X-ray topography of piezoelectric La(3)Ta(14)Ga(5.5)O(14) crystal grown by Czochralski Method.

We performed synchrotron X-ray topography on a La(3)Ta0(0.5)Ga (5.5)O(14) (LTG) crystal grown by the Czochralski method. Since a synchrotron X-ray source can provide high-energy X-rays, one can detect bulk structures by X-ray topography. LTG is one of the most attractive piezoelectric crystals along with La(3)Ga(5)SiO(14) (LGS) because of its excellent acoustic properties (temperature compensation of acoustic losses). Since LTG single crystals can be grown from a stoichiometric melt, it was expected that single crystals with better quality than the LGS crystal, which cannot be grown from a stoichiometric system but only from a congruent melt, can be obtained. However, 60 keV X-ray topography revealed that the LTG crystal quality was not as high as the LGS crystal quality. The crystal quality of the central region was lower than that of the surrounding region.     

Nondestructive diagnostics of microchannel (Macroporous) silicon by X-ray topography

It is demonstrated that X-ray topography can be used for imaging the boundary between a microchannel silicon layer and a substrate, evaluating the quality of this interface, determining the channel depth, and revealing mechanical stresses. This technique can be used for nondestructive monitoring of the structure of a microchannel layer at a spatial resolution of ≥5 μm.     

Nd:GGG激光晶体的同步辐射X射线白光形貌研究

应用同步辐射X射线白光形貌术,对Nd:GGG晶体中的缺陷进行了研究,观察到晶体中的主要缺陷是生长条纹和位错,对生长条纹产生的机理和位错的类型进行了分析讨论,生长条纹是由于温度波动引起生长率的起伏产生的,确定晶体中的位错有刃型位错、螺旋位错和混合位错.根据生长条纹和位错的生成机制,提出了一些改进生长工艺的措施和方法,为生长质量更高的晶体提供了参考.     

X-ray topography contrast of edge dislocations perpendicular to the 6H-SiC crystal surface

Features of the X-ray topography (XRT) images of edge dislocations perpendicular to the (0001) surface of a 6H-SiC single crystal are described. The contrast of topographs obtained in the regime of anomalous X-ray transmission is compared to the contrast of images obtained using section X-ray topography in the transmission geometry.     

同步辐射白光形貌术观察SiC单晶中的微小多型结构

采用同步辐射白光形貌术观察了6H和4H-SiC单晶片中的微小多型结构.基于透射同步辐射形貌术的衍射几何和晶片的取向,计算了SiC晶体中3种主要多型在Lane像中对应不同反射的成像位置,并与实际结果进行了比较.鉴别出6H和4H-SiC单晶中分别存在着少量的4H-SiC和15R-SiC多型的寄生生长.     

Ia型天然金刚石结构缺陷的同步辐射形貌研究

红外吸收光谱表明样品含片状和分散状分布的杂质氮 ,属Ia型金刚石。利用同步辐射对晶体进行了形貌学研究 ,在近完整晶体内近中心的 ( 0 0 1)和 ( 0 10 )结晶学平面内观察到生长带 ,生长方向平行于 ( 10 0 )和 ( 0 10 )。在欠完整晶体内小角度晶界发育 ,取向角达 2 .5°以上。晶体完整性与氮含量无明显相关关系     

X-ray imaging with parametric X-rays (PXR) from a lithium fluoride (LiF) crystal

X-ray imaging produced by parametric X-rays (PXR) is reported. The PXR are generated using an electron beam with energy of 56 MeV and currents up to 6.4 μA, that interacted with a 1.5-mm thick lithium fluoride (LiF) crystal target in Laue geometry. The LiF (2 2 0) crystallographic plane was used with a Bragg angle (θ_B) near 15° to produce PXR with energy 16.6 keV and FWHM of 3%. This intense, directional, and tunable X-ray source was then used to image a small fish, an integrated circuit, and an electrical switch with an intensified CCD camera. The bremsstrahlung from the target crystal is characterized as a source of noise and compared to the PXR.     

In-situ optical reflectance and synchrotron X-ray topography study of defects in epitaxial dilute GaAsN on GaAs

In order to investigate the possibilities of in-situ monitoring of GaAsN bulk layer growth and the crystal quality concerning the formation of misfit dislocations, GaAsN bulk samples with different layer thicknesses were grown using a metal-organic vapor phase epitaxy system equipped with a normal incidence optical reflectance setup. High-resolution X-ray diffractometry and synchrotron radiation X-ray topography were used to characterize the samples after growth. Combining the results from topography images and in-situ reflectance data, the formation of the misfit dislocations can be roughly identified from the reflectance curves and thus observed during growth.     

Sub-boundaries in3He and4He single crystal and their migration below 1K observed by X-ray topography

The observation of alterations in crystal structure at ultra-low temperatures by X-ray diffraction, made possible by the realization of synchrotron radiation use after a quarter of this century, plays an important role in obtaining an understanding of the base structure of solids. For that, two types of³He-⁴He dilution refrigerators with a modified version of the top-loading facilities were installed at the BL-3C₂ and 6C₁ stations of the Photon Factory. In BL-3C₂, the behaviors of lattice defects in solid helium have been studied by X-ray topography. In this note, the migrations of sub-boundaries in³He and⁴He single-crystals are reported as being the result of an annealing effect. After annealing hcp⁴He single crystals for 80min at 0.5K, no change in crystallographic orientations could be easily observed from white SR X-ray topographs. In the same type topographs of bcc³He single crystals after annealing for several hours at 03K, migration of sub-boundaries were conspicuously discerned.     

Synthesis and single crystal X-ray diffraction study of U(VI), Np(VI), and Pu(VI) perchlorate hydrates

The compounds [AnO₂(H₂O)₅](ClO₄)₂ (An = Np, Pu) and [NpO₂(ClO₄)₂(H₂O)₃] were prepared as single crystals, which were studied by X-ray diffraction at 100 K. The structural type at room temperature was determined. The low-temperature modification of [UO₂(H₂O)₅](ClO₄)₂ was found and structurally studied. The coordination polyhedra in [AnO₂(H₂O)₅]²⁺ are weakly distorted pentagonal bipyramids with averaged interatomic distances An-O of 1.754, 1.744, and 1.732 Å in the “yl” groups and of 2.415, 2.416, and 2.409 Å in the equatorial planes for U, Np, and Pu, respectively. Hence, in the complex cations [AnO₂(H₂O)₅]²⁺ the actinide contraction is manifested only in regular shortening of the An-O interatomic distances in the “yl” groups. The compound [NpO₂(ClO₄)₂(H₂O)₃], isostructural to its known uranyl analog, appeared to be the first, proved by single crystal X-ray diffraction, example of a compound with coordination interaction between the perchlorate ion and the neptunyl(VI) cation.     

Dislocations and grain boundaries in polycrystalline ice: a preliminary study by synchrotron X-ray topography

White-beam synchrotron X-ray topography has been used to image dislocations and grain boundaries in high-purity columnar-grained polycrystalline ice. It was found that screw, 30° and 60° basal dislocations with 1 1 ¯2 0 Burgers vectors far outnumber other dislocations: near free surfaces, the dislocations were bent because of image forces. Circular prismatic dislocation loops with [0 0 0 1] Burgers vectors and dipoles were also found. These probably formed due to thermal shock. In one sample, the dislocation structures of three grains were clearly observed simultaneously, although no dislocations were visible in the boundaries.     

Reflection X-ray topography of ZnO thin films on non-orienting substrates

Thin or moderately thick polycrystalline films of ZnO with preferentially oriented crystallites deposited on non-orienting substrates can in some cases be investigated using conventional X-ray topography. Examples of such reflection topographs are presented and their characteristic features are discussed. In particular, it is often possible to observe the texture, the film inhomogeneity and the influence of the deposition conditions on the preferred orientation.     

X-ray topographic study of lattice defects in a gadolinium gallium garnet single crystal

Lattice defects in gadolinium gallium garnet single crystals grown by the Czochralski technique were investigated by means of X-ray topography, under the condition where μ₀·t = 0.35, being different from the normal case. Dislocations, striations, and inclusions were observed and their characteristics were determined. These dislocations originated from seeding process. Some of their Burgers vectors were laid parallel to the (111) growth direction and the others parallel to a (100) direction. This information was useful for the growth of a dislocation free single crystal. It was also found that the inclusions had homogeneous strain fields arround the nuclei.     

A single crystal X-ray diffraction and IR study of (NH4)2[(UO2)C2O4(CH3COO)2]

A single crystal X-ray diffraction study of (NH₄)₂[(UO₂)C₂O₄(CH₃COO)₂] was performed. The compound crystallizes in the monoclinic system; unit cell parameters (at 100 ± 2 K): a = 6.793(2), b = 18.866(6), c = 20.730(7) Å, β = 90.040(7)°, space group P2₁/c, Z = 8, V = 2656.5(14) ų, R = 0.0495. The main structural units of the crystals are mononuclear complexes [(UO₂)C₂O₄(CH₃COO)₂]^2? belonging to crystal-chemical group AB ₃ ⁰¹ (A = UO ₂ ²⁺ , B⁰¹ = CH₃COO^? and C₂O ₄ ^2? ) of uranyl complexes. The uranium-containing anions are linked with ammonium cations by electrostatic interactions and a system of hydrogen bonds. The results of the X-ray diffraction analysis of the compound are well consistent with the IR data.     

A single crystal X-ray diffraction study of R[UO2(C2H5COO)3] (R = K or NH4)

A single crystal X-ray diffraction study of R[UO₂(C₂H₅COO)₃] [R = K (I) or NH₄ (II)] was performed. Both compounds crystallize in the cubic system, unit cell parameters for I: a = 11.4329(3) Å (at 100 K), space group P2₁3, Z = 4; for II: a = 11.60503(7) Å (at 123 K), space group P2₁3, Z = 4. The structures of crystals of I and II contain complex anions [UO₂(C₂H₅COO)₃]^? belonging to crystal-chemical group AB ₃ ⁰¹ of uranyl complexes (A = UO ₂ ²⁺ , B⁰¹ = C₂H₅COO^?). These anions are linked in a framework by electrostatic interactions with outer-sphere cations R and by hydrogen bonds (in case of II). The effect of the kind of carboxylate ion on structural features of R[UO₂L₃] (L is propionate or acetate ion) is discussed.     

可光固化丙烯酸双酯液晶的合成方法研究

以1,4-苯二甲酸[二(4-羧基苯)]酯为介晶基元合成了一系列丙烯酸双酯液晶化合物,研究了两种合成方法与路线,找到了一种合成方法相对简单、产率较高的合成路线,化合物结构通过FTIR、元素分析、质谱和1H-NMR等方法进行了确证.