Controlling the length and shape of gold nanorods

In this paper, we report a new approach to fabricate gold nanowires by controlling the volume of the growth solution. The shape evolutions ranging from fusiform nanoparticles to 1-D rods were observed. Increasing the addition of the growth solution can control the length of nanorods. The length of the rods can be extended to 2 microm, and nanorods with aspect ratios of up to approximately 70 could be obtained.     

Microwave synthesis of highly aligned ultra narrow semiconductor rods and wires

We report on the rapid production, characterization, and spectral properties of highly uniform, ultra narrow semiconductor (ZnS, ZnSe, CdS, CdSe) nanorods and nanowires by microwave irradiation. Quantum-confinement effects are manifested in the light absorption and the PL of the rods and wires. The uniformity of the rods and of the wires is demonstrated in their spontaneous assembly into highly ordered 2D supercrystals. We also observed the stepwise growth of the rods originating from nearly spherical nuclei.     

Preparation and magnetic properties of Cu-ferrite nanorods and nanowires

An aqueous solution method has been developed for preparing Cu-ferrite nanorods (NRs) array and nanowires (NWs) on Cu substrate. The Cu-ferrite NRs exhibit a clear uniaxial anisotropy with the easy axis along rods. The decrease of the reduced remanence from 0.24 in the parallel magnetic field to almost zero in the perpendicular field shows a strong effect of the demagnetizing field perpendicular to the rod axis. The weaker uniaxial anisotropy makes NWs the lower saturation magnetization.     

微波法合成一维结构Cd(OH)2螺旋形纳米线

通过微波辐照法一步合成了长1~3 μm, 直径30~100 nm的螺旋形纳米线, 实验结果表明它是由更细的纳米线组装成束的. 通过改变反应物浓度可以调控螺旋纳米线的直径和长度, 不同的镉盐对产物的结构与形貌有较大的影响. 讨论了螺旋形纳米线可能的形成机理.     

Selective synthesis and characterization of single-crystal silver molybdate/tungstate nanowires by a hydrothermal process

Selective synthesis of uniform single crystalline silver molybdate/tungstate nanorods/nanowires in large scale can be easily realized by a facile hydrothermal recrystallization technique. The synthesis is strongly dependent on the pH conditions, temperature, and reaction time. The phase transformation was examined in details. Pure Ag(2)MoO(4) and Ag(6)Mo(10)O(33) can be easily obtained under neutral condition and pH 2, respectively, whereas other mixed phases of Mo(17)O(47), Ag(2)Mo(2)O(7,) Ag(6)Mo(10)O(33) were observed under different pH conditions. Ag(6)Mo(10)O(33) nanowires with uniform diameter 50-60 nm and length up to several hundred micrometers were synthesized in large scale for the first time at 140 degrees C. The melting point of Ag(6)Mo(10)O(33) nanowires were found to be about 238 degrees C. Similarly, Ag(2)WO(4), and Ag(2)W(2)O(7) nanorods/nanowires can be selectively synthesized by controlling pH value. The results demonstrated that this route could be a potential mild way to selectively synthesize various molybdate nanowires with various phases in large scale.     

Manipulating Nanowire Assembly for Flexible Transparent Electrodes

Manipulating nanowire assembly could help the design of hierarchical structures with unique functionalities. Herein, we first report a facile solution‐based process under ambient conditions for co‐assembling two kinds of nanowires which have suitable composition and functionalities, such as Ag and Te nanowires, for the fabrication of flexible transparent electrodes. Then Te nanowires can be etched away easily, leaving Ag nanowire networks with controllable pitch. By manipulating the assembly of Ag and Te nanowires, we can precisely tailor and balance the optical transmittance and the conductivity of the resulting flexible transparent electrodes. The network of Ag nanowires which have tunable pitch forms a flexible transparent conducting electrode with an averaged transmission of up to 97.3 % and sheet resistances as low as 2.7 Ω/sq under optimized conditions. The work provides a new way for tailoring the properties of nanowire‐based devices.     

Preparation of single-crystalline NdVO4 nanorods, and their emissions in the ultraviolet and blue under ultraviolet excitation

This paper describes a facile sacrifical (NH4)0.5V2O5 nanowires approach to single-crystalline NdVO4 nanorods. The nanorods have a rectangular cross section of about 30 x 30 nm2 to 100 x 200 nm2, and length ranging from 400 to 700 nm. Transmission electron microscopy (TEM) and selected area electron diffraction (SAED) show that the nanorods grew respectively along the [312] and [101] direction on the (NH4)0.5V2O5 nanowires. Ultraviolet (362 nm) and blue (467 nm) emissions can be observed under excitation of 310 nm at room temperature, suggesting that the nanorods should be good candidates for fabricating UV and blue nanodevices.     

Starfruit-shaped gold nanorods and nanowires: synthesis and SERS characterization

Recently, branched and star-shaped gold nanoparticles have received significant attention for their unique optical and electronic properties, but most examples of such nanoparticles have a zero-dimensional shape with varying numbers of branches coming from a quasi-spherical core. This report details the first examples of higher-order penta-branched gold particles including rod-, wire-, and platelike particles which contain a uniquely periodic starfruitlike morphology. These nanoparticles are synthesized in the presence of silver ions by a seed-mediated approach based on utilizing highly purified pentahedrally twinned gold nanorods and nanowires as seed particles. The extent of the growth can be varied, leading to shifts in the plasmon resonances of the particles. In addition, the application of the starfruit rods for surface-enhanced Raman spectroscopy (SERS) is demonstrated.     

Morphology-controllable synthesis of cobalt oxalates and their conversion to mesoporous Co3O4 nanostructures for application in supercapacitors

In this work, one-dimensional and layered parallel folding of cobalt oxalate nanostructures have been selectively prepared by a one-step, template-free, water-controlled precipitation approach by simply altering the solvents used at ambient temperature and pressure. Encouragingly, the feeding order of solutions played an extraordinary role in the synthesis of nanorods and nanowires. After calcination in air, the as-prepared cobalt oxalate nanostructures were converted to mesoporous Co(3)O(4) nanostructures while their original frame structures were well maintained. The phase composition, morphology, and structure of the as-obtained products were studied in detail. Electrochemical properties of the Co(3)O(4) electrodes were carried out using cyclic voltammetry (CV) and galvanostatic charge-discharge measurements by a three-electrode system. The electrochemical experiments revealed that the layered parallel folding structure of mesoporous Co(3)O(4) exhibited higher capacitance compared to that of the nanorods and nanowires. A maximum specific capacitance of 202.5 F g (-1) has been obtained in 2 M KOH aqueous electrolyte at a current density of 1 A g(-1) with a voltage window from 0 to 0.40 V. Furthermore, the specific capacitance decay after 1000 continuous charge-discharge cycles was negligible, revealing the excellent stability of the electrode. These characteristics indicate that the mesoporous Co(3)O(4) nanostructures are promising electrode materials for supercapacitors.     

Two-dimensional pressure-driven nanorod-to-nanowire reactions in Langmuir monolayers at room temperature

Typical two-dimensional surface pressures prevalent within floating monolayer (Langmuir) films are on the order of a few dozen megapascals. One might expect, therefore, that some chemical reactions should be directly and strongly affected by this surface pressure, along with the well-known effect of pressure on the orientational order and the mere proximity of the molecules within the film. Here, we show that the two-dimensional surface pressure in Langmuir films provides a direct driving force, decreasing the activation energy of a cooperative oriented coalescence of ZnS nanorods into nanowires near room temperature. At low film surface pressure or low temperature, the nanorods do not react, while in solution, they react only above 140 degrees C, even though in all of these cases, the rods are organized in similar super-crystalline clusters. Electron microscopy and measurements of the reaction rates give a detailed picture of the order of the rods, their rearrangement, and their coalescence.     

Nanoplasmonic Nanorods/Nanowires from Single to Assembly: Syntheses,Physical Mechanisms and Applications

Gold nanorods are anisotropic and exhibit different optical characteristics in both transverse and longitudinal directions, so the plasmon resonance in the near‐infrared region will reflect two absorption peaks. Because of strong enhancements of electromagnetic fields of gold nanorods, gold nanorods are widely used in medical treatment, biological detection, sensors, solar cells and other fields. Since rapid developments of gold nanorods, it is necessary to sort out the recent achievements. In this review, we select three classifications of single nanorods/nanowires, dimers and assembled nanorods to introduce their syntheses methods, optical properties and applications respectively. We firstly overview the history of nanorods/nanowires syntheses and summarize the improvement of the commonly utilized seed‐mediated growth synthesis method; and then, physically, nano‐plasmonic and optical properties of single and assembled nanorod/nanowires are concluded in detail. Lastly, we mainly summarize the recent advances in applications and provide perspective in different fields.     

Selected-control synthesis of ZnO nanowires and nanorods via a PEG-assisted route

Long-chain polymer-assisted growth of one-dimensional (1D) nanostructures has been investigated in previous research. This kind mild method has lots of merits such as not requiring complex procedures, without template supporting etc. Can the short-chain polymer also be used to grow long nanowires? In the present work, a short-chain polymer (PEG400) was found to promote the formation of 1D ZnO nanostructures, which cannot be obtained by long-chain polymers (such as PEG10000). Moreover, nanowires and nanorods can be selectively synthesized by using short-chain polymers. The influence factors for the formation of 1D ZnO nanostructures were also investigated in detail. The XRD, Raman spectrum, XPS, SEM, TEM, ED, HRTEM, EDXA, and PL spectra have been provided for the characterization of the as-obtained nanowires and nanorods.     

One-step synthesis of silver nanoparticles, nanorods, and nanowires on the surface of DNA network

Here, we describe a one-step synthesis of silver nanoparticles, nanorods, and nanowires on DNA network surface in the absence of surfactant. Silver ions were first adsorbed onto the DNA network and then reduced in sodium borohydride solution. Silver nanoparticles, nanorods, and nanowires were formed by controlling the size of pores of the DNA network. The diameter of the silver nanoparticles and the aspect ratio of the silver nanorods and nanowires can be controlled by adjusting the DNA concentration and reduction time.     

利用牛血清蛋白合成CdS纳米棒和网状纳米线

采用简单易控、对环境友好的矿化方法, 利用牛血清蛋白(BSA)做模板, 通过Cd2+与硫代乙酰胺(TAA)反应制备了形貌均一的CdS纳米棒和网状纳米线. 分别采用透射电子显微镜(TEM)、X射线能谱(EDS)、X射线衍射(XRD)、荧光(PL)发射谱和导电原子力显微镜(C-AFM)等方法对不同实验温度下制备的CdS样品的结构形貌、成分组成和光学性质及微区电子传输行为进行了表征. 结果表明: 在实验反应温度为20 ℃时, 得到的产物为单分散性好的CdS 纳米棒, 长度为250 nm, 直径为30 nm; 在50 ℃时, 得到网状CdS纳米线, 其长度为2-3 μm; CdS纳米棒和网状纳米线均为立方相闪锌矿结构. 荧光性质的测试表明, CdS纳米棒和网状纳米线具有优良的荧光性能, 电流-电压(I-V)特性的表征表明CdS纳米线具有很好的电导特性.     

Dielectrophoretic alignment of metal and metal oxide nanowires and nanotubes: a universal set of parameters for bridging prepatterned microelectrodes

Nanowires and nanotubes were synthesized from metals and metal oxides using templated cathodic electrodeposition. With templated electrodeposition, small structures are electrodeposited using a template that is the inverse of the final desired shape. Dielectrophoresis was used for the alignment of the as-formed nanowires and nanotubes between prepatterned electrodes. For reproducible nanowire alignment, a universal set of dielectrophoresis parameters to align any arbitrary nanowire material was determined. The parameters include peak-to-peak potential and frequency, thickness of the silicon oxide layer, grounding of the silicon substrate, and nature of the solvent medium used. It involves applying a field with a frequency >10(5) Hz, an insulating silicon oxide layer with a thickness of 2.5 μm or more, grounding of the underlying silicon substrate, and the use of a solvent medium with a low dielectric constant. In our experiments, we obtained good results by using a peak-to-peak potential of 2.1 V at a frequency of 1.2 × 10(5) Hz. Furthermore, an indirect alignment technique is proposed that prevents short circuiting of nanowires after contacting both electrodes. After alignment, a considerably lower resistivity was found for ZnO nanowires made by templated electrodeposition (2.2-3.4 × 10(-3) Ωm) compared to ZnO nanorods synthesized by electrodeposition (10 Ωm) or molecular beam epitaxy (MBE) (500 Ωm).     

金、铜金属纳米棒或纳米线的AFM和SERS的研究(英文)

通过电化学氧化法制备具有不同孔径氧化铝模板 ,利用交流电镀的方法在模板中沉积金属 ,再用酸溶解模板可以得到相应尺度的金属纳米线或纳米棒的阵列 .本文利用原子力显微镜和表面增强拉曼技术分别表征了金和铜两种金属纳米线阵列 .研究结果表明 ,作为探针分子的硫氰(SCN )在金属纳米线上的碳氮三键的振动频率随纳米线直径的增大而蓝移 .这一现象可能是因为尺寸效应对纳米线的费米能级造成影响 ,使不同直径的金属纳米线电子结构存在微小的差别 .     

电沉积制备ZnO纳米棒修饰电极上氧化还原蛋白的电化学行为

采用恒电位阴极还原法在金电极表面一步修饰ZnO纳米棒, 制备成ZnO纳米棒修饰电极. 扫描电子显微镜(SEM)和X射线衍射(XRD)结果显示制得的ZnO为直径约100 nm的六棱柱状纤锌矿晶体纳米棒. 使用ZnO纳米棒修饰的金电极研究细胞色素c的直接电化学行为, 结果表明: ZnO纳米棒修饰的金电极能有效探测到细胞色素c的铁卟啉辅基在不同价态下的电化学行为; 细胞色素c吸附后, ZnO纳米棒修饰的金电极对过氧化氢的电流响应呈现良好的线性关系.     

Synthesis and characterization of silver nanowires with zigzag morphology in N,N-dimethylformamide

Zigzag silver nanowires with a uniform diameter of 20±5 nm were prepared by reducing silver nitrate (AgNO₃) with N,N-dimethylformamide (DMF) in the presence of tetrabutyl titanate (TBT) and acetylacetone (AcAc) at 373 K for 18 h. X-ray and selected area electron diffraction (XRD and SAED) patterns reveal that the prepared product is made of pure silver with face centered cubic structure. Transmission electron microscopy (TEM) investigations suggest that the amount of silver nanowires is enhanced with increase in reaction time, and the end-to-end assemblies of silver nanorods are observed during the reaction process. After 18 h reaction, silver nanowires with zigzag morphology are obtained. In this paper, a possible growth process of silver nanowires with this interesting shape is described. Silver nanoparticles with small sizes were obtained by reducing Ag⁺ ions with DMF, providing seeds for homogeneous growth of silver nanorods. With the extending reaction time, the synthesized silver nanorods were connected in an end-to-end manner, and the interface between the connections of two nanorods gradually disappeared. The final product shows zigzag morphology with various angles. The angles between two connecting straight parts of zigzag nanowires exhibit an alterable range of 74-151°. These silver nanowires show tremendous potential applications in future nanoscale electronic circuits.     

Synthesis of variable-aspect-ratio, single-crystalline ZnO nanostructures

Variable-aspect-ratio (length/diameter), one-dimensional (1-D) ZnO nanostructures (nanorods and nanowires) were prepared in alcohol/water solution by reacting a Zn2+ precursor with an organic weak base, tetramethylammonium hydroxide (Me4NOH). The effect of the experimental parameters (temperature, base concentration, reaction time, and water content) on nucleation, growth, and the final morphology of the ZnO nanostructures was investigated. The low-temperature syntheses (75-150 degrees C) yielded aspect ratios of the 1-D ZnO nanostructures that depended on the water content. The individual ZnO nanorods and nanowires were determined to be perfect, single crystals with their c axes as the primary growth direction.     

电子显微镜技术表征聚乙二醇包覆的银纳米线的显微结构特征

以缓慢的水热合成法制备聚乙二醇(PEG)包覆的银纳米线,并用电子显微镜对其微观形貌和结构进行了表征。PEG是一种对银表面呈弱亲和性的水溶性聚合物,它在银纳米线合成中既作为Ag+的还原剂,又作为银线的包覆剂。扫描电镜和透射电镜表征显示,这种银纳米线的直径为80～300 nm,长度大于100μm;并且其中一部分银纳米线首尾相接形成了闭合纳米线圈,是首例以化学法制取的金属闭合纳米线圈。闭合环状纳米线的形成进一步支持了金属纳米线的融合生长机制。透射电镜和选区电子衍射以及银纳米线横截面切片的透射电镜表征显示,这种PEG包覆的银纳米线具有轴对称的五重挛晶结构。银纳米线经过长时间的水热孵化而保持其五重挛晶结构,这一点与某些文献报道的情况有所不同,说明银纳米线结构及其演化具有一定的复杂性。