Yb:Ca5(PO4)3F激光晶体的生长缺陷

采用提拉法生长了质量优异的Yb：Ca5（PO4）2F（Yb：FAP）晶体。运用化学腐蚀,光学显微镜、扫描电子显微镜以及能量散射光谱仪观察了该晶体中的生长条纹和包裹物等宏观缺陷,以及晶体的位错腐蚀形貌、位错密度及其分布情况,同时观察了晶体中亚晶界的形态。由晶体中位错的径向变化以及生长条纹可知：晶体在生长过程中为微凸界面生长。高温下CaF2的挥发造成了在晶体生长后期熔体中组分偏离化学计量比,出现组分过冷,形成包裹物。且位错密度显著增加。Yb：FAP晶体的各向异性使得晶体在（10 10）面的位错蚀坑形状、大小以及深度不同,而（0001）面的位错蚀坑呈规则的六边形;这也是晶体中形成亚晶界结构的主要原因。讨论了减少晶体中缺陷的一些方法。     

Yb∶Ca_5(PO_4)_3F激光晶体的生长缺陷

采用提拉法生长了质量优异的Yb∶Ca5(PO4)3F(Yb∶FAP)晶体。运用化学腐蚀,光学显微镜、扫描电子显微镜以及能量散射光谱仪观察了该晶体中的生长条纹和包裹物等宏观缺陷,以及晶体的位错腐蚀形貌、位错密度及其分布情况,同时观察了晶体中亚晶界的形态。由晶体中位错的径向变化以及生长条纹可知:晶体在生长过程中为微凸界面生长。高温下CaF2的挥发造成了在晶体生长后期熔体中组分偏离化学计量比,出现组分过冷,形成包裹物,且位错密度显著增加。Yb∶FAP晶体的各向异性使得晶体在(10 10)面的位错蚀坑形状、大小以及深度不同,而(0001)面的位错蚀坑呈规则的六边形;这也是晶体中形成亚晶界结构的主要原因。讨论了减少晶体中缺陷的一些方法。     

温梯法生长φ110 mm×80 mm蓝宝石晶体位错的化学腐蚀形貌分析

利用导向籽晶温度梯度法（ＴＧＴ）生长了φ１１０ｍｍ×８０ｍｍ的蓝宝石单晶,应用化学腐蚀、光学方法分析了该晶体不同部位、不同切片的位错腐蚀形貌、位错密度及其分布情况、发现在晶体放肩处的（１１２０）面位错密度约为１０＾４ｃｍ＾－２量级,等径生长过程中造晶体中心处（０００１）面位错密度为（３￣４）×１０＾３ｃｍ＾－２,靠近坩埚壁处（０００１）面晶体位错密度为（５￣６）×１０＾４ｃｍ＾－２,用同样方法分析     

YAG晶体位错密度分布及蚀坑形貌

YAG晶体在光电子领域有着重要的应用，晶体生长的缺陷控制是需要解决的瓶颈问题。本工作研究了缩颈和无缩颈提拉法生长的YAG晶体的位错形貌及密度分布，通过对YAG晶体进行抛光、浓磷酸位错腐蚀和金相显微镜分析研究，发现YAG晶体的头部位错密度最大，等径处的位错密度最小，延伸至收尾处位错密度略升高，缩颈结束收细直径的地方位错密度显著降低；分析了不同晶向的YAG位错腐蚀坑形貌，由表面模型计算了YAG各晶面的表面能，结果表明：YAG晶体位错蚀坑相对稳定的外露面为(110)和(112)面。通过极射投影图进一步说明了(110)和(112)面的稳定性及其与晶面的位置关系是决定位错腐蚀坑形貌的重要原因。     

温度场对白宝石晶体生长质量的影响

熔体提拉法生长晶体时温度场的分布对晶体的质量有着重要影响.采用电阻加热提拉法生长白宝石晶体时,由于腔体内的温度梯度较小,使得晶体的外形难以控制.当液面上坩锅中心附近处的轴、径温度梯度过小时,生长初期放肩就难以控制;且生长晶体的等径度易成螺旋状.当轴、径向温度梯度较大时,虽然晶体外形容易控制,但晶体容易开裂,因而其成品率较低.与此同时晶体的转速决定着固液界面的形状,微凸界面是生长高质量晶体的必要条件.当白宝石晶体外形不好时,其内部容易产生散射颗粒、气泡等缺陷.研究通过调整生长装置和转速,找到了生长优质晶体的温度场.实验获得了Φ60×120mm的优质白宝石晶体.     

高压熔体法生长高质量CdSe单晶

CdSe晶体是一种性能优异的非线性光学材料,但目前常规的生长方法很难生长出高质量单晶。本实验在理论推导的基础上,采用高压熔体法生长出了较大尺寸的CdSe晶体棒,并采用X射线衍射仪、能谱分析仪、腐蚀坑观察、Fourier变换红外光谱仪对单晶性能进行表征。结果表明:高压熔体法生长的CdSe单晶组分接近理想化学计量比(CdSe_(0.989)),且具备结构完整、位错密度小(10~4/cm~2)、结晶质量高(FWHM≤0.1°)、吸收系数低(0.03cm~(-1)以内)等优点,有望用于非线性光学频率转换实验。     

掺钕钨酸钇钠晶体的缺陷

掺钕钨酸钇钠晶体Nd:NaY(WO4)2是一种性能优良的激光晶体.对该晶体中的包裹物、生长台阶等缺陷进行了观察,并分析了缺陷产生的原因.在晶体的不同部位取样进行扫描电镜和能谱分析,发现随着晶体生长过程的进行,晶体中Nd3 的浓度逐渐增加.研究了晶体中位错蚀坑的分布特点,发现位错蚀坑的密度与晶体生长的不同部位、Nd3 的掺杂浓度等因素有关.     

磷锗锌晶体生长与缺陷结构

采用水平双温区法批量合成了高纯ZnGeP2多晶,并用垂直Bridgman法生长出直径为40～50mm的高品质单晶。采用密度泛函理论分析了ZnGeP2晶体中可能存在的点缺陷对其近红外波段透光性的影响,认为V-Zn和Zn0Ge缺陷的影响最大。利用X射线衍射形貌术对晶体中存在的位错、层错、孪晶界、包裹体等微缺陷进行了分析,结果表明,温度场稳定性和固液生长界面形态是缺陷形成的主要因素。     

快速热处理对电子辐照直拉硅中氧沉淀的影响

对n型[111]晶向直拉硅样品进行电子辐照,然后分别在不同温度和降温速率下快速热处理(rapid thermal process,RTP),再在1100℃下进行常规一步退火。研究了RTP温度和降温速率对硅样品内氧沉淀的变化及样品表面清洁区形成的影响。结果表明:经过RTP再经高温一步退火后,硅晶体内形成了密度较高的氧化诱生层错以及完整的位错环,样品表面形成了一定宽度的清洁区;清洁区的宽度随RTP温度及降温速率的升高而变窄。当RTP温度达到1280℃时,样品中的层错和位错环明显减少,此时当RTP降温速率增加至150℃/s时,大部分层错消失,样品中出现了大量的点状腐蚀坑。     

掺镱钇铝石榴石激光晶体生长与开裂

采用提拉法生长了掺杂5%(摩尔分数)Yb3+的Yb:Y3Al5O12(Yb:YAG)晶体,并对晶体生长工艺进行了研究。从理论上分析了生长速率、转速、热应力、晶体尺寸对晶体开裂的影响。确定的最佳工艺条件为:晶体放肩和等径生长速率分别为0.8mm/h和1mm/h;转速为15r/min;轴向温度梯度为0.01～0.05℃/mm。所得晶体的最佳直径为15～25mm。     

掺镱氟磷酸钙(Yb∶FAP)晶体的生长

用高频感应提拉法生长了掺Ｙｂ３＋氟磷酸钙（Ｙｂ∶ＦＡＰ）晶体,获得了理想的生长工艺参数．为消除晶体中通常存在的宏观缺陷,研究了晶体的退火条件．生长的晶体毛坯尺寸为２２ｍｍ×４５ｍｍ．对晶体进行了初步的位错观察,并估算了晶体的位错密度．     

Fracture of Sapphire

The fracture of sapphire was studied using the double-canti-lever-cleavage technique. Fracture surface energies were 7.3 and 6.0 J/m² for the (100) and (012) type planes, respectively. Attempts to measure the fracture surface energy on the (0001) plane were unsuccessful. The failure of sapphire to fracture along the basal plane was attributed to the fact that these planes lack electrostatic charge neutrality. The possibility of fracture-induced dislocation motion in sapphire at room temperature was investigated using etch-pit techniques, but no evidence for dislocation motion could be found. Fracture behavior on (012) planes was erratic, varying from boule to boule. The topology of surfaces formed by crack propagation along this plane is described, but no explanation for the erratic behavior or the observed fracture features is given.     

X-Ray Topography of Czochralski Ruby

Single crystals of ruby (Al₂O₃: 0.05 wt% Cr) were grown by the Czochralski method as 60° type rods. Crystal slices were taken at 30°, 60°, and 90° to the boule axis. Dislocations were observed by Lang X-ray transmission topographs. All sections revealed a relatively defective central region with a dislocation density of about 10⁴/cm². Examples were found of polygenization and small-angle boundaries emanating from the center. Areas near the circumference of the boule had easily resolved dislocation lines and densities as low as 10²/cm². These regions also showed a Frank-type network with node formation. On all slices distinct parallel groups of dislocation lines were observed. Burgers vector, b , for these dislocations was examined by contrast methods involving alternate orientations of the diffraction vector, g. Burgers vector lay along     . A simple model of basal slip of the type (0001)     was used to explain these dislocations.     

Dislocation Structures in Single-Crystal Al2O3

Chemical polishing and etching techniques were used to reveal the dislocation structures of sapphire and ruby crystals grown by the flame-fusion and flux techniques. The average density of edge dislocations lying in prism planes was 3.0 × 10⁵ per cm², which could be changed only slightly by chromium additions and annealing at 2000°C. An average basal dislocation density of 2 × 10⁵ per cm² decreased 35 to 80% on annealing. Crystal orientation (i.e., angle between the c axis and the growth axis) showed no effect on dislocation density but a pronounced effect on subboundary arrangement and density. The substructure of 0° crystals was more complex than that of 90° crystals; 60° crystals possessed a structure intermediate between 0° and 90°. Principal observations included (1) prismatic and basal slip on all as-grown crystals; (2) profuse basal slip, readily polygonized on annealing; (3) dislocation densities of flux crystals lower than those of Verneuil crystals; and (4) a rare form of basal twinning, composition plane , on all flux crystals.     

Grain Growth Control and Solid-State Crystal Growth by Li2O/PbO Addition and Dislocation Introduction in the PMN–35PT System

Grain growth behavior and solid-state single crystal growth (SSCG) in the Pb(Mg_1/3Nb_2/3)O₃–35 mol% PbTiO₃ (PMN–35PT) system have been investigated with varying Li₂O/PbO ratios. The effect of dislocation density on crystal growth has also been studied. For SSCG, a BaTiO₃ single-crystal seed was embedded in a polycrystalline PMN–PT matrix. During annealing, a PMN–PT single crystal grew from the seed at the cost of the small matrix grains. Addition of Li₂O dopant first enhanced and then reduced abnormal grain growth in the matrix. In the 2 mol% Li₂O and 6 mol% PbO excess PMN–PT samples annealed at 1200°C, considerable single-crystal growth occurred without formation of abnormally large grains in the matrix. Increasing the dislocation density in the BaTiO₃ seed crystal resulted in enhanced growth of single crystals. These results were explained in terms of interface reaction-controlled nucleation and growth, based on crystal growth theories.     

Analysis of a Kink Pair Model Applied to a Peierls Mechanism in Basal and Prism Plane Slips in Sapphire (α-Al2O3) Deformed Between 200° and 1800°C

A model based on dislocation glide controlled by the nucleation and propagation of kink pairs in a high Peierls stress crystal is revisited and modified to account for changes in dislocation densities and segment lengths with temperature and stress. It is applied to the critical-resolved shear stress (CRSS) for basal and prism plane slip in sapphire (α-Al₂O₃). According to agreed-upon knowledge on dislocations in sapphire, basal slip and prism plane slip are modeled with undissociated and dissociated dislocations, respectively. In the latter case, partial dislocations move independently. Among a number of sets of fitting parameters, good fits between experimental and modeled CRSS's are obtained in the long segment limit over the whole range of temperatures by making use of physically sound parameters, including a stress dependence of the dislocation density.     

导模法生长蓝宝石晶体的退火工艺

采用导模法生长了片状蓝宝石单晶。由于石墨发热体的高温挥发,使晶体尾部产生黑色絮状包裹体,晶体内部生成色心。为了消除片状蓝宝石晶体内的包裹体和色心,在不同气氛下对生长的晶体样品进行了退火处理。退火实验表明,含有包裹体的尾部样品在1500℃空气中退火20h并以50℃／h的速率降温,可消除晶体内的碳包裹体,晶体变为无色、透明。在氢气中1600℃退火37h后,F色心引起的205mm的吸收峰和Fe^3＋所引起的200～230的吸收峰均被消除。表明高温氢气中退火是消除导模法生长蓝宝石晶体内部F色心和Fe^3＋吸收的最佳退火方法。     

Determination of Pipe Diffusion Coefficients in Undoped and Magnesia-Doped Sapphire (α-Al2O3): A Study Based on Annihilation of Dislocation Dipoles

The breakup of dislocation dipoles in plastically deformed samples of undoped and 30-ppm-MgO-doped sapphire (α-Al₂O₃) was monitored using conventional TEM techniques. Dislocation dipoles break up into prismatic dislocation loops in a sequential process during annealing; i.e., dislocation loops are pinched off at the end of a dislocation dipole. This pinch-off process is primarily controlled by pipe diffusion, and pipe diffusion coefficients at temperatures between 1300° and 1500°C were estimated by monitoring the kinetics of the dipole breakup process. We determined D _P^U= 8.1(_–4.3^+9.1) × 10^–3 exp [–(4.5 ± 1.3 eV )/ kT )] m²/s for the undoped material. The pipe diffusion kinetics for the MgO-doped crystal was determined at 1250° and 1300°C and was about 6 times higher than for undoped sapphire. Finally, climb dissociation of the dislocations constituting the perfect dipoles in sapphire is common; annihilation of one set of partials can result in the formation of faulted dipoles, which can pinch off to form faulted dislocation loops. D _P^U for faulted dipoles in the undoped material was determined at 1300° and 1350°C, and was about 4–10 times higher than for perfect dipoles.     

导模法和温度梯度法生长r面蓝宝石

r面(0112)蓝宝石晶体可用作制备非极性GaN薄膜的衬底.采用温度梯度法(temperature gradient technique,TGT)和导模法(edge-defined film-fedcrystal growth,EFG)生长了质量良好的r面蓝宝石晶体.利用双晶衍射、光学显微镜、光谱仪观察和分析了晶体的结构和缺陷.结果表明:TGT法生长的r蓝宝石晶体的双晶摇摆曲线对称性好,半高宽值仅为18rad·s.位错密度为4×103cm-2,透过率达83%,晶体质量好.与TGT法相比,EFG法生长的r面蓝宝石晶体的结构完整性较差.位错密度为5×105cm-2,透过率仅为75%.但是EFG法具有晶体生长速度快,后期加工成本低的优点.     

Effect of Dislocations on Grain Growth in Strontium Titanate

Two series of experiments were done to investigate the effect of dislocations on grain growth in SrTiO₃. In the first series, we observed the growth behavior of a single-crystal plate toward a TiO₂-excess SrTiO₃ powder compact, containing different dislocation densities on two equivalent {100} surfaces. The surface with a higher dislocation density exhibited faster growth, showing interface mobility enhancement by dislocation. In the second series, a polycrystalline SrTiO₃ sample which had been plastically deformed by hot pressing was embedded in a TiO₂-excess SrTiO₃ powder compact, and its growth behavior toward the powder compact was compared with that of a sample without hot pressing. As with a single crystal, the grains with the higher dislocation density in the plastically deformed sample grew faster. In addition, some grains in the plastically deformed sample showed the characteristic of abnormal grain growth. The transmission electron microscopy (TEM) observations on a sintered TiO₂-excess SrTiO₃ showed that the abnormally large grains contained many dislocations while the fine matrix grains contained practically no dislocations. This result suggests that the uneven distribution of dislocations between grains is possibly one of the causes of the abnormal grain growth in polycrystalline SrTiO₃.