Preliminary Study on Electrical and Optical Properties of ZnO Film Grown by MOCVD

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Temperature effect on ZnO/Si thin film grown using metal organic chemical vapor deposition

We investigated the effect of deposition temperature on the growth and structural quality of ZnO films on Si (100) substrate using the metal organic chemical vapor deposition (MOCVD) technique. We revealed that highly c-axis oriented ZnO thin films were obtained at the temperature of 400°C. The film crystallinity improved and the surface smoothness decreased with increasing growth temperature.     

Influence of annealing on the structural and optical properties of ZnO films grown by MOCVD

The properties of ZnO films grown on Si (1 1 1) substrates by Metal-Organic Chemical Vapor Deposition technique using diethylzinc and H₂O as reactant gases are reported. The primary focus is on understanding the origin of deep-level luminescence. As increasing the annealing temperature, a visible emission is observed both in samples annealing in oxygen atmosphere and nitrogen atmosphere. In addition, this broad defect emission becomes obviously asymmetric when the annealing temperature was increased to 1000 °C in oxygen atmosphere. Theoretical investigations have reported that the formation enthalpy of defects is varied under different conditions. With these results, it is suggested that the visible emission in ZnO films annealed in oxygen atmosphere is related to zinc vacancy and oxygen interstitial defects. While, the green emission in ZnO films which were annealed in nitrogen atmosphere is attributed to oxygen vacancy defects.     

The characterization of various ZnO nanostructures using field-emission SEM

Zinc oxide (ZnO) is a unique material that has prompted a vast amount of research. Various morphologies and sizes of ZnO materials have led to a wide range of promising applications. Although research related to the applications of ZnO is progressing rapidly, it has been an enormous challenge to produce uniform ZnO materials. A unique synthesis method to produce ZnO materials with various morphologies has been studied and is presented in this paper. Field-emission scanningelectron microscopy has been utilized to characterize ZnO materials in this study to show how the synthesis conditions control the morphologies of ZnO.     

A study of film formation on aluminum in aqueous solutions using Rutherford backscattering spectroscopy

The growth of hydrated surface films on 99.99% pure aluminum in aqueous media at 100°C has been studied with Rutherford backscattering spectroscopy (RBS). The effects of the inhibitor anions borate, molybdate, nitrate, phosphate, sulfate, silicate and tungstate, and of ethylene glycol on this reaction were observed at concentration levels typical of automotive coolant formulations. The behavior of the inorganic anions studied is classified roughly into three types. In the first, typical of silicate, the inhibitor reacts with the surface to both prevent formation of the aluminum hydroxide layer, as well as limit the uptake of additional species by the surface. In a second mode, characteristic of nitrate and sulfate additions, the surface hydroxide develops, but at lower levels than those obtained in pure water. In yet another mode, characteristic of phosphate, molybdate and tungstate, the inhibitor anions are continually incorporated into a growing film which appears to be a hydrated aluminum salt of the particular anion, rather than pseudo-boehmite. Ethylene glycol is found to act primarily as a diluent in reducing the overall rate of film growth in aqueous solutions.     

Performance improvement of ZnO film by room-temperature oxygen plasma pretreatment

The room-temperature oxygen plasma treatment before depositing ZnO films on nanocrystalline diamond substrates was studied. The nanocrystalline diamond substrates were pretreated in oxygen plasma at 50 W for 30 min at room temperature and then ZnO films were sputtered on diamond substrates at 400 W. The X-ray diffraction （XRD） patterns show that the c-axis orientation of ZnO film increases evidently after oxygen plasma pretreatment. The AFM and SEM measurements also show that the high c-axis orientation of ZnO film and the average surface roughness is less than 5 nm. The resistivity of ZnO films increases nearly two orders of magnitude to 1.04 - 10^8 Ω.cm. As a result, room-temperature oxygen plasma pretreatment is indeed a simple and effective way to improve the performance of ZnO film used in SAW devices by ameliorating the combination between diamond film and ZnO film and also complementing the absence of oxygen atoms in ZnO film.     

Fe-Cr-Al合金纤维载体上的致密Al2O3薄膜

用SEM、EDS及XRD研究了Al₂O₃或TiO₂修饰对Fe-Cr-Al合金纤维载体表面形成致密α-Al₂O₃膜的影响因素,并分析了致密α-Al₂O₃膜的形成机理。结果表明,在900～1000 ℃范围内,当Fe-Cr-Al合金纤维经过含Al₂O₃的溶胶处理后,形成十分致密α-Al₂O₃膜;经含TiO₂的溶胶处理后,有利于在Fe-Cr-Al合金纤维载体表面形成稳定、均匀的α-Al₂O₃膜。α-Al₂O₃膜具有优异的耐高温、抗氧化特点,可有效提高Fe-Cr-Al合金纤维载体的使用性能。     

Grain boundary defects-mediated room temperature ferromagnetism in Co-doped ZnO film

Zn_0.97Co_0.03O films with and without ZnO buffer layer have been fabricated by magnetron sputtering to investigate the role of grain boundary defects in ferromagnetic ordering in this system. The deposited wurtzite films with (0 0 2) preferred orientation all show intrinsic room temperature ferromagnetism based on the substitutional behavior of Co²⁺. We found that the ZnO/Co:ZnO film grows in smaller grain size, compared with Co:ZnO film, which leads to the increase in grain boundary defects. Meanwhile the increase in oxygen vacancies is confirmed by Co K-edge X-ray-absorption near-edge spectra and the enhancement of saturated magnetization is observed in ZnO/Co:ZnO film. Hence the most important factor for mediating ferromagnetism is proposed to be grain boundary defects, i.e., oxygen vacancies. Bound magnetic polaron mechanism is adopted to explain the intrinsic origin and the mediative effects of grain boundary defects on ferromagnetism in Co-doped ZnO films.     

Characteristics of ZnO thin film deposited on various metal bottom electrodes

ZnO films for electronic applications were deposited by radio-frequency (rf) sputtering onto various metal bottom electrodes (Pt/Ti, W, Ni) to investigate such structural properties as crystallinity and surface morphology. The crystallinity, surface morphology and composition of the as-deposited films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Rutherford back-scattering spectrometry (RBS), respectively. The preferred orientation and surface morphologies were strongly influenced by the type of bottom electrodes. The ZnO films with (200) texturing deposited on Pt/Ti/SiO₂/Si showed a smoother and smaller grain size than those deposited on W and Ni. The ZnO films on Pt and W electrodes exhibited compressive residual stress. This article is based on a presentation made in the 2002 Korea-US symposium on the “Phase Transformations of Nano-Materials”, organized as a special program of the 2002 Annual Meeting of the Korean Institute of Metals and Materials, held at Yonsei University, Seoul, Korea on October 25–26, 2002.     

MOCVD of YSZ coatings using β-diketonate precursors

Metallorganic chemical vapor deposition (MOCVD) was investigated as a more efficient means to fabricate yttria-stabilized zirconia (YSZ) for thermal barrier coating. The MOCVD precursors were Y(tmhd)₃ and Zr(tmhd)₄ (tmhd, 2,2,6,6-tetramethyl-3,5-heptanedianato) and delivered via aerosol-assisted liquid delivery (AALD). The maximum YSZ coating rate was 14.2 ± 1.3 μm h⁻¹ at 827 °C yielding a layered coating microstructure. The growth was first-order with temperature below 827 °C with an apparent activation energy of 50.9 ± 4.3 kJ mol⁻¹. Coating efficiency was a maximum of approximately 10% at the highest growth rate. While homogeneous nucleation remained a problem, the deposition of YSZ with only minor carbon content was achieved.     

Influence of bacteria on film formation inhibiting corrosion

Mild steel coupons were incubated separately in two bacterial cultures namely Pseudomonas flava and Pseudomonas stutzeri. A significant reduction in the corrosion rate was observed in presence of P. flava. With a view to understand the mechanisms of microbially influenced corrosion/corrosion inhibition, various electrochemical and biological experiments such as weight change measurements and electrochemical impedance spectroscopy (EIS) measurements were made. The exposed surfaces were examined using scanning electron microscope (SEM) and energy dispersive X-ray analysis (EDAX). The scraped surface film was also examined using FT-IR (Fourier transform infra red) spectroscopy. The results suggest that P. flava have enhancing effect on corrosion inhibitive properties of phosphate film.     

Solvent dependence of organic superconducting thin film formation

The formation of (TMTSF)₂ClO₄ (tetramethyltetraselenafulvalene (TMTSF)) superconducting films on (TMTSF)₂PF₆ single-crystal templates is found to be strongly solvent dependent. Striking differences are observed by scanning electron microscopy in the structures of (TMTSF)₂ClO₄ coatings obtained by immersion in tetrahydrofuran, toluene, ethanol, 1,1,1-trichloroethane and 1,1,2-trichloroethane electrolyte solutions. However, the solubilities of the bulk (TMTSF)₂PF₆ and (TMTSF)₂ClO₄ materials in the considered media do not account for the observed surface modifications.     

The kinetics of phosphate film formation on the type MA 21 magnesium-lithium alloys

Kinetics of phosphating MA 21 magnesium-lithium alloys in a zinc-nitrate-phosphate solution (0.25 M Zn²⁺+0.34M PO ₄ ³⁻ +0.17M NO ₃ ⁻ +0.02M F⁻, pH = 2.7) at 25°C is studied with various surface preparation procedures. The effect of the alloy surface pretreatment in titanium-containing activating solutions on the electrochemical process rate and the initial stage of the phosphate film crystallization is revealed. Peculiarities of the phosphate film growth during different stages of the magnesium-lithium alloy phosphating are elucidated. Combining the activating pretreatment with zinc-phosphate bath allows accelerated applying finegrain thin phosphate conversion layers with enhanced protective effect on magnesium-lithium alloys. Original Russian Text ? L.A. Isaicheva, N.M. Trepak, L.K. Il’ina, A.L. L’vov, 2006, published in Zashchita Metallov, 2006, Vol. 42, No. 4, pp. 425–429.     

Nonpolar ZnO film growth and mechanism for anisotropic in-plane strain relaxation

Using high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction, we investigated the strain relaxation mechanisms for nonpolar (1 1 ?2 0) a-plane ZnO epitaxy on (1 ?1 0 2) r-plane sapphire, where the in-plane misfit ranges from ?1.5% for the [0 0 0 1]ZnO6[1 ?1 0 ?1]sapphire to ?18.3% for the [?1 1 0 0]ZnO6[?1 ?1 2 0]sapphire direction. For the large misfit [?1 1 0 0]ZnO direction the misfit strains are fully relaxed at the growth temperature, and only thermal misfit and defect strains, which cannot be relaxed fully by slip dislocations, remain on cooling. For the small misfit direction, lattice misfit is not fully relaxed at the growth temperature. As a result, additive unrelaxed lattice and thermal misfit and defect strains contribute to the measured strain. Our X-ray diffraction measurements of lattice parameters show that the anisotropic in-plane biaxial strain leads to a distortion of the hexagonal symmetry of the ZnO basal plane. Based on the anisotropic strain relaxation observed along the orthogonal in-plane [?1 1 0 0] and [0 0 0 1]ZnO stress directions and our HRTEM investigations of the interface, we show that the plastic relaxation occurring in the small misfit direction [0 0 0 1]ZnO by dislocation nucleation is incomplete. These results are consistent with the domain-matching paradigm of a complete strain relaxation for large misfits and a difficulty in relaxing the film strain for small misfits.     

致密WC增强铁基表面复合材料的原位制备与形成机理

利用铸渗复合-热处理工艺制备致密碳化钨增强铁基表面复合材料,研究了不同保温时间下复合材料的物相组成与微观组织.结果表明,不同保温时间下,复合材料表面均有致密碳化钨层生成,反应层厚度最大为148 μm.致密碳化钨层的显微硬度随保温时间无明显变化,均明显高于铁基体.铁基表面致密碳化钨的形成主要依赖于Fe-C-W体系中碳和钨原子的扩散与原位反应.     

致密WC增强铁基表面复合材料的原位制备与形成机理

利用铸渗复合-热处理工艺制备致密碳化钨增强铁基表面复合材料,研究了不同保温时间下复合材料的物相组成与微观组织.结果表明,不同保温时间下,复合材料表面均有致密碳化钨层生成,反应层厚度最大为148 μm.致密碳化钨层的显微硬度随保温时间无明显变化,均明显高于铁基体.铁基表面致密碳化钨的形成主要依赖于Fe-C-W体系中碳和钨原子的扩散与原位反应.     

Thin film epitaxy and structure property correlations for non-polar ZnO films

Heteroepitaxial growth and strain relaxation were investigated in non-polar a-plane (1 1 ?2 0)ZnO films grown on r-plane (1 0 ?1 2)sapphire substrates in the temperature range 200–700 °C by pulsed laser deposition. The lattice misfit in the plane of the film for this orientation varied from ?1.26% in [0 0 0 1] to ?18.52% in the [?1 1 0 0] direction. The alignment of (1 1 ?2 0)ZnO planes parallel to (1 0 ?1 2)sapphire planes was confirmed by X-ray diffraction θ?2θ scans over the entire temperature range. X-ray ?-scans revealed the epitaxial relationship:[0 0 0 1]ZnO6[?1 1 0 1]sap; [–1 1 0 0]ZnO6[?1 ?1 2 0]sap. Depending on the growth temperature, variations in the structural, optical and electrical properties were observed in the grown films. Room temperature photoluminescence for films grown at 700 °C shows a strong band-edge emission. The ratio of the band-edge emission to green band emission is 135:1, indicating reduced defects and excellent optical quality of the films. The resistivity data for the films grown at 700 °C shows semiconducting behavior with room temperature resistivity of 2.2 × 10^?3 Ω-cm.     

From research to manufacture—The evolution of MOCVD

The article provides an overview of the manufacturing capabilities of metalorganic chemical vapor deposition (MOCVD) technology and describes its application to the growth and fabrication of devices in three different material groups: AlGaAs/GaAs, AlInGaP, and AlGaN/GaN. Discussed are GaN blue light-emitting diodes (LEDs), AlInGaP red and yellow LEDs, and AlGaAs/GaAs vertical cavity surface-emitting lasers and high-electron-mobility transistors. Based on these examples, the evolution of MOCVD technology from fundamental materials studies and advanced materials development through the early stages of pilot manufacturing and large-volume manufacturing capabilities is demonstrated.     

The mechanism of oxide film formation on Alloy 690 in oxygenated high temperature water

Oxide films formed on Alloy 690 exposed to 290 °C water containing 3 ppm O₂ were investigated. It was found that Cr rich oxides form initially through solid-state reactions. Ni–Fe spinels gradually develop on surface layer by precipitation with increasing immersion time. Initially formed Cr rich oxides react with outwards diffusing Ni and Fe to form small spinel particles which then vanish gradually. An inner layer develops from oxide/matrix interface through inward diffusion of oxidant. Cr is preferentially oxidized and tends to dissolve into solution. The resultant inner layer consists of predominant NiO which cannot serve as a protective barrier layer.     

The formation of pure aluminium corrosion sensing film on fiber and its electrochemical performance

Recently, more and more attention has been put on the research of taking advantages of a fiber sensor on corrosion monitoring, because of its small volume, low weight, quick response, and excellent electromagnetism disturbing resistance etc. But a report about the application of fiber optical sensor is hardly found. In this paper, with the technology of vacuum sputter, pure aluminum corrosion sensing film was directly deposited on the core of fiber corroded away clad. Metallographic Microscope and Scanning Electron Microscope (SEM) were used to analyze the structure of the film. It shows that the thickness of the pure aluminum corrosion sensing film is about 14.65 μm, and the film is distributed even and firm. Galvanostatic step were used to evaluate the corrosion resistance in NaCl solution with different concentrations (0.001–0.1 mol/L). The result shows that the corrosion resistance of the sensing film is similar to that of industrial pure aluminum in NaCl solution with the concentration less than 0.1 mol/L. The work in this paper contributes to the research of fiber optical corrosion sensor for monitoring corrosion of aluminum.