CsB3O5(CBO)晶体生长和形貌研究

本文采用籽晶浸没法,在Cs2O过量3;的Cs2O-B2O3体系中生长了CsB3O5单晶.生长参数如下:液面以下温度梯度为0.5℃/cm, 晶体旋转速度为12r/min,降温速率0.2℃/d,可获得透明、无包裹体、无开裂、最大尺寸达65×44×49mm3的CsB3O5单晶.研究了CsB3O5的生长形貌,CsB3O5生长没有明显的方向性,总是呈现长柱状,最易出现的晶面是(011)和(101)晶面.     

非线性光学晶体CBO的缺陷形貌分析

以碳酸铯和硼酸为原料采用泡生法生长出三硼酸铯(化学式CsB3O5,简称CBO)晶体,首次报道了利用同步辐射白光X射线形貌术对CBO晶体的(001)面、(010)面和(100)面进行了观察.观察结果表明,CBO晶体的主要缺陷是生长层.缺陷形成的原因是晶体生长炉内热流的非稳态对流和温度振荡导致晶体的微观生长率随时间变化,溶质粒子不能均匀分布在晶体生长前沿.     

紫外非线性光学晶体三硼酸铯的生长和性能

采用泡生法和提拉法生长出三硼酸铯(化学式CsB3O5,简称CBO)晶体,研究了晶体生长工艺条件及晶体生长形态.泡生法生长的CBO晶体的尺寸为40mm×25mm×25mm;生长过程中晶体转速为10～20r/min,降温速率为0.1～0.2℃/d.用提拉法生长出20mm×30mm的CBO晶体;生长过程中液面温度梯度为60℃/cm,提拉速度为8mm/d.在生长过程中Cs2O的挥发速度大于B2O3的挥发速度.CBO单晶的晶面由[011]斜方柱和[010]斜方柱单形组成,属于[011]单形是4个较大的面,属于[101]单形是4个较小的三角形晶面.CBO在紫外波段具有较大的有效非线性光学系数.利用CBO进行Nd∶YAG激光和频获得了高转换率的波长355nm及266nm相干光输出.     

组分挥发对CBO晶体生长影响研究

非线性光学晶体CsB3O5(简称CBO)在生长过程中,原料组分的挥发影响了单晶的生长.本文利用XRD,DTA等手段对挥发物的成分进行表征,结果表明挥发物的主要成分是Cs2O,并探讨了原料组分的挥发对结晶状况的影响,以期探索和优化晶体生长工艺.     

掺杂YCa4O(BO3)3晶体的生长与性质研究

采用提拉方法,首次使用铂坩埚在大气气氛下生长出大尺寸,高质量的非线性光学晶体YCa4O(BO3)3(YCOB).典型晶体尺寸为直径15～20mm,长度30～40mm.对晶体进行掺杂改性研究,已分别生长出掺杂浓度为5;的Nd:YCOB,Er:YCOB和掺杂浓度为20;的Yb:YCOB晶体.对沿不同方向生长的晶体的习性和缺陷进行了研究.晶体的生长是以典型的二维成核层状生长进行的.当沿方向生长时,晶体易出现(010)面孪晶及方向的解理面;而沿〈010〉方向生长时,可避免孪晶和解理面的出现.我们认为〈010〉方向为最佳生长方向.通过测量晶体的室温透过谱发现掺杂的YCOB晶体在深紫外(220nm)有较高的透过率(80;).初步的自倍频实验可观察到Nd:YCOB晶体能够在811nm的LD泵浦下产生较强的绿光,并且阈值较低.这表明掺稀土的YCOB晶体可能是一种有应用前景的自倍频激光材料.     

用提拉法生长的GdCa4O(BO3)3晶体的结构缺陷研究

利用相衬显微镜结合化学腐蚀法,进行了沿 010 方向提拉生长的GdCa4O(BO3)3(GdCOB)晶体中的缺陷观察.发现位错是 010 方向生长的晶体中的重要缺陷.在不同方向的晶体切片上观察了螺位错和刃位错蚀坑,位错塞积,平底蚀坑及尖底蚀坑.位错密度随晶体长度的变化而变化.在晶体的尾部观测到位错密度为103/cm2,而在晶体的初始部位位错密度很低,只有40/cm2.在晶体的X,Z及 401 方向的切片的正反两面观察到的位错蚀坑现象完全不同,可以认为GdCOB晶体为单畴极性晶体,自发极化方向沿z轴方向.     

Na5[B2P3O13]晶体双晶结构的研究

采用泡生法和b向籽晶生长出尺寸为22mm×24mm×20mm的透明Na5[B2P3O13]晶体.晶体定向中发现(100)和(001)晶面的一级衍射出现双峰;正交偏光显微镜下观察晶体的(010)切片,看到清晰的明暗条纹;当一束激光正入射(010)切片时,产生衍射现象;用同步辐射白光X射线形貌术拍摄了(100)、(010)和(001)切片的Laue像,观察到了晶体的孪晶结构,再借助(010)切片的化学腐蚀研究,推出该晶体为规则的聚片双晶,其结合面为(001).     

非线性光学晶体CsB3O5研究进展

非线性光学晶体CsB3O5(CBO)具有大的非线性光学系数、优秀的紫外波段透过能力和高的抗光损伤阈值,在紫外高功率密度全固态激光系统的频率转换方面展现出良好的应用前景。本文综述了CBO晶体的研究概况,报道了高质量CBO晶体生长、折射率温度系数、热学性能及278 nm紫外激光输出的最新研究结果。     

B3O7基团型硼酸盐非线性光学晶体研究进展

以B3O7基团为基本结构单元的硼酸盐非线性光学晶体LiB3O5,CsB3O5,CsLiB6O10具有紫外透过波段宽,非线性光学系数较大,光损伤阈值高的共同特性,有利于紫外波段激光频率变换,本文综合叙述了B3O7基团型硼酸盐非线性光学晶体的研究进展。     

原料的均匀性对CsB3O5晶体光学性质的影响

本文是针对紫外非线性光学晶体CsB3O5的原料处理对晶体光学质量的影响的研究报道.利用液相法合成出高度分散的原料,生长出高光学质量的CBO单晶.消除了晶体内部的光散射颗粒,并测量了该晶体的透过光谱、光学均匀性和抗激光损伤阈值.     

Origin of the Voc enhancement with a p-doped nc-SiOx:H window layer in n-i-p solar cells

The introduction of a nc-SiOx:H material as window layer in single junction a-Si:H n-i-p solar cell leads to a V_oc enhancement of 80 mV compared to a μc-Si:H p-layer. According to numerical modeling of the V_oc, both the higher work function p-layer and the conduction band offset (CBO) at the i/p interface match well with the experimental V_oc increase with the oxygen content. Using the differential temperature method, the built-in voltage (V_bi) of the cells with the two different p-layers is measured to be similar, agreeing well with the CBO model. Thus we attribute the improvement of the V_oc to the reduction of recombination at the i/p interface, as a consequence of the CBO in this region.     

熔体过冷度对透辉石晶体形貌、成分及过渡层性质的影响

在不同过冷度条件下,硅酸盐熔体结晶得到了透辉石晶体含量合适的样品.实验结果表明透辉石晶体形貌的自形程度随过冷度增加而降低.拉曼光谱分析显示晶体的特征谱峰半高宽随过冷度增加而变宽,拉曼光谱还显示出晶体结构继承玻璃结构的特征.运用电子探针详细分析了透辉石晶体及其生长界面附近成分变化的特点,发现存在约几到十几微米厚的过渡层,并且透辉石晶体成分随过冷度增大Al元素进入到晶体的含量也增加,同时Al元素与Mg元素在结晶过程中的协同作用较强.     

Thermal radiation and low-temperature-vapour growth of HgI2 crystal in production furnace

Heat exchanges in a sealed ampoule in the LTVG (low temperature vapour growth) furnace have been modelled in order to compute temperature fields and control the growth of HgI₂ crystals from vapour phase at low temperatures. We use a coupled conductive-radiative model to determine the shapes of the source and the crystal at different equilibrium states (i.e. without growth rate). The model involves conductivity anisotropy in the crystal and radiative exchanges between grey and diffuse surfaces (source and crystal interfaces, Pyrex walls), which are considered as opaque. Internal buoyancy effect is not taken into account as the pressure inside the ampoule is very small. The source temperature is fixed. For different undercoolings, i.e. for different cold finger temperatures, the “equilibrium” isotherm between the source/gas and crystal/gas interface has been numerically obtained. This “equilibrium” isotherm, which is associated with the stop of the growing process, gives a crystal shape. This shape is compared with experimental results given by the ETH-Zürich group. The model would permit a better understanding and control of the future HgI₂ crystal growth experiment. The computations are performed using a finite element package (FIDAP).     

大尺寸掺铊碘化钠晶体生长及闪烁性能

采用坩埚下降法，生长了体积为4 L的大尺寸NaI(Tl)晶体。对晶体进行X射线粉末衍射、紫外可见近红外透射光谱测试，结果表明，生长的晶体具有单一的物相，在600～1 600 nm的透过率高于75%。电感耦合等离子体发射光谱测试结果表明，晶体中的Tl离子浓度从头部到尾部逐渐增加。经过锻压、切割、打磨、抛光、封装等工序将NaI(Tl)晶体毛坯制成100 mm×50 mm×400 mm的方形晶体。闪烁性能测试结果表明，在¹³⁷Cs放射源激发下，晶体的平均能量分辨率为7.9%,不同位置的相对光输出和能量分辨率存在一定差异。     

Simulating vapour growth morphology of crystalline urea using modified attachment energy model

We report a computational model to simulate vapour growth morphology of urea crystal by considering molecular anisotropy and surface relaxation of different crystal faces. It has been argued that the faces' growth occurs through the adsorption of molecular layers rather than a slice of thickness d_hkl. The molecular layer is a 2-D periodic arrangement of molecules in which each molecule has same the orientation. The molecular orientations in a slice of thickness d_hkl may differ from each other and depend on crystallographic orientation of the slice. The discussed approach has been employed to simulate vapour growth shape of crystalline urea by calculating attachment energy of molecular layers using Hartee–Fock and density functional theories. The calculated growth morphology is in good agreement with the vapour grown shape of urea crystal. The role of thermal and growth kinetics affecting the vapour growth morphology has been discussed. The observed polar growth morphology of urea crystal has also been discussed particularly in the context of different atomic environments of (111) and (?1?1?1) faces.     

冷心放肩微量提拉法大尺寸蓝宝石单晶生长过程的模拟分析

利用数值模拟方法计算了冷心放肩微量提拉法(SAPMAC)蓝宝石晶体生长过程.结合晶体直径变化、裂纹出现位置与延续方向、晶体透明性等实验现象,通过与提拉法、温梯法、坩埚移动法等相对比,分析了冷心放肩微量提拉法晶体生长各阶段的工艺特点,并根据模拟计算结果对晶体生长系统和晶体生长控制工艺进行了改进.分别利用增大热交换器的散热参数、降低加热温度、改进降温曲线、调节外加轴向和径向温度梯度的方式来实现对晶体生长的引晶、放肩、等径和收尾控制.通过实验比较证明了改进后的晶体生长系统和晶体生长控制工艺能够生长出性能较好的大尺寸蓝宝石晶体.     

The influence of the growth rate and V/III ratio on the crystal quality of InGaAs/GaAs QW structures grown by MBE and MOCVD methods

The influence of the growth rate and V/III ratio on the crystal quality of In_0.2GaAs/GaAs quantum well structures was examined. The investigated heterostructures were grown by molecular beam epitaxy (MBE) and metalorganic chemical vapour deposition (MOCVD). Reflection high energy electron diffraction (RHEED), photoluminescence measurements (PL), high-resolution X-ray diffraction (HRXRD) and atomic force microscopy (AFM) were applied for evaluation of the interfaces smoothness and the overall layer quality. Comprehensive characterisation of InGaAs/GaAs structures allowed us to establish optimal values of analysed technological parameters. Moreover, the comparison between the results obtained for samples grown by two different epitaxial techniques allowed us to find, which of the analysed growth parameters has the strongest influence on the quality of MBE and MOCVD grown structures. In contrast with the growth temperature and the interruption time, which in different manner impact on the crystal quality of QWs obtained by different method, the growth rate and the V/III ratio play similar role in both epitaxial techniques.     

石英安瓿下降法生长硫镓银晶体的研究

分析了硫镓银晶体的反常热膨胀,主要是由于晶体结构中Ag,Ga,S三种原子形成的四面体随着温度变化发生了畸变;通过采用改变生长安瓿的直径和壁厚,并在生长安瓿外面加一层套管的方法来减小晶体在降温过程中的反常热膨胀作用,有效避免了反常热膨胀可能造成的晶体破裂现象,生长出了完整性较好的大尺寸硫镓银单晶体.     

Segregation of Ga during growth of Si single crystal

Segregation phenomenon of Ga in Czochralski (CZ)–Si crystal growth has been investigated. The effective segregation coefficient, k_eff, of Ga was obtained for different growth rates by assuming the simple relationship between the concentration of Ga in Si crystal and the bulk Ga concentration in melt. Applying BPS theory to effective segregation coefficients which is valid for the melt-solidified fraction up to 0.38, an equilibrium segregation coefficient of Ga was obtained, k₀=0.0079.