MgO单晶一维纳米结构的制备与表征

研究气相法制备MgO一维纳米结构的简单工艺途径.采用直接热蒸发镁粉的化学气相沉积法在不同条件下分别制备了MgO的纳米棒、纳米线、直角网络结构纳米线、晶须等单晶一维纳米结构.温度、氧分压和过饱和MgO蒸气压等参数对形貌具有重要影响.X射线衍射和选区电子衍射确定MgO纳米结构为立方晶系.扫描电镜和透射电镜对不同产物的形貌进行表征,显示其生长受到气一固生长机制控制.光致发光表明MgO纳米线在381 nm处出现强烈的紫色光发射宽峰.     

Effect of Sn on Microstructure and Electrochemical Properties of Mg Alloy Anode Materials

使用硼粉为硼源,硅和镍为催化剂反应成功制备出硼纳米线.硼纳米线的直径为50～100 nm,其长度为几微米.实验表明硅可以促进硼纳米线的生长.在纳米线的生长过程中使用Ni(NO3)2或NiSO4作为镍源,前者催化效率更高.此外,在硼纳米线生长前先合成NixBy催化剂,与同时加入反应物相比较,催化效果得到提高.     

热退火对离子注入制备Au纳米颗粒生长和光学性能的影响

利用金属蒸发真空多弧离子源(MEVVA源)注入机,将Au离子注入到高纯石英玻璃衬底中来制备Au纳米颗粒,Au离子注入的加速电压分别为20、40和60 k V,注入剂量为1×1017ions/cm2,随后将注入样品在普通管式退火炉中700~1000℃退火处理。研究了注入条件和热退火参数对Au纳米颗粒的形成、生长、分布以及光学性能的影响。采用光学吸收谱、扫描电子显微镜和透射电子显微镜对注入样品的光学性能、表面形貌和微观结构进行了测试和表征。实验结果表明,采用该低压离子注入结合热退火工艺的方法,所制备的Au纳米颗粒具有很强的局域表面等离子体共振特性,同时该方法也为制备尺寸和分布可控的Au纳米颗粒提供了一些新的参考途径。     

形貌可控纳米氧化钨的制备

以含WCl6的无水乙醇溶液为前驱液,PVP为表面活性剂,通过溶剂热法制备了氧化钨纳米线。利用X射线衍射、扫描电镜、透射电镜和选区衍射等手段对制备的纳米线进行了表征,通过调整PVP加入量来调控纳米氧化钨的形貌,并对氧化钨纳米线的生长机制和形貌发生改变的原因进行了分析。     

硫化镉纳米结构的制备与光学性质研究

采用直接热蒸发CdS粉末的方法,在不同的生长条件下制备出CdS纳米线和纳米带材料并对其形貌、结构和光学性质进行了研究.CdS纳米线具有单晶结构,且生长方向具有择优取向,而其纳米带不具有上述结构特征.光致发光光谱研究发现,室温下纳米线只在508 nm出现了CdS的本征发射带.然而,纳米带存在2个明显的发光峰,中心峰位分别位于513 nm和756 nm.这2个发射峰可分别指认为CdS的本征发射和V_s~+空位引起的发射.     

类金刚石碳纳米线的制备及生长机理

采用热蒸发法制备了类金刚石碳纳米线,利用透射电子显微镜(TEM)和高分辨率透射电子显微镜(HRTEM)对样品的形貌和结构进行观察,发现该碳纳米线具有圆形实心结构,表面光滑,直径10～40 nm;拉曼光谱研究显示特征峰出现在1 352 cm-1和1 586 cm-1处,为典型的类金刚石结构.用CO辅助生长机理解释类金刚石碳纳米线的形成过程.     

金属及其氧化物磁性纳米线阵列的制备与操控

从磁性纳米线的制备、游离纳米线的操控、纳米线有序阵列的表征和应用几个方面综述了磁性纳米线的最新研究进展.详细地介绍了溶胶-凝胶模板法、热还原法等制备磁性纳米线的方法及其应用情况和发展方向.并且针对目前磁性纳米线在实际应用方面存在的问题,着重阐述了游离纳米线操控(包括微流体排列或搭接、自组装和磁场辅助组装、电场/磁场诱捕)的概念、原理、操作方法、表征手段等.在文中还介绍了磁性纳米线的特殊性质及其潜在的应用领域.     

Al掺杂对ZnO纳米线CO气敏性能的影响

以采用物理热蒸发法制备的纯ZnO纳米线和Al掺杂ZnO纳米线为气敏基料,制备成旁热式气敏元件,用静态配气法对浓度均为100ppm的氨气、甲烷、一氧化碳3种气体进行气敏性能测试。结果表明,Al掺杂后,ZnO纳米线对3种气体灵敏度的最高值分别提高了40%、60%、106%,对CO气体的影响最为显著,并缩短了响应时间和恢复时间。     

Growth of ZnO Nanostructures on Metal-Filled Porous Silicons

在多孔Si上使用不同催化剂成功生长ZnO纳米结构。结果表明,Au作催化剂在Si衬底上得到末端呈六角形的ZnO纳米棒,Cu作催化剂在Si(100)和(111)分别上生长出带状和棒状纳米ZnO,Zn作催化剂在Si衬底上则获得ZnO纳米线。Zn催化制备的ZnO纳米线晶面间距为0.283nm,生长方向是[0110],具有结晶较好的六角纤锌矿晶体结构。比较了不同催化剂制备ZnO的光学性能,发现得到Zn催化制备的ZnO纳米线缺陷绿光峰最弱,因此Zn催化生长制备的纳米ZnO结构质量较好。空气中退火后,3种催化剂生长的纳米ZnO的缺陷发光峰位置不变,而强度变弱。     

SnO_2@TiO_2核-壳纳米线的制备及其光催化性能

通过固-液-气(VLS)生长机制,利用化学气相沉积法(CVD)制备SnO_2纳米线。利用原子层沉积(ALD)以钛酸四异丙酯为前驱体在SnO_2纳米线表面沉积不同厚度的TiO_2壳层,形成SnO_2@TiO_2核-壳纳米线结构。通过中间Al_2O_3插层,分别制备出金红石和锐钛矿2种不同晶型的TiO_2,从而制备出2种不同复合结构的SnO_2@TiO_2核-壳纳米线。实验研究该复合结构中TiO_2的厚度与晶型对紫外光下光催化降解甲基橙溶液活性的影响。     

Effects of temperature and pressure on morphologies of quasi-one-dimensional ZnO nanostructures fabricated via thermal evaporation

Quasi one-dimensional zinc oxide nanomaterials were synthesized by thermal evaporation. The structure, morphologies and composition of ZnO nanomaterials prepared under different conditions were studied by XRD, TEM, SEM and EDX. The morphologies are strongly sensitive to the temperature and the pressure during growth, including nanowires, nanobelts, nanocombs and pyramidal-like nanomaterials.     

Fabrication and luminescence properties of In2O3-capped ZnS nanowires

ZnS-core/In₂O₃-shell nanowires have been prepared by using a two-step process: thermal evaporation of ZnS powders on Si(1 0 0) substrates coated with Au thin films and sputter-deposition of In₂O₃. The ZnS nanowires were a few tens of nanometers in diameter and a few hundreds of micrometers in length. ZnS nanowires have an emission band centered at approximately 570 nm in the yellow region. The yellow emission has been enhanced in intensity by capping the ZnS nanowires with In₂O₃ presumably due to the increase in the concentrations of indium and oxygen interstitials in the very surface region of the ZnS cores and further enhanced by annealing in a reduction atmosphere maybe because of the increase in the concentration of Au_Zn⁻ in the ZnS cores. In contrast, the yellow emission intensity has been decreased by annealing in an oxidation atmosphere due to the conversion of ZnS into ZnO as a result of the reaction of ZnS in the cores with oxygen.     

Synthesis and characterization ofsingle-crystalline alumina nanowires

Alumina nanowires were synthesized on large-area silicon substrate via simple thermal evaporation method of heating a mixture of aluminum and alumina powders without using any catalyst or template. The phase structure and the surface morphology of the as-grown sample were analyzed by X-ray diffractometry(XRD) and scanning electron microscopy (SEM), respectively. The chemical composition and the microstructure of the as-grown alumina nanowires were characterized using transmission electron microscope(TEM). The nanowires are usually straight and the single crystalline has average diameter of 40 nm and length of 3 - 5μm. The growth direction is along the [002] direction. Well aligned alumina nanowire arrays were observed on the surface of many large particles. The catalyst-free growth of the alumina nanowires was explained under the framework of a vapor-solid(VS) growth mechanism. This as-synthesized alumina nanowires could find potential applications in the fabrication of nanodevices.     

Investigation of electrical conductivity in Schottky-barrier devices based on nickel phthalocyanine thin films

Evaporated multilayer sandwich structure of Au/NiPc/Al was fabricated by thermal evaporation technique. The electrical conductivity of Au/NiPc/Al device has been measured both as prepared and after annealing at 623 K for 2 h. Under forward bias conditions, ohmic and SCLC conductions were identified at low and higher voltages respectively. After annealing, a strong rectifying effect was observed. The potential barrier height and the depletion region width for annealed sample were calculated as 0.96 eV and 70 nm, respectively. Hole and trap parameters for as prepared and after annealing devices, also, were evaluated.     

High-density arrays of low-defect-concentration zinc oxide nanowire grown on transparent conducting oxide glass substrate by chemical vapor deposition

High-density ZnO nanowire arrays with low defect concentrations were directly grown on transparent conducting oxide glass substrates under catalyst-free and low temperature conditions by chemical vapor deposition (CVD). A possible growth mechanism of the nanowires is studied. The experiments indicate that correct levels of supersaturation and evaporation temperature are beneficial to the growth of ZnO nanowires. Photoluminescence exhibits a weak ultraviolet emission at 380 nm and a strong green emission at 495 nm. While using a double-tube growth system, the visible light emission diminishes and the 380 nm emission is the only emission, suggesting that ZnO nanowires with few defects can be prepared using the present CVD technique at low temperature.     

硅纳米线的制备技术

硅纳米线作为一种新型的一维纳米材料，在纳米电子器件、光电器件及集成电路方面具有很好的应用前景。介绍了硅纳米线在制备方面的国内外研究现状与进展，重点讨论了基于金属催化气-液-固（VLS）生长机理、氧化物辅助生长机理的硅纳米线制备及模板法等制备硅纳米线的研究成果、特点及生长机理。与金属催化VLS生长机理相比，氧化物辅助生长硅纳米线不需要金属催化剂，能避免金属污染，保证了硅纳米线的纯度，因而是今后深入研究的方向。     

TiO2/SiOx core-shell nanowires generated by heating the multilayered substrates

By heating Au/TiN/Si substrates, we fabricated TiO₂/SiO_x core-shell nanowires. By changing the thickness of predeposited Au layers, we demonstrated that the thickness of the Au layer needs to be optimized to obtain nanowires. High-resolution transmission electron microscopy image, X-ray diffraction spectrum, and selected area electron diffraction pattern coincidentally revealed that the resultant core nanowires had a tetragonal rutile structure of TiO₂, and the shell was comprised of amorphous SiO_x. The dominant growth mechanism was a base-growth mode, in which Au played a catalytic role, resulting in morphological changes with variation of the Au layer thickness. The TiO₂/SiO_x core-shell nanowires exhibited a broad photoluminescence emission band, which comprised four peaks centered at 1.54, 2.34, 2.67, and 2.99 eV, respectively. We expected that the 1.54 eV- and 2.34 eV-centered peaks arised from the TiO₂ core, whereas the 2.67 eV- and 2.34 eV-peaks were ascribed to both the TiO₂ core and the SiO_x shell.     

Thermodynamics of the Au-Si-O System: Application to the Synthesis and Growth of Silicon-Silicon dioxide Nanowires

The Solid-Vapor-Liquid-Solid (SVLS) process is a fundamental mechanism for the growth of nanowires. In this article, experimental observations and assessment of thermodynamic data have been used to explain the Solid-Vapor-Liquid-Solid (SVLS) mechanism for the growth of silicon-based nanowires. The binary phase diagram of nanoparticle (Au-Si) systems has been evaluated from information on Gibbs energy of the bulk and surface tension of the liquid phase. At 1100 °C, temperature commonly used for the growth of nanowires by the SVLS mechanism, it has been shown that the nanometric decreases the melting point of pure Au and Si and more generally the liquidus temperatures. Moreover, the liquid phase region in the binary Au-Si phase diagram is enlarged as the particle size becomes smaller. The presence of SiO in the gaseous phase is a necessary but not sufficient condition for the formation of nanowires. The nanowires’growth cannot be explained by the modification of the Au-Si phase diagram with the size of the particles, neither by the presence of SiO, but by the existence of a metastable equilibrium involving the silicon of the wafer, the deposit of vitreous silica and supersaturated SiO in the gaseous phase.     

A simple catalyst-free route for large-scale synthesis of SiC nanowires

A large number of SiC nanowires were fabricated by a simple catalyst-free method using silicon powders and expandable graphite as raw materials. Digital camera, X-ray diffractometer, Fourier transform infrared spectrometer, field-emission scanning electron microscopy and transmission electron microscopy demonstrate that a large number of loose products were obtained in graphite crucible. The products are composed of single crystalline 3C-SiC nanowires with lengths up to several tens of micrometers and diameters of 20-60 nm. The vapor-solid mechanism was proposed to interpret the growth procedure of SiC nanowires. The expandable graphite as carbon source can provide enough growth space for nanowires, which is helpful to improve the yield of SiC nanowires. The simple method provides a promising candidate for industrial fabrication of SiC nanowires.     

Low-temperature synthesis of novel ZnO nanowire microspheres on silicon substrates

Microspheres covered with ZnO nanowires were fabricated by oxidative evaporation of pure zinc powder without catalyst at 450℃. X-my diffraction （XRD） demonstrates that the as-obtained sample can be indexed to high crystaUinity with wurtzite structure. The structural features associated with different growth stages were monitored using scanning elec- tron microscope （SEM）, which described the direct observation nucleation and growth process. Meanwhile, room temperature photoluminescence （PL） spectrum showed a UV emission at -388 nm and a broad green emission at -505 nm. The ZnO nanowires with the self-catalyzed growth mechanism were discussed in detail.