Temperature-Dependent Electrical Conductance of Bi Nanowires

The single crystal bismuth nanowire arrays grown along [0112] with the diameter of 30 nm was synthesized in the pore of anodic aluminum oxide templates through electrodeposi-tion process. The temperature dependent electric conductance of Bi nanowire arrays was measured from 78 K to 320 K. We found that the semimetal-to-semiconductor transition happened around 230 K for 30 nm Bi nanowires oriented along [01112] and the electric con-ductance of the nanowires had a strong temperature dependence.     

金纳米线阵列制备及其光谱特性

利用电化学沉积方法在重离子径迹模板中制备出直径从45 nm到200 nm, 长径比达700的金纳米线阵列, 利用扫描电子显微镜(SEM)和X射线衍射(XRD)对所制备金纳米线的形貌及晶体结构进行分析, 结果表明, 在1.5 V(无参比电极)沉积电压下所制备出的直径为200 nm金纳米线沿[100]晶向具有较好择优取向. 利用紫外-可见光谱(UV-Vis)对镶嵌在透明模板中平行排列的金纳米线阵列光学特性进行研究, 发现金纳米线直径为45 nm时, 其紫外可见光谱在539 nm处有强烈吸收峰, 随着金纳米线直径增加, 吸收峰红移, 当金纳米线直径达到200 nm时, 其吸收峰峰位移至700 nm. 结合金纳米颗粒相关表面等离子体共振吸收效应对实验结果进行了讨论.     

Polymorph-tuned synthesis of α- and β-Bi2O3 nanowires and determination of their growth direction from polarized Raman single nanowire microscopy

We report polymorph-tuned synthesis of α- and β-Bi(2)O(3) nanowires and their single nanowire micro-Raman study. The single crystalline Bi(2)O(3) nanowires in different phases (α and β) were selectively synthesized by adjusting the heating temperature of Bi precursor in a vapor transport process. No catalyst was employed. Furthermore, at an identical precursor evaporation temperature, α- and β- phase Bi(2)O(3) nanowires were simultaneously synthesized along the temperature gradient at a substrate. The growth direction of α-Bi(2)O(3) nanowires was revealed by polarized Raman single nanowire spectra. For thin β-Bi(2)O(3) nanowires with a very small diameter, the polarized Raman single nanowire spectrum was strongly influenced by the shape effect.     

Direct electrodeposition of highly dense Bi/Sb superlattice nanowire arrays

Ordered arrays of Bi/Sb superlattice nanowires with diameters of about 50 nm have been produced by pulsed electrodeposition technique into the pores of anodic alumina membrane (AAM). The structure of Bi/Sb superlattice nanowire can be modulated by controlling the electrodeposition conditions.     

Large-area highly-oriented SiC nanowire arrays: synthesis, Raman, and photoluminescence properties

Large-area highly oriented SiC nanowire arrays have been fabricated by chemical vapor reaction using an ordered nanoporous anodic aluminum oxide (AAO) template and a graphite reaction cell. Their microstructures were characterized by scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy. The results show that the nanowires are single-crystalline beta-SiC's with diameters of about 30-60 nm and lengths of about 8 microm, which are parallel to each other, uniformly distributed, highly oriented, and in agreement with the nanopore diameter of the applied AAO template. The nanowire axes lie along the [111] direction and possess a high density of planar defects. Some unique optical properties are found in the Raman spectroscopy and photoluminescence emission from oriented SiC nanowire arrays, which are different from previous observations of SiC materials. The growth mechanism of oriented SiC nanowire arrays is also analyzed and discussed.     

ZnO纳米线形态对其光致发光性能的影响

以多孔氧化铝膜为模板,电化学沉积出Zn纳米线,再通过高温氧化得到ZnO纳米线阵列。通过改变制备多孔氧化铝模板的工艺参数来改变模板纳米孔径,进而改变ZnO纳米线的直径,得到不同形态的ZnO纳米线阵列。应用X射线衍射仪、透射电子显微镜测试技术表征了ZnO纳米线的结构与形貌。结果发现,X射线衍射时会出现随ZnO纳米线直径增大衍射峰增多和增强的现象。采用荧光光谱仪测试样品的光致发光性能,通过Gaussian原理对谱峰的拟合分析了ZnO纳米线形态对其光致发光光谱的影响。结果表明,随着纳米线直径从30nm至60nm依次增大,其结晶性和化学计量比逐渐变好。近紫外区和蓝光区的发射峰随着纳米线直径的增大而蓝移,而纳米线直径为60nm的样品则出现随直径增大而红移的现象。结果可见,直径在55~60nm间的某点将是ZnO纳米线的结构和光致发光性能变化的临界点。     

Melting of indium,tin, and zinc nanowires embedded in the pores of anodic aluminum oxide

The melting temperature of metal nanostructures embedded in the matrix is an essential thermodynamic characteristic and a key parameter of the processes of their transformation into semiconductor structures. In this work, great attention is paid to the investigation of the behavior of one-dimensional metal nanocrystals near the melting point. For this purpose, the arrays of In, Sn, and Zn nanowires with different diameters have been electrochemically grown in the pores of anodic aluminum oxide (AAO), which is confirmed by the results of the microscopy and the phase X-ray diffraction analysis. The melting of nanowire arrays with different diameters has been investigated by means of differential scanning calorimetry (DSC). Aside from the expected melting temperature decrease, with decreasing the diameter of nanowires, it has been established that the melting peaks of nanostructure arrays have a complex shape that requires detailed elaboration in order to more accurately define the melting temperature. It is shown that the signal waveform while melting depends on geometric parameters of the structure, and the peak being mapped onto the DSC curve is the result of superposition of the melting peaks of nanowires with several characteristic dimensions. For the arrays of In, Sn, and Zn nanowires in AAO, there have been defined the melting temperature values according to the methodology offered, and there has been presented the dependence of the melting temperature decrease on the nanowires' diameter.     

SERS,AFM and Electrochemical Characterization of Metal Nanorod and Nanowire Arrays

Metal nanowires (nanorods) have novel properties and potential applications in a wide field^[1]. Many two-dimensional nanowire arrays of semiconductors and metals with different diameter and length have been made using template synthesis method^[2]. The nanorod arrays of various metals (e.g., Cu, Ag,Au, Ni and Co) with different diameters from about 15 nm to 130 nm were fabricated by electrodeposition of the metals into the highly ordered nanochannel arrays in alumina film followed by partial removal of the film in phosphoric acid or sodium hydroxide. In the present work, surface-enhanced Raman spectroscopy (SERS), AFM and electrochemical methods have been used to characterize the metal nanorod (nanowire) arrays. Tapping mode AFM and SERS were performed on Nanoscope Ⅲa (Digital Instruments) and on confocal Raman microscopy (LabRam I,Dilor) respectively.     

Size-dependent orientation growth of large-area ordered Ni nanowire arrays

Large-area ordered Ni nanowire arrays with different diameters have been fabricated by the direct current electrodeposition into the holes of porous anodic alumina membrane. The crystal structure and micrograph of nanowire arrays are characterized by X-ray diffraction, field-emission scanning electron microscopy and high-resolution transmission electron microscopy. The results indicate that the growth orientation of Ni nanowires turns from [110] to [111] direction with increasing diameters of nanowires. The mechanism of the growth was discussed in terms of interface energy minimum principle. The size-dependent orientation of Ni nanowire arrays has the important significance for the design and control of nanostructures.     

InSb纳米线阵列的可控制备与光谱表征

采用脉冲电沉积结合阳极氧化铝模板技术制备了不同生长方向的闪锌矿型InSb纳米线阵列. 结果表明, 控制电解液中十二烷基硫酸钠(SDS)的浓度, 可使纳米线的择优生长方向从[400]向[220]方向转变. 利用X射线衍射仪、 场发射扫描电子显微镜、 高分辨透射电子显微镜对所制备纳米线的相组成和微结构进行了表征. 激光拉曼光谱结果表明, 不同生长方向的InSb纳米线阵列的拉曼光谱有明显差异. 与体材料相比, InSb纳米线阵列的红外吸收声子散射峰发生强烈红移, 其吸收带边发生了明显蓝移.     

Synthesis of ordered Al nanowire arrays

Ordered Al nanowire arrays with the same nanowire density but the diameters decrease radially embedded in one piece of anodic alumina membranes were successfully fabricated by two-step synthesis: electrodeposition of Zn and replacement in AlCl₃ solution. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected-area electron diffraction techniques were used to characterize the Al nanowires obtained. SEM and TEM images taken from the different areas of Al nanowire arrays show that we can control the growth of aligned Al nanowires with different diameters in a single process at the same time. The investigation results not only have potential applications in photoelectric devices but also open up a new method for fabricating nano-scale materials.     

ZnO纳米线阵列的电沉积法制备及表征(英文)

利用直流电沉积方法在多孔氧化铝模板的孔洞中生成锌纳米线,在氧气氛围中,于800°C下氧化2h,将氧化铝中的锌氧化成氧化锌.本研究利用氧气氛围进行锌的氧化,大大提高了传统方法的氧化锌纳米线的制备效率.用场发射扫描电子显微镜(FE-SEM)、透射电子显微镜(TEM)和X射线衍射仪(XRD)对其形貌及成分进行表征和分析,结果表明,氧化铝模板的有序孔洞中填充了大尺寸、均匀连续的多晶态氧化锌纳米线.纳米线具有约1000:1的高纵横比,其长度等于氧化铝模板的厚度,直径约为80nm.光致发光(PL)光谱表明,氧化锌纳米线在504nm处有由于氧空位引起的较强蓝绿光发射.这为进一步研究ZnO/AAO组装体发学性质和开发新型功能器件提供了基础.     

Effective deposition potential induced size-dependent orientation growth of Bi-Sb alloy nanowire arrays

The influence of effective deposition potential on the orientation and diameter of Bi(1-x)Sbx alloy nanowire arrays by pulsed electrodeposition technique was reported. X-ray diffraction, field-emission scanning electron microscopy, and transmission electron microscopy analysis show that the orientation of the Bi(1-x)Sbx nanowires can be turned from the [110] to the [202] direction by increasing the effective deposition potential, and the nanowires fully fill in the pores of the AAM in the lower potential region, while in the higher potential region the nanowires partly fill the pores of the AAM. The origin of those phenomena and the growth mechanism of the nanowire are discussed together with composition analysis.     

Hunting for a maximum highly-energetic facet that interplays with spatial charge storage for enhanced catalytic activity

Exposure of highly-energetic facets challenges one's capabilities of designing new substances at the atomic level and of exploiting novel physicochemical properties. We report herein on TiO(2) microspheres with a maximum exposure of the highly-energetic facet (001). Intriguingly, these microspheres were fabricated by bundles of adjacent nanowires that grow roughly parallel along the c-axis from sphere centres to outward surfaces. In between these nanowires, there existed nanoscale boundary cavities. Reducing the nanowire diameter led to a lattice expansion, and meanwhile nanoscale boundary cavities in between nanowires were tailored to possess an optimum charge storage at a nanowire diameter of 6.2 nm. This charge storage could suppress the combination of photo-generated holes and electrons. Furthermore, owing to the lattice expansion, photo-generated holes were promoted to transfer along the c-axial to the highly-energetic facet (001) to produce reactive hydroxyl radicals. As a consequence, under UV-light irradiation, microspheres with a nanowire diameter of 6.2 nm showed a maximum photocatalytic activity among all nanowire diameters. When the microspheres were broken into segments, the catalytic activities were further enhanced and even superior to commercial P25, because of sufficient utilization of incident light. The methodology reported in this work is fundamentally important, and may offer opportunities for exploring highly-energetic facets of micro-architectures that interplay with spatial charge storage to active novel surface activities, potentially useful in various catalytic applications.     

CdSe纳米线阵列的制备及其表征(英)

通过在含有SeSO₃^2-和Cd²⁺的室温水溶液中，用模板-电沉积法在纳米孔阵列阳极氧化铝膜(AAM)模板中制备了高有序性的CdSe纳米线阵列，并对其形貌、结构和组分进行了表征。扫描电子显微镜(SEM)和透射电子显微镜(TEM)结果表明，纳米线阵列中的CdSe纳米线具有相同的长度和直径，分别对应于使用的AAM模板的厚度和孔径；X-射线衍射(XRD)和X-射线能谱(EDAX)结果表明，CdSe纳米线中Cd和Se的化学组成非常接近于1∶1，其结构为立方CdSe。另外，对模板-电沉积法制备CdSe纳米线的机理进行了讨论。     

Hierarchical Titanate Nanostructures through Hydrothermal Treatment of Commercial Titania Powders

Hierarchical titanate nanostructures were hydrothermally synthesized in concentrated base solutions using commercial titania powders as starting materials. By varying the base concentration, nanowire arrays, flowers of nanosheets and nanotubes, and urchin‐like nanostructures of nanowires and nanotubes were sequentially fabricated. If the NaOH concentration was higher than 6 M , hydrated Na₂Ti₆O₁₃ nanowire arrays, with nanowire diameters of 20–90 nm and an aspect ratio of 1100–5000, were produced at suitable reaction temperatures over a large area. In 10 M KOH solutions, aligned nanowires with a diameter of 30 nm and a lenght of 80 μm formed. In 4 M NaOH solutions, micrometer‐sized flowers of nanotubes and nanosheets formed. Reactions in 2 M NaOH solutions produced urchin‐like materials with a size of ca. 10 μm that were composed of nanotubes and nanowires. The adsorption behavior of the urchin‐like materials resembled macroporous materials with micropores. Since both base concentration and reaction temperature affected the reaction rate, the formation of various titanate nanostructures was proposed as a growth speed controlled process.     

High density germanium nanowire assemblies: contact challenges and electrical characterization

The conductive properties of vertically aligned germanium nanowires, with mean diameters of 50 and 100 nm, within anodized aluminum oxide (AAO) templates have been characterized by conductive atomic force microscopy (C-AFM) and macrocontact measurements. C-AFM was used to determine the electrical transport properties of individual nanowires within the arrays, while macrocontacts were used to measure the mean current-voltage characteristics of groups of nanowires. Contact resistance between the nanowires and metal macrocontacts was minimized by polishing and gradual etching of the AAO surface, to expose the nanowires, prior to deposition of the contacts. Impedance measurements were used to analyze the importance of defects on the charge transport properties of the germanium nanowire arrays. Conductivity data from C-AFM and macrocontact measurements were found to be comparable suggesting that both methods are inherently suitable for evaluating the electrical transport properties of encapsulated nanowires within a matrix. These results are significant as the ability to make good ohmic contacts to nanowires, within well-defined arrays, is key for the future "bottom-up" fabrication of multilayered device architectures for future electronic and optoelectronic devices.     

Length‐Dependent Charge Generation from Vertical Arrays of High‐Aspect‐Ratio ZnO Nanowires

Aqueous chemical growth of zinc oxide nanowires is a flexible and effective approach to obtain dense arrays of vertically oriented nanostructures with high aspect ratio. Herein we present a systematic study of the different synthesis parameters that influence the ZnO seed layer and thus the resulting morphological features of the free‐standing vertically oriented ZnO nanowires. We obtained a homogeneous coverage of transparent conductive substrates with high‐aspect‐ratio nanowire arrays (length/diameter ratio of up to 52). Such nanostructured vertical arrays were examined to assess their electric and piezoelectric properties, and showed an electric charge generation upon mechanical compressive stress. The principle of energy harvesting with these nanostructured ZnO arrays was demonstrated by connecting them to an electronic charge amplifier and storing the generated charge in a series of capacitors. We found that the generated charge and the electrical behavior of the ZnO nanowires are strictly dependent on the nanowire length. We have shown the importance of controlling the morphological properties of such ZnO nanostructures for optimizing a nanogenerator device.     

双层分等级TiO_2纳米线制备及其光伏性能研究

采用两步溶剂热反应制备了底层为分等级锐钛矿的TiO_2纳米线阵列,上层为分等级锐钛矿的TiO_2纳米线薄膜的双层结构电极.通过XRD和SEM对其组成和形貌进行了表征,并考察了纳米线薄膜对染料敏化太阳电池(DSSC)光伏性能的影响.实验结果表明,分等级锐钛矿的TiO_2纳米线作为DSSC的光阳极,光电转换效率为4.39%,其效率高于光滑的TiO_2纳米线光阳极电池效率(2.07%).     

一种新的电化学方法制备CdS纳米线阵列

用一种新的电化学方法在多孔氧化铝模板中制备了CdS纳米线阵列体系,并用XRD、TEM对样品进行表征,结果显示CdS纳米线为立方相和六方相的多晶混合结构,对沉积机理进行了讨论.荧光光谱测量显示CdS纳米线阵列体系有三个强的紫外发光带和一个黄绿发光带.该文所使用的方法可以用来在氧化铝模板中制备其它材料的纳米线阵列体系.