Synthetic control of large-area, ordered silver nanowires with different diameters

Silver (Ag) nanowires with different diameters (28, 38, 55, 80, 200 nm) have been successfully fabricated into the anodic alumina membranes (AAMs) by direct-current electrochemical deposition technique. X-ray diffraction and selected area electron diffraction analysis show that the as-synthesized samples have preferred (220) orientation independent of the nanowire diameters. Transmission electron microscopy and field-emission scanning electron microscopy investigation reveal that the large-area and highly ordered Ag nanowire arrays with smooth surface and uniform diameter are synthesized, and they have the high aspect ratio. The formation mechanism of the silver nanowires is also discussed. The nanowire arrays with different diameters may have potential applications in the future nanodevices.     

Preparation and characteristics of large-area and high-filling Ag nanowire arrays in OPAA template

Highly ordered porous anodic aluminum oxide (OPAA) on aluminum substrate with an ultrathin barrier layer was prepared by a two-step aluminum anodic oxidation plus a step-by-step voltage decrement process. Ag nanowire arrays have been successfully electrodeposited into the OPAA template through constant current technique. The morphology, composition and structure of the nanowire arrays were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The results show that Ag nanowires possess smooth surface and high aspect ratio up to 330 with a diameter of 70-80 nm. Nearly 100% of the pores were filled by Ag nanowires, which have face center cubic structure and (111) preferential orientation. The branch of originally straight pores at the formation front was demonstrated and the branched pores favor the formation of several nucleation sites in each pore at the beginning of the electrodeposition.     

Growth of TiO2 nanowire bundle arrays and their application in dye-sensitized solar cells

Highly oriented single-crystalline TiO₂ nanowire bundle arrays on transparent conductive fluorine-doped tin oxide substrates are prepared by hydrothermal method using the precursors of titanium butoxide, deionized water and hydrochloric acid. The structure and morphology characteristics of all the samples have been analyzed by X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy. Results show that the diameter, length, and density of the nanowire bundle arrays can be varied by changing the growth parameters, such as growth time, initial reactant concentration and acidity. The enhanced (002) peak in XRD patterns indicate that the nanowire is well crystallized and grow perpendicular to the substrate. The high resolution transmission electron microscope images and selected-area electron diffraction patterns confirm that there are approximately 10–30 nanowires in each bundle. The nanowire is single crystalline. Dye-sensitized solar cells assembled from oriented TiO₂ nanowire bundle arrays as the photoanode are studied. The light-to-electricity conversion efficiency is about 2.17 %.     

Electrochemical template synthesis of large-scale uniform copper selenides nanowire arrays

Ordered Cu₃Se₂ nanowire arrays have been prepared by electrochemical template synthesis based on anodic alumina membranes at room temperature. After annealing in argon ambient at 300 °C for 1 h, Cu₂Se nanowire arrays were obtained by structural change. Field emission scanning electron microscopy (FE-SEM), x-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and selected-area electron diffraction (SAED) results show that single crystal copper selenides nanowires with a high filling rate are dense, smooth, and uniform in large area. The effects of several electrodeposition parameters on high-filling, stoichiometric and single crystal copper selenides were discussed.     

合成和表征NiFe2O4纳米线阵列

采用真空灌注结合溶胶-凝胶和氧化铝模板法,在多孔氧化铝模板中制备了平均直径为50 nm的NiFe2O4纳米线阵列.X射线衍射结果显示所制备的纳米线是纯相的NiFe2O4纳米线,透射电镜和电子衍射的结果显示已制备的纳米线是多晶的且表面光滑,场发射扫描电镜图片显示纳米线是大面积且平行有序的、纳米线的长度和所用的氧化铝模板的厚度相当.磁测量的结果显示此纳米线阵列有形状各向异性,同块状材料相比矫顽力有所增强.对纳米线的生长机理做了简单的讨论.     

Characterization of ordered Cu2O nanowire arrays prepared by heat treated Cu/PAM composite

Cu nanowire arrays were synthesized via a porous alumina membrane (PAM) template with a high aspect ratio, uniform pore size (120–140 nm), and ordered pore arrangement. The Cu₂O nanowire arrays were prepared from the oxidization of Cu metal nanowire arrays. The electrochemical deposition potential of Cu metal nanowires (?180 mV vs. SCE) was determined from X-ray diffraction (XRD) patterns. The microstructure and chemical composition of Cu nanowire arrays were characterized using field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), and X-ray diffraction (XRD). Results indicate that the Cu/Cu₂O nanowire arrays assembled into the nanochannel of the porous alumina template with diameters of 120–140 nm. The valence of copper was controlled by the porous alumina template during the annealing process. Copper nanowires transformed to the Cu₂O phase with the space limitation of the PAM template. Single-crystal Cu₂O nanowire arrays were also obtained under the template embedded.     

无电金属沉积法硅纳米线阵列的制备研究

采用无电金属沉积法在硅衬底上制备出了大面积规整的硅纳米线阵列,并对其形貌控制的影响因素和形成机理进行了研究。用扫描电子显微镜(SEM)、X射线衍射仪(XRD)对硅纳米线阵列和相应银枝晶的形貌和结构进行了表征。结果表明,硅纳米线阵列的形貌受水热体系中溶液配比、温度和时间的影响,在温度为50℃、HF和AgNO3浓度分别为4.6和0.02mol/L的条件下,容易得到大面积排列规整的硅纳米线阵列,并且硅纳米线的长度为30～50μm,直径为200nm左右。无电金属沉积法为硅纳米线及其阵列的制备提供了一种设备简单、条件温和的制备方法。     

Structure, photoluminescence and wettability properties of well arrayed ZnO nanowires grown by hydrothermal method

Well aligned ZnO nanowire arrays with high crystal quality were grown on Si substrates at a low temperature (50 degrees C) by hydrothermal method using a pre-formed ZnO seed layer. ZnO seeds were prepared via radio-frequency magnetron sputtering onto Si substrates. The morphologies of the ZnO nanowire arrays were shown by field emission scanning electron microscopy. X-ray diffraction spectra showed that the full width at the half maximum of the (0002) peak of the nanowire arrays without any heat treatment was only 0.07 degrees, indicating very high crystal quality. Furthermore, the room-temperature photoluminescence spectra of the ZnO nanowire arrays exhibited excellent UV emission. The special micro/nano surface structure of the ZnO nanowire arrays can enhance the dewettability for surfaces modified via low surface energy materials such as long chain fluorinated organic compounds. The surface of the ZnO nanowire arrays is also found to be superhydrophobic with a contact angle of 165 degrees +/- 1 degrees, while the sliding angle is 3 degrees.     

Effect of the Electrodeposition Frequency,Wave Form,and Thermal Annealing on Magnetic Properties of [Co0.975Cr0.025]0.99Cu0.01 Nanowire Arrays

Highly ordered [Co _0.975Cr _0.025]_0.99Cu _0.01 nanowire arrays were electrodeposited by conducting alternating current (AC) conditions from sulfate-based electrolyte into nanopores of anodic aluminum oxide (AAO) template with 37 nm pore diameter and the interpore distances of almost 50 nm. Fabricated nanowire arrays were characterized using scanning electron microscopy, alternating gradient force magnetometer, and X-ray diffraction. The results illustrated that varying frequency, wave form, and annealing procedure had influence on magnetic properties of as deposited nanowires. The nanowire arrays electrodeposited at different electrodeposition frequencies show remarkably different magnetic behaviors. Due to increasing of the electrodeposition frequency, the rate of ions for reduction was decreased. The nanowires prepared at various wave form illustrated insignificant impact on magnetic properties. X-ray diffraction patterns display that both as-deposited and annealed nanowire arrays expose the same structure. The raised value of coercivity has been determined in annealed nanowire arrays. Magnetization measurements show that the maximum value of coercivity for [Co _0.975]_0.99Cu _0.01 nanowires is observed at high temperature.     

Synthesis and optical properties of ordered 30 nm PbS nanowire arrays fabricated into sulfuric anodic alumina membrane

Crystalline PbS nanowire arrays have been successfully fabricated by AC applied DC electrochemical deposition from aqueous solutions of dimethylsulfoxide DMSO solution containing lead chloride and elemental sulfur into sulfuric anodic alumina membranes (AAM). These nanowires have uniform diameters of approximately 30 nm, and their lengths are up to tens of micrometers. Scanning electron microscopy indicates that the ordered PbS nanowire arrays are completely embedded. The results of X-ray diffraction show that the as-synthesized nanowires are crystalline with highly preferential orientation. Energy dispersive spectrometer analysis shows that the composition ratio is very close to 1:1. Finally PL and UV–VIS illustrate the quantum confinement effects of PbS nanowire arrays.     

Fabrication and magnetic properties of Fe<Subscript>3</Subscript>Co<Subscript>7</Subscript> alloy nanowire arrays

Fe₃Co₇ alloy nanowire arrays have been fabricated by direct current electrodeposition of Fe²⁺ and Co²⁺ into anodic aluminum oxide (AAO) templates. The phase structure and magnetic properties of the nanowires were studied by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction (XRD), and vibrating sample magnetometer (VSM). Magnetic measurements show that the coercivity and remanence of the as-deposited Fe₃Co₇ Alloy nanowires increase dramatically after heat-treatment at 773 K for 2 h, and the nanowire arrays exhibit uniaxial magnetic anisotropy with easy magnetization direction along the nanowire axes owing to the large shape anisotropy. The great difference between practical coercivity and ideal coercivity was also discussed in detail.     

Preparation of dendritic Ag/Au bimetallic nanostructures and their application in surface-enhanced Raman scattering

Dendritic Ag/Au bimetallic nanostructures have been synthesized via a multi-stage galvanic replacement reaction of Ag dendrites in a chlorauric acid (HAuCl₄) solution at room temperature. After five stages of replacement reaction, one obtains structures with protruding nanocubes; these will mature into many porous structures with a few Ag atoms that are left over dendrites. The morphological and compositional changes which evolved with reaction stages were analyzed by using scanning electron microscopy, transmission electron microscopy, UV-visible spectroscopy, selected area electron diffraction and energy-dispersive X-ray spectrometry. The replacement of Ag with Au was confirmed. A formation mechanism involving the original development of Ag dendrites into porous structures with the growth of Au nanocubes on this underlying structure as the number of reaction stages is proposed. This was confirmed by surface-enhanced Raman scattering (SERS). The dendritic Ag/Au bimetallic nanostructures could be used as efficient SERS active substrates. It was found that the SERS enhancement ability was dependent on the stage of galvanic replacement reaction.     

The catalyst-free synthesis of large-area tungsten oxide nanowire arrays on ITO substrate and field emission properties

Tungsten oxide nanowire arrays have been grown on indium tin oxide coated glass substrate using tungsten trioxide powders as source by thermal evaporation approach without any catalysts. When the O₂/Ar flow rate ratio was 1/100, large-scale, high-density and uniformly distributed tungsten oxide nanowire arrays were obtained. The morphology and structure properties of the tungsten oxide nanowires were characterized by scanning electron microscopy, X-ray diffraction, and transmission electron microscopy. The influences of the oxygen concentration on the growth, density, shape and structure of the nanowires were investigated. The possible growth mechanism which governs the various types of nanowire arrays as the O₂/Ar flow rate ratios changed is also discussed. Field emission properties of tungsten oxide nanowire arrays were studied at a poor vacuum condition. The remarkable performance reveals that the tungsten oxide nanowire arrays can be served as a good candidate for commercial application as electron emitters.     

Electrochemical Fabrication of Pd-Ag Alloy Nanowire Arrays in Anodic Alumina Oxide Template

The synthesis of Pd-Ag alloy nanowires in nanopores of porous anodic aluminum oxide （AAO） template by electrochemical deposition technique was reported. Pd-Ag alloy nanowires with 16%-25% Ag content are expected to serve as candidates of useful nanomaterials for the hydrogen sensors. Scanning electron microscopy （SEM） and energy dispersed X-ray spectroscopy （EDX） were employed to characterize the morphologies and compositions of the Pd-Ag nanowires. X-ray diffraction （XRD） was used to characterize the phase properties of the Pd-Ag nanowires. Pd-Ag alloy nanowire arrays with 17.28%-23.76% Ag content have been successfully fabricated by applying potentials ranging from -0.8 to -1.0 V （vs SCE）. The sizes of the alloy nanowires are in agreement with the diameter of AAO nanopores. The underpotential deposition of Ag＋ on Pd and Au plays an important role in producing an exceptionally high Ag content in the alloy. Alloy compositions can still be controlled by adjusting the ion concentration ratio of Pd^2＋ and Ag＋ and the electrodeposition processes. XRD shows that nanowires obtained are in the form of alloy of Pd and Ag.     

三维结构磷酸铁锂纳米线阵列的制备及其电化学性能

采用阳极氧化铝模板(AAO),通过溶胶-凝胶法制备出磷酸铁锂(LiFePO_4)纳米线阵列。场发射扫描电镜(FESEM)和透射电镜(TEM)表征均说明制得的LiFePO_4阵列是分散均匀且相互平行的。X射线衍射(XRD)和能谱图(EDS)表征均说明LiFePO_4纳米线是纯相橄榄石型结构。电化学性能测试表明纳米线阵列具有较好的循环稳定性,1C电流密度下循环100次后容量几乎不衰减,容量保持率为99.1%,10C电流密度下循环350次后容量保持率为91.6%。纳米线阵列的倍率性能较同等条件下制备的纳米粉体有较大提升,0.1C、10C电流密度下容量可分别达156.4mAh/g、106.9mAh/g。     

Fabrication of highly-ordered nanopatterned copper nanowire arrays by photolithography

Two different patterns, one being circular and the other being QDU, of copper (Cu) nanowire arrays were successfully produced by electrochemical deposition and photolithography. The highly-ordered patterns of Cu nanowire arrays were observed to stand freely on the substrate using scanning electron microscopy (SEM). Chemical analyses have been performed on Cu nanowires using energy dispersive X-ray spectroscopy (EDS). The results confirmed that it is mainly composed of Cu. Selected-area electron diffraction (SAED) pattern indicated the nanowires are single crystalline and the growth direction of the nanowires is along the [220] direction. With the deposition time increasing, the length of Cu nanowires increaseed.     

MBE法生长ZnO纳米线阵列的结构和光学性能

在氧等离子体辅助的MBE系统中, 以1 nm厚的Au薄膜为催化剂, 基于气?液?固(VLS)机制实现了低温ZnO纳米线阵列在Si(111)衬底表面的生长. 通过场发射扫描电子显微镜(FE-SEM)可以观察到, ZnO纳米线阵列垂直生长在衬底上, 直径为20~30 nm. X射线衍射(XRD)和高分辨透射电镜(HRTEM)结果表明: ZnO纳米线为六方纤锌矿结构, 具有沿c轴方向的择优取向. 光致发光(PL)谱显示在380 nm附近有强烈ZnO本征发射峰, 475~650 nm可见光区域有较强的缺陷导致的发射峰.     

Synthesis of PbTe nanowire arrays using lithographically patterned nanowire electrodeposition

We describe the preparation by electrodeposition of arrays of lead telluride (PbTe) nanowires using the lithographically patterned nanowire electrodeposition (LPNE) method. PbTe nanowires had a rectangular cross-section with adjustable width and height ranging between 60-400 nm (w) and 20-100 nm (h). The characterization of these nanowire arrays using X-ray diffraction, transmission electron microscopy and electron diffraction, scanning electron microscopy, atomic force microscopy, and X-ray photoelectron spectroscopy (XPS) is reported. PbTe nanowires were electrodeposited using a cyclic electrodeposition-stripping technique that produced polycrystalline, stoichiometric, face-centered cubic PbTe with a mean grain diameter of 10-20 nm. These nanowires were more than 1 mm in length and two additional processing steps permitted their suspension across 25 microm air gaps microfabricated on these surfaces. The LPNE synthesis of lithographically patterned PbTe nanowires was carried out in unfiltered laboratory air. Nanowires with lengths of 70-100 microm showed an electrical resistivity comparable to bulk PbTe. XPS reveals that exposure of PbTe nanowires to air causes the formation on the nanowire surface of approximately one monolayer of a mixed lead oxide and tellurium oxide within a few minutes.     

3D nano-arrays of silver nanoparticles and graphene quantum dots with excellent surface-enhanced Raman scattering

Active surface-enhanced Raman scattering (SERS) substrates, 3D nano-arrays of Ag nanoparticles (NPs) and graphene quantum dots (GQDs), were prepared using a photochemical approach and an electrophoresis deposition technique with the formation mechanism addressed. The GQDs (ca. 6?nm average) fit into the inter-particle gaps between Ag NPs, as verified by their scanning electron microscopy and high-resolution transmission electron microscopy. This deliberately designed 3D assembly of Ag NPs and GQDs could promote the synergistic effects of both components to further enhance the SERS performances according to both electromagnetic mechanism and chemical mechanism. Preliminary experiments show that the 3D substrates exhibited strong SERS signals comparing with bare Si substrates. This work provides a promising way for 3D SERS substrates.     

高性能锂离子电池用Ni2Si纳米线阵列

采用化学气相沉积方法制备了镍硅合金(Ni2Si)纳米线阵列,研究分析了纳米线阵列的形貌随反应气氛的变化。该材料用作锂电池负极材料,显示出了优良的循环性能,有潜在的应用价值。