Bismuth telluride (Bi2Te3) nanowires: synthesis by cyclic electrodeposition/stripping, thinning by electrooxidation, and electrical power generation

Nanowires composed of the thermoelectric material Bi2Te3 were synthesized on highly oriented pyrolytic graphite (HOPG) electrodes using the electrochemical step edge decoration (ESED) method. Nanowire synthesis was initiated by applying a voltage pulse of -0.75 V versus SCE for 5 ms to an HOPG electrode in an aqueous solution containing both Bi3+ and TeO22-, thereby producing nuclei at the step edges. Bi2Te3 was electrodeposited onto these nuclei using a cyclic electrodeposition-stripping scheme that involved the electrodeposition of bismuth-rich Bi2Te3 on a negative-going voltammetric scan (to -0.05 V) and the subsequent anodic stripping of excess bismuth from these nanowires during a positive-going scan (to +0.35 V). When this cycle was repeated 10-50 times, Bi2Te3 nanowires in the 100-300-nm-diameter range were obtained. These nanowires were narrowly dispersed in diameter (RSDdia = 10-20%), were more than 100 microm in length, and were organized into parallel arrays containing hundreds of wires. Smaller nanowires, with diameters down to 30 nm, were obtained by electrooxidizing 150-nm-diameter Bi2Te3 nanowires at +0.37 V under conditions of kinetic control. This oxidation process unexpectedly improved the uniformity of Bi2Te3 nanowires, and X-ray photoelectron spectroscopy (XPS) shows that these nanowires retain a Bi2Te3 core but also have a thin surface layer composed of Bi and Te oxides. The ability of Bi2Te3 nanowires to generate electrical power was assessed by transferring ensembles of these nanowires onto cyanoacrylate-coated glass surfaces and evaporating 4-point nickel contacts. A dimensionless figure of merit, ZT, ranging from 0 to 0.85 was measured for fresh samples that were less than 1 day old. XPS reveals that Bi2Te3 nanowires are oxidized within a week to Bi2O3 and TeO2. These oxides may interfere with the application by evaporation of electrical contacts to these nanowires.     

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.     

Interfacial bonding of gold nanoparticles on a H-terminated Si(100) substrate obtained by electro- and electroless deposition

Dome-shaped gold nanoparticles (with an average diameter of 10.5 nm) are grown on H-terminated Si(100) substrates by simple techniques involving electro- and electroless deposition from a 0.05 mM AuCl3 and 0.1 M NaClO4 solution. XPS depth profiling data (involving Au 4f core-level and valence band spectra) reveal for the first time the formation of gold silicide at the interface between the Au nanoparticles and Si substrate. UV-visible diffuse reflectance spectra indicate that both samples have surface plasmon resonance maxima at 558 nm, characteristic of an uniform distribution of Au nanoscale particles of sufficiently small size. Glancing-incidence XRD patterns clearly show that the deposited Au nanoparticles belong to the fcc phase, with the relative intensity of the (220) plane for Au nanoparticles obtained by electroless deposition found to be notably larger than that by electrodeposition.     

Effects of gold nanoparticle and electrode surface properties on electrocatalytic silver deposition for electrochemical DNA hybridization detection

In this paper we report the catalytic effects of various gold nanoparticles for silver electrodeposition on indium tin oxide (ITO)-based electrodes, and successfully apply this methodology for signal amplification of the hybridization assay. The most widely used gold nanoparticle-based hybridization indicators all promote silver electrodeposition on the bare ITO electrodes, with decreasing catalytic capability in order of 10 nm gold, DNA probe-10 nm gold conjugate, streptavidin-5 nm gold, and streptavidin-10 nm gold. Of greater importance, these electrocatalytic characteristics are affected by any surface modifications of the electrode surfaces. This is illustrated by coating the ITO with an electroconducting polymer, poly(2-aminobenzoic acid)(PABA), as well as avidin molecules, which are promising immobilization platforms for DNA biosensors. The catalytic silver electrodeposition of the gold nanoparticles on the PABA-coated ITO surfaces resembles that on the bare surfaces. With avidin covalently bound to the PABA, it is interesting to note that the changes in electrocatalytic performance vary for different types of gold nanoparticles. For the streptavidin-5 nm gold, the silver electrodeposition profile is unaffected by the presence of the avidin layer, whereas for both the 10 nm Au and DNA probe-10 nm gold conjugate, the deposition profiles are suppressed. The streptavidin-5 nm gold is employed as the hybridization indicator, with avidin-modified (via PABA) ITO electrode as the immobilization platform, to enable signal amplification by the silver electrodeposition process. Under the conditions, this detection strategy offers a signal-to-noise ratio of 20. We believe that this protocol has great potential for simple, reproducible, highly selective and sensitive DNA detection on fully integrated microdevices in clinical diagnostics and environmental monitoring applications.     

Selective growth of ag nanowires on Si(111) surfaces by electroless deposition

Electroless deposition of Ag on atomically flat H-terminated Si(111) surfaces in aqueous alkaline solutions containing Ag ions produced two different sizes of Ag nanowires along atomic step edges: (1) a narrow nanowire of 10 nm in width and 0.5 nm in height and (2) a wide nanowire of 35 nm in width and 11 nm in height. The narrow and wide nanowires were formed by immersion in the solutions containing less than 1 ppb and 8 ppm dissolved-oxygen concentrations, respectively. This result indicates that the dissolved oxygen initiates the formation of Ag nucleation sites and that the fabrication method has a possibility of controlling the size of Ag nanowires.     

Ultrathin gold nanowires can be obtained by reducing polymeric strands of oleylamine-AuCl complexes formed via aurophilic interaction

This Communication describes a facile route to the preparation of ultrathin gold nanowires using linear chains formed from [(oleylamine)AuCl] complex via aurophilic interaction. The linear chains, with AuI...AuI bonds as the backbone and surrounded by oleylamines, can group together to form bundles of polymeric strands. When the AuI was reduced to Au0 by reacting with Ag nanoparticles in hexane, the polymeric strands functioned as both the source of Au and the template to mediate the nucleation and growth of Au nanowires. Using this method, we were able to produce Au nanowires with an average diameter of approximately 1.8 nm and an aspect ratio of >1000 in high yields (approximately 70%).     

偶氮吡啶分子结的制备、表征及电学性质初步研究

具有特异电学性质的分子结的制备及电子输运特性研究是分子电子学领域中的主要内容,对构筑分子电子器件具有重要意义．但是,由于分子结的尺度通常在100nm以下,这使得分子结的低缺陷制备和准确有效的电学特性研究面临困难．目前,自组装方法已经成为降低分子结缺陷的主要手段,     

Early stages of mercury electrodeposition on HOPG

The electrodeposition of mercury on highly oriented pyrolytic graphite (HOPG) from nitrate solution was studied using cyclic voltammetry, potentiostatic current transients, and in situ scanning tunneling microscopy (STM), in order to correlate the results of the kinetic nucleation with the deposit morphology. At relatively low overpotentials, the mercury deposition can be described by a model involving progressive nucleation on active sites and diffusion-controlled 3D growth without overlapping of diffusion zones. The deposition was initiated on step edges and surface defects forming 3D islands following the Volmer–Weber mechanism. The small number of atoms in the critical nucleus (n_k=1), together with the linear log J vs. η dependence, indicated that the nucleation process can be described by the atomistic model.     

电化学沉积法制备金（核）-铜（壳）纳米粒子阵列

以组装在有机分子自组装膜/金基底电极上的Au纳米粒子阵列为电化学沉积模板,制备了金(核)-铜 (壳)纳米粒子阵列.选用巯基十一胺（AUDT）和巯基癸烷（DT）混合自组装膜作为基底电极与Au纳米粒子的耦联层,可以在一定的电位下实现金属Cu在Au纳米粒子上的选择性沉积.将沉积电位控制在－0.03 V（vs SCE）时,沉积初期（t ≤ 15 s,沉积粒子粒径 ≤ 20 nm ）金(核)-铜 (壳)粒子具有良好的单分散性和近似球形,而且粒径实验值同计算值非常吻合.     

ITO导电玻璃表面直接电沉积Au的机理

用循环伏安和电位阶跃法研究Au在氧化铟锡(ITO)透明导电膜玻璃表面的电沉积过程的初期阶段. 发现在ITO表面Au的电沉积经历成核过程以及受[AuCl₄]^-扩散控制的晶核生长过程. 通过改变扫描速率分析循环伏安曲线的变化, 当扫描速率较快时, 发现Au在ITO表面的沉积过程经历[AuCl₄]^-→[AuCl₂]^-→Au两步进行; 当扫描速率较慢时, 受歧化反应作用影响而只表现为一步沉积[AuCl₄]^-→Au. 通过电位阶跃实验, 验证了Au的两步沉积过程, 并求得[AuCl₄]^-的扩散系数为1.3×10^-5 cm²·s^-1. 将成核曲线与理论曲线对照, 得出Au在ITO表面的沉积符合瞬时成核理论. 通过场发射扫描电镜(FE-SEM)对Au核形貌进行分析, 根据扫描电镜图可以得到阶跃时间和阶跃电位对电沉积Au的形貌的影响.     

Electronic and geometric properties of Au nanoparticles on Highly Ordered Pyrolytic Graphite (HOPG) studied using X-ray Photoelectron Spectroscopy (XPS) and Scanning Tunneling Microscopy (STM)

Au nanoparticles grown on mildly sputtered Highly Ordered Pyrolytic Graphite (HOPG) surfaces were studied using Scanning Tunneling Microscopy (STM) and X-ray Photoelectron Spectroscopy (XPS). The results were compared with those of Ag nanoparticles on the same substrate. By varying the defect densities of HOPG and the Au coverages, one can create Au nanoparticles in various sizes. At high Au coverages, the structures of the Au films significantly deviate from the ideal truncated octahedral form: the existence of many steps between different Au atomic layers can be observed, most likely due to a high activation barrier of the diffusion of Au atoms across the step edges. This implies that the particle growth at room temperature is strongly limited by kinetic factors. Hexagonal shapes of Au structures could be identified, indicating preferential growth of Au nanostructures along the (111) direction normal to the surface. In the case of Au, XPS studies reveal a weaker core level shift with decreasing particle size compared to the 3d level in similarly sized Ag particles. Also taking into account the Auger analysis of the Ag particles, the core level shifts of the metal nanoparticles on HOPG can be understood in terms of the metal/substrate charge transfer. Ag is (partially) positively charged, whereas Au negatively charged on HOPG. It is demonstrated that XPS can be a useful tool to study metal-support interactions, which plays an important role for heterogeneous catalysis, for example.     

低频交流电沉积金纳米线阵列的AFM研究

迄今,人们已采用许多方法制备纳米材料,如刻蚀技术、化学法和模板法等［1]．其中,引起科学界广泛兴趣的模板法,在合成有序纳米材料上占有极其重要的地位．常用的模板有两种,一种是有序孔洞阳极氧化铝（Anodic Aluminum Oxide,AAO）模板[2],另一种是含有孔洞无序分布的高分子模板．AAO模板具有耐高温,绝缘性好,孔洞分布均匀有序,而且大小可控等特点［3]．可以利用 AAO模板来制备各种纳米纤维和纳米管,如导电聚合物［4]、金属［5]、半导体［6]、碳［7]和其它一些材料．由于纳米材料的应用具有广阔的前景,如光催化、电化学、酶固定等方面,因而不同材料纳米线的制备备受关     

Size-dependent electrocatalytic activity of gold nanoparticles on HOPG and highly boron-doped diamond surfaces

Gold nanoparticles were prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron-doped, epitaxial 100-oriented diamond layers. Using a potentiostatic double pulse technique, the average particle size was varied in the range from 5 nm to 30 nm in the case of HOPG as a support and between < 1 nm and 15 nm on diamond surfaces, while keeping the particle density constant. The distribution of particle sizes was very narrow, with standard deviations of around 20% on HOPG and around 30% on diamond. The electrocatalytic activity towards hydrogen evolution and oxygen reduction of these carbon supported gold nanoparticles in dependence of the particle sizes was investigated using cyclic voltammetry. For oxygen reduction the current density normalized to the gold surface (specific current density) increased for decreasing particle size. In contrast, the specific current density of hydrogen evolution showed no dependence on particle size. For both reactions, no effect of the different carbon supports on electrocatalytic activity was observed.     

Au nanocrystal growth on nanotubes controlled by conformations and charges of sequenced peptide templates

A new biological approach to fabricate Au nanowires was examined by using sequenced peptide nanotubes as templates. The sequenced histidine-rich peptide molecules were assembled on nanotubes, and the biological recognition of the sequenced peptide selectively trapped Au ions for the nucleation of Au nanocrystals. After Au ions were reduced, highly monodisperse Au nanocrystals were grown on nanotubes. The conformations and the charge distributions of the histidine-rich peptide, determined by pH and Au ion concentration in the growth solution, control the size and the packing density of Au nanocrystals. The diameter of Au nanocrystal was limited by the spacing between the neighboring histidine-rich peptides on nanotubes. A series of TEM images of Au nanocrystals on nanotubes in the shorter Au ion incubation time periods reveal that Au nanocrystals grow inside the nanotubes first and then cover the outer surfaces of nanotubes. Therefore, multiple materials will be coated inside and outside the nanotubes respectively by controlling doping ion concentrations and their deposition sequences. It should be noted that metallic nanocrystals in diameter around 6 nm are in the size domain to observe a significant conductivity change by changing the packing density, and therefore this system may be developed into a conductivity-tunable building block.     

Modification of composites of block copolymers–gold nanoparticles with enzymes and their characterization by electrochemical techniques

In this work, the poly(styrene-vynil pyridine) block copolymer was used as a porous pattern to study the electrodeposition of gold inside the pores, as a new method to obtain gold nanoparticles. The porous pattern left by the copolymer film onto a conductive glass surface was characterized by atomic force microscopy (AFM), evidencing pores of 30 nm diameter. After the electrodeposition, 30 nm diameter gold nanoparticles were obtained and they were characterized by cyclic voltammetry (CV) and AFM, and then used to study the adsorption of glucose oxidase enzyme. The adsorption process of glucose oxidase on gold nanowires was investigated by CV and electrochemical impedance spectroscopy. The morphological and capacitance results indicate that the block copolymer–gold nanoparticle composite seems to be a good candidate to design biosensors and immunosensors.     

Electrodeposition of tubular-rod structure gold nanowires using nanoporous anodic alumina oxide as template

One-dimensional tubular-rod structure gold nanowires have been prepared using electrodeposition method at constant current mode with confined nanochannels of porous anodic aluminum oxide template. The reduction mechanism of gold ions and formation process of tubular-rod structure gold nanowires are studied. Electron microscopy results show that the tubular-rod structure gold nanowires transform to solid nanorods when the electrodeposition time is long enough. The tubular-rod structure gold nanowires have an average diameter of 180 nm, which coincide with the diameter of the template used. X-ray diffraction results confirm that the tubular-rod structure gold nanowires are crystalline structure.     

n型半导体硅电极表面Au的电化学成核机理

在成功实现半导体硅表面电沉积致密金膜的柠檬酸盐镀金实际应用体系中,运用循环伏安和电位阶跃法研究了Au在n型Si(111)电极表面的电沉积过程和成核机理.结果表明,在该体系中, Au在Si表面呈现不可逆电极过程,成核过电位达到250 mV;根据Cottrell方程求得扩散系数D = (1.81 ± 0.14) × 10^-4 cm₂·s^-1;运用Scharifker-Hills (SH)理论模型对比分析拟合实验结果,表明Au在n型Si表面遵循扩散控制下的三维连续成核机理;通过扫描电子显微镜观察Au初期成核、生长形貌,进一步证实了Au的三维连续成核机制,并讨论了阶跃电位和阶跃时间对Au核形貌和密度的影响.     

Local surface patterning by chitosan-stabilized gold nanoparticles using the direct mode of scanning electrochemical microscopy (SECM)

An approach for patterning surfaces with prepared nanoparticles is described. Chitosan-stabilized gold nanoparticles (Au/chitosan NPs) were locally deposited on stainless steel (StSt), indium tin oxide (ITO), and highly-ordered pyrolytic graphite (HOPG). Deposition was driven by local pH gradient formed between a surface and a scanning electrochemical microscopy tip set in the direct mode. The pH at the substrate was increased upon biasing the surface by negative potentials, which caused the reduction of water. As the pH on the surface exceeded that of $ {\mathrm{pK}}_{{\mathrm{chitosanH}}^{+}}\sim 6.3 $ deprotonation of the amino groups of chitosan caused the irreversible deposition of the chitosan/AuNPs. The effect of different parameters, such as tip–surface distance and time, on deposition was studied. While the potential duration showed no clear influence, smaller tip–substrate distance and more negative potentials applied to the surface caused larger deposits. The overpotential needed for the deposition of nanoparticles on HOPG was the highest while that for StSt was the lowest. On the former, the sluggish kinetics caused the deposition of ring-shaped structures while disk-shaped deposits were formed on the other surfaces.     

模板合成法制备金纳米线的研究

近年来,利用化学和物理方法制备各种高度有序的纳米结构材料已经成为学术界的研究热点之一．其中,在特定的模板中沉积各种材料而构建纳米点阵的方法,具有制备简便,成本较低等优点,而且在尺度上可以突破刻蚀技术的局限性,具有广泛的应用前景［１］．常用的模板有阳极氧化多孔铝（ＡＡＯ）、多孔硅和聚合物等,其中ＡＡＯ模板具有耐高温,绝缘性好,孔洞分布均匀有序,而且大小可控等特点［２］,是使用较为广泛的一种．利用阳极氧化铝为模板,采用电化学方法［３～７］或压差注入法［８］制备有序的纳米粒子点阵,已经在润滑［９］、电…     

Controllable growth of gold nanowires and nanoactuators via high-frequency AC electrodeposition

An electrochemical deposition method using high-frequency alternating current (AC) signal is reported here for the in situ synthesis and assembly of Au nanowires and nanoactuators on microelectrodes without using any masks or templates. High conductivity of 3.79 ± 0.14 × 10⁷ Ω^− 1 m^− 1 is achieved on the Au nanowires assembled between electrodes. Au nanoactuators with expansion ratio of more than 500% can be fabricated at higher frequency. The actuators can act as claws to grab SiO₂ nanoparticles in a water solution when driven by an alternating electric field. Disconnected nanowires and nanoparticles which self-aligned around the electrodes were also obtained at lower gold ion concentration, indicating a different current transfer mode in AC electrodeposition.