Disorder, band offsets and dopability of transparent conducting oxides

N-type transparent conducting oxides are based on ionic oxides with s-like cation conduction bands. The effect of disorder on their conduction band states is found to be small, because angular disorder has no effect on s states. Aliovalent impurities give rise to shallow states at the conduction band, which leads to an absence of a conduction band tail of localized states. This leads to a higher electron mobility than in typical p state amorphous materials like a-Si, the ability to move the Fermi level well into the conduction band and an absence of electrical instability as in a-Si:H. The band offsets are used to suggest appropriate oxide dielectrics for their thin transistors.     

GO改性铕(Ⅲ)-二苯甲酰甲烷-三苯基氧膦及其发光性能研究

采用超声辅助溶剂热法合成一种氧化石墨烯(GO)改性铕(Ⅲ)-二苯甲酰甲烷-三苯基氧膦(Eu-DBMTPPO-GOs)近紫外转换红光材料,通过元素分析、紫外光谱、红外光谱、热重、X射线粉末衍射、扫描电镜和荧光对结构和性能进行表征。结果表明:配体与铕原子有效配位,适量GO添加改性能提高材料发光性能和品质。添加质量为0.009%时,分解温度达到230℃以上,在300~500nm呈现强激发带,在611nm发射强特征红光,量子产率23.5%,荧光寿命0.212ms,色坐标(0.655,0.340),并结合结构和性能对GO改性机理进行了分析。     

Synthesis,characterization and photoresponse study of undoped and transition metal (Co,Ni, Mn) doped ZnO thin films

The synthesis, characterization and photoresponse studies of undoped and transition metal doped zinc oxide thin films are carried out in this work, in prospect of visible light photo detection and sensor applications. The undoped and transition metal ions such as, Co, Ni and Mn doped ZnO films in this study were synthesized by chemical solution deposition, involving spin-coating. We have characterized the deposited films using X-ray diffraction, scanning electron microscopy, photoluminescence and UV–vis spectroscopy studies. The devices of the films for photoresponse study were fabricated by top Ag contacts on the film surface in metal–semiconductor–metal configuration. The current–voltage characteristics and switching measurements of these devices were studied under the illumination of an incandescent lamp. We found a high ON/OFF ratio of 8 and highest photocurrent density of 0.7 mA/cm² for Ni doped ZnO film.     

Structural, morphological and optical properties of thermal annealed TiO thin films

Structural, morphological and optical properties of TiO thin films grown by single source thermal evaporation method were studied. The films were annealed from 300 to 520 °C in air after evaporation. Qualitative film analysis was performed with X-ray diffraction, atomic force microscopy and optical transmittance and reflectance spectra. A correlation was established between the optical properties, surface roughness and growth morphology of the evaporated TiO thin films. The X-ray diffraction spectra indicated the presence of the TiO₂ phase for the annealing temperature above 400 °C.     

Structural, electrical and optical properties of zirconium-doped zinc oxide films prepared by radio frequency magnetron sputtering

Transparent and conducting zirconium-doped zinc oxide films have been prepared by radio frequency magnetron sputtering at room temperature. The ZrO₂ content in the target is varied from 0 to 10 wt.%. The films are polycrystalline with a hexagonal structure and a preferred orientation along the c axis. As the ZrO₂ content increases, the crystallinity and conductivity of the film are initially improved and then both show deterioration. Zr atoms mainly substitute Zn atoms when the ZrO₂ content are 3 and 5 wt.%, but tend to cluster into grain boundaries at higher contents. The lowest resistivity achieved is 2.07 × 10^− 3 Ω cm with the ZrO₂ content of 5 wt.% with a Hall mobility of 16 cm² V^− 1 s^− 1 and a carrier concentration of 1.95 × 10²⁰ cm^− 3. All the films present a high transmittance of above 90% in the visible range. The optical band gap depends on the carrier concentration, and the value is larger at higher carrier concentration.     

Saturation vapor pressure and critical constants of H2O,D2O,T2O,and their isotopic mixtures

Reliable data on the vapor pressure and critical constants of H₂O isotopes and their isotopic mixtures are required for the generation of thermophysical properties data over a wide range of temperatures and pressures. In this study, vapor pressure equations for D₂O and T₂O have been developed based on the latest experimental and theoretical information. Considering the similarity among H₂O isotopes, the functional form of the Saul and Wagner equation, fully proven for H₂O, has been employed. The present equation for D₂O shows a lower trend by up to 0.09% than the widely used Hill and MacMillan equation at temperatures below 150°C. For the vapor pressure of the isotopic mixtures, the available experimental data have been examined for the validity of Raoult's law. Then it has been shown that the critical temperature and the critical pressure of the isotopic mixture can also be predicted as simple mole-fraction average values.     

Effect of Nb, Cr, Sn additions on gas sensing properties of TiO2 thin films

The effect of Nb and Cr dopants as well as Sn⁴⁺ additions on the electronic structure of rf-sputtered TiO₂ thin films and its subsequent influence on gas sensor performance is reported. The changes in the electrical conductivities of TiO₂ thin films doped with up to 10 at.% Nb, 4 at.% Cr and TiO₂-SnO₂ in the full range of compositions upon exposure to hydrogen and oxygen are demonstrated. The spectral dependence of the absorption coefficient in the vicinity of the band gap transition of TiO₂ is shown to be affected by doping.     

Transparent, conducting, and ferromagnetic multilayer films based on ZnO/Fe3O4 by pulsed laser deposition technique

Multilayer thin films based on zinc oxide (ZnO) and iron oxide (Fe₃O₄) are fabricated using pulsed laser deposition method. The structural, electrical, and magnetic properties of these multilayer films are studied. X-ray diffraction study shows that ZnO film is highly oriented along (002) direction, while Fe₃O₄ film has preferred orientation along (222) direction. These films are transparent, conducting, and ferromagnetic at room temperature. The temperature dependence of resistance measurement shows semiconducting nature and charge transportation in these films is due to tunneling. Negative magneto-resistance of 0.28% is observed at room temperature.     

Electrical,optical, and structural properties of thin films with tri-layers of AZO/ZnMgO/AZO grown by filtered vacuum arc deposition

Transparent conductive oxides (TCO) are indispensable as front electrode for most of thin film electronic devices such as transparent electrodes for flat panel displays, photovoltaic cells, windshield defrosters, transparent thin film transistors, and low emissivity windows. Thin films of aluminum-doped zinc oxide (AZO) have shown to be one of the most promising TCOs. In this study, three layered Al-doped ZnO (AZO)/ZnMgO/AZO heterostructures were prepared by filtered cathodic arc deposition (FCAD) on glass substrates. The objective is to find a set of parameters that will allow for improved optical and electrical properties of the films such as low resistivity, high mobility, high number of charge carriers, and high transmittance. We have investigated the effect of modifications in thickness and doping of the ZnMgO inner layer on the structural, electrical, and optical characteristics of the stacked heterostructures.     

Nitrogen-doped tungsten oxide nanowires: low-temperature synthesis on Si, and electrical, optical, and field-emission properties

Very dense and uniformly distributed nitrogen-doped tungsten oxide (WO(3)) nanowires were synthesized successfully on a 4-inch Si(100) wafer at low temperature. The nanowires were of lengths extending up to 5 mum and diameters ranging from 25 to 35 nm. The highest aspect ratio was estimated to be about 200. An emission peak at 470 nm was found by photoluminescence measurement at room temperature. The suggested growth mechanism of the nanowires is vapor-solid growth, in which gaseous ammonia plays a significant role to reduce the formation temperature. The approach has proved to be a reliable way to produce nitrogen-doped WO(3) nanowires on Si in large quantities. The direct fabrication of WO(3)-based nanodevices on Si has been demonstrated.     

Highly conductive, undoped ZnO thin films deposited by electron-cyclotron-resonance plasma sputtering on silica glass substrate

The electrical and optical properties of undoped ZnO films deposited by electron cyclotron resonance (ECR) plasma sputtering at room temperature were characterized. The lowest resistivity we achieved was 2.6 × 10^− 3 Ωcm with optical transmittance at visible wavelengths higher than 85%. The X-ray diffraction (002) peak was weak and the rocking curve was asymmetrical, indicating that oxygen vacancies prevented large crystalline domains from forming. At low argon-sputtering-gas pressure, carrier concentration and Hall mobility increased with increasing argon pressure. When the optimum pressure (40 mPa) was exceeded, however, Hall mobility and optical transmittance were severely reduced, which indicated that excess Zn atoms were populated at the interstitials of the network. Admitting only 0.67 mPa of O₂ gas during deposition deteriorated resistivity over 1 MΩcm due to high excitation efficiency in the ECR plasma. Deposition under a higher magnetic field produced lower resistivities.     

A Supercompressible,Elastic, and Bendable Carbon Aerogel with Ultrasensitive Detection Limits for Compression Strain,Pressure, and Bending Angle

Ultralight and compressible carbon materials have promising applications in strain and pressure detection. However, it is still difficult to prepare carbon materials with supercompressibility, elasticity, stable strain–electrical signal response, and ultrasensitive detection limits, due to the challenge in structural regulation. Herein, a new strategy to prepare a reduced graphene oxide (rGO)‐based lamellar carbon aerogels with unexpected and integrated performances by designing wave‐shape rGO layers and enhancing the interaction among the rGO layers is demonstrated. Addition of cellulose nanocrystalline and low‐molecular‐weight carbon precursors enhances the interaction among rGO layers and thus produces an ultralight, flexible, and superstable structure. The as‐prepared carbon aerogel displays a supercompressibility (undergoing an extreme strain of 99%) and elasticity (100% height retention after 10 000 cycles at a strain of 30%), as well as stable strain–current response (at least 10 000 cycles). Particularly, the carbon aerogel is ultrasensitive for detecting tiny change in strain (0.012%) and pressure (0.25 Pa), which are the lowest detection limits for compressible carbon materials reported in the literature. Moreover, the carbon aerogel exhibits excellent bendable performance and can detect an ultralow bending angle of 0.052°. Additionally, the carbon aerogel also demonstrates its promising application as wearable devices.     

纳米WO_3的结构、制备及应用前景

在国内外最新研究文献的基础上总结了纳米WO3的多种制备方法及各自优缺点,其中详细介绍了溶-胶凝胶法、溅射法、化学气相沉积法、蒸发法等,并对纳米WO3的潜在应用进行了介绍,并展望了其发展方向.     

Nanobelts,Nanowires, and Nanodiskettes of Semiconducting Oxides—From Materials to Nanodevices

Novel nanostructures of semiconducting oxides are reviewed here. It is shown that nanobelts, nanowires, and nanodiskettes of materials such as zinc oxide, gallium oxide, silica, and tin oxide can be fabricated using a vapor‐phase evaporation method. Two applications of these materials—in field effect transistors and as gas sensors—are highlighted.     

Synthesis,Crystal Structural and Electrical Conductivity Properties of Fe-Doped Zinc Oxide Powders at High Temperatures

The synthesis,crystal structure and electrical conductivity properties of Fe-doped ZnO powders(in the range of 0.25-15 mol%) were reported in this paper.I-phase samples,which were indexed as single phase with a hexagonal(wurtzite) structure in the Fe-doped ZnO binary system,were determined by X-ray diffraction(XRD).The solubility limit of Fe in the ZnO lattice is 3 mol% at 950℃.The above mixed phase was observed.And the impurity phase was determined as the cubic-ZnFe 2 O 4 phase when compared with standard XRD data using the PDF program.This study focused on single I-phase ZnO samples which were synthesized at 950℃ because the limit of the solubility range is the widest at this temperature.The lattice parameters a and c of the I-phase decreased with Fe-doping concentration.The morphology of the I-phase samples was analyzed with a scanning electron microscope.The grain size of the I-phase samples increased with heat treatment and doping concentration.The electrical conductivity of the pure ZnO and single I-phase samples was investigated using the four-probe dc method at 100-950℃ in air atmosphere.The electrical conductivity values of pure ZnO,0.25 and 3 mol% Fe-doped ZnO samples at 100℃ were 2×10-6,1.7×10-3 and 6.3×10-4 S.cm-1,and at 950℃ they were 3.4,8.5 and 4 S.cm-1,respectively.     

Initial stages of deposition and film formation during spray pyrolysis — Nickel oxide, cerium gadolinium oxide and mixtures thereof

The formation of nickel oxide (NiO), cerium gadolinium oxide (CGO) and NiO-CGO thin films by air blast spray pyrolysis was studied at two scales. First, single droplets of precursor were deposited on sapphire substrates and the morphology of the formed residue was studied as a function of the substrate surface temperature, type of metal salt, salt saturation, and organic solvent in the precursor. Second, the synthesis of continuous films from repetitively deposited droplets and crack formation in the films were studied as a function of substrate temperature and salt decomposition kinetics. Nitrates, acetates, perchlorates and chlorides of nickel, cerium and gadolinium were the metal salts used, and mixtures of ethanol or water with di-, tri- and tetraethylene glycol were used as solvents.Regular ring- or disc-shaped deposits were formed from single droplets that evaporated without boiling and were mainly observed with metal acetate- and chloride-based spray solutions or at low substrate temperatures. Disc-shaped residues were obtained for saturated salt solutions and changed to rings with diminishing rim thickness with decreasing salt saturation. The formation of bubbles in the droplet from boiling or salt decomposition during evaporation resulted in the distortion of the circular shape and was predominantly observed for metal nitrate-based precursors and at high substrate surface temperatures.Continuous, dense and crack-free films of CGO and NiO-CGO with thicknesses up to 500 and 800 nm, respectively, were prepared from metal nitrate/chloride mixtures in a tetraethylene glycol-based solvent. The maximum crack-free thickness decreased with decreasing deposition temperature and was correlated to the metal salt decomposition kinetics.     

Ru Doping of Perovskite Manganites: An Effective Route to Ferromagnetism, Metallicity, and CMR

The doping of Mn sites by Ru in manganites has been studied. It is shown that, whatever the nature of the antiferromagnetic data of the undoped perovskite, CE or pseudo-CE type, like for Ln_0.5Ca_0.5MnO₃ and Ln_0.4Ca_0.6MnO₃, or A type as for Pr_0.5Sr_0.5MnO₃, or C type as for Sm_0.2Ca_0.8MnO₃, or G type as for CaMnO₃, ferromagnetism and metallicity can be induced by Ru doping in a very effective manner, leading to colossal magnetoresistance (CMR) properties. Thus a dramatic modification of the magnetic phase diagrams can be obtained by Ru doping, as shown for the Sm_{1 – y} Ca_y Mn_0.88Ru_0.12O₃ system where the T_C of the ferromagnetic insulating (FMI) region (0.12 y 0.40) has been increased significantly by Ru doping. But more important, the charge-ordered state of the electron rich region (0.40 y < 0.80) has been spectacularly replaced by a ferromagnetic metallic (FMM) state with a very high T_C, up to 235 K by Ru substitution. The peculiar nature of the so obtained FMM state is shown to be related to the structural phase separation. This particular efficiency of ruthenium, compared to chromium, is discussed in terms of not only valency effect due to the presence of Ru⁵⁺ that increases the Mn³⁺ content, but also valency fluctuation between Ru⁵⁺ and Ru⁴⁺, and in terms of strong ferromagnetic superexchange interactions between ruthenium and manganese, due to orbital hybridization, so that Ru⁴⁺ and Ru⁵⁺ participate in the band formation.     

锌合金ZZnAl4—1中Mg,Fe,Pb,Sn的光谱分析方法

本文法提供了将样品采用稀硝酸溶解，蒸干，在４００℃温度下灼烧成硝酸盐氧化物，研磨成细粉，以光谱纯碳粉作缓冲剂，用电弧激发试样进行分析，其准确度：Ｍｇ±４．４％，Ｆｅ±７．４％，Ｐｂ±２．７％，Ｓｎ±３．１％，现已用于生产分析。     

氢火焰气相色谱法快速检测工作场所空气中的丙烯、环氧乙烷、环氧丙烷

在化工企业工作场所空气中经常存在着一些可燃性气体,需测定其含量,以便在施工动火时避开可燃性气体的爆炸极限浓度,确保施工安全。本文主要针对某化工企业工作场所空气中含有的丙烯、环氧乙烷、环氧丙烷3种可燃性气体进行分析。