硅酸钇晶体的生长、腐蚀形貌和光谱性能研究

本文采用中频感应提拉法成功生长了未掺杂的Y2SiO5(YSO)晶体,经过定向、切割、抛光后得到样品.经过腐蚀后,利用大视场显微镜和扫描电镜在样品表面上观察到了菱形和四边形的位错蚀坑、小角晶界和包裹物等缺陷;测试了经过氢气、空气退火前后,辐照前后YSO晶体的透过谱,结果表明:YSO晶体的吸收边大约在202nm,氢气退火后在200～300nm波段透过率增加,空气退火后透过率显著降低;辐照后,氢气退火的样品在200～500nm波段透过率显著降低.     

Etching Figures in Neodymium Gallate and Yttrium Aluminate Crystals

The dislocations existing in single crystals of neodymium gallate and yttrium aluminate grown by the Czochralski technique have been studied by means of etch pits. The data concerning their solubility in cases of different directions of a face orientation, various treatment temperatures and several enchant types are reported. The investigation of etch pits in the twinned YAlO₃ and NdGaO₃ crystals showed that twins are formed during a growth process. In the [110]‐pulled NdGaO₃ crystals the discrepancy between the twin and matrix parts of a crystal is accommodated by the dislocation congestion and the dislocation low‐angle boundaries whereas in [010]‐pulled YAlO₃ crystals the microcracks perform this function.     

准同型相界组分PMNT弛豫铁电单晶的畴结构与极化特性

采用坩埚下降法生长了具有准同型相界(MPB)组分的65Pb(Mg1/3Nb2/3)O3-35PbTiO3 (PMNT65/35)弛豫铁电单晶.用偏光显微镜研究了(001)、(110)和(111)三个结晶学取向的铁电畴结构,观察到明暗交替的变化.通过对极化前后电畴形状的比较,分析了极化前后铁电畴形态的变化原因.晶片极化条件为:600 V/mm 的电场并保持10～15 min.研究了极化介质不同对极化后晶片压电性能的影响.     

An optical microscopy study of the biaxial ‐ calamitic nematic lyotropic phase transition

Lyotropic nematic textures are investigated, using optical microscopy, near the reentrant isotropic (I_RE) ‐ discotic nematic (N_D^‐) ‐ biaxial nematic (N_B) ‐ calamitic nematic (N_C⁺) ‐ isotropic (I) phase transitions in a lyotropic mixture of potassium laurate, decanol and D₂O. The N_B, intermediate phase between the two uniaxial nematic ones, is characterized by optical birefringence measurements. In this way, using a polarizing microscope and a colour CCD digital camera, the N_B – N_C⁺ phase transition is identified as well as the domain of the N_B phase and N_D^‐ – N_B transition point in accordance with optical birefringence data (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

高温高压与CVD金刚石单晶衬底质量对比研究

本文通过高分辨X射线衍射(HRXRD)、激光拉曼光谱(Raman)、晶格畸变检测等测试分析方法对多组高温高压(HTHP) Ⅰb、HTHP Ⅱa和化学气相沉积(CVD)型(100)面金刚石单晶样品进行对比研究。HRXRD和Raman的检测结果均表明HTHP Ⅱa型金刚石单晶的结晶质量接近天然金刚石,其XRD摇摆曲线半峰全宽和Raman半峰全宽分别为0.015°~0.018° 和1.45~1.85 cm^-1。晶格畸变检测仪的检测结果表明,HTHP Ⅱa型金刚石单晶的应力分布主要有两种:一种几乎无明显应力分布,另一种沿<110>方向呈对称的放射状分布,其他区域无晶格畸变。HTHP Ⅰb和CVD型金刚石单晶应力分布均相对分散,晶格畸变复杂,与其HRXRD和Raman的检测结果相符。进一步利用等离子体刻蚀法对三种类型金刚石单晶(100)面位错缺陷进行对比分析,结果表明,HTHP Ⅱa型金刚石位错密度为三者中最低,仅为1×10³ cm^-2。本研究为制备高质量大尺寸CVD金刚石单晶的衬底选择提供了实验依据。     

Synthesis and mesomorphic properties of novel high birefringence azobenzene liquid crystals with lateral fluorosubstituent

In order to obtain liquid crystals with high birefringence (Δn), four azobenzene compounds based on lateral fluorinated bistolane moieties with trifluoromethyl terminal groups were synthesized with Hagihara–Sonogashira cross-coupling reaction. The molecular structures of the compounds were confirmed by Fourier transform infrared, ¹H-nuclear magnetic resonance. The transition temperatures, optical textures, and optical anisotropies were determined by differential scanning calorimetry, polarizing optical microscopy. The effect of the alkyl substituents on liquid crystal behavior is discussed in detail. The compounds have showed higher birefringence values.     

2μm波段激光晶体Tm:YAP的生长缺陷

采用提拉法沿a、b、c轴方向生长了Tm:YAP晶体,研究了该晶体的几种常见缺陷.通过化学腐蚀,利用光学显微镜观察了Tm:YAP晶体主要晶面的位错腐蚀坑形貌,发现在沿b轴生长晶体的(010)面上存在位错蚀坑密度不同的区域,对其成因进行了分析.借助偏光显微镜研究了晶体中的孪晶及消光现象,分析了成因并提出了消除措施.用He-Ne激光对晶体内的散射颗粒分布进行了研究,在扫描电镜(SEM)下观察到形状不规则的散射颗粒夹杂.上述研究结果对获得优质Tm:YAP晶体具有重要意义.     

温梯法Ce:YAG闪烁晶体的宏观缺陷观察

采用温度梯度法(TGT)成功生长了直径为76mm高光学质量的Ce:YAG高温闪烁晶体,采用偏光显微镜研究了Ce:YAG闪烁晶体中的主要宏观缺陷,观察到了生长条纹、侧心、气泡、包裹物以及应力双折射等宏观缺陷.实验结果表明,晶体中的气泡、包裹物以及应力双折射等宏观缺陷主要集中在晶体边缘部分,因此温梯法可以获得高质量的Ce:YAG闪烁晶体.     

6H-SiC单晶中的微管和小角度晶界

利用透射偏光显微术、同步辐射X射线形貌术、高分辨X射线衍射方法对6H-SiC(0001)晶片中的微管和小角度晶界等缺陷进行了研究.实验发现,在透射偏光显微镜下,微管通常呈现为蝴蝶形,这是由于微管周围存在着应力场,且应力分布不均匀,当线偏振光在通过微管周围区域时传播速度不同造成的.从X射线背反射同步辐射形貌像得到晶片中微管的Burgers矢量大小在2c到10c之间.从晶片00012衍射的双晶衍射摇摆曲线可以看出,晶片的中间大部分区域质量很好,双晶衍射峰为单峰且半峰宽很窄,一般为35"左右.在外围区域双晶衍射峰的半峰宽变宽,有些区域还会出现衍射峰的分裂,这说明外围区域有嵌镶块结构存在.     

Optical birefringence images of dislocations in large gallium phosphide crystals

The optical birefringence induced by the strain field of a dislocation has been used to follow dislocation lines through large gallium phosphide crystals. Dislocations could be seen whether their lines were parallel to the imaging light beam or were steeply inclined to it. The images obtained so far suggest that it would be possible to resolve individual dislocations in crystals that contain ?5 × 10⁵ dislocations per cm².     

Optical Sign Determinations on Cholesteric Lyotropic Mesophases

Optical signs of type I and II micellar cholesteric lyotropic mesophases were for the first time determined. Lyomesophases were prepared from the following amphiphiles: potassium l-N-lauroyl-serinate, potassium laurate, sodium decylsulfate, cesium decylsulfate and decyl-ammonium chloride. Cholesterol was added to all mesophases in order to obtain the chevron pattern for magnetically oriented samples. The method involves the direct observation of the textures at the polarizing microscope. Using a quartz-wedge retardation plate the directions of the slow and fast light vibration components are determined. This method is simpler than the usual observation, under conoscopic illumination, of the basal interference figure which is hardly obtained in micellar lyotropic cholesteric mesophases. All type I cholesteric lyotropic mesophases here investigated exhibited a positive optical sign, whereas all type II cholesteric lyomesophases showed a negative birefringence.     

Interaction between a dislocation and monovalent anion in various alkali halide crystals

It was investigated from (L₀/L)² versus ϕ₀ curve that the Friedel relation between the effective stress and the average length of dislocation segments, L, is appropriate for the interaction between a dislocation and the monovalent anion in various alkali halides single crystals (NaCl: Br^‐, NaBr: Cl^‐ or I^‐, KCl: Br^‐or I^‐, and RbCl: Br^‐ or I^‐). Here, L₀ represents the average spacing of monovalent anions on a slip plane and ϕ₀ is the bending angle at which the dislocation breaks away from the anion at the temperature of 0 K. This is because the anions are the weak obstacles such as impede the dislocation at ϕ₀ above about 150 degrees, where the Friedel relation agrees with the Fleischer one (L₀² = L²(π–ϕ₀)/2). Furthermore, the values of (L /L₀) were found to be within 4.05 to 5.87 for the crystals. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fabrication of Pre-tilted Vertical Alignment Layers for High-Speed Liquid Crystal Display Using Bi-functional Photoreactive Monomers

Abstract

To enable recent 3D and moving picture applications, liquid crystal displays (LCD) must exhibit fast response and wide viewing angle characteristics. Pre-tilted vertical alignment layers for high-speed LCD were fabricated using bi-functional photoreactive monomers. The monomers can be confined to the polyimide layer and photo-polymerized by UV exposure under voltage. Response characteristics of photo-controlled alignment films according to the structure were investigated. Vertical alignment properties were evaluated using a polarizing optical microscope, and electro-optical characteristics were compared through the voltage-transmittance curve and response time measurement. Faster response speed could be obtained by using photoreactive monomers having a long alkyl chain.     

Characterization of dislocation structures in copper single crystals using electron channelling contrast technique in SEM

The dislocation structures induced by low‐plastic‐strain‐amplitude cyclic deformation of [111] multiple‐slip‐oriented Cu single crystals were investigated using electron channelling contrast (ECC) technique in scanning electron microscopy (SEM). At a low plastic strain amplitude γ_pl of 8.8 × 10^–5, the saturated dislocation structure is mainly composed of labyrinth‐like vein structure (or irregular labyrinths), and the cyclic hardening behavior at such a low γ_pl is interpreted as being the result of dislocation multiplication by a Frank‐Read mechanism. As γ_pl increases to 4.0 × 10^–4, the unsaturated dislocation structure exhibits two kinds of distinctive configurations, i.e., dislocation walls and misoriented cells. Interestingly, these misoriented dislocation cells are strictly aligned along the primary slip plane (111), constituting a unique persistent slip band (PSB) structure. Here, these cells are thus called PSB cells. In addition, there is a locally distinctive region comprising some cells having a recrystallization‐like feature in the whole structure of PSB cells. The formation of the structure of PSB cells is discussed. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Birefringence simulation of annealed ingot of magnesium fluoride single crystal

We developed a method for simulating birefringence of an annealed ingot of MgF₂ single crystal for lithography optics. This method provides the optical path difference caused by crystal symmetry and residual stress existing in the crystal. The method consists of the heat conduction analysis, the residual stress analysis and the birefringence analysis. Because there exists no experimental data on the inelastic behavior of MgF₂ single crystal, the residual stress was estimated with the elastic thermal stress analysis using the finite element method by assuming a stress-free temperature. In this analysis, the temperature dependence of material properties and crystal anisotropy were taken into account. In the birefringence analysis, the distributions of optical path difference were calculated by an approximate method using the result of the residual stress analysis. This approximate method uses the average stress along the wave normal and is equivalent to the exact method in case of low stress dealt with the present study. In this analysis, it is possible to consider both the intrinsic birefringence and the stress birefringence in any crystal orientation. The distribution of the optical path difference in the annealed ingot obtained from the present calculation agrees qualitatively with that of the experiment. Its calculated value also agrees reasonably well with that of the experiment, when a stress-free temperature is adequately selected.     

晶格畸变检测仪研究碳化硅晶片中位错缺陷分布

利用晶格畸变检测仪研究了SiC晶片位错分布情况,通过对熔融KOH腐蚀后的SiC晶片进行全片或局部扫描,从而得到完整SiC晶片或局部区域的位错分布。与LEXT OLS4000 3D激光共聚焦显微镜扫描腐蚀图进行比较,晶格畸变检测仪扫描腐蚀图可以将晶片上位错腐蚀坑信息完全呈现出来,且根据腐蚀坑呈现的颜色及尺寸大小,可以分辨出三种不同类型的穿透型位错,其中黑点腐蚀坑对应螺位错,小尺寸白点腐蚀坑对应刃位错,大尺寸白点腐蚀坑对应混合型位错。采用晶格畸变测试仪研究了4英寸(101.6 mm)N型4H-SiC晶体不同生长时期的位错密度及分布情况,结果表明随着晶体生长,位错密度呈现逐渐降低的趋势,生长后期晶片的总位错密度降为生长前期晶片总位错密度的近1/3,有利于反馈位错缺陷在SiC晶体生长过程中的延伸和转化特性信息,以指导SiC晶体生长工艺改进。     

Mesomorphic and DFT studies of terminal ester containing salicylaldimines and their copper (II) complexes

In this article, we report synthesis and characterization of a novel homologous series of butyl 4-(4′-(alkoxy)-2-hydroxybenzylideneamino)benzoates, C_nLH (n = 6, 8, 10, 12, 14, 16) and their copper(II) complexes. The mesomorphic properties of these compounds were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and powder X-ray diffraction (XRD) studies. The ligands and their copper(II) complexes exhibit wide range of enantiotropic smectic A mesophase as confirmed by their typical optical texture under polarizing microscope. Thermal stability of the compounds is determined by thermo gravimetric analyses. DFT calculations have been performed using GAUSSIAN-09 program at B3LYP level to obtain the stable electronic structure of the ligand and its copper(II) complex.     

Defect Structure of Strained Heteroepitaxial In(1—x)Al(x)P Layers Deposited by MOVPE on (001) GaAs Substrates

Weak-beam, large angle convergent beam electron diffraction and high resolution transmission electron microscope experiments have revealed, that after strain relaxation due to plastic deformation dislocation networks can be observed in In_(1—x)Al_(x)P heteroepitaxial layers grown on (001) GaAs substrates under compressive stress. The 60° slip dislocations are mostly dissociated into partials of Shockley type whereas in the particular case of layers grown under tension twins are predominantly formed by successive nucleation and slip of 90° Shockley partials on adjacent {111} glide planes lying inclined to the (001) surface. When a few 90° Shockley partials pile up during extension of twins, then planar incoherent twin boundaries with {112} coincidence planes have been formed during strain relaxation. Due to the space group symmetry ((InAl)P belongs to the space group F4-3m) there is a striking asymmetry in defect formation, i.e. defect nucleation and slip on the planes (111) and (1-1-1) slip of the [1-10] zone are preferred to nucleation and slip on the {111} planes of the [110] zone. Apparently, the occupacy of the atomic sites in the dislocation core with either group-III or group-V atoms is responsible for this behaviour. The nature of the defects implies that their spontaneous nucleation should have taken place at the growing surface. Under tensile strain the 90° Shockley partial is nucleated first and the 30° one trails. Under compressive strain this sequence is reversed. It is evident, for dissociated dislocations lying at the interface always the 30° partial, i.e. the partial with less mobility or with higher friction force, is detained near or directly in the interface. Thus, in layers grown under tension the stacking fault associated with the dissociated 60° dislocation lies inside the GaAs substrate. For layers grown under compression it is located inside the ternary layer.     

8英寸导电型4H-SiC单晶衬底制备与表征

使用物理气相传输法(PVT)通过扩径技术制备出直径为209 mm的4H-SiC单晶,并通过多线切割、研磨和抛光等一系列加工工艺制备出标准8英寸SiC单晶衬底。使用拉曼光谱仪、高分辨X射线衍射仪、光学显微镜、电阻仪、偏光应力仪、面型检测仪、位错检测仪等设备,对8英寸衬底的晶型、结晶质量、微管、电阻率、应力、面型、位错等进行了详细表征。拉曼光谱表明8英寸SiC衬底100%比例面积为单一4H晶型;衬底(004)面的5点X射线摇摆曲线半峰全宽分布在10.44″~11.52″;平均微管密度为0.04 cm^-2;平均电阻率为0.020 3 Ω·cm。使用偏光应力仪对8英寸SiC衬底内部应力进行检测表明整片应力分布均匀,且未发现应力集中的区域;翘曲度(Warp)为17.318 μm,弯曲度(Bow)为-3.773 μm。全自动位错密度检测仪对高温熔融KOH刻蚀后的8英寸衬底进行全片扫描,平均总位错密度为3 293 cm^-2,其中螺型位错(TSD)密度为81 cm^-2,刃型位错(TED)密度为3 074 cm^-2,基平面位错(BPD)密度为138 cm^-2。结果表明8英寸导电型4H-SiC衬底质量优良,同比行业标准达到行业先进水平。     

Influence of defects and impurities on the deteriorated border region in multicrystalline silicon ingots

The origin of the lower minority carrier lifetime in the border region of multicrystalline silicon (mc‐Si) ingots was investigated. Based on minority carrier lifetime measurements and chemical analyses, distributions of defects and impurities were studied. It is found that the content of oxygen, carbon and other metal impurities in the border region were almost at the same level as that in the bulk, while the concentration of Fe‐B pairs is significantly higher. More interestingly, the dislocation density in the border region was observed to be much lower than that in the adjacent part. It is elucidated that the lower dislocation density in the border region leads to more iron existing in the form of Fe‐B pairs, which could be responsible for the low lifetime. In addition, it is shown that the low minority carrier lifetime in the border region can be improved effectively by phosphorous gettering. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)