He离子辐照6H-SiC引入缺陷的光谱研究

实验采用300 keV的He²⁺辐照6H-SiC,辐照温度分别为室温,450,600和750 ℃,辐照剂量范围为1×10¹⁵–1×10¹⁷ cm^-2,辐照完成后对样品进行拉曼散射和紫外可见透射光谱测试与研究. 这两种分析方法的实验结果表明,He离子辐照产生的缺陷以及缺陷的恢复与辐照剂量和辐照温度有着直接关系. 室温下辐照会使晶体出现非晶化,体现在拉曼特征峰消失,相对拉曼强度达到饱和(同时出现了较强的Si-Si峰);高温下辐照伴随着晶体缺陷的恢复过程,当氦泡未存在时,高温辐照很容易导致Frenkel对、缺陷团簇等缺陷恢复,当氦泡存在时,氦泡会抑制缺陷恢复,体现在相对拉曼强度和相对吸收系数曲线斜率的变化趋势上. 本文重点讨论了高温辐照情况下氦泡对缺陷聚集与恢复的影响,并与高温下硅离子辐照碳化硅结果进行了对比. 关键词： 6H-SiC 氦泡 拉曼散射光谱 紫外可见透射光谱     

圆柱体骰子最终面朝向概率的研究

下落物体的最终静止状态取决于物体的几何特征、运动状态、材料特性等多种因素.本文以圆柱体骰子为研究对象,基于动力学模型,探究了圆柱体骰子初始速度、角速度、高度、质量以及恢复系数等因素对骰子落地后最终面朝向的影响,并探讨了使圆柱体骰子每一面最终朝向概率相等时应具有的几何特征和物理条件.本文结果可为此类研究提供思路和借鉴.     

四元正交探测器抗红外干扰弹干扰方法综述

介绍了四元正交探测器以及红外干扰弹的工作原理,对四元正交探测器导引系统抗红外干扰的7种方法(即时间相关选择和视场收缩技术、惯性跟踪机制、实时记忆准则、幅值鉴别法、脉冲宽度鉴别法、脉冲幅值序列鉴别法和脉冲宽度幅值鉴别法)等进行了讨论.最后给出了这7种抗红外干扰弹干扰方法的使用条件.     

Effects of Grain Boundary Characteristics on Its Capability to Trap Point Defects in Tungsten

As recombination centers of vacancies(Vs) and self-interstitial atoms(SIAs), firstly grain boundaries(GBs)should have strong capability of trapping point defects. In this study, abilities to trap Vs and SIAs of eight symmetric tilt GBs in tungsten are investigated through first-principles calculations. On the one hand, vacancy formation energy E~f_V rapidly increases then slowly decreases as the hard-sphere radius r_0 of the vacancy increases.The value of E~f_V is the largest when r_0 is about 1.38 ?, which is half the distance between the nearest atoms in equilibrium single crystal tungsten. That is, any denser or looser atomic configuration around GBs than that in bulk is helpful to form a vacancy. On the other hand, SIA formation energy E~f_(SIA) at GBs decreases monotonically with increasing the hard-sphere radius of the interstitial sites, which indicates that GBs with larger interstitial sites have stronger ability to trap SIAs. Based on the data obtained for GBs investigated in this study, it is found that the ability to trap Vs increases as the GB energy increases, and the capability of trapping SIAs linearly increases as the excess volume of GB increases. Due to its lowest GB energy and smallest excess volume among all GBs studied, twin GB ∑3(110)[111] has the weakest capability to trap both Vs and SIAs.