二维磁振子晶体中点缺陷模的耦合性质研究

在超原胞近似下, 利用平面波展开法数值计算了多点缺陷的二维磁振子晶体带结构及其部分缺 陷模的磁化强度场分布. 研究结果表明, 点缺陷模间的能量发生了耦合, 使自旋波沿着缺陷方向传播. 利用该性质可将含多点缺陷体的二维磁 振子晶体作为自旋波导波器件的制作材料.     

Pre-irradiation effect on the defect formation in CdS-Ni subjected to electrodeless discharge

Samples of CdS: Cu, Pb were subjected to electrodeless discharge wherein the samples washed with Ni nitrate solution showed different absorption peaks near the absorption edge as compared to the samples which were previously irradiated, washed with Ni nitrate solution and again irradiated.     

近红外量子点的发光机理研究

近红外量子点具有独特的光学性质,如荧光量子产率高,荧光寿命长,荧光发射波长可调,半峰宽窄且斯托克斯位移较大,耐光漂白能力强等, 及“近红外生物窗口”的优势,使它们在生物荧光标记、太阳能电池、量子化计算、光催化、化学分析、食品检测及活体成像等领域具有巨大的潜在应用价值。目前对近红外量子点的发光机理研究还不够完善,针对国内外的研究现状,重点对核/壳结构的量子点(CdTe/CdSe,CdSe/CdTe/ZnSe等)、三元量子点(Cu-In-Se,CuInS₂等)和掺杂型量子点(Cu∶InP等)三种不同类型近红外量子点的发光机理进行了综述。其中,Type-Ⅱ型核/壳结构量子点的发光机理多为带间复合发光,三元量子点以本征缺陷型发光为主,掺杂型量子点多为杂质缺陷型发光。探讨了近红外量子点发光原理存在的问题及发展的方向。对近红外量子点的发光机理进行系统地研究不仅有助于我们理解近红外量子点的发光性质,而且对完善相似高品质量子点的合成方法具有重要意义。     

Possible isotope effect on Frenkel defect production in ionic crystals

An argument is given for the possibility that differing isotope masses for anions in ionic crystals cause a sizeable effect in defect production.     

Theoretical analysis of the influence of flexoelectric effect on the defect site in nematic inversion walls

Based on the experimental phenomena of flexoelectric response at defect sites in nematic inversion walls conducted by Kumar et al., we gave the theoretical analysis using the Frank elastic theory. When a direct-current electric field normal to the plane of the substrate is applied to the parallel aligned nematic liquid crystal cell with weak anchoring, the rotation of ± 1 defects in the narrow inversion walls can be exhibited. The free energy of liquid crystal molecules around the +1 and-1 defect sites in the nematic inversion walls under the electric field was formulated and the electric-field-driven structural changes at the defect site characterized by polar and azimuthal angles of the local director were simulated. The results reveal that the deviation of azimuthal angle induced by flexoelectric effect are consistent with the switching of extinction brushes at the +1 and-1 defects obtained in the experiment conducted by Kumar et al.     

Hole‐extraction layer dependence of defect formation and operation of planar CH3NH3PbI3 perovskite solar cells

Three planar CH₃NH₃PbI₃ (MAPbI₃) solar cells having the same structure except a hole‐extraction layer (HEL) showed distinctive difference in operation characteristics. Analysis of frequency‐dependent capacitance and dielectric‐loss spectra of the three MAPbI₃ devices showed two types of recombination‐loss channels with different time constants that we attributed respectively to interface and bulk defects. Discrepancy in defect formation among the three devices with a HEL of PEDOT:PSS, NiO_x, or Cu‐doped NiO_x was not surprising because grain‐size distribution and crystalline quality of MAPbI₃ can be affected by surface energy and morphology of underlying HELs. We were able to quantify interface and bulk defects in these MAPbI₃solar cells based on systematic and simultaneous simulations of capacitance and dielectric‐loss spectra, and current–voltage characteristics by using the device simulator SCAPS.

     

研究激光激发的声表面波与材料近表面缺陷的振荡效应

根据激光激发声表面波的热弹运动方程及热传导方程, 采取有限元技术对方程进行求解, 得到声表面波传播波形图. 当声表面波经过近表面缺陷时, 声表面波与近表面缺陷之间产生一种振荡效应, 通过近表面缺陷的振荡波形幅值存在一个逐渐增加后又逐渐减小的过程. 当声表面波经过不同深度的近表面缺陷时, 振荡信号中心频率存在一定的变化规律. 数值仿真结果表明: 当近表面缺陷深度从0.1 mm到0.5 mm变化时, 振荡效应产生的振荡信号中心频率从0.4 MHz到0.76 MHz变化, 振荡信号中心频率与近表面缺陷深度呈近似线性关系, 这为近表面缺陷的定量检测提供了一种理论基础.     

聚乙烯薄膜中空间电荷短路放电复合率的发光法研究

通过对在直流高压作用下低密度聚乙烯薄膜中注入的空间电荷的短路放电发光测量,研究了聚乙烯薄膜中空间电荷的复合率.通过短路放电光子数的测量及定量分析考察了电压极性、场强大小及加压时间对短路下电荷复合率的影响.结果表明发光强度（复合率）随外加场强的变化明显,而与加压时间的关系不显著.但场强高于80 MV/m时发光强度（复合率）的增大速度变慢.结合本实验结果及他人的相关数据,得出了聚乙烯薄膜样品的发光效率约为5.9×10^-6,短路初始阶段的0.2 s内样品的电荷复合率约为2.8%. 关键词： 空间电荷 短路放电 复合发光 复合率     

Investigation of defect luminescence from multicrystalline Si wafer solar cells using X‐ray fluorescence and luminescence imaging

Multicrystalline silicon wafer solar cells reveal performance‐ reducing defects by luminescence. X‐ray fluorescence spectra are used to investigate the elemental constituents from regions of solar cells yielding reverse‐bias or sub‐bandgap luminescence from defects. It is found that a higher concentration of metals is present in regions yielding reverse‐bias electroluminescence than in regions yielding sub‐bandgap electroluminescence. This suggests, dislocations do not create strong breakdown currents in the absence of impurity precipitates.

     

Photoluminescence of a BaSiO3:Yb3+ crystal

We present the results of a study of the luminescence and luminescence excitation spectra, and also the luminescence kinetics of a BaSiO₃:Yb³⁺ crystal. We have established the mechanism for emission by the matrix and energy transfer from the matrix to the rare earth ion. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 73, No. 4, pp. 478–482, July–August, 2006.     

氮掺杂金刚石{100}晶面的缺陷发光特性

氮是金刚石中最常见的杂质之一, 其对金刚石的缺陷发光具有重要的影响. 氮可以与金刚石中的本征缺陷形成复合缺陷. 本文首先利用阴极射线发光照片(CL)对一个高温高压合成的氮掺杂金刚石进行表征, 发现{100}晶面为蓝色, 然后利用透射电子显微镜(TEM)对该晶面进行电子辐照及后续退火处理, 以引入本征点缺陷进而形成含氮的复合缺陷, 并利用低温光致发光光谱(PL光谱)表征其缺陷发光特性, 发现该晶面主要以氮-空位复合缺陷(NV中心)发光为主, 并伴随着较弱的503 nm发光. 关键词： 金刚石 缺陷 发光     

Si3O cluster: excited properties under external electric field and oxygen-deficient defect models

This paper investigates the excited states of Si₃O molecule by using the single-excitation configuration interaction and density functional theory. It finds that the visible light absorption spectrum of Si₃O molecule comprises the yellow and the purple light without external electric field, however all the visible light is included except the green light under the action of external electric field. Oxygen-deficient defects, which also can be found in Si₃O molecule, have been used to explain the luminescence from silicon-based materials but the microstructures of the materials are still uncertain. Our results accord with the experimental values perfectly, this fact suggests that the structure of Si₃O molecule is expected to be one of the main basic structures of the materials, so the oxygen-deficient defect structural model for Si₃O molecule also has been provided to research the structures of materials.     

离子和冷却电子重组的高分辨谱研究(英文)

给出了在CRYRING重离子储存环上测量到的在很低能量下电子与离子重组的最新实验结果和有关速率系数增强的新的数据 .主要讨论类锂、类钠和类铜离子的共振双电子重组的新近测量结果 ,以及从这些共振谱中所导出的非常精确的离子能级劈裂值 ,从而将严格检验相对论效应、电子关联效应和量子电动力学效应 .其中 ,对类锂Kr3 3 + 离子 2s1/2 能级Lamb移位的确定精度达到了0 .1%. We present our latest results on recombination of electrons with ions at very low energies obtained at the CRYRING heavy-ion storage ring. New data on the enhanced rate coefficient are shown. Then we concentrate on recent measurements of dielectronic recombination resonances with Li-like, Na-like, and Cu-like ions, where from the spectra of resonances very accurate values for energy splittings are derived for crucial tests of relativistic, correlation, and QED effects.     

Low-temperature thermoluminescence study of GaSe:Mn layered single crystals

Mangan doped GaSe single crystals have been studied by thermoluminescence measurements performed with various heating rates between 0.4 and 1.0 K/s in the temperature range of 10?300 K. Thermoluminescence spectra exhibited four distinguishable peaks having maximum temperatures at 47, 102, 139 and 191 K revealing the existence of trapping levels in the crystals. Curve fitting and initial rise methods were applied to observed peaks to determine the activation energies of four trapping levels. Capture cross-sections of each level were also evaluated using the obtained energy values. Moreover, heating rate dependencies of the obtained peaks were investigated. It was shown that increase in the heating rate resulted in the decrease in thermoluminescence intensity and shift of the peak maximum temperatures to higher values. Discrete, single trap behaviour was established for acceptor level related with the peak at 191 K by analysing the sequentially obtained peaks with different stopping temperatures between 15 and 65 K.     

A Debye model for point defects in aluminosilicate crystals

Summary In aluminosilicate lattices, exchanges between silicon and aluminum ions are expected to originate charged point defects of opposite signs. Thermodynamic arguments, based on a model analogous to the Debye electrolyte model, allow evaluation of the equilibrium density of defects as a function of temperature. The electric field of point defects is found to be screened by charge distribution even at distances small enough to affect the ground-state energy of electrons trapped by the defect positive charges. Calculations show that large fluctuations of trapped electron energy are expected. These results agree with data from thermoluminescence experiments on different aluminosilicates, which showed broad distributions of electron traps.     

N vacancy,substitutional O,and AI defects in the bandgap of composition-tunable nonstoichiometric AIN powder

AlN powders are prepared by direct nitridation via Al liquid and vapor phases in mixed atmospheres of N2 and NH3 with different NH3/N2 ratios. The reaction analysis reveals that NH3 acts as catalyst for N2 dissociation and the transportations of N, O, and Al in the liquid phase are different from those in the vapor phase. Accordingly, the products are Al-rich and composition-tunable nonstoichiometric AlN in which N, O, and Al content values change with nitridation atmosphere and temperature, leading to the variation of the relevant defect concentration. Therefore, the AlN powders exhibit prominent absorption bands around 5.30, 3.40, and 1.50 eV, which are tentatively assigned to VN, ON donors, and AlN acceptor respectively. Furthermore, a new donor named [VN-ON] complex is predicted at 4.40 eV within the 5.90 eV bandgap. It is demonstrated that the optical spectra of nonstoichiometric AlN are preferable to the nominal stoichimometric one for the identification of the defects energy level.     

Effect of point defect concentration in NaCl and LiF crystals on the saturation field of the magnetoplastic effect

The effect is studied of the calcium impurity concentration in NaCl crystals and of preliminary x-ray irradiation of NaCl and LiF crystals on the magnetic saturation field B₀ characterizing the transition from the conventional proportionality of the dislocation mean path length l to the magnetic induction B squared(l∝B²) to saturation (l=const). B₀ is shown to increase with the calcium concentration in NaCl crystals and with the dose of x-ray irradiation of NaCl and LiF. This finding indicates that the dislocation breakaway from local defects in weak magnetic fields is controlled by the mechanism of longitudinal spin relaxation in a system of radical pairs that form due to interaction between dislocation cores and paramagnetic centers.     

二维过渡金属硫族化合物中的缺陷和相关载流子动力学的研究进展

原子级厚度的单层或者少层二维过渡金属硫族化合物因其独特的物理特性而被寄希望成为下一代光电子器件的重要组成部分.然而,二维材料的缺陷在很大程度上影响着材料的性质.一方面,缺陷的存在降低了材料的荧光量子效率、载流子迁移率等重要参数,影响了器件的性能.另一方面,合理地调控和利用缺陷催生了单光子源等新的应用,因此,表征、理解、...     

Localized vibrational modes of a persistent defect in ion-implanted SiC

The low-temperature luminescence spectrum of an intrinsic defect in ion-implanted cubic SiC reveals a number of high-energy localized modes. One has an energy of 164·7 meV, equivalent to the highest lattice frequency in diamond, and far above the 120·5 meV lattice limit of SiC. A carbon di-interstitial is a plausible model for the defect, which appears after a 1300°C anneal, and persists after a 1700°C anneal.     

光学膜层缺陷分布特征对损伤行为的影响

对多层介质反射膜与单层化学增透膜的损伤形貌、损伤过程及膜层的吸收特性进行了实验研究。结果表明：缺陷除了可以从其形态和光学特征分类外,还可以按缺陷的功能来划分,即以缺陷的损伤阈值来区分不同缺陷的抗激光损伤能力。通过对缺陷吸收率的测量,表明膜层的损伤阈值与缺陷的分布密度和热吸收具有显著的一致性。通过对损伤阈值分布曲线研究,可以有效地对缺陷进行分级判断,从而分析光学元件表面功能性缺陷的分布状况。