暗视场及相衬显微术及其对Nd:YAG晶体中缺陷研究

暗视场及相衬显微术的分辨率可达10～500(?),采用这两种技术可以十分清淅地观察到用引上法及温梯法生长的Nd:YAG晶体中的点缺陷集团,小尺寸位错环,蜷线位错,片状缺陷时精细结构.特别是观察到非缀饰刃位错及混台位错的图像.对非缀饰位错的观察已用化学腐浊,光双折射貌相术及X射线形貌术作了证明.     

α—SiC晶体中的位错

用腐蚀法和X射线形貌术研究了α-SiC晶体中的位错。所用的腐蚀剂为熔融氢氧化钾。证实了尖底蚀坑与位错的一一对应关系。由于[0001]方向的螺型位错的Burgers矢量比刃型位错的Burgers矢量大得多,故可从蚀坑的深浅来判别螺型位错和刃型位错。给出了蚀坑形状和多型体晶体结构的对应关系。研究了表面生长蜷线的形态与SiC晶体中的位错及位错运动的关系。X射线形貌图显示了α-SiC晶体中相当数量的位错处于基面C面上。生长位错从晶体“根部”成核并随着晶体生长前沿的向前推进而延伸,因而位错线的方向常常沿[101O]和[1120]方向。将腐蚀法和X射线形貌术结合起来才能全面显示α-SiC晶体中的位错。 关键词：     

BeAl_2O_4:Cr晶体的缺陷研究

用化学腐蚀、光学显微镜、X射线形貌术以及电子显微分析等方法研究了引上法生长的BeAl_2O_4:Cr晶体中的缺陷.其结果如下:1)获得了对低指数面(100)、(010)及(001)面位错的理想腐蚀剂,2)晶体中的位错分布不均匀,位错产生的来源有二:一是从晶种中,另一是由包裹物引起.大多数位错是刃型位错,其柏格氏矢量为〈100〉方向、滑移面为(010)面.3)在晶体中常出现的包裹物如气泡,管状物及第二相沉积物,它们是由于原料中的杂质及生长过程中的组分过冷引起的.     

LiNbO_3晶体中缺陷的X射线形貌研究

用X射线透射扫描形貌方法观察了直拉法生长LiNbO~3晶体中各种类型点阵缺陷,诸如铁电畴壁、生长层、位错、亚晶界和胞状组织等;用不同衍射矢量对[001]和[210]方向生长的晶体的形貌消象规律,结合X射线铁电异常散射效应和光学显微观察,讨论了晶体中180°铁电畴和生长层的衬度及其分布,并研究了LiNbO~3晶体中180°畴壁形成及其相互关系。     

LiNbO3晶体中缺陷的X射线形貌研究

用X射线透射扫描形貌方法观察了直拉法生长LiNbO₃晶体中各种类型点阵缺陷,诸如铁电畴壁、生长层、位错、亚晶界和胞状组织等;用不同衍射矢量对[001]和[210]方向生长的晶体的形貌消象规律,结合X射线铁电异常散射效应和光学显微观察,讨论了晶体中180°铁电畴和生长层的衬度及其分布,并研究了LiNbO₃晶体中180°畴壁形成及其相互关系。 关键词：     

直拉硅单晶原生微缺陷的观察

对沿<100>方向生长的p型和沿<111>方向生长的n型宏观无位错直拉硅单晶,用铜缀饰X射线形貌术和腐蚀法观察到两种不同类型的微缺陷,对n型硅单晶还观察到一种特殊组态的微缺陷。对观察到的微缺陷的分布、组态进行了初步的分析。本文首次采用X射线透射投影和截面形貌术对硅单晶原生微缺陷进行直接观察,获得了相应的微缺陷图。所观察到的微缺陷的组态、尺度、分布等与铜缀饰X射线透射形貌图所示结果一致。 关键词：     

GaAs/AlGaAs分子束外延材料的X射线双晶形貌观察

本文介绍了用非平行非对称(+、-)双晶X射线形貌术研究Ⅲ—Ⅴ族化合物外延晶体的设置和原理。分析了外延后形成的弯曲样品造成的衍射效应。对分子束外延(MBE)法生长的GaAs/AlGaAs衬底和外延层分别进行了X射线形貌术观察。讨论了外延层中存在的失配位错、生长小丘、沾污和局部微差取向等缺陷。对位错的组态和来源进行了初步分析。本实验结果也表明,有应变超晶格过渡层的MBE法对生长优质的GaAs/AlGaAs外延片是有利的。     

钇铝石榴石单晶缺陷的X射线透射形貌术观察

对提拉法生长的YAG单晶首次用X射线透射形貌术观察。揭示了YAG单晶的生长条纹、奇异小面以及垂直于生长条纹的位错线束等生长缺陷,并对这些缺陷作了简要的分析。 关键词：     

合成氟金云母单晶缺陷的X射线研究

本文报道了人工合成大面积氟金云母单晶中缺陷的X射线研究结果。X射线劳厄法的研究表明,在合成云母中存在着较大程度的一维无序,并因而出现许多堆垛错排区及其亚晶界。X射线衍射形貌术的研究表明,合成云母中的亚晶界和位错线大部分是从晶种起源并向生长表面的法线方向延伸的。晶体的靠近表面的区域缺陷较密集,中心部分较少。探讨了合成云母与天然云母中缺陷分布的差别。对用于制作电容器的合成云母片的缺陷与性能的关系作了分析和讨论。 关键词：     

磷酸铝(AlPO_4)晶体中缺陷的X射线形貌研究

用X射线衍射形貌法研究了AlPO_4晶体中的微观缺陷。在所研究的晶体中,主要晶体缺陷是生长层,沉淀物和位错。位错密度在晶体表面附近最大,晶体中部较低。位错主要起源于热应力和由沉淀物或生长层所造成的晶格畸变。多数位错的柏氏矢量是b=(a+c)<1123>型,部分的是b=a[2TT0]。分析了晶体缺陷与生长条件之间的关系。控制生长过程中的温度波动,特别是晶体出炉时的冷却速度,对提高晶体完美性是重要的。     

用阴极发光显微术研究YAG:Nd~(3+)晶体中的缺陷

采用扫描电子显微镜中的阴极发光显微术获得了YAG:Nd~(3+)激光晶体中不同缺陷所形成的显微发光图象。据此进一步分析了这些缺陷的形成机制及其对材料性能的影响。     

Effect of XeCl laser irradiation on the defect structure of Nd:YAG crystals

This paper presents the effect of XeCl laser irradiation on Nd:YAG single crystal samples with various number of pulses at different repetition rates and laser fluences. Effects of the irradiation on the optical and structural properties of the crystal are analyzed by UV–vis-NIR spectroscopy. Annihilation of some point defects of the crystal structure is observed following laser irradiation at a fluence of 100 mJ cm⁻² with 100 and 500 pulses. Increasing the laser fluence and pulse numbers leads to saturation and new defects are found to be formed in the crystal. Additional absorption spectra of the irradiated samples show that oxygen vacancies in the Nd:YAG crystals are removed during the low-dose irradiation. The laser irradiation is compared to the thermal annealing process for Nd:YAG crystal modification. Additional absorption spectrum of an annealed sample reveals that induced negative absorption band at 236 nm is correlated with the annihilation of the oxygen vacancy center. Our results also demonstrate that XeCl laser treatment has several advantages upon annealing at high temperatures in the Nd:YAG crystal quality improvement. Thus, the present work can give a new approach to modify Nd:YAG crystals to be used in a wide variety of solid-state laser engineering.     

直拉法生长的GGG和YAG单晶体中螺型位错的双折射像

在直拉法生长的GGG和YAG单晶体中,从实验上首次获得了沿位错线观察的(viewed end-on)螺型位错的双折射像,确立了沿位错线观察和垂直于位错线观察(viewed from the side)的双折射像间的一一对应关系,以及与蚀斑间的一一对应关系,并基于石榴石晶体弹-光性质的各向异性,给出了沿位错线观察的螺型位错双折射像的成像规律,得到了理论与实验一致的结果。 关键词：     

Optical and ESR study of Nd:YAG transparent polycrystalline ceramics

In this Letter, ceramic Nd:YAG is charactrizeby electron spin resonance(ESR) measurements. The ESR results indicate that the polycrystalline ceramic Nd:YAG has barely native defects and impurity ions localization defects, compared to an Nd:YAG crystal with the same Nd doping concentration, due to its density structure by sintering in a vacuum pure raw material and additives during the fabrication. It may conclude that the high quality ceramic Nd:YAG may have greater ability on optical characteristic, mechanical performance,and laser damage than that of the crystals, which is a promising candidate to use on laser diode-pumped solid-state lasers.     

4H-SiC同质外延的绿带发光与缺陷的关系

利用室温光致发光谱(PL)对CVD法生长的4H-SiC同质外延特性进行研究,发现有绿带发光(GL)特性.用扫描电子显微镜(SEM) 、二次离子质谱(SIMS)和X射线光电子谱(XPS)技术获得了4H-SiC样品纵截面形貌和元素相对含量分布.结果表明,GL与4H-SiC晶体中碳空位(V_C)及络合体缺陷相关,V_C和缓冲层的扩展缺陷(点缺陷和刃位错等)是GL微观来源.GL的半峰宽(FWHM) 反映了参与复合发光的V_C及其络合缺陷能级分散的程度.室温下获得的样品GL强度和光谱波长度可用于分析4H-SiC外延中缺陷分布和晶体质量. 关键词： 绿带发光 4H-SiC同质外延 晶体缺陷     

Application of the model of an edge dislocation in the form of a uniformly charged filament for description of light diffraction from alkali halide and covalent crystals

The interaction of an optical electromagnetic wave with a system of parallel charged edge dislocations in alkali halide and covalent crystals is studied. The optical activity of dislocations is associated with the existence of shielding clouds of mobile point defects with a radius of the order of the wavelength of incident light. Expressions relating the amplitude of the diffracted wave to the parameters of crystal defects (the density of point defects and the density and linear charge of dislocations) are obtained. Methods for the experimental estimation of defect parameters from the characteristics of the diffraction pattern are proposed.     

Growth,structural, spectral and optical studies on 2,4-dinitrophenol organic single crystal

Single crystals of 2,4-dinitrophenol were grown by slow evaporation solution growth technique in room temperature. Crystallinity of the grown crystal was confirmed by powder X-ray diffraction technique. UV transmission study shows the good optical transmission in the entire visible region. The dielectric loss is very low at high frequency which shows that the crystal contains low level defects. Photoconductivity reveals the positive nature of the photocurrent in these crystals. The powder second harmonic generation test was also carried out using Q-switched Nd:YAG laser.     

直拉法生长Y3Al5O12(YAG)单晶体中的位错和包裹物

通过光双折射貌相法研究了YAG单晶体中位错、包裹物以及生长层间的关系,结果表明,包裹物优先吸附于固液界面上的位错露头点,而包裹物的大小与该处生长台阶的大小有关。 关键词：     

Microhardness studies on melt-grown single-phase mixed (NaK)Cl and solution-grown two-phase NaClKCl crystals

Microhardness studies were carried out on melt-grown (NaK)Cl crystals. The quenching strains and the difference in the ionic sizes of the cations constituting the mixed system introduced large numbers of defects, viz. dislocations, grain boundaries, etc. The etching experiments and supplementary X-ray studies clearly revealed that the Na⁺ or K⁺ ions are precipitated at the dislocation sites. These phase particles strongly interact with dislocations so as to obstruct the mobility of the latter contributing to the hardening mechanism. Results are compared with solution-grown two-phase mixed NaClKCl pure NaCl and pure KCl crystals.