拓扑绝缘体Bi_2Se_3中层堆垛效应的第一性原理研究

运用第一性原理方法,研究了拓扑绝缘体Bi_2Se_3块体和薄膜中的层堆垛对其结构、电子态、拓扑态和自旋劈裂的影响.发现不同的堆垛会引起Bi_2Se_3层间的相互作用,改变系统的中心对称性.块体的ABC和AAA堆垛都具有中心对称性和相似的能带结构.ABA堆垛破坏了体系的中心对称性,能带发生很大改变,并且产生了很大的能带自旋劈裂.用能带反转的方法判定体系的拓扑相,在不同堆垛的Bi_2Se_3块体中,考虑自旋轨道耦合时都发生了能带反转,因而具有不同堆垛的Bi2Se3仍是拓扑绝缘体.进一步研究了Bi_2Se_3薄膜中的堆垛效应,发现非中心对称的ABA堆垛在Bi_2Se_3薄膜中引起明显的自旋劈裂,并且提出和验证了用应变调控自旋劈裂的方法.     

Analysis of Atomic Electronic Excitation in Nonequilibrium Air Plasmas

Electronic excitation of atoms is studied in nonequilibrium air plasmas with the electronic temperature be- tween 8000 K and 2000OK. By using the modified Saha-Boltzmann equation, our simplified method takes into account significant radiative processes and strong self-absorption of the vacuum ultraviolet lines. Calculations are carried out at three trajectory points of the Fire 1I flight experiment. Good agreement with the detailed collisional-radiative model is obtained, and the performance of this method in applications to highly nonequi- librium conditions is better than Park＇s quasi-steady-state model and Spradian-9.0. A short discussion on the influence of optical thickness of the vacuum ultraviolet radiation is also given. It costs about 2.9 ms on the average to solve one cell of the shock layer on a low cost computer, which shows that the present method is fast and efficient.     

气相色谱法测定养殖环境沉积物中硫丹及代谢物残留

建立了养殖环境沉积物中α-硫丹、β-硫丹和硫丹硫酸盐残留的气相色谱测定方法.用丙酮和石油醚提取沉积物中的硫丹,用由下至上依次填充弗罗里硅土、活性炭和无水硫酸钠的玻璃层析柱净化提取物,浓缩后气相色谱(ECD检测器)检测.结果显示,浓度范围为0.500～100μg/L线性良好,最低检出限和最低定量限分别为0.9μg/kg和...     

三相中空纤维液相微萃取-离子色谱法测定环境水中苯酚含量

提出了离子色谱法测定环境水中苯酚含量的方法。样品采用三相中空纤维液相微萃取法萃取,以正辛醇为萃取溶剂,在600 r·min^-1转速下萃取40 min。经SH-2 Anion色谱柱分离,以12 mmol·L^-1氢氧化钠溶液为淋洗液洗脱。苯酚的质量浓度在1.00～500μg·L^-1范围内呈线性,方法的检出限（3S/N）为0.8μg·L^-1。方法用于地表水中苯酚的测定,加标回收率在90.1%～109%之间。     

沉积温度对等离子增强化学气相沉积法制备的SiNx:H薄膜特性的影响

利用Centrotherm公司生产的管式等离子增强化学气相沉积(PECVD)设备在p型抛光硅片表面沉积SiN_x:H薄膜, 研究沉积温度对SiN_x:H薄膜的组成及光学特性、结构及表面钝化特性的影响. 然后采用工业化的单晶硅太阳电池制作设备和工艺制作太阳电池, 研究不同温度制备的薄膜对电池电性能的影响. 测试结果表明: SiN_x:H薄膜的折射率随着沉积温度的升高而变大, 分布在1.926-2.231之间, 这表明Si/N摩尔比随着沉积温度的增加而增加; 当沉积温度增加时, 薄膜中Si－H键和N－H键浓度呈现减小趋势, 而Si－N键浓度逐渐升高, 薄膜致密度增加; 随着沉积温度的升高, SiN_x:H薄膜中的氢析出导致了钝化硅片的有效少子寿命先升高后降低, 并且有效少子寿命出现明显的时间衰减特性. 当沉积温度为450 °C时, 薄膜具有最优的减反射和表面钝化效果. 采用不同温度PECVD制备的5组电池的电性能测试结果也验证了这一结果.     

Hardness of Wurtzite-Structured Semiconductors

rickets hardness calculations of eleven wurtzite-structured semiconductors are performed based on the microscopic hardness model. All the parameters are obtained from first-principles calculations. There are two types of chemical bonds in wurtzite-structured crystals. The overlap populations of the two types of chemical bonds in lonsdaleite are chosen as Pe for wurtzite structure. The calculated bond ionicity values of the wurtzite-structured semiconductors are in good agreement with the ionicities from the dielectric definition. When the hardness of wurtzite-structured crystal is higher than 20 GPa, our calculated rickets hardness is within 10% accuracy. Therefore, the hardness of novel wurtzite-structured crystal could be estimated from first-principles calculations.     

自散焦向自聚焦转换中背景光作用的理论分析

理论分析了背景光辐照在光折变晶体中从自散焦向自聚焦特性转化过程中的作用,得到了R>1是不同类型（Δn<0和Δn>0）晶体中这种转变的条件.实验观察到了铌酸锂晶体中这种转变的现象.并依据Glass常量的光伏打效应表征意义,提出了光伏孤子形成过程中载流子的竞争效应模型.基于此,分析了折射率变化为负的光生伏打晶体在背景光和信号光Glass常量比大于1条件下的载流子竞争效应,得到了与实验现象和已知理论分析相一致的结论.研究表明,背景光引起的载流子竞争效应是影响晶体自散焦向自聚焦特性转换的内在物理本质.     

有温度反馈阶跃引入负反应性瞬变的解

考虑有温度反馈反应堆阶跃引入负反应性过程的变化规律,对点堆中子动力学方程的解进行研究,给出不同的分析模型,分析发现,（1）用于瞬发超临界的分析模型及其结果不能用于引入大的负反应性过程的分析.（2）在相同的初始功率时,先驱核瞬跳近似模型的结果要优于目前比较普遍的中子瞬跳近似模型的结果.（3）无论初始功率与引入负阶跃反应性的大小,温度瞬跳近似模型的结果总是优于先驱核瞬跳近似与中子瞬跳近似模型的结果.故而温度瞬跳近似模型是目前最为准确的解析模型.     

Delay Effect on Coherent Transfer of Optical Frequency Based on a Triple-Pass Scheme

We demonstrate a triple-pass scheme for coherent transfer of optical frequency and the delay effect on the fiber phase noise compensation. It is theoretically proved that the delay effect consists of both fiber delay and servo delay. The delay effect confines the servo bandwidth within 1/8 and induces a residual fiber phase noise after noise compensation. For a 25-km-long fiber, the servo bandwidth is found to be around 1 k Hz, and the fiber phase noise is suppressed approaching to the theoretical limitation. The triple-pass scheme enables the simultaneous transfer of optical frequency to multiple remote users. The performance of noise compensator in the triple-pass scheme can achieve a similar level result compared with that in the double-pass scheme.