Effect of Impurity Concentration and Plastic Deformation on Dislocation Density of KCl Crystals

Using the etch pit technique both the distribution and density of dislocations in undeformed and dynamically deformed nominally pure and Sr²⁺ or Pb²⁺ doped KCl crystals are examined. Additionally, the role of specimen geometry in the plastic deformation within the I deformation stage is determined. For all the crystals examined the relationship between screw dislocation density and plastic flow stress obeys the formula τ ⋍ ϱ_sc.^1/2.     

Microhardness and Resistivity Anisotropy of ZnO Plastic Deformation

In the work is shown that hydrothermally grown ZnO crystals are characterized by the mosaic structure of ‘columnar’ type. The experimental and theoretical data about geometry of the slip systems in ZnO crystals are obtained and also anisotropy of the microhardness is measured.     

High-temperature Localization of Plastic Deformation in Lithium Fluoride Single Crystals

Experimental results on the superlocalization of plastic deformation at high strains and high temperatures in LiF single crystals are described. The physical conditions of transition to a localized plastic flow in the temperature range of 603 K to 1073 K T (0.53–0.94T_mp) using constant strain rate compression tests under strain rates from 10⁻³s⁻¹ to 10⁻²s⁻¹ are found. The results indicate that the deformation mechanism involves dislocation climb, controlled by diffusion. The connection of high temperature flow instability with an excessive concentration of point defects (strain vacancies) in zone of shear has been confirmed.     

Plastic Deformation of Cesium Iodide Single Crystals at High Temperatures

The plastic deformation of CsI crystals of three crystallographic orientations 〈100〉. 〈110〉. and 〈111〉 at temperatures from 423 to 773 K (0.5 to 0.86T_m) and strain rates from 2 × 10⁻³ to 10⁻⁵ s⁻¹ is studied. Four-stage stres-strain curves were found, three stages being more and more distinct with an increase in temperature up to 623 K above which stage III prevails. For all the temperatures, strain rates and oreintations studied the superplasticity features (jerky flow, deformation localization, active dynamical recovery etc.) were observed. The thermal activatoin analysis has shown that the rate of high temperature deformation of CsI is controlled by dislocation climb limited in its turn by mobility of cation vacancies (quasiviscous creep).     

Defect Structure in Te-doped GaAs single Crystals after Plastic Deformation (I). Twins and Stacking Faults

At temperatures above the brittle-to-ductile transition (490 °C) in Te-doped GaAs three types of predominant defect configurations have been observed after uniaxial compression along a [001] direction: (i) twins and stacking faults (500 … 520 °C), (ii) slip zones of dislocations (≈ 550 °C) and (iii) dislocation cells (580 … 590 °C). In Part I quantitative details of the appearance of twins and stacking faults are given. Most frequently found were 30° partials in twins and stacking faults.     

ZnWO4单晶衬底上ZnO薄膜的晶核发育与形貌分析

ZnWO4单晶的a晶面与氧化锌c晶面晶格匹配很好,是制备氧化锌薄膜的优良衬底.本文采用溶胶-凝胶法在ZnWO4单晶衬底上制备出透明的ZnO薄膜.通过光学显微镜对薄膜晶核发育过程和形貌进行了详细的分析.实验结果表明:在结晶刚开始,系统将经历成核--长大的过程,随着生长过程的进行,在主晶轴上(一次轴)上又长出二次轴、三次轴等等,最后逐渐形成树枝状晶核.由于ZnO晶核是在非平衡条件下生长的,故在晶核发育过程中又出现了三种不同的生长形态--成核生长、枝晶生长和分形生长.     

化学气相输运法制备ZnO晶体

采用化学气相输运法在常压开放系统中,以ZnO粉体为原料,HCl和NH3为输运气体,O2和H2O为反应气体,适度过量的HCl作为刻蚀性气体,在(0001)方向的蓝宝石籽晶片上制备了(0002)方向定向生长的ZnO晶体,且a、b轴生长速度明显高于c轴方向.以(0002)方向的ZnO籽晶片作基片,制备了ZnO单晶厚膜,晶体呈螺旋状外延生长,正极面的单晶摇摆曲线半高宽为543.6弧秒.     

How to Avoid Plastic Deformation in GaAs Wafers during Molecular Beam Epitaxial Growth

Plastic deformation in two‐inch diameter GaAs wafers resulted from standard thermal treatments which accompanied epitaxial growth in molecular beam epitaxy (MBE) machines of three different makes. Synchrotron based X‐ray transmission topography was used to distinguish between thermal treatment induced dislocation bundles and misfit dislocations. Eradication of the wafer slip related dislocation bundles has been achieved by modifications to the sample holder of a user built MBE machine. These modifications are discussed, the extent of the problem is briefly outlined, and an extrapolation of the susceptibility of GaAs wafers of higher diameters to this type of plastic deformation is given.     

The Real Structure of Ge Ions-implanted Si Crystals Subjected to Thermal Annealing

In the experiment an (111) oriented silicon plate was subjected to implantation by 80 keV Ge ions. Then, the thermal annealing of this sample was carried out in a vacuum of 5 · 10⁻⁸ Tr. The effectiveness of the annealing has been analyzed by means of X-ray topography, double crystal X-ray spectrometry and reflection high energy electron diffraction. The rocking curves in reflection and transmission as well as changes in anomalous absorption coefficient were measured. The results have been compared with effects of pulsed-laser annealing investigated by AULEYTNER et al. an thermal annealing (PRUSSIN ).     

Defect Structure in Te-doped GaAs Single Crystals after Plastic Deformation (II). Dislocation Slip and Cell Formation

At temperatures above the brittle-to-ductile transition (490 °C) in Te-doped GaAs three types of predominant defect configurations have been observed after uniaxial compression along a [001] direction: (i) twins and stacking faults (500 … 520 °C), (ii) slip zones of dislocations (≈550 °C) and (iii) dislocation cells (580 … 590 °C). In Part II quantitative details of the appearance of slip and cell formation are given. Leading segments of gliding half loops are mainly of 60° type. Cell walls were formed by multiple slip of perfect dislocations.     

ZnO单晶的生长表面形貌及形成机制研究

采用石墨辅助化学气相传输法生长了ZnO单晶体.利用XRD、金相显微镜和扫描电镜等对晶体结构和表面形貌进行研究,发现其表面由大量六边形台阶堆垛而成,单个晶粒呈六方伞状结构并始终显露(001)面.同一平面内台阶的大小、陡峭程度存在差异,台阶之间为平行走向.通过形成机制分析,获得生长体系的过饱和度σv约为7;,发现生长表面的腐蚀形貌为六边形平底蚀坑,确定在化学气相法中ZnO单晶呈台阶生长的主要条件是螺旋位错.     

大尺寸掺铥铝酸钇晶体生长工艺研究

通过提拉法制备了直径50 mm,长度144 mm的大尺寸、高质量的Tm:YAP激光晶体,研究了不同的温场结构对于晶体完整性以及晶体质量的影响,结果表明上空腔温度梯度较小,温度均匀性较高的温场设计能够有效的解决Tm:YAP晶体开裂、解理、弥散状散射和絮状物现象.     

In和过渡金属离子共掺杂对ZnO晶体形貌的影响

采用水热法,KOH作矿化剂,在ZnO前驱物中添加适量的CoCl2·6H2O,FeCl2·4 H2O,NiCl2·6H2O,In2O3,其中Co:In:Zn,Fe:In:Zn,Ni:In:Zn 分别为5:1:100,5:1:100,3:1:100.3 mol/L KOH作矿化剂,温度430 ℃,填充度35;,反应24 h,制备了In和过渡族金属离子共掺的ZnO晶体.结果表明,掺杂In2O3时,所合成的过渡族金属离子掺杂的ZnO晶体均呈现六角片状晶体,晶体形貌规则,表面光滑,直径为5～10 μm.和未掺杂In的晶体相比,掺杂In后,晶体c轴极性生长速度得到明显的控制,a、b轴方向生长速度提高,大面积显露+c{0001}、负极面-c{0001}面,另外还显露正锥面+p{1011}、负锥面-p{101-1-}.     

常压混合碱液条件下ZnO单晶生长习性的研究

采用常压混合碱液法,以NaOH、LiOH和H2O的混合碱液作助熔剂,重复生长了无色透明的六方片状、六方柱状和带六方双锥的完整单晶.经X射线衍射确认所生长的晶体均为六方纤锌矿型ZnO.实验表明,生长体系中NaOH与LiOH的物质的量比及ZnO的物质的量分数都对晶体的形貌有明显影响.NaOH与LiOH物质的量比为10:1、ZnO物质的量分数为0.077时,获得ZnO晶体的尺寸、透明度为最佳.     

Na+对KDP晶体生长的影响

本文利用传统的降温法和"点籽晶"快速生长法在不同Na+掺杂浓度的溶液中生长KDP晶体,定量研究了Na+对KDP晶体生长的影响.实验发现:Na+的存在降低了溶液的稳定性,致使KDP晶体柱面容易扩展.Na+的存在对KDP晶体的光学性能基本没有影响.     

不同类型宝石级金刚石生长过程中石墨的不同析出形式

在压力5.3 GPa、温度1603 K的FeNiCo(wt; 55∶ 29∶ 16)触媒中沿{111}面合成Ⅰb型及Ⅱa型宝石级金刚石过程中金刚石周围分别伴随有片状及粉末状石墨析出.这两种不同形态的石墨均会对金刚石生长产生不利影响.对这两种石墨进行XRD和SEM测试分析表明:生长Ⅰb型和Ⅱa型金刚石时所析出的石墨分别为再结晶石墨和微晶石墨.本文分析了这两种石墨析出原因的异同点.     

Comparative Study of Real Structure of LiNbO3 : ZnO Crystals Grown by Direct and Homogeneous Doping

Crystallography Reports - A comparative study of the optical and structural homogeneity of a LiNbO3 crystal with a congruent composition and LiNbO3 : ZnО ([ZnО]...     

碱土金属离子对ZnO极性生长的影响

本文采用水热法,以3mol/L KOH为矿化剂,填充度35%,温度430℃,通过添加适量比例的MgCl2.7H2O和CaO,合成了非极性生长的ZnO晶体。当Mg2 :Zn2 =2%和Ca2 :Zn2 =2~3%时,晶体c轴方向生长速度明显减弱,{0001}方向的极性生长得到控制,所合成的晶体大面积显露正极面 c{0001},同时显露负极面-c{1001-}、正锥面 p{101-1}、负锥面-p{101-1-}和柱面m{101-0}。X光能谱(EDS)没有检测到晶体中含有碱土金属离子。     

On the Preparation of ZnO Single Crystals

ZnO single crystals were prepared by means of two methods:i slow cooling of ZnO/PbF₂ (PbO) high temperature solution, (ii) flux reaction technique, hydrolysis of ZnF₂ in PbF₂ as a solvent. At cooling rate ≥ 0.9 K/h the known plates, hexagonal prisms, and hollow crystals were obtained. At the cooling rate 0.6 K/h compact crystals have grown. This habit was also formed with the flux reaction technique. An estimation of the deposition rates of both methods has shown approximative agreement between the cooling runs with 0.6 K/h and the flux reaction technique under the chosen conditions. The deposition rate appears to be a relevant parameter for forming compact ZnO crystals in these systems.     

Studies on the Growth Rates of Crystals

The crystal growth rates are calculated from the nucleation rate of two-dimensional square shaped nucleus in four different models. In all these models, the growth is initiated by the birth of the critical nuclei. Two limiting values of the lateral spreading velocities perpendicular to the side of the growing island are considered in first two models and finite spreading velocities are treated in other two models.