Metal organic chemical vapor deposition of ZnO from β‐ketoiminates

ZnO is a high‐mobility electron conductor being considered for high‐throughput electronics in flexible and transparent formats. We demonstrated the Zn β‐ketoiminate system, based on acetylacetimine with N‐propyl, isopropyl, and butyl groups, as a vehicle for preparing ZnO thin films for electronic applications. Surface carbon was a primary impurity, and the precursors studied afforded films with the lowest surface carbon contamination at deposition temperatures near 400°C. Thermal annealing of the films reduced the surface carbon content and afforded semiconducting materials. Annealing also gave larger‐grained, better connected films. Thinner films were associated with semiconducting as opposed to ohmic behavior; such films will be adaptable for transparent logic circuits. Copyright © 2012 John Wiley & Sons, Ltd.     

One‐Pot Hydrothermal Synthesis of Heterostructured ZnO/ZnS Nanorod Arrays with High Ethanol‐Sensing Properties

ZnO/ZnS heterostructured nanorod arrays with uniform diameter and length were synthesized from zinc substrates in a one‐pot procedure by using a simple hydrothermal method. Structural characterization by HRTEM indicated that the heterostructured nanorods were composed of parallel segments of wurtzite‐type ZnO and zinc‐blende ZnS, with a distinct interface along the axial direction, which revealed the epitaxial relationship, ZnO (10$\bar 1$ 0) and ZnS ($\bar 1$ 1$\bar 1$ ). The as‐prepared ZnO/ZnS nanorods showed only two green emissions at around 523 nm and 576 nm. We also found that the nanorods exhibited high sensitivity to ethanol at relatively low temperatures, owing to their smaller size and structure.     

CuO/ZnO Nanocomposite Gas Sensors Developed by a Plasma‐Assisted Route

CuO/ZnO nanocomposites were synthesized on Al₂O₃ substrates by a hybrid plasma‐assisted approach, combining the initial growth of ZnO columnar arrays by plasma‐enhanced chemical vapor deposition (PE‐CVD) and subsequent radio frequency (RF) sputtering of copper, followed by final annealing in air. Chemical, morphological, and structural analyses revealed the formation of high‐purity nanosystems, characterized by a controllable dispersion of CuO particles into ZnO matrices. The high surface‐to‐volume ratio of the obtained materials, along with intimate CuO/ZnO intermixing, resulted in the efficient detection of various oxidizing and reducing gases (such as O₃, CH₃CH₂OH, and H₂). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites.     

活性炭上化学气相沉积法生长纳米碳纤维

利用流化床技术,以天然气为碳源,负载于活性炭上的纳米镍粒子为催化剂,在750 ℃下采用化学气相沉积法制备了气相生长纳米碳纤维(VGCNFs)/活性炭(AC)复合物。通过对样品进行XRD、激光拉曼光谱、扫描电镜和氮吸附检测,发现VGCNFs生长在活性炭的各个侧面上,以顶部生长模式为主,纤维的直径在40～120 nm之间,由于粗糙的纤维表面和石墨片层的翘曲而缺陷较多。VGCNFs/AC复合物与原料活性炭相比,BET比表面积从2 367 m²·g^-1降到了1 474     

Incorporating Zn2SnO4 Quantum Dots and Aggregates for Enhanced Performance in Dye‐Sensitized ZnO Solar Cells

The performance of dye‐sensitized ZnO solar cells was improved by a facile surface‐treatment approach through chemical‐bath deposition. After the surface treatment, the quantum dots of Zn₂SnO₄ were deposited onto ZnO nanoparticles accompanied by the aggregations of Zn₂SnO₄ nanoparticles. The ZnO film displayed a better resistance to acidic dye solution on account of the deposited Zn₂SnO₄ nanoparticles. Meanwhile, the open‐circuit photovoltage was greatly enhanced, which can be ascribed to the increased conduction‐band edge of ZnO and inhibited interfacial charge recombination. Although the deposition of Zn₂SnO₄ decreased the adsorption amounts of N719 dye, the aggregates of Zn₂SnO₄ with a size of 350–450 nm acted as the effective light‐scattering layer, thereby resulting in an improved short‐circuit photocurrent. By co‐sensitizing 10 μm‐thick ZnO film with N719 and D131 dyes, a top efficiency of 4.38 % was achieved under the illumination of one sun (AM 1.5, 100 mW cm^?2).     

CdS‐Encapsulated TiO2 Nanotube Arrays Lidded with ZnO Nanorod Layers and Their Photoelectrocatalytic Applications

A novel TiO₂ nanotube array/CdS nanoparticle/ZnO nanorod (TiO₂ NT/CdS/ZnO NR) photocatalyst was constructed which exhibited a wide‐absorption (200–535 nm) response in the UV/Vis region and was applied for the photoelectrocatalytic (PEC) degradation of dye wastewater. This was achieved by chemically assembling CdS into the TiO₂ NTs and then constructing a ZnO NR layer on the TiO₂ NT/CdS surface. Scanning electron microscopy (SEM) results showed that a new structure had been obtained. The TiO₂ NTs looked like many “empty bottles” and the ZnO NR layer served as a big lid. Meanwhile the CdS NPs were encapsulated between them with good protection. After being sensitized by the CdS NPs, the absorption‐band edge of the obtained photocatalyst was obviously red‐shifted to the visible region, and the band gap was reduced from its original 3.20 eV to 2.32 eV. Photoelectric‐property tests indicated that the TiO₂ NT/CdS/ZnO NR material maintained a very high PEC activity in both the ultraviolet (UV) and the visible region. The maximum photoelectric conversion efficiencies of TiO₂ NT/CdS/ZnO NR were 31.8 and 5.98 % under UV light (365 nm) and visible light (420–800 nm), respectively. In the PEC oxidation, TiO₂ NT/CdS/ZnO NR exhibited a higher removal ability for methyl orange (MO) and a high stability. The kinetic constants were 1.77×10^?4 s^?1 under UV light, which was almost 5.9 and 2.6 times of those on pure TiO₂ NTs and TiO₂ NT/ZnO NR, and 2.5×10^?4 s^?1 under visible light, 2.4 times those on TiO₂ NT/CdS.     

ZnO/CdS复合材料的合成与可见光催化性能

采用喷雾辅助气相沉积法在水热法合成的ZnO纳米线上沉积CdS纳米颗粒。采用X射线衍射仪（XRD）、激光拉曼仪（Raman）、扫描电镜（SEM）、透射电镜（TEM）、X射线光电子能谱分析谱（XPS）和紫外可见漫反射光谱等测试手段对复合光催化剂进行表征。结果表明,3~10 nm的CdS纳米粒子修饰在直径约为100 nm ZnO纳米线的表面。XPS和Raman表明复合材料中ZnO和CdS之间存在化学相互作用。可见光催化降解罗丹明B实验结果表明ZnO/CdS复合材料的催化性能优于单相CdS或ZnO,沉积时间为30 s合成的ZnO/CdS速率常数分别是CdS和ZnO的2.91和4.03倍,且具有较高的稳定性。ZnO/CdS复合材料光催化性能增强的可能原因为光吸收范围的拓展和光生载流子分离效率的提高。     

Effects of temperature on the properties of TiO2 photocatalysts prepared by the chemical vapor deposition (CVD) method

In this study, a TiO₂ film was prepared in an annular reactor by the chemical vapor deposition (CVD) method. Results indicated that anatase crystals were formed, except for at a deposition temperature of 200°C without calcination. At a calcination temperature of 850°C, anatase crystal was the major species formed with a small amount of rutile crystals. After conducting a photocatalytic reaction of toluene, the best activity was found with a preparation temperature of 350°C for the deposition, and 550°C for calcination.     

Large‐Area Plasmonic Substrate of Silver‐Coated Iron Oxide Nanorod Arrays for Plasmon‐Enhanced Spectroscopy

One‐dimensional iron oxide materials fabricated on conducting glass substrates and their unique properties make these nanostructures promising candidates for a wide range of applications. Herein, vertically oriented α‐Fe₂O₃ nanorod arrays synthesized under hydrothermal conditions over a large area are described, as an active platform for surface‐enhanced resonance Raman scattering (SERRS) and surface‐enhanced fluorescence (SEF). From scanning electron microscopy images the formation of a homogeneous distribution of vertically oriented rods in a large area is confirmed. For activating the localized surface plasmon resonances, which are responsible for SERRS and SEF, a 6 nm layer of Ag is deposited onto the α‐Fe₂O₃ nanorod arrays by physical vapor deposition to form Ag islands.     

Light‐Regulated Polymerization under Near‐Infrared/Far‐Red Irradiation Catalyzed by Bacteriochlorophyll a

Photoregulated polymerizations are typically conducted using high‐energy (UV and blue) light, which may lead to undesired side reactions. Furthermore, as the penetration of visible light is rather limited, the range of applications with such wavelengths is likewise limited. We herein report the first living radical polymerization that can be activated and deactivated by irradiation with near‐infrared (NIR) and far‐red light. Bacteriochlorophyll a (Bachl a) was employed as a photoredox catalyst for photoinduced electron transfer/reversible addition–fragmentation chain transfer (PET‐RAFT) polymerization. Well‐defined polymers were thus synthesized within a few hours under NIR (λ=850 nm) and far‐red (λ=780 nm) irradiation with excellent control over the molecular weight (M_n/M_w<1.25). Taking advantage of the good penetration of NIR light, we showed that the polymerization also proceeded smoothly when a translucent barrier was placed between light source and reaction vessel.     

ZnGa2O4 Nanorod Arrays Decorated with Ag Nanoparticles as Surface‐Enhanced Raman‐Scattering Substrates for Melamine Detection

The availability of sensitive, reproducible, and stable substrates is critically important for surface‐enhanced Raman spectroscopy (SERS)‐based applications, but it presently remains a challenge. In this work, well‐aligned zinc gallate (ZnGa₂O₄) nanorod arrays grown on a Si substrate by chemical vapor deposition were used as templates to fabricate SERS substrates by deposition of Ag nanoparticles onto the ZnGa₂O₄ nanorod surfaces. The coverage of the Ag nanoparticles on the ZnGa₂O₄ nanorod surfaces was easily controlled by varying the amount of AgNO₃. SERS measurements showed that the number density of Ag nanoparticles on the ZnGa₂O₄ nanorod surfaces had a great effect on SERS activity. The SERS signals collected by point‐to‐point and SERS mapping images showed that as‐prepared SERS substrates exhibited good spatial uniformity and reproducibility. Detection of melamine molecules at low concentrations (1.0×10^?7 M ) was used as an example to show the possible application of such a substrate. In addition, the effect of benzoic acid on the detection of melamine was also investigated. It was found that the SERS signal intensity of melamine decreased greatly as the concentration of benzoic acid was increased.     

Near‐Infrared‐Activated Nanocalorifiers in Microcapsules: Vapor Bubble Generation for In Vivo Enhanced Cancer Therapy

Photothermal therapy based on gold nanostructures has been widely investigated as a state‐of‐the‐art noninvasive therapy approach. Because single nanoparticles cannot harvest sufficient energy, self‐assemblies of small plasmonic particles into large aggregates are required for enhanced photothermal performance. Self‐assembled gold nanorods in lipid bilayer‐modified microcapsules are shown to localize at tumor sites, generate vapor bubbles under near‐infrared light exposure, and subsequently damage tumor tissues. The polyelectrolyte multilayer enables dense packing of gold nanorods during the assembly process, which leads to the formation of vapor bubbles around the excited capsules. The resulting vapor bubbles achieve a high efficiency of suppressing tumor growth compared to single gold nanorods. In vivo experiments demonstrated the ability of soft‐polymer multilayer microcapsules to cross the biological barriers of the body and localize at target tissues.     

Enhanced Electrochemical Performance of Supercapacitors via Atomic Layer Deposition of ZnO on the Activated Carbon Electrode Material

Fabricating electrical double-layer capacitors (EDLCs) with high energy density for various applications has been of great interest in recent years. However, activated carbon (AC) electrodes are restricted to a lower operating voltage because they suffer from instability above a threshold potential window. Thus, they are limited in their energy storage. The deposition of inorganic compounds’ atomic layer deposition (ALD) aiming to enhance cycling performance of supercapacitors and battery electrodes can be applied to the AC electrode materials. Here, we report on the investigation of zinc oxide (ZnO) coating strategy in terms of different pulse times of precursors, ALD cycles, and deposition temperatures to ensure high electrical conductivity and capacitance retention without blocking the micropores of the AC electrode. Crystalline ZnO phase with its optimal forming condition is obtained preferably using a longer precursor pulse time. Supercapacitors comprising AC electrodes coated with 20 cycles of ALD ZnO at 70 °C and operated in TEABF₄/acetonitrile organic electrolyte show a specific capacitance of 23.13 F g⁻¹ at 5 mA cm⁻² and enhanced capacitance retention at 3.2 V, which well exceeds the normal working voltage of a commercial EDLC product (2.7 V). This work delivers an additional feasible approach of using ZnO ALD modification of AC materials, enhancing and promoting stable EDLC cells under high working voltages.     

A Study on the Influences of Processing Parameters on the Growth of Oxide Nanorod Arrays by Sol Electrophoretic Deposition

Template-based sol electrophoretic deposition has been demonstrated as an attractive method for the synthesis of oxide nanorod arrays, including simple and complex oxides in the forms of amorphous, polycrystalline, and single crystal. This paper systematically studied a number of processing parameters to control nanorod growth by sol electrophoretic deposition. The influences of particle and template zeta potentials, condensation rate, deposition rate (or externally applied electric field), the presence of organic additives, and sol concentration on the growth of nanorod arrays were studied. It was found that higher zeta potential or electric field resulted in higher growth rates but less dense packing. Templates with charge opposite to that of the sol particles prevented formation of dense nanorods, sometimes resulting in nanotubes, depending on the field strength during electrophoresis. In addition, the pH of the sol and chelating additives were also varied and likely affected the deposition process by affecting the condensation reactions.     

Plasma Synthesis of Advanced Metal Oxide Nanoparticles and Their Applications as Transparent Conducting Oxide Thin Films

This article reviews and summarizes work recently performed in this laboratory on the synthesis of advanced transparent conducting oxide nanopowders by the use of plasma. The nanopowders thus synthesized include indium tin oxide (ITO), zinc oxide (ZnO) and tin-doped zinc oxide (TZO), aluminum-doped zinc oxide (AZO), and indium-doped zinc oxide (IZO). These oxides have excellent transparent conducting properties, among other useful characteristics. ZnO and TZO also has photocatalytic properties. The synthesis of these materials started with the selection of the suitable precursors, which were injected into a non-transferred thermal plasma and vaporized followed by vapor-phase reactions to form nanosized oxide particles. The products were analyzed by the use of various advanced instrumental analysis techniques, and their useful properties were tested by different appropriate methods. The thermal plasma process showed a considerable potential as an efficient technique for synthesizing oxide nanopowders. This process is also suitable for large scale production of nano-sized powders owing to the availability of high temperatures for volatilizing reactants rapidly, followed by vapor phase reactions and rapid quenching to yield nano-sized powder.     

Band‐Structure Engineering of ZnO by Anion–Cation Co‐Doping for Enhanced Photo‐Electrochemical Activity

To look for efficient visible light‐driven catalysts for photo‐electrochemical (PEC) water‐splitting, the band structure and optical absorption of monodoped, compensated, and noncompensated n–p pairs of co‐doped bulk ZnO are systemically studied by using both general gradient approximation and hybrid density functional theory approaches (PBE and HSE). Calculations show that n–p co‐doping cannot only enhance the stability that stems from the strong electrostatic attraction between the n‐ and p‐type dopants, but also effectively reduce the band‐gap of ZnO. More importantly, compensated (Ti+C) and noncompensated (Sc+C) and (Cr+C) co‐doped ZnO may be compelling candidates for PEC water‐splitting because of their narrowed band‐gaps, potentially reduced electron–hole recombination centers, appropriate band‐edge positions, enhanced optical absorption, and good stability.     

The Role of Oxygen Dissociation in Plasma Enhanced Chemical Vapor Deposition of Zinc Oxide from Oxygen and Diethyl Zinc

The influence of electron impact dissociation of oxygen on neutral chemistry was studied for plasma-enhanced chemical vapor deposition (PECVD) of zinc oxide using oxygen and diethyl zinc. Electron conditions in the reactor were estimated based on simulations of well-known Ar-O₂ plasmas, while the majority of the thermal chemistry was abstracted from the combustion literature. A rudimentary model of film growth was developed using the rate of oxygen dissociation as the lone adjustable parameter.n Model results were compared directly with experimental measurements of deposition rates and neutral species densities for a wide range of conditions. Good quantitative agreement between experiments and model were observed as a function of composition and rf power. The system is highly sensitive to the electron impact dissociation of oxygen, which creates the radical pool that drives the majority of the chemistry. The approach detailed here provides a framework for the development of models of oxide PECVD derived from other metalorganic precursors.