不同氧气含量下镍铬系平板集热器选择性吸收薄膜的制备和性能表征

采用双极脉冲磁控溅射系统,在不同氧气含量的氩氧混合气体中制备了单层镍-铬金属-电介质复合光谱选择性吸收薄膜。采用X射线衍射仪(XRD)、激光共焦显微拉曼光谱仪、椭偏仪和紫外-可见-近红外分光光度计分别对薄膜的物相结构和光学特性进行了表征。结果表明:实验获得了由金属镍和镍、铬的氧化物(NiO、Cr2O3)组成的复合膜,薄膜对300~1 200 nm波段的太阳光有较强的吸收,而对波长大于1 200 nm的太阳光则吸收较弱,具有良好的光谱选择性,可用作高效太阳光谱选择性吸收涂层。     

双注磁控注入电子枪

为了增加回旋管的功率,采用双注磁控注入电子枪产生相对论电子注。与双阳极磁控注入电子枪相比,双注磁控注入电子枪产生双束电子注,在不影响电子注质量的基础上,增加电子枪的电流;电子枪产生相同电流时,双注磁控注入电子枪电子注电流小,电子注电子之间的空间电荷效应小,能够降低电子注的速度零散,提高电子注的质量。采用MAGIC软件数值模拟双注磁控注入电子枪,设计出一支大束流、低速度零散的双注磁控注入电子枪。     

磁控溅射制备微球表面金属Mo涂层的研究

利用磁控溅射制备了各种工艺参数不同的微球表面金属Mo涂层样品,并通过白光干涉仪和扫描电子显微镜对样品的表面及剖面进行了系统的测试分析。分别探究了溅射工作气压和沉积制备时间对微球表面Mo涂层表面形貌以及结晶质量的影响规律。结果表明通过优化工艺参数可制备微球直径约为800μm、涂层厚度为3.5μm到14.1μm、厚度均匀性良好的微球表面Mo涂层。Mo涂层中的晶粒呈现出柱状结构致密堆积在一起,且随涂层的厚度增加晶粒间空隙增大。     

Microwave ferromagnetic properties of as-deposited Co_2FeSi Heusler alloy films prepared by oblique sputtering

The Co2 FeSi films are deposited on Si(100) substrates by an oblique sputtering method at ambient temperature. It is revealed that the microwave ferromagnetic properties of Co2 FeSi films are sensitive to sample position and sputtering power. It is exciting that the as-deposited films without any magnetic annealing exhibit high in-plane uniaxial anisotropy fields in a range of 200 Oe–330 Oe(1 Oe = 79.5775 A·m-1), and low coercivities in a range of 5 Oe–28 Oe. As a result,high self-biased ferromagnetic resonance frequency up to 4.75 GHz is achieved in as-deposited oblique sputtered films.These results indicate that Co2 FeSi Heusler alloy films are promising in practical applications of RF/microwave devices.     

Structures and optical properties of tungsten oxide thin films deposited by magnetron sputtering of WO_3 bulk:Effects of annealing temperatures

Tungsten oxide thin films were deposited on glass substrates by the magnetron sputtering of WO3 bulk at room temperature. The deposited films were annealed at different temperatures in air. The structural measurements indicate that the films annealed below 300℃ were amorphous, while the films annealed at 400℃ were mixed crystalline with hexagonal and triclinic phases of WO3. It was observed that the crystallization of the annealed films becomes more and more distinct with an increase in the annealing temperature. At 400℃, nanorod-like structures were observed on the film surface when the annealing time was increased from 60 min to 180 min. The presence of W=O stretching, W–O–W stretching, W–O–W bending and various lattice vibration modes were observed in Raman measurements. The optical absorption behaviors of the films in the range of 450–800 nm are very different with changing annealing temperatures from the room temperature to 400℃. After annealing at 400℃, the film becomes almost transparent. Increasing annealing time at 400℃ can lead to a small blue shift of the optical gap of the film.     

Discharge characteristics of the DUHOCAMIS with a high magnetic bottle-shaped field

For the purpose of producing high intensity, multiply charged metal ion beams, the dual hollow cathode ion source for metal ions （DUHOCAMIS） was derived from the hot cathode Penning ion source combined with the hollow cathode sputtering experiments in 2007. To investigate the behavior of this discharge geometry in a stronger magnetic bottle-shaped field, a new test bench for DUHOCAMIS with a high magnetic bottle-shaped field up to 0.6 T has been set up at the Peking University. The experiments with magnetic fields from 0.13 T to 0.52 T have indicated that the discharge behavior is very sensitive to the magnetic flux densities. The slope of discharge curves in a very wide range can be controlled by changing the magnetic field as well as regulated by adjusting the cathode heating power; the production of metallic ions would be much greater than gas ions with the increased magnetic flux density; and the magnetic field has a much higher influence on the DHCD mode than on the PIG mode.     

Effect of growth stoichiometry on the structural properties of AlN films on thermally nitrided sapphire $(11\bar 20)$

High‐quality AlN epilayers were grown via pulsed sputtering deposition on thermally nitrided sapphire $(11\bar 20)$ with precise control of the N/Al ratio. Under slightly Al‐rich growth conditions, the growth of AlN epilayers on the thermally nitrided sapphire proceeded in a two‐dimensional mode from the initial stage of growth, and their surfaces were atomically flat stepped and terraced structures. The FWHM values of the X‐ray rocking curves were as low as 87 arcsec and 339 arcsec for the 0002 and $1 \bar 102$ diffractions, respectively, at a film thickness of 400 nm. The present approach is therefore quite promising for the low‐cost fabrication of AlGaN‐based UV optical devices. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Non‐hydrogenated amorphous germanium carbide with adjustable microstructure and properties: a potential anti‐reflection and protective coating for infrared windows

Amorphous non‐hydrogenated germanium carbide (a‐Ge_1?xC_x) films have been deposited using magnetron co‐sputtering technique by varying the sputtering power of germanium target (P_Ge). The effects of P_Ge on composition and structure of the a‐Ge_1?xC_x films have been analyzed. The FTIR spectrum shows that the C–Ge bonds were formed in the a‐Ge_1?xC_x films according to the absorption peak at ~610 cm^?1. The Raman results indicate that the amorphous films also contain both Ge and C clusters. The XPS results reveal that the carbon concentration decreased as P_Ge increased from 40 to 160 W. The fraction of sp³ C–C bonds remains almost constant when increasing P_Ge from 40 to 160 W. The sp² C–C content of a‐Ge_1?xC_x film decreases gradually to 35.9% with P_Ge up to 160 W. Nevertheless, sp³ C–Ge sites rose with increasing P_Ge. Furthermore, the hardness and the refractive index gradually increased with increasing P_Ge. The excellent optical transmission of annealed a‐Ge_1–xC_x double‐layer coating at 400 °C suggests that a‐Ge_1?xC_x films can be used as an effective anti‐reflection coating for the ZnS IR window in the wavelength region of 8–12 µm, and can endure higher temperature than hydrogenated amorphous germanium carbide do. Copyright © 2012 John Wiley & Sons, Ltd.     

Global optimization of parameters in the reactive force field ReaxFF for SiOH

We have used unbiased global optimization to fit a reactive force field to a given set of reference data. Specifically, we have employed genetic algorithms (GA) to fit ReaxFF to SiOH data, using an in‐house GA code that is parallelized across reference data items via the message‐passing interface (MPI). Details of GA tuning turn‐ed out to be far less important for global optimization efficiency than using suitable ranges within which the parameters are varied. To establish these ranges, either prior knowledge can be used or successive stages of GA optimizations, each building upon the best parameter vectors and ranges found in the previous stage. We have finally arrive‐ed at optimized force fields with smaller error measures than those published previously. Hence, this optimization approach will contribute to converting force‐field fitting from a specialist task to an everyday commodity, even for the more difficult case of reactive force fields. © 2013 Wiley Periodicals, Inc.