Dielectric characteristics of cation deficient TbMnO3

Cation deficient polycrystalline Tb_1−xMnO₃ (x= 0.05, 0.10) and TbMn_1−yO₃ (y =0.05, 0.10) samples were fabricated by conventional solid-state reaction. The complex dielectric properties of the cation deficient TbMnO₃ were investigated as the function of temperature (77 K≤T≤350 K) and frequency (100 Hz≤ f≤ 200 kHz) separately. Compared to the parent TbMnO₃, the cation deficient TbMnO₃ samples exhibit not only high dielectric constant but also low dissipation factor. Nyquist plots of complex impedance show that the dielectric properties originate from two main relaxation sources, i.e. bulk contributions and grain boundary effects.     

Highly efficient double-ended diffusion-bonded Nd:YVO4 1525-nm eye-safe Raman laser under direct 880-nm pumping

A highly efficient 880-nm diode-pumped actively Q-switched eye-safe laser at 1525 nm with a double-ended diffusion-bonded YVO₄–Nd:YVO₄–YVO₄ crystal as the self-Raman medium is demonstrated. As high as 19.2% diode-to-Stokes optical conversion efficiency is obtained with an absorbed pump power of 5.2 W at a pulse repetition rate of 20 kHz.     

激光诱导击穿光谱定量分析中的分析线自动选择方法

为了实现激光诱导击穿光谱分析中的分析线自动选择,定义了元素发射谱线的相对强度比(RDTIR)、波长偏差(WDDT)两个参数,并据此对检测谱线进行筛选,通过设定合理的阈值,剔除自吸收和干扰严重的谱线。通过对高合金钢(GBW01605)实验数据的分析,分别选定了样品中主要元素铁、铬、镍、锰、铜的分析线,选线结果符合谱线的选取原则。     

Kinetics of crystallization process of Mg–Cu–Gd based bulk metallic glasses

The crystallization behavior of Mg₆₁Cu₂₈Gd₁₁ and (Mg₆₁Cu₂₈Gd₁₁)₉₈Cd₂ bulk metallic glasses was studied using DSC in the mode of continuous and isothermal heating, and its crystallization process and microstructure were confirmed by XRD and TEM. In continuous heating, the activation energies of glass transition, onset and peak crystallization were determined by the Kissinger method, which yields 110 ± 12, 77 ± 9 and 79 ± 10 kJ/mol, respectively, for Mg₆₁Cu₂₈Gd₁₁ glassy alloy, and 144 ± 10, 126 ± 6 and 131 ± 5 kJ/mol, respectively, for (Mg₆₁Cu₂₈Gd₁₁)₉₈Cd₂ glassy alloy. The isothermal kinetics was modeled by the Johnson-Mehl-Avrami equation. The Avrami exponent of the base alloy was in the range from 1.98 to 2.56 (± 0.01), which indicated a decreasing nucleation rate and a diffusion-controlled growth. For Cd-added glassy alloy, the Avrami exponent was in the range from 3.26 to 4.08, which indicated an increasing nucleation rate. The activation energies in isothermal process were calculated to be 88 ± 2 and 132 ± 2 kJ/mol, respectively, for the base and Cd-added glassy alloys. It was found that Mg₂Cu phase was the primary phase in the initial crystallization and the strong affinity between Cd and Mg/Gd tended to impose resistance to the formation of Mg₂Cu phase and thus improves the thermal stability.     

铂纳米颗粒生长和表面结构的理论预测

本文应用最近所建立的凝结势模型[2009物理学报583293;2009J.Chem.Phys.130164711]来确定铂纳米颗粒的表面结构,利用分子动力学模拟验证了该模型的可靠性.基于该模型所进行的第一性原理计算表明,各种形状的铂颗粒表面都以fcc的(111)面为主(约80%),(100)面形成的概率约10%,该结果与已有实验观测相符合.由于凝结势计算简单,该模型应是一种从理论上确定纳米颗粒表面结构的简便方法.     

非对称HALO掺杂栅交叠轻掺杂漏围栅MOSFET的解析模型

为抑制短沟道效应和热载流子效应, 提出了一种非对称HALO掺杂栅交叠轻掺杂漏围栅MOSFET新结构. 通过在圆柱坐标系中精确求解三段连续的泊松方程, 推导出新结构的沟道静电势、阈值电压以及亚阈值电流的解析模型. 结果表明, 新结构可有效抑制短沟道效应和热载流子效应, 并具有较小的关态电流. 此外, 分析还表明栅交叠区的掺杂浓度对器件的亚阈值电流几乎没有影响, 而栅电极功函数对亚阈值电流的影响较大. 解析模型结果和三维数值仿真工具ISE所得结果高度符合.     

原子光刻中驻波场与基片距离的判定方法研究

原子光刻实验中, 激光驻波场能起到原子透镜的效果, 实现原子汇聚. 激光驻波场与沉积基片间的距离对形成纳米条纹结构的质量具有重要影响. 利用高斯光束传播规律, 提出了一种能够定量判断激光驻波场与沉积基片相对位置的实验方法. 该方法通过调节装载有凸透镜和反射镜的精密位移台改变驻波场距基片的距离, 利用光电探测器接收反射光强的变化, 将位移改变量转变为接收器的电压信号. 利用驻波场激光束光斑直径值, 实现准确定位驻波场与基片的距离. 对上述实验过程进行数值模拟, 数值计算的结果和实验结果高度符合. 该方法实现了准确定位驻波场距基片的距离, 为后续深入研究驻波场和基片间距离对沉积纳米条纹结构质量的影响提供实验基础.     

多间隙气体开关绝缘子寿命

针对设计的一种堆栈式结构多间隙气体开关,分析了绝缘子污染对开关寿命的影响机理。对绝缘子表面电场分布进行了模拟计算,实验研究了绝缘子污染对开关自击穿电压的影响,得到了开关自击穿电压和绝缘子表面绝缘电阻的变化规律,开关在放电电流32 kA实验条件下工作13 000次后,自击穿电压平均值由171.5 kV降低至130.8 kV,绝缘子表面绝缘电阻由200 G下降至22.6 G,绝缘子已无法正常使用。同时提出了提高绝缘子抗污染能力、延长绝缘子寿命的措施和方法。     

2 MV激光触发气体开关实验研究

介绍了2 MV激光触发多级气体开关在强光一号加速器上的实验研究工作。给出了实验方案,激光触发信号采用轴向引入的方法,激光光路穿过二极管,沿水线轴向引入开关;分析了开关自击穿实验和触发实验的实验结果,总结了实验中出现的问题并对其原因进行了分析,提出了改进措施。 结果表明,开关最大工作电压2 MV,最大电流大于600 kA,当欠压比88.3%时,激光触发开关的平均延时34.2 ns,抖动小于3.86 ns。     

小型方波脉冲磁场装置的研制

完成了小型方波脉冲磁场装置的双线圈负载设计,在一定区域内获得了近似匀强磁场。采用阻抗2 的6级脉冲形成网络作为初级储能和脉冲形成单元,对匹配电阻放电产生了方波脉冲电流波形。研制了一种场畸变气体火花间隙作为主放电开关,有效减小了装置的动作时延和分散性。实验结果表明:负载中心峰值磁感应强度达到0.04 T,方波磁场平顶时间约3 s,平顶度小于5％,上升前沿（磁感应强度峰值10％～90％）小于0.5s,装置的动作时延抖动小于10 ns（标准偏差）。