基于PSpice的半导体激光高频调制系统设计

为了实现高频率的调制激光输出,设计了一种驱动系统由信号放大、电流调制、过流保护和具有慢启动功能的直流偏置电路高度集成的半导体激光高频调制系统。此系统采用了结构简单的直接调制方式,运用线性调频的高频信号去控制半导体激光器发射激光的强度,从而实现高频调制。在运用OrCAD/PSpice对高频调制驱动系统进行模拟仿真的基础上,最终研制出的半导体激光高频调制系统实现了频率为40.02 MHz、直流偏置为493.326 mA、正弦波调制电流峰峰值为850 mA的高频调制输出,调制激光平均功率为300 mW。     

高温超导直流电缆系统设计及漏热分析

近年来,高温超导技术研究在输配电领域取得了显著的进展,超导电缆应用技术成为其重点发展方向。其中,冷却系统的设计是保证超导电缆输配电系统稳定运行的关键技术。针对一套高温超导直流电缆系统中的终端恒温器、电流引线和超导电缆本体等关键部件进行了漏热分析,并通过理论计算和有限元仿真,对高温超导电缆系统的热负荷进行了评估,为该系统可靠运行提供了保障。     

用于FEL-THz电子束测量的LW系统北大核心CSCD

基于汤姆逊背散射的激光丝扫描(LW)方法作为无阻拦电子横向尺寸测量手段,近年来广泛应用于高能对撞机和能量回收环直线加速器。为在连续模式下测量高平均功率相干强太赫兹源的直流光阴极电子枪(DC-gun)电子束横向束斑,本文提出了一种基于驱动激光器分束的高重复频率,较低脉冲功率的新型LW系统。通过理论及模拟分析,证明该系统相对于常规LW系统具有成本低、精度高、探测时间短、对电子束影响小的优势,并给出了用于自由电子激光太赫兹(FEL-THz)装置DC-gun出口电子束LW系统的实验设计。     

Sputtering pressure influence on growth morphology,surface roughness,and electrical resistivity for strong anisotropy beryllium film

The strong anisotropy beryllium （Be） films are fabricated at different sputtering pressures by direct current magnetron sputtering. With the increase of pressure, the deposition rate of Be film first increases, and when the pressure exceeds 0.8 Pa, it gradually descends. The X-ray diffraction analysis indicates that Be film is of α-Be phase, its surface always reveals the （101） crystal plane possessing the low surface energy. As for the growth morphology of Be film, the surface is mainly characterized by the fibrous grains, while the cross section shows a transition from a columnar grain to a mixed grain consisting of a cone-shaped grain and a columnar grain as the sputtering pressure increases. The large grain fraction decays exponentially from 75.0% to 59.3% with the increase of sputtering pressure p, which can improve the grain size uniformity. The surface roughness increases due to the insufficient atom diffusion, which is comparable to its decrease due to the etching effect at p 〈 0.8 Pa, while it increases drastically at p 〉 0.8 Pa, and this increase is dominated by the atom diffusion. The electrical resistivity values of Be films range from 1.7 μΩ m to 2.7 μΩ m in the range 0.4 Pa-1.2 Pa, which is 50 times larger than the bulk resistivity.     

Nitriding molybdenum： Effects of duration and fill gas pressure when using lO0-Hz pulse DC discharge technique

Molybdenum is nitrided by a 100-Hz pulsed DC glow discharge technique for various time durations and fill gas pressures to study the effects on the surface properties of molybdenum. X-ray diffractometry （XRD）, scanning electron microscopy （SEM）, and atomic force microscopy （AFM） are used for the structural and morphological analysis of the nitrided layers. Vickers＇ microhardness tester is utilized to investigate surface microhardness. Phase analysis shows the formation of more molybdenum nitride molecules for longer nitriding durations at fill gas pressures of 2 mbar and 3 mbar （1 bar = 105 Pa）. A considerable increase in surface microhardness （approximately by a factor of 2） is observed for longer duration （10 h） and 2-mbar pressure. Longer duration （10 h） and 2-mbar fill gas pressure favors the formation of homogeneous, smooth, hard layers by the incorporation of more nitrogen.     

脉冲管制冷机第三种直流敏感性实验研究

直流是脉冲管制冷机中重要的机理性问题。本文介绍了脉冲管制冷机第三种直流效应的最新理论研究结果,深入分析了第三种直流效应的产生机理和影响因素。结合制冷机系统的流动和热力学非对称性,通过实验研究了脉冲管制冷机第三种直流效应对几何结构、冷头温度、频率、压力等参数的敏感性。     

Effects of Annealing on Schottky Characteristics in A1GaN/GaN HEMT with Transparent Gate Electrode

A1GaN/GaN heterostructure transistors are promising for power and switching applications. In addition, the transparent wide band-gap A1GaN/GaN heterostructure systems have received considerable attention to transparent electronics. Nowdays, Al-doped ZnO （AZO） thin film plays an increas- ingly important role in various fields of transparent electronics.The AZO-gated A1GaN/GaN HEMT with good dc characteristics and frequency character- istics has been reported. Annealing is widely used to improve the electri- cal characteristics of A1GaN/GaN HEMTs. It is re- ported that the Schottky leakage current can be re- duced by over four orders of magnitude by annealing in an A1GaN/GaN heterostructure with ITO/Ni/Au electrode. Pei et al. reported that the transparency of Ni/ITO gates of A1GaN/GaN HEMTs has been sig- nificantly improved after annealing. However, the evaluation of Schottky C V characteristics was ab- sent. Up to now, few results are reported on the Schot- tky annealing characteristics of AZO in A1GaN/GaN HEMT. Thus the effects of annealing on the leakage current, transparency and interface states character- istics need further study.     

倾斜直流场下的介质板击穿统计分析

传统分析介质板次级电子倍增问题的粒子追踪算法方法存在运算耗时长、运算量大等缺点,为此采用统计方法实现了倾斜强直流场下介质击穿过程中次级电子倍增效应的数值模拟,给出了击穿过程中电子数量,电子渡越时间等关键参数的时间图像,同时研究了倾斜角、介质表面光滑度和次级电子产生率对次级电子倍增效应的影响。研究结果表明:强直流场下的次级电子倍增效应存在倾斜角的区域,倾斜角太大或者太小,都可能不会发生次级电子倍增效应,如果倾斜角位于区域内,则饱和状态时电子数目随着倾斜角度的变大而变小;选取光滑系数和次级电子产生系数越小的介质材料,抑制次级电子倍增效应的效果越好。     

高择优取向Mo薄膜的直流磁控溅射制备及其电学性能

使用直流磁控溅射法在玻璃基底上沉积Mo薄膜,采用X射线衍射仪、原子力显微镜和四探针测试系统研究了溅射工艺对Mo薄膜的结构、形貌和电学性能的影响.结果表明:当基片温度为150 ℃时,薄膜获得(211)晶面择优取向生长,而在低于250 ℃的其它温度条件下,样品则表现为(110)晶面择优取向生长.进一步的表面形貌分析显示:薄膜的粗糙度随基片温度变化不明显,其值大约为0.35 nm,随溅射功率密度的增大而变大|电学性能方面:随着溅射功率密度的升高,薄膜导电性能迅速增强,电阻率呈现近似指数函数衰减|随着基底温度的升高,薄膜的电阻率先减小后增大,当基底温度为150 ℃时,薄膜电阻率降低至最小值2.02×10-5 Ω·cm.     

发射光谱研究多针对板电晕放电O活性原子特性

利用发射光谱技术在大气压下测量了空气中多针对板负直流电晕放电和正电晕流光放电产生的O(3p5 P→3s 5 S02777.4nm)活性原子发射光谱。在负电晕放电中,研究了放电功率、电极间距、N2含量和相对湿度等因素对O活性原子产生过程的影响;在正电晕流光放电阶段,研究了O活性原子相对密度在放电反应空间的分布特点。结果表明:O活性原子产量随放电功率的增加而增大,随电极间距增大而减少,随相对湿度和氮气含量的增加,其产量先增大后减少;O活性原子相对密度沿针尖轴向呈先增大后减小的趋势。