sharp ultraviolet emission at 375 nm and a broad green-band emission.     

Synthesis, Structure and Growth Mechanism of ZnS Nanowires with High Aspect Ratio

ZnS nanowires were successfully synthesized through the direct reaction of Zn and S vapor via carbon-assisted chemical evaporation deposition method with Au catalyst. The investigations indicated that the size of ZnS nanowires with a diameter of approximately 40 nm was uniform along the axis of the wire and the surfaces were slick. The ZnS nanowire with a hexagonal wurtzite structure was a typical single crystalline structure. HRTEM and SEAD results demonstrated that the nanowire grew along [100] direction, which was different from the common direction reported in literatures. The growth of nanowires was controlled by vapor-liquid-solid (VLS) mechanism.     

One-step chemical vapor growth of Ge/SiC(x)N(y) nanocables

Single-step synthesis of one-dimensional Ge/SiCxNy core-shell nanocables was achieved by chemical vapor deposition of the molecular precursor [Ge{N(SiMe3)2}2]. Single crystalline Ge nanowires (diameter approximately 60 nm) embedded in uniform SiCxNy shells were obtained in high yields, whereby the growth process was not influenced by the nature of substrates. The shell material exhibited high oxidation and chemical resistance at elevated temperatures (up to 250 degrees C) resulting in the preservation of size-dependent semiconductor properties of germanium nanowires, such as intact transport of charge carriers and reduction of energy consumption, when compared to pure Ge nanowires.     

Controlled growth of semiconducting oxides hierarchical nanostructures

Semiconducting ZnO hierarchical nanostructure, where ZnO nanonails were grown on ZnO nanowires, has been fabricated under control experiment with a mixture of ZnO nanopowders and Sn metal powders. Sn nanoparticles are located at or close to the tips of the nanowires and the growth branches, serving as the catalyst for the vapor-liquid-solid growth mechanism. The morphology and microstructure of ZnO nanowire and nanonail were measured by scanning electron microscopy and high-resolution transmission electron microscopy. The long and straight ZnO nanowires grow along [0001] direction. ZnO nanonails are aligned radially with respect to the surface the ZnO nanowire. The long axis direction of nanonails forms an angle of ∼30° to the [0001] direction.     

Attachment-driven morphology evolvement of rectangular ZnO nanowires

The rectangular cross-sectional ZnO nanowires were synthesized in a solution method. An attachment-driven growth mechanism was proposed for the morphology evolvement of ZnO nanocrystals from nanoparticles to nanoplates and eventually to nanowires. Due to the pileup attachment of the nanoplates to recrystallize into nanowires, unique one-dimensional (1D) ZnO nanowires with the rectangular cross section were obtained, which is different from those nanowires in the previous reports. It is the first time the evidence that "oriented attachment" can occur not only for nanoparticles but also for nanoplates was obtained, suggesting that "oriented attachment" is an intrinsic behavior for nanosized materials. According to the growth model proposed based on the direct TEM observations, ZnO nanocrystals can be easily controlled as nanoparticles, nanoplates, or nanowires by tuning the synthetic parameters.     

Comparative structure and optical properties of Ga-, In-, and Sn-doped ZnO nanowires synthesized via thermal evaporation

ZnO nanowires doped with a high concentration Ga, In, and Sn were synthesized via thermal evaporation. The doping content defined as X/(Zn + X) atomic ratio, where X is the doped element, is about 15% for all nanowires. The nanowires consist of single-crystalline wurtzite ZnO crystal, and the average diameter is 80 nm. The growth direction of vertically aligned Ga-doped nanowires is [001], while that of randomly tilted In- and Sn-doped nanowires is [010]. A correlation between the growth direction and the vertical alignment has been suggested. The broaden X-ray diffraction peaks indicate the lattice distortion caused by the doping, and the broadening is most significant in the case of Sn doping. The absorption and photoluminescence of Sn-doped ZnO nanowires shift to the lower energy region than those of In- and Ga-doped nanowires, probably due to the larger charge density of Sn.     

Synthesis and Characterization of ZnO Nanowires

Zinc oxide is a wide bandgap (3.37 eV) semiconductor with a hexagonal wurtzite crystal structure. ZnO prepared in nanowire form may be used as a nanosized ultraviolet light-emitting source. In this study, ZnO nanowires were prepared by vapor-phase transport of Zn vapor onto gold-coated silicon substrates in a tube furnace heated to 900 ?C. Gold serves as a catalyst to capture Zn vapor during nanowire growth. Size control of ZnO nanowires has been achieved by varying the gold film thickness…     

采用高分子自组装ZnO纳米线及其形成机理

介绍了一种能在各种晶面的硅衬底上制备垂直于衬底取向生长的ZnO纳米线阵列的新方法. 该法采用高分子络合和低温氧化烧结反应, 以聚乙烯醇(PVA)高分子材料作为自组装络合载体来控制晶体成核和生长. 首先通过PVA侧链上均匀分布的极性基团羟基(—OH)与锌盐溶液中的Zn²⁺离子发生络合作用, 然后滴加氨水调节络合溶液pH值为8.5±0.1, 使络离子Zn²⁺转变为Zn(OH)₂, 再将硅片浸入此溶液中, 从而在硅衬底表面得到较均匀的Zn(OH)₂纳米点, 随后在125 ℃左右Zn(OH)₂纳米点通过热分解转化为ZnO纳米点, 其后在420 ℃烧结过程中衬底上的ZnO纳米点在PVA高分子网络骨架对其直径的限域下逐渐取向生长成ZnO纳米线, 并且烧结初期PVA碳化形成的碳通过碳热还原ZnO为Zn, 再在氧气氛中氧化为ZnO的方式在纳米线顶端形成了催化活性点, 促进了纳米线顶端ZnO的吸收. 烧结后碳逐渐氧化被完全去除. 采用场发射扫描电镜(FE-SEM)、透射电镜(TEM, HR-TEM)和X射线衍射(XRD)对纳米线的分析结果表明, ZnO纳米线在硅衬底上分布均匀, 具有六方纤锌矿结构, 并且大多沿[0001]方向择优取向生长, 直径为20～80 nm, 长度可从0.5至几微米. 提出了聚合物控制ZnO结晶和形貌的网络骨架限域模型以解释纳米线的生长行为.     

Controlling the morphology of ZnO nanostructures in a low-temperature hydrothermal process

ZnO nanostructures of different morphologies were grown in a controlled manner using a simple low-temperature hydrothermal technique. Controlling the content of ethylenediamine (soft surfactant) and the pH of the reaction mixture, nanoparticles, nanorods, and flowerlike ZnO structures could be synthesized at temperatures 80-100 degrees C with excellent reproducibility. High-resolution electron microscopy revealed the well crystalline nature of all the nanostructures with preferential growth along the [002] direction for linear structures. Photoluminescence spectra of the as-grown nanostructures revealed oxygen-vacancy-related defects in them, which could be reduced by air annealing at 250 degrees C. Possible mechanisms for the variation of morphology with synthesis parameters are discussed.     

A simple route to synthesize scales of aligned single-crystalline SiC nanowires arrays with very small diameter and optical properties

Scales of aligned single-crystalline SiC nanowires (SiCNWs) arrays with very small diameter were synthesized by a simple thermal evaporation of ZnS and carbon on silicon wafer. The as-received SiCNWs possess a uniform size distribution centered at approximately 8.0 nm, even with a minimum of approximately 3.0 nm. The highly oriented SiCNWs usually grew along [111] direction with a clean surface, very thin oxide shell, and small quantity of stacking faults. A crystalline tube-like SiC nanostructure is also obtained. The optical properties, including photoluminescence and Raman scattering spectra of the SiCNWs, were investigated, respectively. In the end, a growth model on basis of the experimental data is suggested.     

Growth of ultrathin films of amorphous ruthenium-phosphorus alloys using a single source CVD precursor

Thin films ( approximately 30 nm) of amorphous RuP alloys (P approximately 15-20%) can be grown by CVD from the single source precursor cis-H2Ru(PMe3)4 at 250-300 degrees C and 200 mTorr pressure on native SiO2.     

氧化锌纳米带的低温无催化热蒸发制备及其表征

通过纯锌粉蒸发，在600 ℃无催化条件下成功制备了高质量的不同形貌的ZnO纳米带.该制备方法中控制产物形貌和尺寸的关键是氧、氩及锌蒸气的流速及分压.扫描电镜及高分辩透射电镜观察显示，氧化锌纳米带具有规整光滑及齿状等不同形貌，且皆为单晶，其生长由固-气机理控制.室温光致发光谱表明，齿状氧化锌纳米带在390 nm附近形成紫外发射峰；在455～495 nm时，形成绿光发射峰，该处由4个次级发射峰组成.     

Synthesis and characterization of ZnO nanowires by thermal oxidation of Zn thin films at various temperatures

In this research high-quality zinc oxide (ZnO) nanowires have been synthesized by thermal oxidation of metallic Zn thin films. Metallic Zn films with thicknesses of 250 nm have been deposited on a glass substrate by the PVD technique. The deposited zinc thin films were oxidized in air at various temperatures ranging between 450 °C to 650 °C. Surface morphology, structural and optical properties of the ZnO nanowires were examined by scanning electron microscope (SEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX) and photoluminescence (PL) measurements. XRD analysis demonstrated that the ZnO nanowires has a wurtzite structure with orientation of (002), and the nanowires prepared at 600 °C has a better crystalline quality than samples prepared at other temperatures. SEM results indicate that by increasing the oxidation temperature, the dimensions of the ZnO nanowires increase. The optimum temperature for synthesizing high density, ZnO nanowires was determined to be 600 °C. EDX results revealed that only Zn and O are present in the samples, indicating a pure ZnO composition. The PL spectra of as-synthesized nanowires exhibited a strong UV emission and a relatively weak green emission.