Growth and Characterization of the Laterally Enlarged Single Crystal Diamond Grown by Microwave Plasma Chemical Vapor Deposition

Laterally enlarged single crystal diamond is grown on(001) diamond substrates by microwave plasma chemical vapor deposition. Based on the largest side-to-side width of the seed of 7.5 mm, we achieve the as-grown epilayer with the width of about 10 mm between the same two sides. The luminescence difference between the broadened part of the single crystal diamond and the vertically epitaxial part is investigated by characterizing the vertical cross section of the sample, and the possible growth mechanism is suggested. Vertical epitaxy on the top(001)surface and lateral growth on the side surfaces occur simultaneously, and thus the growth fronts along the two directions adjoin and form a coalescence zone extending from the edge of the substrate towards the edge of the expanded single crystal diamond top surface. The luminescence intensity of the nitrogen-vacancy center is relatively high in the coalescence zone and a laterally grown part right below, which are attributed mainly to the higher growth rate. However, stress change and crystal quality change are negligible near the coalescence zone.     

一位值得纪念的普通物理学工作者——悼春先老友

春先走得十分突然.我一直以为他近来身体状况比较稳定,不会出意外.然而,他竟在刚刚跨入"古稀"的门槛时,匆匆离去.虽说杜甫曾经断言"人生七十古来稀",但现今科学昌明的时代,"古稀"不稀,已是普遍现象,春先此时离去,实在是早了点.     

二次电子衬度曲线法研究PVC/MBS共混物断面的分形特征

利用二次电子衬度曲线法测定了聚氯乙烯甲基丙烯酸甲酯丁二烯苯乙烯共聚物(PVCMBS)共混物冲击断面的形貌特征及对应的分形维数值.结果表明,材料的断口或微观结构并不是严格的分形结构,这种自相似性仅存在于一定尺码范围内,不同断面形貌特征所对应的分形维数测量值不同,随着MBS用量增加,PVCMBS共混物缺口冲击强度随满足自相似原理的形貌特征所对应的分形维数值增大而增大.本文从理论上讨论了材料断裂韧性与分形维数的关系.     

Temperature dependence of single event transient in 90-nm CMOS dual-well and triple-well NMOSFETs

This paper investigates the temperature dependence of single event transient (SET) in 90-nm complementary metat-oxide semiconductor (CMOS) dual-well and triple-well negative metal-oxide semiconductor field-effect transistors (NMOSFETs). Technology computer-aided design (TCAD) three-dimensional (3D) simulations show that the drain current pulse duration increases from 85 ps to 245 ps for triple-well but only increases from 65 ps to 98 ps for dual-well when the temperature increases from -55℃ to 125℃, which is closely correlated with the source of NMOSFETs. This reveals that the pulse width increases with temperature in dual-well due to the weakening of anti-amplification bipolar effect while increases with temperature in triple-well due to the enhancement of the bipolar amplification.     

对某惯性设备随动系统参数改进设计及性能分析

某惯性设备随动系统刚度偏低,控制精度较差,同时在使用过程中常会由于系统的个性差异导致系统稳定性变差,直接影响系统的使用。为此对控制系统进行了数学建模,用Matlab对系统进行了仿真和幅频/相频特性的分析,对系统进行了改进设计,大大提高了系统刚度和控制精度;并通过大量的仿真、实验和数据分析,对实际工作中由于系统个性差异引起的系统稳定性变差、稳定时间变长等问题提出了切实可行的解决方法。试验结果表明：系统的精度由原来的1.2°提高到0.3°,超调量由原来的50%降低到30%,满足总体性能要求。     

月尘静电浮扬现象的理论模拟

对月球上的月尘静电浮扬现象进行了理论研究,对比分析了影响月球表面静电浮扬强弱的主要因素．研究过程分为两个步骤:首先采用一维PIC（particle in cell）模拟计算了月尘和月球表面的充电过程,然后基于这一结果引进试验粒子,对月尘的静电浮扬现象进行了分析研究．结果表明月尘的静电浮扬主要受两个因素的影响:太阳角和月尘颗粒的大小．月尘静电浮扬现象在日出日落时分更容易发生,即太阳角越小越容易引起剧烈的月尘浮扬现象;并且月尘粒径越小,其浮扬高度越高．     

AlGaN/GaN MIS-HEMT using NbAlO dielectric layer grown by atomic layer deposition

We present an AlGaN/GaN metal-insulator-semiconductor high electron mobility transistor (MIS-HEMT) with an NbAlO high-k dielectric deposited by atomic layer deposition (ALD).Surface morphology of samples are observed by atomic force microscopy (AFM),indicating that the ALD NbAlO has an excellent-property surface.Moreover,the sharp transition from depletion to accumulation in capacitance-voltage (C-V)curse of MIS-HEMT demonstrates the high quality bulk and interface properties of NbAlO on AlGaN.The fabricated MIS-HEMT with a gate length of 0.5 μm exhibits a maximum drain current of 960 mA/mm,and the reverse gate leakage current is almost 3 orders of magnitude lower than that of reference HEMT.Based on the improved direct-current operation,the NbAlO can be considered to be a potential gate oxide comparable to other dielectric insulators.     

氮化物MOCVD反应室流场的仿真与分析

在立式MOCVD反应室中,通过对生长氮化镓(GaN)薄膜材料的仿真,发现衬底表面反应物三甲基镓物质的量的浓度分布与实际生长的GaN薄膜的厚度分布一致,同时,仿真结果表明,薄膜的厚度分布与反应室内涡旋的分布相关.通过分析涡旋产生的原因,对反应条件和反应室的几何条件作了进一步优化,发现在较低的反应室压强、较低的壁面温度和较大的气体入口半径条件下,能使涡旋明显减小,提高薄膜生长的均匀性.     

立式MOCVD反应室中一种刻槽基座的热分析

在立式感应加热的氮化物MOCVD反应室中, 提出了一种刻槽结构的基座;利用有限元法,给出了使衬底温度分布最均匀的槽的位置和大小.与传统的基座相比,这种刻槽优化后的基座,使衬底温度分布的均匀性显著提高.另外,通过对基座温度随加热时间变化的分析,发现刻槽基座的热传导规律,即刻的槽改变了基座中感应产生热量的热传导方向,衬底中的热量是由槽上下基座部分传递而来的,且随时间的增大,基座的温度趋于恒定,衬底的温度趋于均匀,均匀的衬底温度有利于提高生长薄膜的质量.     

一种频率自适应的同步相位与对称分量检测方法

电网不对称故障时,快速、准确地检测同步相位和对称分量是电力电子装置实现控制与保护的关键问题之一.分析了负序分量对传统三相锁相环检测性能的影响,设计了一种频率自适应的同步相位与瞬时对称分量检测新方法.该方法利用瞬时对称分量理论在两相静止坐标系下实现对称分量的实时检测,利用广义二阶积分器实现90°相移,用测得的基波正序电压q轴分量作为锁相环的输入,用锁相环的输出角频率作为相移电路的谐振角频率,达到谐波抑制与频率自适应跟踪,是一个闭环的实时检测系统.分析了该方法的实现机理,给出了检测电路的实现框图,进行了实验验证.结果表明,该方法既能在被测电压不对称时准确检测同步相位和对称分量,又能消除电压频率变化对检测同步相位和对称分量的影响.