PVT法SiC单晶生长传热分析

研究了PVT法生长SiC过程中的传热行为,以优化生长条件、获得高质量单晶.该研究是针对坩埚盖(籽晶粘附于坩埚盖上)和炉盖之间的传热行为进行的.研究认为,坩埚盖上部石墨毡开孔形状和大小对坩埚盖的径向温度场有很大影响.采用本文简化的模型可以估算坩埚在不同位置下、不同的石墨毡开孔形状和大小时坩埚盖和炉盖之间总的辐射热阻和传热量.对影响坩埚盖和炉盖之间传热的因素进行了讨论.另外,讨论了在生长过程中动态调整坩埚盖散热条件的可行性.     

硼磷酸盐晶体BaBPO5的非线性光学系数研究

用Maker条纹方法测量了硼磷酸盐晶体BaBPO5的非线性光学系数d11(BaBPO5)=(0.439±O.002)d36(KH2PO4),d12(BaBPO5)=(0.425±0.008)d36(KH2PO4),相应的相干长度为:l11=16.985±0.301μm,l12=16.972±0.304μm.确定了非线性光学系数的相对符号,d11(BaBPO5)和d12(BaBPO5)符号相反.BaBPO5晶体激光损伤阈值大于900 MW/cm2.     

硝酸钾铵混晶性质的研究

采用恒速冷却法首次制得了不同比例的Kx(NH4)1-xNO3(0相似文献   

一维声子晶体的传输特性

推导出一维声子晶体的转移矩阵,研究了一维声子晶体的传输特性.得出:声波在一维声子晶体中传播时会出现一系列禁带,各级禁带的频率中心是等间隔的,各级禁带的频率宽度是相等的.相邻禁带的频率中心的间隔随介质的厚度成反比变化,禁带的频率宽度随介质的厚度成反比变化.禁带的频率宽度随两介质声阻抗的差值的减小而减小.     

Analysis of Fluid Flow and Heat Transfer in a Gas Phase Crystal Growth Furnace

Steady-state simulations of fluid flow and temperature field are presented for an equipment that is used to grow Zinc Selenide single crystals from the gaseous phases via physical (PVT) or chemical vapour transport (CVT). Due to the horizontal arrangement of the air-filled furnace pipe calculating the natural convection in the air requires a 3D (three-dimensional) treatment of the problem. The simulations have been done by applying the commercial finite-element package FIDAP. The Navier-Stokes equation is solved with the Boussinesq approximation. The heat transfer analysis comprises also internal radiation wall-to-wall exchange. Due to the presence of the ampoule in the pipe, the development of vortices with higher velocities is restrained, so that the maximum velocity is roughly 1/4 of that in the case without an ampoule.     

Nd0.007Gd0.993VO4晶体折射率和折射率温度系数的测量

利用自准直法,在20℃到170℃温度范围和0.4880μm、0.6328μm、1.0640μm、1.0795μm、1.3414μm等波长测量了Nd0.007Gd0.993VO4晶体的折射率,得到了这种晶体的Sellmeier方程和折射率温度系数.为了验证得到结果的可靠性,利用得到的Sellmeier方程计算1.0640μm的寻常光和异常光的折射率,并与实验测量的结果进行比较,两者的差异不大于2.2×10-4,处在测量误差的范围内.测量结果表明在室温下,对1.0640μm波长的双折射率为0.2201,双折射率温度变化率为4.3×10-6/℃.因此,与YVO4相仿,这种晶体不仅是一种优秀的激光基质材料,而且是一种优秀的双折射晶体.     

尿素晶体线性和非线性光学系数的计算

本文使用从头计算平面波赝势法计算了尿素晶体的电子能带结构、线性和非线性光学系数,折射率和倍频系数的计算结果与实验结果基本符合.计算发现尿素晶体中C、N和O元素的2p轨道电子态发生了明显杂化,而能量较高的2p轨道电子态的杂化是其非线性光学效应的主要来源.     

绿柱石晶体的水热法生长及特征研究

采用温差水热法,以分析纯的Al(OH)3和BeO以及无色纯净的石英为原材料,球形和//s(1121)的片状无色绿柱石为籽晶,在复杂的盐酸混合溶液中生长了无色透明的绿柱石晶体.利用双圈反射测角仪、电子探针、X射线衍射仪和红外光谱仪等仪器,对合成绿柱石晶体的形态、成分及晶体结构进行了详细的研究.结果表明,合成的绿柱石晶体为六方短柱状,主要发育平行双面c{0001}、六方柱m{1010}、a{1120}和六方双锥p{1011}四种单形.合成的绿柱石晶体的成分中(Na2O+ K2O)的质量分数约为0.59;,且c0/a0值为0.9988,可归属于"正常"绿柱石向"四面体"绿柱石的过渡范畴.在中性或弱碱性环境体系中,通过调整绿柱石中各成分的百分含量,有望在更低的温度、压力条件下合成出高质量的板柱状绿柱石晶体.     

Investigation of the Solution Structures and Determination of the Growth Units of Cadmium Mercury Thiocyanate Crystal

To get a better understanding of the growth of cadmium mercury thiocyanate (CMTC), a promising nonlinear optical crystal, we have investigated the structures of its growth solutions by using Raman spectra. It has been found that Hg(II) ions coordinate with SCN^‐ through S atoms, forming the most stable complex of [Hg(SCN)₄]^2‐ in the solutions while Cd(II) ions bind to SCN^‐ around Hg(II) through the other end N atom. Thereby, taking [Hg(SCN)₄]^2‐ anions as centers, a network structure of Cd(II)‐N‐C‐S‐Hg(II) is formed in the solutions as in the crystal lattice. It is notably that there are other complexes, mostly the Cd(SCN)_n (n < 4) complexes, in the solutions. Therefore, the solution structure of CMTC is complicated, which is believed to contribute greatly to the difficulty of growing large single crystals. Based on the analysis of the solution structures, the reasonable growth units of CMTC are proposed.     

The Crystal Structure of [La(NO3)6{Cu(2,2′-bipy)2}2][La(NO3)6Cu(2,2′-bipy)2]CH3CN with the Most Profuse Modes of Nitrate Coordination

The title compound [La(NO₃)₆{Cu(2,2′-bipy)₂}₂][La(NO₃)₆Cu(2,2′-bipy)₂] CH₃CN was synthesized, the crystal and molecular structures were determined at room temperature. The complex formed monoclinic crystals, space group P21/n (No.14), a = 10.354 (3) A, b = 23.440 (9) A, c = 32.817 (9) A, b = 90.39 (2)°, Z = 4. The crystal structure consisted of a discrete [La(NO₃)₆{Cu(2,2′-bipy)₂}₂]⁺ cation and [La(NO₃)₆Cu(2,2′-bipy)₂]^- anion and a non-coordinated CH₃CN molecule. Each La(III) ion was 12-coordinate with twelve oxygen atoms from six chelating nitrate ligands. There were four modes of nitrate coordination and the coordination geometry of all three copper ions was different in the crystal structure.     

KDP晶体缺陷对生长应力分布的影响

本文采用有限元法分析了不同尺寸、形状的晶体缺陷对大口径KDP晶体生长应力分布的影响.结果表明,晶体中的缺陷导致了晶体内部应力集中,且应力集中程度与缺陷尺寸、晶体生长尺寸呈反向变化,而最大主应力与缺陷尺寸、晶体生长尺寸呈正向变化.当缺陷含有棱边或尖角时,应力集中程度和最大主应力值都明显增加.由于KDP晶体易脆性开裂,随着最大主应力值的增大,开裂机率也增大.     

磺基水杨酸锶分光晶体生长的研究

本文采用液相法合成了高纯度磺基水杨酸锶(简称SSS)多晶粉末原料,并采用热分析、红外光谱和XRD分析对多晶粉末原料进行表征。以水为溶剂分别在不同pH值下(pH=2.50、1.50和0.60)进行了SSS结晶习性实验。结果表明,在水溶液中当pH=0.60时SSS结晶性最好,实验还测定了SSS晶体在不同pH值溶液中的溶解度曲线,并进行了过饱和溶液成核机理的研究。研究结果表明,当生长溶液pH为0.60时,控制单晶生长温度在40～50℃区间,采用水溶液降温法可生长出63 mm×25 mm×3 mm的透明单晶。     

Experimental Verification of the Numerical Model for a CaF2 Crystal Growth Process

Large calcium fluoride (CaF₂) single crystals are required for the fabrication of lenses in so‐called wafer‐steppers of future IC‐lithography technologies operating at 193 nm and 157 nm. Numerical simulation plays an important role to design an adequate growth setup and processing conditions for the growth of high quality crystals. An important issue is the consideration of the internal heat transfer by radiation in the semitransparent CaF₂ during the crystal growth process. Results of the numerical modeling of the heat transport are presented, which are obtained by using the software package CrysVUn++ with different models considering the internal heat transport in CaF₂. To improve the availability of experimental data on CaF₂ bulk growth, an especially designed R&D‐facility was built. This growth system is equipped with a variety of in‐situ measurement systems to detect the temperature distributions in the crystal and melt region. Calculated temperature distributions are compared with experimental data. Also first results on single crystal growth will be reported.     

用于红外变频的大尺寸AgGaS2晶体生长

在红外变频非线性光学应用中需要高光学质量大尺寸AgGaS2晶体元件.我们采用改进的Bridgman方法生长直径28mm、长度60～80mm的晶体棒.成功生长的关键是要采用C向籽晶.[001]籽晶生长的晶体中很少发现裂纹、聚片孪晶等宏观缺陷.在Ag2S共存下的热处理能有效地排除晶体中的异相沉淀,显著改善透明度.我们制备的Ⅰ型相位匹配8mm×10mm×16mm和5mm×5mm×15mm?AgGaS2晶体元件分别成功地应用于差频、和频激光实验.     

Yb:FAP晶体生长

采用中频感应提拉法生长了Yb：FAP晶体。对晶体生长中影响晶体质量的因素特别是原料的处理、CaF2的挥发等进行了研究和讨论。运用ICP-AES测定Yb^3＋离子在Yb：FAP晶体中的分凝系数。对Yb：FAP晶体进行了高分辨X射线的四圆衍射实验,结果表明晶体具有比较高的晶格完整性。     

结晶生长的化学键合理论

针对一般晶体的生长过程,在测定相应溶液(熔体)组成结构的基础上,我们引入了晶体生长过渡相区的概念,并采用键价模型来衡量生长过程中发生变化的化学键的键强度。过饱和溶液(熔体)中的生长单元经过生长过渡相区时,依据彼此之间弱的化学键合作用来微调其内部强的化学键,并以单个生长单元或者生长单元的简单连接体的形式键合进入晶格。在整个结晶生长过程中,生长单元之间弱的键合作用对整个结晶过程(生长速度、晶相的形成)起着决定性作用;同时,中等强度的化学键在生长过渡相区中的变化情况对晶体的最终形貌具有重要影响。     

碲锌镉垂直布里奇曼法晶体生长过程固液界面的演化

计算模拟了半导体材料碲锌镉垂直布里奇曼法单晶体生长过程,以等温线图展示了固液界面形状的演化,分析了温度梯度和坩埚移动速率对固液界面形状以及晶体内组分偏析的影响.计算结果表明在凝固的初始段,固液界面的凹陷深度较大,随后有较大幅度的减小.整个凝固过程中固液界面的凹陷深度值有一定的波动性.提高温度梯度、降低坩埚移动速率均能有效地减小固液界面的凹陷,改善晶体的径向组分偏析.     

提拉法制备铜单晶研究

采用提拉法生长出大尺寸(111)铜单晶,晶体尺寸为ф(12～19)mm×85 mm.通过XRD、金相显微分析讨论了铜单晶的晶体结构与生长缺陷,并采用双臂电桥测定(111)铜单晶的电阻率.结果表明:晶体具有(111)取向、强度高,表明晶体取向良好;蚀坑呈典型三角锥形,位错密度在105～106 cm-2之间;在室温下,(111)铜单晶电阻率为1.289×10-8Ω·m.     

Heat and Mass Transport Computation at the Sublimation Growth of SiC

Steady‐state heat and mass transport at the SiC growth process are computed by the general‐purpose finite‐element package FIDAP^TM. Specific features are the radiation exchange in several cavities at temperatures up to 2700 K and concentration dependent Stefan velocities resulting from sublimation/condensation at the vapour‐solid interfaces. The article describes the computational procedure in order to achieve convergence of the temperature and velocity field. The transport rate of the SiC building species meets the range of experimental results.     

氧化锌晶体生长基元模拟

本文利用Hyperchem分子模拟软件对氧化锌晶体生长基元Zn(OH)42-进行了系统的模拟.通过模拟分析生长基元的结合方式,提出了生长基元的结合规律.结果表明:Zn原子数(生长基元)与共用O原子数(O桥)的比例越大所形成的络合物越稳定;当分子中Zn原子和共用O原子比例一定时,羟基数目越少则越稳定.并且通过计算机模拟生长基元直线状结合情况解释了单晶ZnO纳米线状或纳米棒状的结构很难在实验中获得的原因.