Electrochemical deposition of branched hierarchical ZnO nanowire arrays and its photoelectrochemical properties

Branched hierarchical ZnO nanowire arrays are synthesized on fluorine-doped tin oxide (FTO) substrate via a two-step electrochemical deposition process, which involves the electrodeposition of ZnO nanowire arrays on conductive glass substrate, followed by the electrochemical growth of ZnO nanorod branches on the backbones of the primary ZnO nanowires. The formation mechanism of the branched hierarchical nanostructure is discussed. It is demonstrated that coating the primary nanowire arrays with ZnO nanoparticles seed layer plays a key role in synthesising the branched hierarchical ZnO nanostructure. By adjusting the concentration of Zn(CH₃COO)₂ colloid in coating process and the reaction time of the second-step deposition, the density and the length of the secondary nanorod branches in the hierarchical nanostructures can be both varied. Moreover, the photoelectrochemical properties of the dye-sensitized solar cell (DSSC) based on branched hierarchical ZnO nanowire arrays are investigated. Due to the enlargement of the internal surface area within the branched nanostructure photoelectrode, the DSSC consisting of branched hierarchical ZnO nanowire arrays yields a power conversion efficiency of 0.88%, which is almost twice higher than that of the DSSC fabricated using bare ZnO nanowire arrays.     

One-pot synthesis of Bi-Ni nanowire and nanocable arrays by coelectrodeposition approach

ABSTRACT: A novel and convenient one-pot electrodeposition approach has been developed for precisely controlled fabrication of large-scale Bi-Ni nanowire and nanocable arrays. Using porous anodic aluminum oxide as a shape-directing template, by simply changing the electrochemical deposition mode, desired Bi-Ni hybrid nanowires and Bi-Ni core-shell nanocables have been obtained in the CV and CC modes, respectively. The structure, morphology, and composition of the as-prepared samples were characterized using X-ray powder diffraction, transmission electron microscopy, elemental mapping, and energy-dispersive X-ray spectrometry.     

氧化钛纳米线阵列的溶胶凝胶模板合成与表征

采用二次阳极氧化工艺制备了高度规则排列的多孔氧化铝（PAA）模板,并利用模板法与溶胶-凝胶法结合的模板组装技术制备了氧化钛纳米线阵列,得到了直径在50 nm左右,线间距约为50 nm的纳米线阵列.研究了模板组装过程不同压力条件对溶胶向模板孔洞中填充度的影响,发现在一定的负压条件下,有利于PAA孔中气体的排出,得到高的溶胶填充度,进而制备出高质量的纳米线阵列.分别通过SEM及XRD技术表征了PAA模板及纳米线的形貌及相结构.SEM观察发现纳米线彼此平行,表面光洁,不存在龟裂,纳米线的长度和直径与所使用模板的厚度和直径一致,表明纳米线的生长受控于模板;XRD分析表明模板为单一的θ-Al₂O₃晶型,纳米线为锐钛矿型TiO₂.     

不锈钢丝网上氧化锌纳米线阵列的 可控生长及光催化性能研究

利用水热法在不锈钢丝网上制备了氧化锌纳米线阵列,借助扫描电镜（SEM）对产物的形貌进行了表征,探讨了反应物浓度和反应时间对产物形貌的影响,并以橙黄Ⅱ为目标降解物,研究了不同生长条件下氧化锌纳米线阵列的光催化降解性能。研究结果表明：硝酸锌浓度和反应时间对氧化锌纳米线阵列的密度、长度、直径和晶形有重要影响,在硝酸锌浓度为0.1 mol/L、反应时间为6 h条件下,制得的氧化锌纳米线阵列具有较佳的光催化活性,多次循环实验结果表明其稳定性较高。另外,双层叠合的氧化锌纳米线的光催化降解性能优于单层氧化锌纳米线的实验结果,其不锈钢丝网的网状结构为制备多维纳米阵列和薄膜提供了一种新的研究思路。     

Size-selected growth of transparent well-aligned ZnO nanowire arrays

This paper reports the effect of precursor concentration, growth temperature, and growth time on the size and density of ZnO nanowire arrays (ZNAs). The well-aligned ZNAs were grown on indium tin oxide substrate using a facile chemical bath deposition method. The results showed that the ZnO nanowires could be tailored to the desired sizes with a simple variation of the growth parameters. Optical transmission spectra revealed a sufficient transparency of the ZNAs, qualifying them for photovoltaic and other optoelectronic applications. An inverted hybrid solar cell was fabricated using the ZNAs as the electron collecting layer, and the solar cell exhibited a power conversion efficiency of 0.91%.     

Homoepitaxial regrowth habits of ZnO nanowire arrays

ABSTRACT: Synthetic regrowth of ZnO nanowires [NWs] under a similar chemical vapor transport and condensation [CVTC] process can produce abundant ZnO nanostructures which are not possible by a single CVTC step. In this work, we report three different regrowth modes of ZnO NWs: axial growth, radial growth, and both directions. The different growth modes seem to be determined by the properties of initial ZnO NW templates. By varying the growth parameters in the first-step CVTC process, ZnO nanostructures (e.g., nanoantenna) with drastically different morphologies can be obtained with distinct photoluminescence properties. The results have implications in guiding the rational synthesis of various ZnO NW heterostructures.     

核-壳结构的TiO_2/ZnO纳米材料的制备

采用电化学阳极氧化法在含氟溶液中制得结构规则、有序核-壳结构的TiO2纳米管,再以上述TiO2纳米管为基质,在一定条件下水热合成制得TiO2/ZnO纳米复合材料,对所制备的纳米复合材料进行表征。在阳极氧化电压为60 V、反应时间9 h、溶液pH=6时制得的TiO2纳米管形貌最佳,当锌浓度为0.2 mmol/L时制得TiO2/ZnO纳米复合材料的包覆明显且清晰;同等条件下采用SDS制得的纳米材料尺寸比用CTAB的小。     

Fabrication of vertically aligned Pd nanowire array in AAO template by electrodeposition using neutral electrolyte

A vertically aligned Pd nanowire array was successfully fabricated on an Au/Ti substrate using an anodic aluminum oxide (AAO) template by a direct voltage electrodeposition method at room temperature using diluted neutral electrolyte. The fabrication of Pd nanowires was controlled by analyzing the current–time transient during electrodeposition using potentiostat. The AAO template and the Pd nanowires were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) methods and X-Ray diffraction (XRD). It was observed that the Pd nanowire array was standing freely on an Au-coated Ti substrate after removing the AAO template in a relatively large area of about 5 cm², approximately 50 nm in diameter and 2.5 μm in length with a high aspect ratio. The nucleation rate and the number of atoms in the critical nucleus were determined from the analysis of current transients. Pd nuclei density was calculated as 3.55 × 10⁸ cm⁻². Usage of diluted neutral electrolyte enables slower growing of Pd nanowires owing to increase in the electrodeposition potential and thus obtained Pd nanowires have higher crystallinity with lower dislocations. In fact, this high crystallinity of Pd nanowires provides them positive effect for sensor performances especially.     

Nanostructured materials prepared by use of ordered porous alumina membranes

We report on three different methods to prepare nanostructured materials using highly ordered porous alumina membranes as templates: (1) firstly, a new and simple method, termed as the paired cell method, was developed for the preparation of inorganic nanowires. Several kinds of inorganic nanowires were synthesized using this method. The structure and composition of these nanowires were determined by field emission scanning electron microscopy, transmission electron microscopy and energy dispersive X-ray spectroscopy. (2) Secondly, highly ordered platinum nanowire arrays were prepared by electrochemical method with the help of porous alumina membrane templates. The structure and composition of these nanowire arrays were also characterized by various experimental techniques. The electrochemically active surface area of the nanowire arrays was determined by cyclic voltammetry based on hydrogen adsorption. Results showed that the platinum nanowire arrays exhibited a large surface area. (3) Finally, we also present a simple and reliable procedure for the preparation of highly ordered metal nanohole and nanopillar arrays, based on the anodic oxidation of aluminum and vacuum evaporation technology. The field emission scanning electron microscopic images revealed that these metal nanostructure arrays were highly ordered over a large area. The nanoimprinting of aluminum surfaces using the as-prepared chromium nanopillar arrays was demonstrated, resulting in periodic indentation on the aluminum surface.     

Electrodeposition of CdSe coatings on ZnO nanowire arrays for extremely thin absorber solar cells

We report on electrodeposition of CdSe coatings onto ZnO nanowire arrays and determine the effect of processing conditions on material properties such as morphology and microstructure. CdSe-coated ZnO nanowire arrays have potential use in extremely thin absorber (ETA) solar cells, where CdSe absorbs visible light and injects photoexcited electrons into the ZnO nanowires. We show that room-temperature electrodeposition enables growth of CdSe coatings that are highly crystalline, uniform, and conformal with precise control over thickness and microstructure. X-ray diffraction and transmission electron microscopy show nanocrystalline CdSe in both hexagonal and cubic phases with grain size ∼5 nm. Coating morphology depends on electrodeposition current density. Uniform and conformal coatings were achieved using moderate current densities of ∼2 mA cm⁻² for nanowires with roughness factor of ∼10, while lower current densities resulted in sparse nucleation and growth of larger, isolated islands. Electrodeposition charge density controls the thickness of the CdSe coating, which was exploited to investigate the evolution of the morphology at early stages of nucleation and growth. UV–vis transmission spectroscopy and photoelectrochemical solar cell measurements demonstrate that CdSe effectively sensitizes ZnO nanowires to visible light.     

Angle-dependent photodegradation over ZnO nanowire arrays on flexible paper substrates

In this study, we grew zinc oxide (ZnO) nanowire arrays on paper substrates using a two-step growth strategy. In the first step, we formed single-crystalline ZnO nanoparticles of uniform size distribution (ca. 4 nm) as seeds for the hydrothermal growth of the ZnO nanowire arrays. After spin-coating of these seeds onto paper, we grew ZnO nanowire arrays conformally on these substrates. The crystal structure of a ZnO nanowire revealed that the nanowires were single-crystalline and had grown along the c axis. Further visualization through annular bright field scanning transmission electron microscopy revealed that the hydrothermally grown ZnO nanowires possessed Zn polarity. From photocatalytic activity measurements of the ZnO nanowire (NW) arrays on paper substrate, we extracted rate constants of 0.415, 0.244, 0.195, and 0.08 s^-1 for the degradation of methylene blue at incident angles of 0°, 30°, 60°, and 75°, respectively; that is, the photocatalytic activity of these ZnO nanowire arrays was related to the cosine of the incident angle of the UV light. Accordingly, these materials have promising applications in the design of sterilization systems and light-harvesting devices.     

Fabrication and characterization of hexagonally patterned quasi-1D ZnO nanowire arrays

Quasi-one-dimensional (quasi-1D) ZnO nanowire arrays with hexagonal pattern have been successfully synthesized via the vapor transport process without any metal catalyst. By utilizing polystyrene microsphere self-assembled monolayer, sol–gel-derived ZnO thin films were used as the periodic nucleation sites for the growth of ZnO nanowires. High-quality quasi-1D ZnO nanowires were grown from nucleation sites, and the original hexagonal periodicity is well-preserved. According to the experimental results, the vapor transport solid condensation mechanism was proposed, in which the sol–gel-derived ZnO film acting as a seed layer for nucleation. This simple method provides a favorable way to form quasi-1D ZnO nanostructures applicable to diverse fields such as two-dimensional photonic crystal, nanolaser, sensor arrays, and other optoelectronic devices.     

氧化铝模板中Ag纳米线阵列的选择性生长

利用Ag离子与Br离子之间的化学沉积作用在孔隙中充满明胶的阳极氧化铝（AAO）模板中制备了AgBr/AAO纳米介孔复合材料.材料选择性曝光后,利用原位显影液对其进行化学显影,在AAO模板中选择性得到Ag纳米线阵列.实验结果表明：Ag纳米线是连续的、致密的,且具有多晶结构,充满了曝光部分的模板孔隙.本文还对影响Ag纳米线选择性生长的因素进行了简单讨论.     

Controllable synthesis of branched ZnO/Si nanowire arrays with hierarchical structure

A rational approach for creating branched ZnO/Si nanowire arrays with hierarchical structure was developed based on a combination of three simple and cost-effective synthesis pathways. The crucial procedure included growth of crystalline Si nanowire arrays as backbones by chemical etching of Si substrates, deposition of ZnO thin film as a seed layer by magnetron sputtering, and fabrication of ZnO nanowire arrays as branches by hydrothermal growth. The successful synthesis of ZnO/Si heterogeneous nanostructures was confirmed by morphologic, structural, and optical characterizations. The roles of key experimental parameters, such as the etchant solution, the substrate direction, and the seed layer on the hierarchical nanostructure formation, were systematically investigated. It was demonstrated that an etchant solution with an appropriate redox potential of the oxidant was crucial for a moderate etching speed to achieve a well-aligned Si nanowire array with solid and round surface. Meanwhile, the presence of gravity gradient was a key issue for the growth of branched ZnO nanowire arrays. The substrate should be placed vertically or facedown in contrast to the solution surface during the hydrothermal growth. Otherwise, only the condensation of the ZnO nanoparticles took place in a form of film on the substrate surface. The seed layer played another important role in the growth of ZnO nanowire arrays, as it provided nucleation sites and determined the growing direction and density of the nanowire arrays for reducing the thermodynamic barrier. The results of this study might provide insight on the synthesis of hierarchical three-dimensional nanostructure materials and offer an approach for the development of complex devices and advanced applications.     

Synthesizing vertical porous ZnO nanowires arrays on Si/ITO substrate for enhanced photocatalysis

In this work, porous ZnO nanowires arrays (NWAs) which are perpendicular to the substrate were synthesized using facile and simple hydrothermal process approaches. The surface of ZnO nanowires (NWs) was increased by chemical electroless etching many macropores on them, which results in better photocatalytic activity, which is 1.73 times in terms of the rate constant for methyl orange (MO) degradation for porous ZnO NWAs compared with ZnO NWAs. The absorption of the vertical porous ZnO NWAs was considerably enhanced in the visible region. The optical band-gap became slightly narrower from 3.24 eV (ZnO NWAs) to 3.22 eV (porous ZnO NWAs). Thus, the vertical porous ZnO NWAs can be employed for various applications, such as gas sensor, photocatalyst, and solar cell.     

ZnO纳米棒阵列的改进水热方法制备、银修饰及光催化活性研究

ZnO纳米棒阵列是近来研究较多的光催化剂,通过银等贵金属修饰可提高光催化活性。以硝酸锌和六亚甲基四胺为前驱物,通过优化水热合成参数（包括种子层和水热生长液浓度等）以及光化学还原沉积银制备高活性ZnO纳米棒阵列。利用扫描电子显微镜、X射线粉末衍射以及紫外-可见漫反射光谱对样品进行表征。结果表明,种子层和水热反应液浓度均对ZnO纳米棒阵列的活性产生影响。银修饰后,光吸收增强,吸收带边从紫外光区拓展到可见光区。光催化降解甲基橙溶液结果表明,银修饰的ZnO纳米棒阵列较纯ZnO纳米棒阵列降解甲基橙的活性提高30%。     

氨溶法制备肤色氧化锌的研究

报道了用氨水溶解氢氧化锌 ,再通过蒸氨制备肤色氧化锌的方法。氨溶法制备的肤色氧化锌呈碎薄片状聚集 ,色彩均匀     

氧化锌纳米粒子的制备

以ＺｎＳＯ_４· ７Ｈ_２ Ｏ为原料,添加 ＮａＯＨ溶液和 ＮＨ_４ ＨＣＯ_３粉末,制备出晶粒细小的碱式碳酸盐前驱体。８０℃干燥后,分别在３００、４００、５００℃焙烧１ｈ,制备出氧化锌ＺｎＯ纳米粒子。经ＸＲＤ和ＴＥＭ检测,粒径为１０、１４、２０ｎｍ。由于采用了对盐渍化的凝胶状前驱体先焙烧,然后用蒸馏水浸洗除去硫酸钠的方法,氧化锌纳米粒子粒径细小而均匀。     

Al doping influences on fabricating ZnO nanowire arrays: Enhanced field emission property

Increase of free electrons concentration and decrease of defects density are the most desirable solution for stimulating the field emission property in semiconductor nanostructures. To implement this, herein we study the field emission efficiency of Al-doped ZnO nanowire arrays with different Al doping concentration, which were prepared by a simple facile hydrothermal method. The Al doping concentration plays a very important role on the structure, morphology, photoluminescence and field emission properties of the as-assembled samples. The results indicate that Al-doped ZnO nanowire arrays with Al doping concentration of 7 at% exhibit the highest quality crystalline structure and lowest defect density relative to others samples thanks to the suitable modification of Al doping, and this led to the increase of free electrons concentration and decrease of defects density, which have an excellent field emission performance with the lower turn on field of 1.03 V/μm and higher field enhancement factor of 20658. This remarkable field emission performances of the Al-doped ZnO nanowire arrays may provide promising applications for different field emission devices.     

离子束增强沉积制备p-ZnO薄膜

采用离子束增强沉积技术制备了ZnO薄膜,分析了退火温度、退火气氛对所制备ZnO薄膜的结构、电学特性和发光特性的影响。利用IBED法获得的薄膜p型N-In共掺ZnO薄膜在氮气下退火,随着退火温度的升高,薄膜电阻值先降低后升高,然后再降低。而在氧气下退火,即使退火温度只有400℃,薄膜的电阻很快变大。