Control of diameter of ZnO nanorods grown by chemical vapor deposition with laser ablation of ZnO

We made a study of controlling diameters of well-aligned ZnO nanorods grown by low-pressure thermal chemical vapor deposition combined with laser ablation of a sintered ZnO target, which was developed by us. Until now, it has been impossible to control diameters of ZnO nanorods, while the growth orientation was maintained well-aligned. In this study we developed a multi-step growth method to fabricate well-aligned nanorods whose diameters could be controlled. Metal Zn vapor and O₂ are used as precursors to grow ZnO nanorods. N₂ is used as a carrier gas for the precursors. A substrate is an n-Si (111) wafer. A sintered ZnO target is placed near the substrate and ablated by a Nd–YAG pulsed laser during ZnO nanorod growth. The growth temperature is 530 C and the pressure is 66.5 Pa. A vertical growth orientation of ZnO nanorods to the substrate is realized in the first-step growth although the diameter cannot be controlled in this step. When an O₂ flow rate is 1.5 sccm, well-aligned nanorods with 100 nm diameter are grown. Next, the second-step nanorods are grown on only the flat tip of the first-step nanorods. The diameters of the second-step nanorods can be controlled by adjusting the O₂ flow rate, and the growth direction is kept the same as that of the first-step nanorods. When the O₂ flow rate in second-step growth is smaller than 0.6 sccm, the diameter of the second-step nanorods is 30–50 nm. When the O₂ flow rate is between 0.75 and 3.0 sccm, the diameter is almost same as that of the first-step nanorods. When the O₂ flow rate is larger than 4.5 sccm, the diameter is increased with increasing O₂ flow rate. Further, the third-step ZnO nanorods with gradually increased diameters can be grown on the second-step nanorods with 1.5 sccm O₂ flow rate and without laser ablation.     

钴的表面增强拉曼散射中的电磁增强因子计算

本文初步探讨了钴电极的表面增强拉曼散射机理。采用二维阵列理论模型在 0 .5～ 4.0eV的光子能量范围对钴纳米椭球阵列的表面增强拉曼散射 (SERS)现象进行了理论分析。有关计算表明 ,经过合适的表面粗糙化的钴金属电极能产生较弱的表面增强效应 (SERS增强因子约 1 0 2 ～ 1 0 4 ) ,制备出具有高纵横比的纳米粒子阵列是得到钴体系较大的SERS增强因子的关键     

La2Zr2O7:Eu3+纳米棒的合成、表征及其荧光性能

采用传统固相法和水热法成功地制备出棒状La₂Zr₂O₇:Eu³⁺荧光粉. 利用X射线粉末衍射仪、透射电镜和荧光光谱仪等分析了产物的结构、形貌和发光特性. 结果表明红色荧光粉La₂Zr₂O₇:Eu³⁺有良好的晶相,属于立方结构,空间点群为Fd3m; 其形貌主要为纳米棒, 平均直径约47 nm, 长度为50～700 nm. 并对纳米棒的生长机理进行了探讨. 在466 nm蓝光激发下,La₂Zr₂O₇:Eu³⁺荧光粉能发射出Eu³⁺的特征红色荧光,发射主峰位于616 nm处,归属于Eu³⁺的⁵DO_→⁷F2_{超灵敏电偶极跃迁.此外,在产物的发射光谱中能够观察到⁵D}1_→⁷FJ _{(J=0, 1, 2)跃迁和⁵D}1_→⁷FJ _{(J=1, 2, 4)跃迁的劈裂峰,这说明Eu³⁺处在低对称性的晶体场格位中.}     

一维锰氧化物纳米棒在以O2为氧源的苯甲醇氧化反应中的催化性能

采用水热法合成MnOOH一维纳米线,通过MnOOH在不同气氛和温度中煅烧得到尺寸和形貌相似的不同锰氧化物,并用于以O₂为氧源的苯甲醇液相氧化反应. 结果表明,MnO₂对苯甲醇氧化反应具有较高的催化活性. 通过XPS、SEM、TEM和H₂-TPR等手段对催化剂的形貌和结构进行了表征,并讨论了可能影响反应活性的一些因素. MnO₂的良好催化性能可能与其晶格氧具有较高的迁移率以及氧化还原能力有关. 通过简单的焙烧处理,可以使MnO₂催化剂在苯甲醇氧化反应中具有良好的重复使用性.     

One-step growth of gold nanorods using a β-diketone reducing agent

The synthesis and characterisation of gold nanorods have been carried out by reduction of the gold salt HAuCl₄. This has been done using a single reducing agent, acetylacetone, rather than the two reducing agents, sodium borohydride and ascorbic acid, normally required by standard wet chemistry methods of gold nanorod formation. Using this novel method, the nanorods were synthesised at several different pH values which were found to greatly affect both the rate at which the nanorods form and their physical dimensions. The concentrations of acetylacetone and silver nitrate used relative to the gold salt were found to alter the aspect ratio of the nanorods formed. Rods with an average length of 42 nm and an aspect ratio of 4.6 can be easily and reproducibly formed at pH 10 using this method. Nanorods formed under optimum conditions were investigated using TEM. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Optical imaging and magnetophoresis of nanorods

Peclet number analysis is performed to probe the convective motion of nanospheres and nanorods under the influence of magnetophoresis and diffusion. Under most circumstances, magnetophoretic behaviour dominates diffusion for nanorods, as the magnetic field lines tend to align the magnetic moment along the rod axis. The synthesis and dispersion of fluorophore-tagged nanorods are described. Fluorescence microscopy is employed to image the nanorod motion in a magnetic field gradient. The preliminary experimental data are consistent with the Peclet number analysis.     

Nylon and nylon blend nanotubes and nanorods

Nylon nanorods and nanotubes (200 nm diameter) were fabricated by the membrane wetting technique (solvent and melt wetting) from a range of nylons (6; 6,6; 6,9; 6,10; 6,12; 11; 12, 6(3)T) and nylon blended with different dyes (Nylon Cast Blue, Nylon 6/6 Black) or with molybdenum disulfide (Nylon cast MDS). The 65-μm long nylon nanotubes and nanorods were characterized by scanning electron microscopy. The nanoscale nylon 6,6 served as an effective high surface area alternative to a nylon membrane as a solid support in a chemiluminescent assay for nylon-bound biotinylated nucleic acids based on streptavidin- alkaline phosphatase and chemiluminescent detection of the bound alkaline phosphatase label with the dioxetane substrate, CDP-Star. Layer-by-layer deposition of the cationic polymer (Sapphire-II™; Tropix) onto the nylon 6,6 nanostructures prior to UV-cross-linking with biotinylated DNA resulted in further enhancement of binding and detection of biotinylated DNA.     

Aligned Nanorod Arrays: Additive and Emergent Properties

Studies of one-dimensional nanostructures of various types (such as quantum wires, nanorods, nanotubes and nanobelts) have progressed substantially during the past decade and have been reviewed by a number of authors. Here, we provide a concise overview of the synthesis and special properties of arrays of parallel nanorods, whose behavior is often quite distinct from that of individual nanorods of the same material. We show that the distinctive behavior of such nanorod arrays may occur due to their exhibiting either additive or emergent properties. The former originates from a simple amplification of some advantageous property shown by a single nanorod, thus making it usable in a practical device; while the latter necessarily involves the presence of the array, and would not be observable from a single nanorod. Nanorod arrays have been shown to have possible applications in diverse areas that include nanolasers, microcavities, surface enhanced Raman effect, photovoltaic cells, field emission sources, gas sensing, electrical discharge and in hydrophobic surfaces. We first present an overview of some of the physical and chemical synthesis strategies for nanorod arrays, followed by a brief review of their applications in the areas just mentioned.     

Structural and magnetic properties of self assembled Fe-doped Cu2O nanorods

Cuprous oxide (Cu₂O) nanorods doped with iron impurities have been synthesized by the polyol method using sodium dodecyl sulfate as the surfactant. The X-ray diffraction measurement reveals the pure phase of simple cubic Cu₂O and the electron microscopy displays its one dimensional morphology. Ferromagnetism was observed at room temperature in the magnetic measurements of the doped samples while undoped sample exhibits only diamagnetism. Room temperature Mössbauer spectra for the samples exhibited only doublets but no sextet, which corresponds to the presence of paramagnetic iron sites. As magnetic moment contribution of the doped ions was insignificant for the observed magnetism, ferromagnetic property in the doped samples could have been originated from the defects as cation vacancies. Existence of the defects was supported by the room temperature photoluminescence spectra of the doped samples in reference to the undoped sample.     

不同结构CoPt纳米棒磁学性能

运用电位置换结合化学还原方法制备了两种不同结构的CoPt纳米棒材料,一种为实心结构(CoPt-a),一种为空心结构(CoPt-b).采用透射电镜(TEM)和能量散射光谱(EDS)研究了其形貌和组成.在5和300K下测试了两种纳米棒的磁学性能.结果显示,CoPt-a和CoPt-b纳米棒在5K时的矫顽力分别为6.5和9.3A·m-1,温度升至300K时,两种结构CoPt纳米棒矫顽力均减小为0A·m-1.场冷曲线(FC)和零场冷曲线(ZFC)结果表明两种结构的CoPt纳米棒均表现出超顺磁性,阻塞温度(TB)分别为10.0和9.0K.两种CoPt纳米棒组成、结构等不同可能是引起其矫顽力、磁化强度和阻塞温度差异的主要原因.