镉的硫族化合物半导体纳米线阵列的模板法合成及其紫外可见吸收光谱研究(英文)

以多孔氧化铝为模板 ,用交流电分别通过含有相应的CdCl2 、ZnCl2 、单质S、Se等的二甲亚砜 (DMSO)溶液 ,沉积CdS、CdSe以及CdxZn1-xS半导体纳米线阵列并研究其紫外可见吸收光谱 .实验结果表明 ,当半导体纳米线的直径小于 2 5nm时 ,其吸收边相对于体相的吸收边产生蓝移 ,而且蓝移的幅度随着半导体纳米线直径的减小而增加 ,显示了明显的量子限域效应 .     

Free-standing aluminium nanowire architectures made in an ionic liquid

We report on the electrochemical synthesis of free‐standing aluminium nanowire architectures through a template‐assisted electrodeposition technique. For this purpose, nuclear track‐etched polycarbonate membranes were employed as templates. One side of the template was sputtered with a thin gold film to serve as a working electrode. Subsequently the nanowires were made in the ionic liquid 1‐ethyl‐3‐methylimidazolium chloride ([EMIm]Cl)/AlCl₃ (40/60 mol %) under potentiostatic conditions. Two different electrodeposition procedures were employed to fabricate strongly adherent Al nanowire structures on an electrodeposited Al layer. In the first procedure, electrodeposition simultaneously occurs along the pores of the template and on the Au‐sputtered side of the template. In the second procedure, electrodeposition takes place in two different steps: first a thick supporting film of Al is deposited on the sputtered side of the membrane and second Al nanowires are grown within the pores. After chemical dissolution of the membrane in dichloromethane, an aluminium foil of a controlled thickness with a three‐dimensional nanowire structure on one side was obtained. Different nanowire architectures, such as free‐standing nanowires, vertically aligned tree‐shaped arrays, and bunched nanowire films, were obtained. Such nanowire architectures are of particular interest for applications in Li‐ion micro‐batteries.     

CdS和CdSe新型纳米结构的高效溶剂热合成

采用快速高效的溶剂热法合成了海星形CdS纳米结构和一维CdSe纳米结构。用XRD、SEM和UV-Vis等表征手段对产物进行了表征，结果表明产物为单一的CdS和CdSe纳米结构，且CdS纳米结构具有良好的分散性，其形成极大地受到pH值影响，而CdSe先形成层状的二维结构、再形成一维纳米结构。     

AC Electrochemical Deposition of CdS Nanowire Arrays

Since the successful growth of carbon nanotubes, one-dimensional materials have been a focused research field both because of their fundamental importance and the wide-ranging potential applications in nano devices. Many approaches are used to fabricate nanowires, such as crystal growth. In order to obtain nanowires whose growth is more easily controlled, electrochemical synthesis in a template is taken as one of the most efficient methods. To date, Co, Fe, Ni, CuCo1-3 and other nanowire arrays have been fabricated successfully by electrodepositing corresponding metal ion into the porous aluminum oxide (PAO) membrane or other non-magnetic materials. Cadmium sulfide(CdS), as one of the most important semiconductor material, is a n-type semiconductor. The ability to fine tune their fundamental electronic and optical properties by simply varying the cruster size, rather than composition, makes them highly attractive for a variety of possible application. In this paper, we report our work of fabricating CdS nanowire arrays based on AC electrolysis into the pores of an anodic aluminum oxide(AAO), the structure and morphology were characterized by XRD and TEM.     

Highly efficient photoelectrochemical hydrogen generation using a ZnO nanowire array and a CdSe/CdS co-sensitizer

Highly efficient photoelectrochemical (PEC) hydrogen generation was achieved by fabricating CdSe deposited ZnO/CdS core/shell nanowire (NW) array photoanodes by a facile three-step solution-based method. Well-defined electrical pathways in 1-dimensional (1D) NW structures allowed efficient charge carrier collection, and CdSe/CdS co-sensitization enabled utilization of the visible region in the solar spectrum. PEC devices using CdSe/CdS/ZnO NW arrays showed improved absorption spectra, and they demonstrated a remarkable enhancement in PEC performance. Our proposed structure is a promising candidate photoanode for solar energy-to-hydrogen conversion devices.     

Architectural control syntheses of CdS and CdSe nanoflowers, branched nanowires, and nanotrees via a solvothermal approach in a mixed solution and their photocatalytic property

Wurtzite CdS and CdSe nanostructures with complex morphologies such as urchin-like CdS nanoflowers, branched nanowires, and fractal nanotrees can be produced via a facile solvothermal approach in a mixed solution made of diethylenetriamine (DETA) and deionized water (DIW). The morphologies of CdS and CdSe nanocrystals can be easily controlled via tuning the volume ratio of DETA and DIW. Urchin-like CdS nanoflowers made of CdS nanorods are in a form of highly ordered hierarchical structures, while the nanowires are branched nanowires, and the fractal CdS nanotrees are a buildup of branched nanopines. The results demonstrated that solvothermal reaction in a mixed amine/water can access a variety of complex morphologies of semiconductor materials. The photocatalytic activity of CdS particles with different morphologies has been tested by the degradation of acid fuchsine under both UV and visible light, showing that the as-prepared branched CdS nanowires exhibit high photocatalytic activity for degradation of acid fuchsine.     

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.     

Toward highly efficient CdS/CdSe quantum dots-sensitized solar cells incorporating ordered photoanodes on transparent conductive substrates

A series of ordered photoanodic architectures (including ordered TiO(2) nanotube arrays (TNT), ZnO nanorods, ZnO/TiO(2) core/shell nanostructures) for CdS/CdSe sensitized solar cells (QDSCs), were fabricated directly on transparent conductive oxide glasses by a facile sol-gel assisted template process. The morphologies, optical and electrical properties of TNTs and CdS/CdSe co-sensitized TNTs have been demonstrated. The effect of CdSe deposition time on the cell performance was clarified, and the growth mechanism of the CdSe quantum dots on the surface of the TNTs has been proposed as well. Furthermore, the evolution of open-circuit photovoltage (V(oc)) towards CdSe deposition time has been investigated by electrochemical impedance spectroscopy (EIS). A promising light-to-electricity conversion efficiency of up to 4.61% has been achieved with 3 μm long TNT arrays, which is the best record for sandwich-type ordered TNT-based QDSCs.     

Spatial bandgap engineering along single alloy nanowires

Bandgap engineering of semiconductor nanowires is important in designing nanoscale multifunctional optoelectronic devices. Here, we report a facile thermal evaporation method, and realize the spatial bandgap engineering in single CdS(1-x)Se(x) alloy nanowires. Along the length of these achieved nanowires, the composition can be continuously tuned from x = 0 (CdS) at one end to x = 1 (CdSe) at the other end, resulting in the corresponding bandgap (light emission wavelength) being modulated gradually from 2.44 eV (507 nm, green light) to 1.74 eV (710 nm, red light). In spite of the existing composition (crystal lattice) transition along the length, these multicolor nanowires still possess high-quality crystallization. These bandgap engineered nanowires will have promising applications in such as multicolor display and lighting, high-efficiency solar cells, ultrabroadly spectral detectors, and biotechnology.     

PHOTORESPONSES OF SEMICONDUCTOR POLYCRYSTALLITES SEPARATING TWO AQUEOUS SOLUTIONS

Solar cells using polycarbonate membranes, with CdS deposited on them, were made by a very simple way; the CdS-containing membrane separates a Lucite cell into two compartments. On illumination, about 150 mV photovoltage ( V _op) and 0.5 μA cm^-2 photocurrent ( I _sc) could be produced; one side of the membrane acted as photoanode, and the other side as photocathode. By means of coating Victoria Blue B (VBB) onto the membrane before CdS deposition, the maximum V _op and I _sc of the CdS-deposited membrane could reach 500 mV and 3.0 (μA cm^-2, respectively. A mixture of CdS and CdSe deposited membrane has also been tested and found to have both the advantages of high photovoltage (over 400 mV) and good stability after modification. Even more interesting results were also obtained with CdSe pellets in place of the CdS-deposited membrane, in which V _op and I _sc of the cell were 1.2 V and 6 mA cm^-2, respectively. The essential aspect of the system, modelled after the photosynthetic thylakoid membrane, contains an asymmetrical, ultrathin semiconductor crystallite layer separating two aqueous solutions.     

Formation of gold-silver nanowires in thin surfactant solution films

Thin, long gold/silver nanowires were grown on substrates in thin surfactant solution films. This growth process occurred exclusively in thinning aqueous films as the water evaporated, and elongated surfactant template structures were formed. The nanowire growth depended on the presence of a relatively high concentration of silver ions (typical Ag:Au mole ratio of 1:1). Tuning the pH value to about 5 in the growth solution was crucial for the nanowire growth. Further development of this process may lead to a simple wet chemical technique for the fabrication of relatively uniform arrays of metal nanowires on surfaces.     

水溶性CdSe/CdS量子点的合成及其与牛血清蛋白的共轭作用

用巯基乙酸(TGA)作为稳定剂，合成了水溶性的CdSe和核壳结构的CdSe/CdS半导体量子点。吸收光谱和荧光光谱研究表明，核壳结构的CdSe/CdS半导体量子点比单一的CdSe量子点具有更优异的发光特性。用TEM、电子衍射(ED)和XPS分别表征了CdSe和CdSe/CdS纳米微粒的结构、形貌及分散性。红外光谱和核磁共振谱证实了巯基乙酸分子中的硫原子和氧原子与纳米微粒表面的金属离子发生了配位作用。在pH值为7.4的条件下，将合成的CdSe和CdSe/CdS量子点直接与牛血清白蛋白(BSA)相互作用。实验发现，两种量子点均对BSA的荧光产生较强的静态猝灭作用；而BSA对两种量子点的荧光则具有显著的荧光增敏作用，存在BSA时CdSe/CdS量子点的荧光增强是不存在BSA时体系荧光强度的3倍。     

CdS/CdSe/TiO2多级空心微球光阳极中量子点覆盖度的提高

TiO₂多级空心微球(THHSs)具有高的比表面积、强的光散射效应以及良好的电子传输性质,以此作为光阳极材料,可以显著提升CdS/CdSe敏化太阳能电池(QDSSCs)的性能。但基于化学浴沉积方法获得的这一类电池中量子点在光阳极表面的覆盖度通常不高(50%左右),本文发展了一种基于表面选择性吸附原理的多步沉积方法,选取特定分子(正十二硫醇)限制已有量子点的生长,通过二次沉积成功提高了CdS/CdSe在TiO₂多级空壳微球表面的覆盖度。使用此方法最终得到高达85.4%的覆盖度。结果表明,量子点覆盖度的增加有效提高了电池对太阳光的利用率,使得光电流获得了明显的增加。同时,二氧化钛空白表面积的减小还可以抑制电子和空穴的复合。优化后的电池光电流密度为15.69 mA·cm^-2,填充因子为0.583,电压为0.605 V,最高光电转换效率为5.30%。     

Temperature and pH influences on the structural and the emission properties of electrodeposited CdSe nanowires

Cadmium selenite (CdSe) nanowires have been electrodeposited by potentiostatic method using polycarbonate membranes as template. For the same potential value, the pH modification of the solution or the temperature variation of the substrate leads to drastic differences of the CdSe composition. A meticulous study of the influence of both temperature and pH value on the stoichiometry of electrodeposited CdSe nanowires has been done and several combinations of temperature/pH leading to the 50–50 CdSe composition have been found. The as-electrodeposited CdSe nanowires under these specific conditions reveal a good crystallinity with a <111> preferred growth orientation exhibiting a luminescence band in the visible range corresponding to the CdSe gap.     

Nanowire-based nanogap electrodes by annealing of multisegmented Pt/Au/Pt nanowires in air

A simple thermally lithographic method for fabricating nanowire-based metallic nanogap electrodes is presented, in which the multisegmented Pt/Au/Pt nanowires were electrodeposited in the pores of porous anodic aluminum oxide (AAO) templates first and then thermally annealed to form a nanoscale gap at the interface of Au/Pt. We proposed that the breaking of the multisegmented Pt/Au/Pt nanowires is due to the chemical and physical transformations of the Au segment with O₂. These electrodes are ideally suited for electron-transport studies of chemically synthesized nanostructures, and their utility is demonstrated here by measuring the electronic conduction of short (54-base-pairs) double-stranded (ds) DNA molecules in a dry state.     

水溶性的CdSe/CdS/ZnS量子点的合成及表征

用L-半胱氨酸盐(Cys)作为稳定剂,合成了水溶性的双壳结构的CdSe/CdS/ZnS半导体量子点。吸收光谱和荧光光谱结果表明,双壳结构的CdSe/CdS/ZnS纳米微粒比单一的CdSe核纳米粒子和单核壳结构的CdSe/CdS纳米粒子具有更优异的发光特性。用透射电子显微镜(TEM)、ED、XRD、XPS和FTIR等方法对CdSe核和双壳层的CdSe/CdS/ZnS纳米微粒的结构、分散性及形貌分别进行了表征。     

一步湿化学法合成超细金纳米线

以氯金酸(HAuCl₄)为前驱物, 油胺同时作为溶剂、表面稳定剂和还原剂, 通过简单的一步湿化学法合成超细金纳米线. 制备出的超细金纳米线不仅产量高、纯度高, 而且纵横比大, 纳米线平均直径~2 nm, 长度可达数十微米. 如果添加另一种还原剂油酸并调节油胺和油酸的体积比为1:1, 将生成直径为~9 nm的金纳米线. 通过改变反应温度和还原剂用量, 对该种超细金纳米结构的生长机制进行阐述说明: 以油胺为模板, 在油胺和一价金卤化物(AuCl)亲金键合形成的一维聚合链作用下, 被还原的金原子附着在已成核颗粒表面, 一维地生长成超细金纳米线.     

Hydrothermal synthesis of ultralong and single-crystalline Cd(OH)2 nanowires using alkali salts as mineralizers

Ultralong and single-crystalline Cd(OH)(2) nanowires were fabricated by a hydrothermal method using alkali salts as mineralizers. The morphology and size of the final products strongly depend on the effects of the alkali salts (e.g., KCl, KNO(3), and K(2)SO(4) or NaCl, NaNO(3), and Na(2)SO(4)). When the salt is absent, only nanoparticles are observed in TEM images of the products. The 1D nanostructure growth method presented herein offers an excellent tool for the design of other advanced materials with anisotropic properties. In addition, the Cd(OH)(2) nanowires might act as a template or precursor that is potentially converted into 1D cadmium oxide through dehydration or into 1D nanostructures of other functional materials (e.g., CdS, CdSe).     

Solution-based II-VI core/shell nanowire heterostructures

We demonstrate the solution-phase synthesis of CdS/CdSe, CdSe/CdS, and CdSe/ZnTe core/shell nanowires (NWs). On the basis of bulk band offsets, type-I and type-II heterostructures are made, contributing to the further development of low-dimensional heteroassemblies using solution-phase chemistry. Core/shell wires are prepared by slowly introducing shell precursors into a solution of premade core NWs dispersed in a noncoordinating solvent at moderate temperatures (215-250 degrees C). Resulting heterostructures are characterized through low- and high-resolution transmission electron microscopy, selected area electron diffraction, and energy dispersive X-ray analysis. From these experiments, initial shell growth appears to occur through either Stranski-Krastanov or Volmer-Weber island growth. However, beyond a critical shell thickness, nucleation of randomly oriented nanocrystals results in a polycrystalline coat. In cases where overcoating has been achieved, corresponding elemental analyses show spatially varying compositions along the NW radial direction in agreement with expected element ratios. Electronic interactions between the core and shell were subsequently probed through optical studies involving UV-vis extinction spectroscopy, photoluminescence experiments, and transient differential absorption spectroscopy. In particular, transient differential absorption studies reveal unexpected shell-induced changes in core NW Auger kinetics at high carrier densities. Previously seen three-carrier Auger kinetics in CdS (bimolecular in CdSe) NWs were suppressed by the presence of a CdSe (CdS) shell. These observations suggest the ability to influence NW optical/electrical properties by coating them with a surrounding shell, a method which could be important for future NW optical studies as well as for NW-based applications.     

Photoluminescence resulting from semiconductor-metal solid solution observed in one-dimensional semiconductor nanostructures

A narrow band photoluminescence (PL) emission peak resulting from CdS-Au solid solution was observed when growing one-dimensional nanostructures of CdS via the vapor-liquid-solid mechanism by using Au as the catalyst. This emission peak was located at 680 nm, a wavelength longer than the near band edge emission of CdS at 520 nm, and was shown not to be caused by the usual trap states of CdS which lead to a broad band emission. Here, the one-dimensional nanostructures of CdS were grown in a simple, low-temperature (360 degrees C) metal-organic chemical vapor deposition process with a single source precursor of CdS. Straight nanowires of diameter 50-70 nm and wormlike nanorods of diameter 100-200 nm were obtained. Both the upper and lower portions of the nanorods/nanowires possessed single crystallinity as judged from the corresponding high-resolution transmission electron microscopy images and selected area electron diffraction data. This work demonstrates the feasibility of adjusting PL emission peaks of optoelectronic semiconductors through alloying with metals.