Controllable assembly of aligned ZnO nanowires/belts arrays

We describe a simple method to assemble ZnO nanowires/belts into highly ordered arrays. ZnCu(2) alloy was used as the Zn source, which reacted with water vapor to generate ZnO nanocrystals. The reaction was performed in a mild way, which facilitated the easy control of the reaction conditions. By simply controlling the water bath temperature and carrier gas flux in our experiments, we obtained ZnO nanowires/belts aligned to form ordered arrays. The highly ordered nature of the ZnO arrays is suggested to be related both with the polarities of the H(2)O molecule and the ZnO (0001) surface. Photoluminescence (PL) microscopy revealed that the comblike structures had waveguide properties, where green light enhancement was observed at the tips of the branches. The light enhancement property reveals their promising applications as light source arrays.     

Growth mechanism, photoluminescence, and field-emission properties of ZnO nanoneedle arrays

ZnO nanoneedle arrays have been grown on a large scale with a chemical vapor deposition method at 680 degrees C. Zn powder and O(2) gas are employed as source materials, and catalyst-free Si plates are used as substrates. Energy-dispersive X-ray and X-ray diffraction analyses show that the nanoneedles are almost pure ZnO and preferentially aligned in the c-axis direction of the wurtzite structure. The growth mechanism of ZnO nanoneedle arrays is discussed with the thermodynamic theory and concluded to be the result of the co-effect of the surface tension and diffusion. Photoluminescence spectrum of the as-grown products shows a strong emission band centering at about 484 nm, which originates from oxygen vacancies. Field-emission examination exhibits that the ZnO nanoneedle arrays have a turn-on voltage at about 5.3 V/microm.     

Electrical and gas sensing properties of ZnO nanorod arrays directly grown on a four-probe electrode system

A method for measuring the electrical characteristics of aligned ZnO nanorod arrays (NRAs) directly grown on a pre-patterned four-point probe system in solution was proposed. This four-probe method enabled us to perform electrical measurements directly on the as-grown ZnO nanorod arrays without any additional processing. The location, shape and length of the rods directly grown on the four-probe electrodes were well controlled. The current–voltage characteristics showed a low turn-on voltage and a high saturation current. These ZnO NRAs devices were implemented as gas sensors for detecting hydrogen. The sensitivity increased with the concentration of H₂ and the operating temperature.     

液相法制备取向ZnO纳米线阵列的场发射特性(英文)

采用水热合成工艺,在不同条件下制备了不同的一维取向ZnO纳米线阵列样品.用X射线衍射仪(XRD)、扫描电镜(SEM)及透射电镜(TEM)对样品的晶体结构和形貌等进行了表征,对样品的场发射特性进行了分析和比较,并用Fowler-Nordheim方程对影响ZnO纳米线场发射的因素进行了研究.结果表明,具有较低生长密度分布、较高的长径比和较尖锐生长端的ZnO纳米线阵列样品具有较好的场发射特性.     

Theoretical analysis of growth of ZnO nanorods on the amorphous surfaces

Semiconductor nanorod arrays on a substrate have a preferential alignment orientation that minimizes the excessive free energy of the system. In the case of wet chemically synthesized zinc oxide (ZnO) nanorod on the amorphous surfaces, the thermodynamic driving force determines the orientation to be normal to the surface. Among the various kinds of amorphous surfaces, the spherical seed layer composed of ZnO precursors gives isotropic radially aligned arrays. For other surfaces, such as wrinkled and planar ZnO precursor thin film, nanorod arrays are aligned to be perpendicular to the tangential line of the surface. The maximum value of the aspect ratio of the nanorod is determined by the thermodynamic relationship. The number density of nanorods per unit precursor particles decreases with increasing contact angle of the seed particles.     

Density-controlled growth of aligned ZnO nanowires sharing a common contact: a simple, low-cost, and mask-free technique for large-scale applications

An effective, low cost, simple, and mask-free pathway is demonstrated for achieving density control of the aligned ZnO nanowires grown for large-scale applications. By a slight variation of the thickness of the thermally evaporated gold catalyst film, a significant change in the density of aligned ZnO nanowires has been controlled. The growth processes of the nanowires on an Al(0.5)Ga(0.5)N substrate has been studied based on the wetting behavior of gold catalyst with or without source vapor, and the results classify the growth processes into three categories: separated dots initiated growth, continuous layer initiated growth, and scattered particle initiated growth. This study presents an approach for growing aligned nanowire arrays on a ceramic substrate with the simultaneous formation of a continuous conducting electrode at the roots, which is important for device applications, such as field emission.     

Low-temperature growth of ZnO nanorods by chemical bath deposition

Aligned ZnO nanorod arrays were synthesized using a chemical bath deposition method at normal atmospheric pressure without any metal catalyst. A simple two-step process was developed for growing ZnO nanorods on a PET substrate at 90-95 degrees C. The ZnO seed precursor was prepared by a sol-gel reaction. ZnO nanorod arrays were fabricated on ZnO-seed-coated substrate. The ZnO seeds were indispensable for the aligned growth of ZnO nanorods. The ZnO nanorods had a length of 400-500 nm and a diameter of 25-50 nm. HR-TEM and XRD analysis confirmed that the ZnO nanorod is a single crystal with a wurtzite structure and its growth direction is [0001] (the c-axis). Photoluminescence measurements of ZnO nanorods revealed an intense ultraviolet peak at 378.3 nm (3.27 eV) at room temperature.     

Preparation of dye-sensitized solar cells using template free TiO2 nanotube arrays for enhanced power conversion

Journal of Sol-Gel Science and Technology - By using the vertically aligned ZnO nanorod arrays (NRAs), TiO2 nanoparticles attached ZnO nanorods (TiO2@ZnO) and TiO2 nanotube arrays (NTAs) were...     

Pattern and feature designed growth of ZnO nanowire arrays for vertical devices

An approach is demonstrated for growing aligned ZnO nanowire/nanorod arrays following a predesigned pattern and feature with controlled site, shape, distribution, and orientation. The technique relies on an integration of atomic force microscopy (AFM) nanomachining with catalytically activated vapor-liquid-solid (VLS) growth. The pattern and growth locations are defined by the catalyst distribution created by AFM, and the orientation is determined by the epitaxial growth on a single-crystal substrate. The technique opens a variety of possibilities of using nanowire arrays as sensor arrays, piezoelectric antenna arrays, nanolasers, photonic band gap crystal, biosensors, and field emitters with controlled density, location, shape, and distribution according to a designed pattern and feature.     

Conversion of ZnO nanorod arrays into ZnO/ZnS nanocable and ZnS nanotube arrays via an in situ chemistry strategy

Vertically aligned ZnO nanorods with uniform diameter and length have been synthesized on a zinc foil substrate with ammonium persulfate as oxidant via a facile, larger scale production and inexpensively synthesized method without any templates or additives. SEM and XRD studies indicate that ZnO nanorods are well-oriented along the c-axis. The PL spectrum indicates that our as-synthesized ZnO nanorods with a stronger and wider green emission are promising candidates as electron nanoconductors in nano-optoelectronic devices. Furthermore, by an effective thioglycolic acid-assisted solution route, well-aligned ZnO/ZnS nanocable and ZnS nanotube arrays have been successfully synthesized. ZnS nanotubes show a perfect hexagonal and obvious tubular shape. Our present strategy shows mild growth conditions and good reproducibility.     

Growth of uniformly aligned ZnO nanowire heterojunction arrays on GaN, AlN, and Al0.5Ga0.5N substrates

Vertically aligned single-crystal ZnO nanorods have been successfully fabricated on semiconducting GaN, Al0.5Ga0.5N, and AlN substrates through a vapor-liquid-solid process. Near-perfect alignment was observed for all substrates without lateral growth. Room-temperature photoluminescence measurements revealed a strong luminescence peak at approximately 378 nm. This work demonstrates the possibility of growing heterojunction arrays of ZnO nanorods on AlxGa1-xN, which has a tunable band gap from 3.44 to 6.20 eV by changing the Al composition from 0 to 1, and opens a new channel for building vertically aligned heterojunction device arrays with tunable optical properties and the realization of a new class of nanoheterojunction devices.     

Wet Purification of Aligned Carbon Nanotube Arrays and Its Impact on the Morphology of the Carbon Nanotube Arrays

A simple acid treatment method was applied to remove the catalyst impurities and other residues contaminated in the vertically aligned carbon nanotube arrays. We demonstrated that acid treatment was an efficient approach for aligned carbon nanotube purification. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology of the aligned carbon nanotube arrays and to determine the efficiency of the purification. Using hydrochloric acid could efficiently eliminate catalyst impurities and retain the original structures of the aligned carbon nanotube arrays. The method provided a simple, economical, and effective way to purify the aligned carbon nanotubes, and it would promote the applications of vertically aligned carbon nanotube arrays in electronic field.     

湿法纯化碳纳米管阵列及其对碳纳米管阵列形貌的影响

采用酸溶液处理方法对垂直于衬底生长的碳纳米管阵列的纯化进行了研究. 利用扫描电子显微镜、X射线光电子能谱等手段对纯化前后的碳纳米管阵列的结构、形貌及化学组成进行表征. 实验结果表明, 通过控制条件, 酸溶液处理方法能够在有效地去除催化剂粒子等杂质的同时又保持阵列的相对完整性. 纯化后的碳纳米管阵列会促进其在电子学领域的进一步应用.     

Enhanced electron field emission properties of high aspect ratio silicon nanowire-zinc oxide core-shell arrays

The enhanced electron field emission (EFE) properties of high aspect ratio, vertically aligned SiNW-ZnO core-shell arrays are presented. These core-shell arrays are prepared by a thin, controlled, highly crystalline and conformal coating of zinc oxide as shell using the plasma assisted-atomic layer deposition (PA-ALD) route on vertically aligned silicon nanowire arrays core. The core-shell nanostuctures are confirmed by HRTEM imaging along with the individual elemental mapping demonstrating the conformal deposition of 10 nm ZnO on the SiNWs. EFE properties of va-SiNW-ZnO core-shell arrays showed a high emission current density of 51 μA cm(-2) and a low turn on field of 7.6 V μm(-1) (defined at a current density of 1 μA cm(-2)) compared to the 3.2 μA cm(-2) emission current density and 9.1 V μm(-1) turn on field for SiNWs. The field enhancement factor (β) of 4227 for the devices demonstrates that these core-shell nanowire arrays are excellent field-emitters. Such an enhancement in the field emission originates from the details of the band structure of this peculiar material combination resulting in good electron transport from SiNW to ZnO as evident from the band diagram of the core-shell material. This is further supported by the conducting AFM studies where lowering in threshold voltage by 1 eV confirms the role of ZnO coating in the enhancement of the emission characteristics.     

籽晶层制备方式对氧化锌纳米棒阵列的影响

采用3种不同的方式制备ZnO薄膜籽晶层:旋涂、喷雾热解和脉冲激光沉积。对于每一种制备方式,其薄膜的晶体结构、形貌、表面粗糙度等性能分别用X射线衍射(XRD)、扫描电子显微镜(SEM)和原子力显微镜(AFM)进行了表征。之后,通过水热合成方法,在3种籽晶层衬底上制备得到具有不同结构和形貌特征的ZnO纳米棒阵列。结果表明,ZnO纳米棒生长和籽晶层制备方式具有极强的相关性。最后,对两者相关性的生长机理进行了解释。     

Conducting Polyaniline Nanowire Arrays Modified Electrode for High Performance Supercapacitor and Enhanced Catalysis of Nitrite Reduction

Vertically aligned conducting polymer nanowire arrays had great potential applications in supercapacitor electrode material and exhibited enhanced electrocatalytic behavior towards the reduction of nitrite. In this paper, a facial template‐free approach to synthesize large arrays of vertically aligned polyaniline (PANI) nanowires on electrochemically pretreated glassy carbon electrodes was reported by using a galvanostatic current method. The as‐prepared large arrays of PANI nanowires had very narrow diameters and were oriented perpendicular to the substrate, which was a benefit to the ion diffusion when being used as the supercapacitor electrode. The highest specific capacitance of PANI nanowire arrays was measured and kept high at a large charge‐discharge current density. Furthermore, it also can detect nitrite with ultrahigh sensitivity of 62.99 µA mM^?1 cm^?2 and a remarkable fast response time of less 1 s. The results indicated that the vertically aligned PANI nanowires could dramatically enhance the electrochemical performance.     

Morphology evolution of ZnO thin films from aqueous solutions and their application to solar cells

This paper reports a reproducible low-temperature solution-based process for the preparation of ZnO films of nanorod arrays and their application to dye-sensitized solar cells (DSSCs). A two-step approach was employed for the epitaxial growth of ZnO. We began with the preparation of a (002)-oriented ZnO seed layer by the electrochemical deposition method. After the treatment the substrate was soaked in an aqueous solution containing ZnCl2 and complex agents. A large-scale fabrication of ZnO nanorod arrays on transparent conductive oxides has been achieved after soaking at 95 degrees C for 1-48 h. The as-deposited ZnO film has a large surface area, therefore permitting a great amount of dye loading. The individually separated nanorod forms a linear nanoroad which should show more effective electron transportation than that in the film derived from ZnO powders. The DSSCs using these ZnO films as photoelectrodes show a conversion efficiency of about 0.6% at AM1.5.     

Electrochemical synthesis of poly(3,4‐ethylenedioxythiophene) nanotube arrays using ZnO templates

A new method toward vertically oriented poly(3,4‐ethylenedioxythiophene) (PEDOT) nanotube arrays on transparent conductive oxide substrates is presented. The approach is based on the use of ZnO nanowire arrays as templates for the electropolymerization of PEDOT. Robust arrays of vertically oriented PEDOT nanotubes with different lengths and wall thicknesses were obtained by modifying the ZnO nanowire length and charge density passed during the electropolymerization, respectively. Furthermore, PEDOT nanotubes with different morphologies (top‐closed and mushroom‐like) were successfully designed by varying the PEDOT electropolymerization kinetics or monomer diffusion or both. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Electrochemical synthesis of CdS/ZnO nanotube arrays with excellent photoelectrochemical properties

A facile electrochemical method was developed to synthesize CdS/ZnO nanotube arrays. Implemented as the photoanode in a photoelectrochemical cell, the CdS/ZnO nanotube arrays exhibited a photocurrent as high as 10.64 mA cm(-2).     

Double template electrosynthesis of ZnO nanodot array

This communication describes the preparation of highly-ordered nanodot arrays of ZnO, a technologically important material, by the double template approach developed by Bartlett and co-workers. Colloidal polystyrene spheres were used as the primary template, and electrodeposited polypyrrole was used as the secondary template in this study. The ZnO nanodot arrays were prepared on a polycrystalline Au substrate by electrodeposition using the pyrrole secondary template after making it insulating by potentiodynamically deactivating it. The ZnO nanodot array was characterized by scanning electron microscopy, energy-dispersive X-ray analyses, and laser Raman spectroscopy.