CdZnTe晶片4种化学钝化工艺效果的比较

常用于X射线和γ射线探测器中的CdZnTe(CZT)晶片经机械抛光后表面存在损伤层和许多肉眼看不到的划痕,采用溴甲醇(Br2-CH3OH)腐蚀可有效去除损伤层和划痕,使表面变得光亮平整.但经Br2-CH3OH腐蚀的表面富Te而产生较大的表面漏电流,为此,采用H2O2溶液,NH4F/H2O2溶液,KOH-KCl溶液+NH4F/H2O2溶液二步法和溴水4种湿法化学钝化工艺,对CZT晶片表面进行了钝化处理,并对比了其钝化效果.结果表明:二步法钝化效果最好,表面漏电流降低4个数量级,NH4F/H2O2对CZT晶片表面的钝化效果较好,表面漏电流降低3个数量级.     

原子氧处理减小多晶PZT-PMN薄膜漏电流的实验研究

漏电流是铁电薄膜应用过程中的关键问题。本文通过磁控溅射法制备了结晶性能良好的铌镁锆钛酸铅(PZT-PMN)铁电薄膜,并在室温下用原子氧对其进行处理,研究了原子氧对PZT-PMN薄膜表层微观结构和漏电流的影响。实验结果表明:经原子氧处理后的PZT-PMN薄膜,①表面粗糙度下降且有非晶层形成;②表层有大量的氧原子进入;③漏电流密度减小了大约一个数量级,外加电压为2.5 V时,未处理样品的漏电流密度为3×10-5A/cm2,处理样品的漏电流密度降为4.5×10-6A/cm2。原子氧对PZT-PMN薄膜内部晶界、缺陷的钝化是薄膜漏电流减小的原因。     

Au与p-CZT晶体的接触特性及其CZT表面处理状态的影响

对不同腐蚀、钝化表面处理的CZT晶片与Au接触的I-V特性进行了研究.用XPS分析了钝化前后CZT晶体表面成分,发现钝化后CZT晶片表面形成厚度为3.1nm的TeO2氧化层.用Agilent 4339B高阻仪进行未腐蚀、腐蚀与腐蚀钝化的CZT晶片I-V特性测试,结果表明腐蚀和腐蚀钝化均能不同程度提高Au/p-CZT接触的势垒高度,相应地减小了漏电流.     

SiO2/聚酰亚胺/SiO2复合薄膜绝缘性能及基于聚酰亚胺复合薄膜的后栅型场致发射性能的研究

使用射频磁控溅射和化学溶液法制备了SiO2/聚酰亚胺(PI)/SiO2绝缘膜。分别使用X射线衍射、扫描电镜对薄膜结构和薄膜表面形貌进行了表征;利用超高阻微电流测试仪测试了SiO2/PI/SiO2复合绝缘膜漏电流和电压击穿特性;采用SiO2/PI/SiO2作为绝缘膜,制作了后栅型场致发射器件,使用场发射测试系统测试了器件的开启电压、发射电流以及发光亮度。结果表明:SiO2/PI/SiO2复合绝缘膜具有高的击穿电压和低的漏电流密度,后栅器件中栅极对阴极表面的电场强度调控作用明显,阳极电压为750V时,栅极开启电压为91 V,阳极电流可达384μA,栅极漏电流仅为59μA,器件最高亮度可达600 cd/m2。     

SiC/DLC过渡层对类金刚石薄膜力学性能的影响

采用等离子体浸没离子注入及沉积技术在钛合金(Ti6Al4V)表面制备了类金刚石薄膜和含有SiC/DLC过渡层的类金刚石薄膜。采用拉曼光谱及扫描电子显微镜分析了薄膜的成分和结构,并利用超显微硬度计、薄膜结合力测试仪和往复式摩擦实验机研究了薄膜的硬度、韧性、膜/基结合力和耐磨性。研究结果表明,SiC/DLC过渡层可以提高钛合金(Ti6Al4V)表面类金刚石薄膜的韧性及膜/基结合力,与未制备过渡层的类金刚石薄膜相比,含有SiC/DLC过渡层的类金刚石薄膜的耐磨性明显提高。     

靶电流对掺钨类金刚石膜的结构与摩擦学行为的影响EI北大核心

利用真空阴极电弧+磁控溅射+阳极层条形离子源制备了带梯度过渡层的掺钨类金刚石(DLC)膜,并研究了靶电流对掺钨DLC膜结构和性能的影响,结果表明:制备的掺钨DLC膜光滑致密,表面存在1~2μm的液滴。靶电流不大于3.5A时,随着靶电流的增加,掺钨DLC膜的钨含量逐渐增加,但sp3的含量基本不变;靶电流为5A时,制备的薄膜成分接近WC的理想化学计量比,薄膜中的sp3含量增加到48%。当靶电流不大于2A时,靶电流对掺钨DLC膜的显微硬度和摩擦系数影响较小;在高的靶电流条件下,掺钨DLC膜的显微硬度和摩擦系数随着靶电流的增加而明显增大。     

PECVD制备掺氮类金刚石薄膜的电化学特性

利用混合离子束系统,通过辉光放电等离子体增强化学气相沉积(PECVD)方法制备出类金刚石薄膜(DLC)和掺氮类金刚石薄膜(N-DLC),用可见拉曼光谱、X射线光电子能谱和扫描探针显微镜表征薄膜微观结构和表面形貌,采用电化学工作站测量了薄膜的电化学性能。结果表明,DLC薄膜的表面光滑致密、粗糙度低,掺氮增加了薄膜中的sp2团簇相并形成了C-N键,并使C-O键含量和薄膜表面的活性位点增加。N-DLC薄膜电极在硫酸溶液中的电化学势窗达4.5 V和较低的背景电流(0.3±0.2μA/cm2);在铁氰化钾溶液中电极的电流响应明显,表现为受扩散控制的准可逆过程。电极具有很好的重复性和稳定性。     

电应力对HfO2栅介质漏电流的影响

使用导电原子力显微镜（Conductive Atomic Force Microscopy,CAFM）对电压应力作用下HfO2栅介质薄膜局域漏电点的形成和产生机制进行了研究,结果表明,在电压应力作用下,HfO2介质层中的缺陷被驱动和聚集形成导电通道,产生漏电点。漏电点产生的数量、漏电流大小均受电压应力和作用时间的影响。HfO2栅介质层中晶界处的缺陷密度高于晶粒处,导致晶界处更容易产生漏电通道。在栅介质击穿过程中,电压应力在诱发漏电流产生的同时产生焦耳热,对HfO2介质表面造成热损伤,导致击穿后HfO2介质表面出现凹陷。     

快速热氧化制备超薄二氧化硅层及其钝化效果

二氧化硅(SiO2)是制备高效晶体硅太阳电池常用的钝化手段。本文利用快速热氧化(RTO)技术在晶体硅表面制备超薄SiO2层,考察其对硅表面的钝化作用。在100%O2气氛下,900℃RTO处理180s,可以使样品的少子寿命达到146.6μs的最佳值。采用RTO方法制备的SiO2薄膜厚度可以控制在几个纳米范围。通过与等离子体增强化学气相沉积(PECVD)系统沉积的氮化硅(SiNx)薄膜形成叠层钝化膜,可以进一步提高对太阳电池表面的钝化效果。单层SiNX薄膜钝化的样品有效载流子寿命为51.67μs,SiO2/SiNx叠层薄膜钝化的样品有效载流子寿命提高到151.18μs。     

7A04铝合金表面DLC薄膜制备及性能研究

为提高7A04铝合金的表面性能,利用射频辅助等离子体浸没离子注入与沉积设备,在其表面制备类金刚石(DLC)薄膜。由于DLC薄膜与铝合金基体力学性能差别较大,导致膜基结合力差。本研究采用非平衡磁控溅射技术预先沉积一层Si膜,作为过渡层改善膜基结合力;利用激光拉曼光谱仪、维式显微硬度计、纳米划痕仪、摩擦磨损试验机等设备,系统分析了薄膜结构、显微硬度、膜基结合力及耐磨损性能。结果表明,Si过渡层的制备提高了基体的承载能力和膜基结合力,进而使耐磨损性能得到大幅度提高。     

As-cast microstructures and behavior at high temperature of chromium-rich cobalt-based alloys containing hafnium carbides

Hafnium is often used to improve the high temperature oxidation resistance of superalloys but not to form carbides for strengthen them against creep. In this work hafnium was added in cobalt-based alloys for verifying that HfC can be obtained in cobalt-based alloys and for characterizing their behavior at a very temperature. Three Co–25Cr–0.25 and 0.50C alloys containing 3.7 and 7.4 Hf to promote HfC carbides, and four Co–25Cr– 0 to 1C alloys for comparison (all contents in wt.%), were cast and exposed at 1200 °C for 50 h in synthetic air. The HfC carbides formed instead chromium carbides during solidification, in eutectic with matrix and as dispersed compact particles. During the stage at 1200 °C the HfC carbides did not significantly evolve, even near the oxidation front despite oxidation early become very fast and generalized. At the same time the chromium carbides present in the Co–Cr–C alloys totally disappeared in the same conditions. Such HfC-alloys potentially bring efficient and sustainable mechanical strengthening at high temperature, but their hot oxidation resistance must be significantly improved.     

Measurement of the thermal expansion of metal and FRPs

Thermal expansion is an important parameter for characterization of different binding forces, lattice dynamics, band and crystal structure of any solids. Many investigators have focused their attention to study this property theoretically and experimentally at different temperatures. It is one of the important properties of metals and its alloys, which helps to calculate the thermal stress. This parameter is also used to determine the compatibility of an insulator as load bearing materials. Different experimental setups have been developed to study thermal expansions of the materials using different techniques namely capacitance method, interferometric principle, LASER, optical, quartz tube etc. This paper reviews most of the experimental setups available to measure thermal expansion of metals, alloys, polymers and fibre-reinforced plastics at temperature ranging from 1 to 1100 K.     

Real gas choked flow conditions at low reduced-temperatures

Real gas choked mass flux is calculated for a frictionless stream expanding isentropically until it reaches the speed of sound and without phase changes. The other parameters associated with the choked state are the pressure, density, temperature ratios, and the speed of sound. Departure of the choked mass flux from the ideal gas model is discussed first in absolute terms and then in relative terms, using the Principle of Corresponding States, for gases with boiling points in the low temperature range. Reduced-stagnation pressures are examined up to values of 30 for hydrogen, neon, nitrogen, argon, methane, krypton, xenon, and R-14 and up to 100 for ⁴He. The corresponding reduced-stagnation temperatures go down to 1.4 and in some cases down to 1.2 for nitrogen and argon. Also discussed are the limiting values of stagnation parameters for which no phase change occurs in the choked state. Compared to the ideal gas, the mass flux may almost double and the critical pressure ratio may decrease by an order of magnitude. The relevance of results is discussed qualitatively and quantitatively for Joule-Thomson cryocooling.     

Development of No-Vent™ liquid hydrogen storage system for space applications

A number of technological advances required to store and maintain normal-boiling-point and densified cryogenic liquids, including liquid hydrogen, under zero boil-off conditions in-space, for long periods of time, have been developed. These technologies include (1) thermally optimized compact cryogen storage systems that reduce environmental heat leak to the lowest-temperature cryogen, which minimizes cryocooler size and input power, and (2) actively-cooled shields that surround the storage systems and intercept heat leak. The processes and tools used to develop these technologies are discussed. A zero boil-off liquid hydrogen storage system technology demonstrator for validating the actively-cooled shield technology is presented.     

Analysis of optimum configuration of two-stage thermoelectric modules

In this paper, the theoretical analysis and stimulating calculation were conducted for a basic two-stage thermoelectric module, which contains one thermocouple in the second stage and several thermocouples in the first stage. The study focused on the configuration of the two-stage thermoelectric module, especially investigating the influences of some parameters, such as the allocation of the junction temperature difference in the module, the length of thermocouples and the number of thermocouples, on the cooling performance of the module. The obtained analysis results indicate that changing the junction temperature difference in the second stage, the length of thermocouples and the number of thermocouples in the first stage can improve the cooling performance of the module. These results can be used to optimize the configuration of the two-stage thermoelectric module, and provide guides for the design and application of thermoelectric cooler.     

Development of a miniature cryogenic fluid circuit and a cryogenic micropump

This article presents the development of a miniaturized cryogenic fluid circuit for distributed cooling of low-temperature tracking detectors in high-energy physics (HEP). The heart of the circuit is a prototype cryogenic micropump. This volumetric pump is compatible with cooling powers of about 10-100 W, and capable of producing pressure heads of up to around 0.3 MPa. Besides detector and electronics cooling in HEP, potential applications are found in the field of superconductor technology.     

Effect of cryogenic treatment on microstructure, mechanical and wear behaviors of AISI H13 hot work tool steel

This paper focuses on the effects of low temperature (subzero) treatments on microstructure and mechanical properties of H13 hot work tool steel. Cryogenic treatment at −72 °C and deep cryogenic treatment at −196 °C were applied and it was found that by applying the subzero treatments, the retained austenite was transformed to martensite. As the temperature was decreased more retained austenite was transformed to martensite and it also led to smaller and more uniform martensite laths distributed in the microstructure. The deep cryogenic treatment also resulted in precipitation of more uniform and very fine carbide particles. The microstructural modification resulted in a significant improvement on the mechanical properties of the H13 tool steel.     

Effect of different treatments of copper surface on its total hemispherical absorptivity bellow 77 K

Total hemispherical absorptivity of copper surfaces treated with standard industrial methods was measured in dependence on the temperature of thermal radiation, varying from 25 K to 300 K. The sample temperature was typically from 5 K to 40 K and did not exceed 70 K. Usability of chemical and mechanical Cu surface finishing as well as Cu plating with Ni and Au for cryogenic design is discussed. As an example of practical application of our results, the cryogenic design of a LN₂ trap is presented.     

Percolation and the resistive transition of the critical temperature Tc of Nb3Sn

The relationship between the distribution of the critical temperature, the percolation function, and the resistive transition of the critical temperature is explored for polycrystalline Nb₃Sn. In the neighborhood of the critical temperature, Nb₃Sn is assumed to be a random mixture of superconducting and normal grains. Percolation concepts are applied to a study of the resistivity. A general analysis is made showing that the onset and shape of the resistive transition for composite conductors are determined by the percolation function and the distribution of the critical temperature. An approximate form of the percolation function is determined based on a linear FEM analysis. Example resistive transitions are calculated for an assumed normal distribution of the critical temperature. An argument is presented that relates grain orientation and strain dependence in Nb₃Sn. It is noted that a dependence of the distribution of T_c with strain, in addition to the usual shift in T_c with strain, would be the result of a strain dependence that is a function of grain orientation. The analysis shows the extent to which the slope of the resistive transition is a measure of the distribution of the critical temperature, and therefore a measure of the grain orientation strain sensitivity. Finally, a method is described to determine the percolation function experimentally.