Controllable growth of well-aligned ZnO nanorod arrays by low-temperature wet chemical bath deposition method

Well-aligned ZnO nanorod arrays were synthesized by low-temperature wet chemical bath deposition (CBD) method on Si substrate under different conditions. Results illustrated that dense ZnO nanorods with hexagonal wurtzite structure were vertically well-aligned and uniformly distributed on the substrate. The effects of precursor concentration, growth temperature and time on nanorods morphology were investigated systematically. The mechanism for the effect of preparation parameters was elucidated based on the chemical process of CBD and basic nucleation theory. It is demonstrated that the controllable growth of well-aligned ZnO nanorods can be realized by readily adjusting the preparation parameters. Strong near-band edge ultraviolet (UV) emission were observed in room temperature photoluminescence (PL) spectra for the samples prepared under optimized parameters, yet the usually observed defect related deep level emissions were nearly undetectable, indicating high optical quality ZnO nanorod arrays could be achieved via this easy process chemical approach at low temperature.     

Controlled synthesis of oriented ZnO nanorod arrays by seed-layer-free electrochemical deposition

Oriented ZnO nanorod arrays were successfully prepared on transparent conductive substrates by seed-layer-free electrochemical deposition in solution of Zn(NO₃)₂ at a low temperature of 70 °C without using any catalysts, additives, and additional seed crystals. The effects of the Zn(NO₃)₂ concentration, deposition time and applied current on the localized nanorod arrays are investigated. X-ray powder diffraction (XRD) and field emission scanning electron microscopy (FE-SEM) were used to characterize the structures and the morphologies of ZnO nanorod arrays. The heights and diameters of ZnO nanorods can be tuned by controlling the electrodeposition parameters.     

Ultraviolet emission of ZnO film prepared by electrophoretic deposition

We deposited high quality ZnO film by electrophoretic deposition (EPD) using high quality ZnO powder prepared by solid-state pyrolytic reaction. X-ray photoelectron spectroscopy (XPS) and the infrared (IR) absorption spectrum clearly indicate that the ZnO phase powder has been prepared. Transmission electron microscope (TEM) imaging and x-ray diffraction (XRD) show that the average grain size of the powder is about 20nm. XRD and selected-area electron diffraction (SAED) reveal that the ZnO film has a polycrystalline hexagonal wurtzite structure. Only a strong ultraviolet emission peak at 390nm can be observed at room temperature.     

Well-aligned ZnO rod arrays grown on glass substrate from aqueous solution

Well-aligned ZnO rod arrays have been successfully synthesized on glass substrate from the aqueous solution of Zn(NO₃)₂·6H₂O and C₆H₁₂N₄ (HMT). Some critical issues such as seed layers, concentration and reaction time were investigated. The results show that ZnO seed layers were pre-requisite for the aligned growth of ZnO rod arrays. The length of rods is tunable in a range from 2 μm to 3 μm by varying the solution concentration and reaction time. X-ray diffraction results demonstrate that ZnO rods are wurtzite crystal structures preferentially orienting in the direction of the c-axis. Microstructure observation by scanning electron microscope confirms that ZnO rods grew up perpendicular to the substrate. Room-temperature photoluminescence (PL) spectrum of rod arrays shows a strong emission band at about 396 nm.     

Control growth of catalyst-free high-quality ZnO nanowire arrays on transparent quartz glass substrate by chemical vapor deposition

ZnO nanowire arrays have been successfully synthesized on transparent quartz glass substrate by chemical vapor deposition technique. Our work demonstrates the critical role of the growth temperature and the buffer layer on the effective control of the morphology of ZnO nanowires. A proper growth temperature and the thicker buffer layer could promise the good alignment and high density of the nanowires. The room-temperature photoluminescence spectrum shows that the buffer layer has also great effects on optical properties of ZnO nanowire arrays. The integrated intensity ratio [I_UV/I_{Visible band}] of the ZnO UV emission peak to visible band emission decreases with the increase of the thickness of the buffer layers. The obtained nanowire arrays have transmittance of above 50% in the visible region.     

Nanoporous Ag–GaN thin films prepared by metal‐assisted electroless etching and deposition as three‐dimensional substrates for surface‐enhanced Raman scattering

Three‐dimensional (3D) nanoporous gallium nitride (PGaN) scaffolds are fabricated by Pt‐assisted electroless hydrofluoric acid (HF) etching of crystalline GaN followed by in situ electroless deposition of Ag nanostructures onto the interior surfaces of the nanopores, yielding a large surface area substrate for surface‐enhanced Raman scattering (SERS). The resulting 3D SERS‐active substrates have been optimized by varying reaction parameters and starting material concentration, exhibiting enhanced Raman signals 10–100× more intense than either (1) sputtered Ag‐coated porous GaN or (2) Ag‐coated planar GaN. The increase in SERS signal is attributed to a combination of the large surface area and the inherent transparency of PGaN in the visible spectral region. Overall, Ag‐decorated PGaN is a promising platform for high sensitivity SERS detection and chemical analysis, particularly for reaction and metabolic products that can be trapped inside the highly anisotropic nanoscale pores of PGaN. The potential of this sampling mode is illustrated by the ability to acquire Raman spectra of adenine down to 5 fmol. Additionally, correlated SERS and laser desorption/ionization mass spectrometry spectra can be acquired from same sample spot without further preparation, opening new possibilities for the investigation of surface‐bound molecules with substantially enhanced information content. Copyright © 2012 John Wiley & Sons, Ltd.     

电泳法制备ZnO/YBCO异质结及电学性质研究

采用电泳方法及高温煅烧工艺制备ZnO/YBCO异质结,XRD图谱显示ZnO具有c轴方向的择优取向。在SEM的截面图中可观察到ZnO与YBCO结合致密,放大500倍的表面形貌图呈现织构(textured)的微结构特征,放大5000倍的表面形貌图中可观察微米量级的六方晶粒。通过对ZnO/YBCO异质结的电学性质进行测试,结果显示整流特性。     

Li–N dual-doped ZnO thin films prepared by an ion beam enhanced deposition method

Li–N dual-doped ZnO films [ZnO:(Li,N)] with Li doping concentrations of 3 at.%–5 at.% were grown on a glass substrate using an ion beam enhanced deposition(IBED) method. An optimal p-type ZnO:(Li,N) film with the resistivity of 11.4 Ω·cm was obtained by doping 4 at.% of Li and 5 sccm flow ratio of N2. The ZnO:(Li,N) films exhibited a wurtzite structure and good transmittance in the visible region. The p-type conductive mechanism of ZnO:(Li,N) films are attributed to the Li substitute Zn site(LiZn) acceptor. N doping in ZnO can forms the Lii–NOcomplex, which depresses the compensation of Li occupy interstitial site(Lii) donors for LiZnacceptor and helps to achieve p-type ZnO:(Li,N) films. Room temperature photoluminescence measurements indicate that the UV peak(381 nm) is due to the shallow acceptors LiZnin the p-type ZnO:(Li,N) films. The band gap of the ZnO:(Li,N) films has a red-shift after p-type doping.     

脉冲激光沉积法制备的ZnO薄膜的低阈值电抽运紫外随机激射

分别采用直流反应溅射法和脉冲激光沉积法在硅衬底上沉积ZnO薄膜, 用X射线衍射、扫描电镜、光致发光谱等手段对两种方法沉积的ZnO薄膜的结晶状态、 表面形貌和光致发光等进行了表征. 进一步对比研究了以上述两种方法制备的ZnO薄膜作为发光层的金属-绝缘体-半导体结构器件的电抽运紫外随机激射. 结果表明, 与以溅射法制备的ZnO薄膜作为发光层的器件相比, 以脉冲激光沉积法制备的ZnO薄膜为发光层的器件具有更低的紫外光随机激射阈值电流和更高的输出光功率. 这是由于脉冲激光沉积法制备的ZnO薄膜中的缺陷更少, 从而显著地减少了紫外光在光散射过程中的光损耗. 关键词： 随机激射 ZnO薄膜 脉冲激光沉积 溅射     

Au cluster growth on ZnO thin films by pulsed laser deposition

Nanostructures formed by Au nanoparticles on ZnO thin film surface are of interest for applications which include medical implants, gas-sensors, and catalytic systems. A frequency tripled Nd:YAG laser (λ = 355 nm, τ_FWHM ∼ 10 ns) was used for the successive irradiation of the Zn and Au targets. The ZnO films were synthesized in 20 Pa oxygen pressure while the subsequent Au coverage was grown in vacuum. The obtained structures surface morphology, crystalline quality, and chemical composition depth profile were investigated by acoustic (dynamic) mode atomic force microscopy, X-ray diffraction, and wavelength dispersive X-ray spectroscopy. The surface is characterized by a granular morphology, with average grain diameters of a few tens of nanometers. The surface roughness decreases with the increase of the number of laser pulses applied for the irradiation of the Au target. The Au coverage reveals a predominant (1 1 1) texture, whereas the underlying ZnO films are c-axis oriented. A linear dependence was established between the thickness of the Au coverage and the number of laser pulses applied for the irradiation of the Au target.     

Nitrogen-doped ZnO prepared by capillaritron reactive ion beam sputtering deposition

Nitrogen-doped ZnO thin films have been prepared by reactive ion beam sputtering deposition utilizing a capillaritron ion source. X-ray diffraction (XRD) analysis of the as-deposited film exhibits a single strong ZnO (002) diffraction peak centred at 34.40°. Post-growth annealing causes increase of grain size and decrease of c-axis lattice constant. Micro-Raman spectroscopy analysis of the as-deposited film shows strong nitrogen-related local vibration mode at 275, 582, 640 and 720 cm⁻¹, whereas the E₂ mode of ZnO at 436 cm⁻¹ can barely be identified. Annealing at 500-800 °C causes decrease of 275, 582, 640 and 720 cm⁻¹ and increase of 436 cm⁻¹ intensity, indicating out-diffusion of nitrogen and improvement of ZnO crystalline quality. Unlike un-doped ZnO, the surface roughness of nitrogen-doped ZnO deteriorates after annealing, which is also attributed to the out-diffusion of nitrogen. A nitrogen concentration of ∼10²¹/cm³ was observed while type conversion from n-type to p-type was not achieved, which is likely due to the formation of Zn_I-N_O or (N₂)_O that act as donor/double donors.     

Double‐layer channel structure based ZnO thin‐film transistor grown by atomic layer deposition

A double channel structure has been used by depositing a thin amorphous‐AlZnO (a‐AZO) layer grown by atomic layer deposition between a ZnO channel and a gate dielectric to enhance the electrical stability. The effect of the a‐AZO layer on the electrical stability of a‐AZO/ZnO thin‐film transistors (TFTs) has been investigated under positive gate bias and temperature stress test. The use of the a‐AZO layer with 5 nm thickness resulted in enhanced subthreshold swing and decreased V_th shift under positive gate bias/temperature stress. In addition, the falling rate of the oxide TFT using a‐AZO/ ZnO double channel had a larger value (0.35 eV/V) than that of pure ZnO TFT (0.24 eV/V). These results suggest that the interface trap density between dielectric and channel was reduced by inserting a‐AZO layer at the interface between the channel and the gate insulator, compared with pure ZnO channel. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Seed‐mediated growth method for electroless deposition of AgNPs on glass substrates for use in SERS measurements

In this work, an electroless deposition method for silver nanoparticles (AgNPs) on glass substrates was developed for use in surface‐enhanced Raman scattering (SERS) measurements. To obtain evenly distributed AgNPs of suitable size on the glass substrates, a seeding procedure was utilized as a pretreatment before the electroless deposition of AgNPs. The AgNPs thus formed were affected by both the seeding and growing procedures. To optimize the procedures for preparation of SERS substrates, several factors, including reaction time, the concentration of silver ions, and the concentration of reducing agents (glucose) for seeding and growing procedures, were varied. The morphologies of the seeds and the resulting AgNPs on the glass substrates were characterized by field‐emission scanning electron microscopy (FE‐SEM) and correlated with the SERS signals from probing with para‐nitrothiophenol (pNTP). The results indicated that only the seeding time and the concentration of silver ions significantly influenced the distribution and sizes of the Ag seeds on the substrates. In the growing procedures, both the concentration of silver nitrate and the reducing agent affected the morphologies of the resulting AgNPs and, hence, the SERS signals. The substrates prepared using this newly developed method offer 2–5 times improvement of the SERS signals compared to substrates prepared without seed treatment. Also, the AgNPs prepared by this method can be easily controlled to designated sizes with even spatial and size distributions. Copyright © 2009 John Wiley & Sons, Ltd.     

Characteristics and electrochemical performance of Ni-coated ZnO prepared by an electroless plating process

ZnO was coated homogeneously with amorphous Ni film by an electroless plating process. After electroless Ni plating, transmission electron microscope (TEM) images and energy dispersive spectrometry spectra (EDS) of ZnO clearly indicated that Ni was coated on the surface of ZnO, the coatings and ZnO contacted enough. X-ray diffraction and high-resolution TEM showed that the Ni film on ZnO was amorphous. Electrochemical performance of Ni-coated ZnO was investigated by the galvanostatic charge/discharge cycling test. Compared to that of uncoated ZnO, the charging–discharging performance of Ni-coated ZnO was obviously improved, e.g. the average discharge capacity of the Ni-coated ZnO increased 71.5% at the stage of stable cycling test.     

The super hydrophobicity of ZnO nanorods fabricated by electrochemical deposition method

Electrochemical deposition method was employed to fabricate ZnO nanorods on zinc foil substrate in this paper. The structural observations of ZnO nanorods with different aspect ratios were carried out by field-emission scanning electron microscopy. The microstructures of ZnO nanorods were also characterized by X-ray diffraction and the changes in surface hydroxyls with electrochemical deposition time were analyzed by X-ray photoelectron spectroscopy. The study results show the aspect ratios of ZnO nanorods and the density of their surface hydroxyls are responsible for their superhydrophobicity. The fluorinated polymer coated ZnO nanorods showed an excellent superhydrophobic behavior with 167° contact angle of water droplet, which is larger than that of fluorinated polymer flat surface. The more the surface hydroxyls are, the more hydrophilic the surfaces are. Meanwhile, the larger the aspect ratio of ZnO nanorod arrays is, the larger its drophobicity is. The results of this study might pave a simple and feasibility pathway to the fabrication of superhydrophobic cleaning materials used in engineering fields.     

Fabrication of p-type Li-doped ZnO films by pulsed laser deposition

p-Type ZnO thin films have been realized via doping Li as acceptor by using pulsed laser deposition. In our experiment, Li₂CO₃ was used as Li precursor, and the growth temperature was varied from 400 to 600 °C in pure O₂ ambient. The Li-doped ZnO film prepared at 450 °C possessed the lowest resistivity of 34 Ω cm with a Hall mobility of 0.134 cm² V⁻¹ s⁻¹ and hole concentration of 1.37 × 10¹⁸ cm⁻³. X-ray diffraction (XRD) measurements showed that the Li-doped ZnO films grown at different substrate temperatures were of completely (0 0 2)-preferred orientation.     

Aligned ZnO nanorod arrays fabricated on Si substrate by solution deposition

Aligned ZnO nanorod arrays were fabricated by chemical solution deposition based on Si substrate which was spin coated with ZnO colloid as nucleation seeds. Their microstructures were characterized by X-ray diffraction, scanning electron microscopy, and high-resolution transmission electron microscopy. The results indicated that ZnO nanorods nucleated and grew vertically on Si substrates along the [0 0 1] direction with single-crystalline structure. The diameter of ZnO nanorods was greatly affected by the grain size of ZnO seeds. Room-temperature photoluminescence of nanorods has a strong emission band at about 384 nm.     

Electrical characterisation of phosphorus-doped ZnO thin films grown by pulsed laser deposition

Phosphorus-doped ZnO films were grown by pulsed laser deposition using a ZnO:P₂O₅-doped target as the phosphorus source with the aim of producing p-type ZnO material. ZnO:P layers (with phosphorus concentrations of between 0.01 to 1 wt%) were grown on a pure ZnO buffer layer. The electrical properties of the films were characterised from temperature dependent Hall-effect measurements. The samples typically showed weak n-type conduction in the dark, with a resistivity of 70 Ω cm, a Hall mobility of μ_n0.5 cm² V ⁻¹ s⁻¹ and a carrier concentration of n3×10¹⁷ cm⁻³ at room temperature. After exposure to an incandescent light source, the samples underwent a change in conduction from n- to p-type, with an increase in mobility and decrease in concentration for temperatures below 300 K.     

Fast synthesis of ZnO nanostructures by laser-induced chemical liquid deposition

ZnO nanostructures were obtained by directly irradiating a small volume of a solution of precursor on a fused-quartz substrate using an unfocused continuous wave CO₂ laser for 2-30 s at laser powers ranging from 20 to 40 W. The laser-based thermochemistry approach allows rapid non-isothermal heating and convection enhanced mass transport which opens new growth mechanisms for the rapid deposition of nanomaterials at predetermined locations on a substrate. The deposits consist of a variety of ZnO nanostructure morphologies, including aggregated nanoparticles, nanorods, faceted nanocrystals and nanowires. The samples were characterized by scanning and transmission electron microscopy, X-ray diffraction and photoluminescence spectroscopy. They were found to exhibit an intense room-temperature photoluminescence, which is characterized by the presence of a strong UV peak around 390 nm and no visible emission. The relationship between the PL signal characteristics and specific ZnO nanostructures was investigated in order to point up optimal nanostructures for possible luminescent devices.