Characterization of Growth Defects in ZnTe Single Crystals

1994 ◽  
Vol 299 ◽  
Author(s):  
W. Zhou ◽  
J. Wu ◽  
M. Dudley ◽  
C.H. Su ◽  
M.P. Volz ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Dislocation Cell ◽  
Interference Microscopy ◽  
Dislocation Slip ◽  
Asymmetric Distribution ◽  
Twin Boundaries ◽  
X Ray ◽  
Atomic Structures ◽  
Slip Bands ◽  
White Beam

Abstract(111) wafers sliced from a boule of ZnTe grown by horizontal physical vapor transport (PVT) have been characterized using synchrotron white beam X-ray topography. The growth axis was about 6° off [311]. The presence of dislocation slip bands, subgrain structures and [111] axis 180° rotational twins were revealed. The slip bands were observed to break up the ordered dislocation cell structures comprising the subgrain boundaries. The initiation of slip at regions of stress concentration at the junctions of subgrain boundaries and twin boundaries was observed. The asymmetric distribution of slip bands either side of the twinned region of crystal suggests that twin boundaries can act as barriers for slip. Several types of detailed twin boundary configuration were determined from the topographs. Using a combination of white beam X-ray topography and Nomarski interference microscopy, the three dimensional shapes of the twin boundaries were determined. Approximate atomic structures at these boundaries are presented.

Characterization of Growth Defects in ZnTe Single Crystals

1993 ◽  
Vol 302 ◽  
Author(s):  
W. Zhou ◽  
J. Wu ◽  
M. Dudley ◽  
C.H. Su ◽  
M.P. Volz ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Dislocation Cell ◽  
Interference Microscopy ◽  
Dislocation Slip ◽  
Asymmetric Distribution ◽  
Twin Boundaries ◽  
X Ray ◽  
Atomic Structures ◽  
Slip Bands ◽  
White Beam

ABSTRACT(111) wafers sliced from a boule of ZnTe grown by horizontal physical vapor transport (PVT) have been characterized using synchrotron white beam X-ray topography. The growth axis was about 6° off [311]. The presence of dislocation slip bands, subgrain structures and [111] axis 180° rotational twins were revealed. The slip bands were observed to break up the ordered dislocation cell structures comprising the subgrain boundaries. The initiation of slip at regions of stress concentration at the junctions of subgrain boundaries and twin boundaries was observed. The asymmetric distribution of slip bands either side of the twinned region of crystal suggests that twin boundaries can act as barriers for slip. Several types of detailed twin boundary configuration were determined from the topographs. Using a combination of white beam X-ray topography and Nomarski interference microscopy, the three dimensional shapes of the twin boundaries were determined. Approximate atomic structures at these boundaries are presented.

Characterization of Growth Defects in CdZnTe Single Crystals by Synchrotron White Beam X-ray Topography

1995 ◽  
Vol 378 ◽  
Author(s):  
H. Chung ◽  
B. Raghothamachar ◽  
J. Wu ◽  
M. Dudley ◽  
D. J. Larson ◽  
...  
Keyword(s):  
Thermal Stress ◽  
Single Crystals ◽  
Thermal Stresses ◽  
Structural Defects ◽  
Dislocation Slip ◽  
Accelerated Cooling ◽  
Cooling Rates ◽  
X Ray ◽  
Slip Bands ◽  
White Beam

AbstractSynchrotron white beam X-ray topography has been used to characterize structural defects in microgravity grown CdZnTe single crystals. Defects such as dislocations, slip bands, 180° rotation twins, precipitates and subgrain boundaries are observed but their density is much lower than those in crystals grown under normal gravity. The observed results also indicate that the defect structures of the as grown crystals are strongly influenced by cooling rates. X-ray transmission topographs recorded from regions grown at different cooling rates show that the dislocation density in rapidly cooled regions is higher than that in slowly cooled regions. The formation of dislocations is presumably attributed to the thermal stress caused by accelerated cooling rates, which is greater than the critical resolved shear stress. As the cooling rate is accelerated, the magnitude of thermal stress is increased and more dislocations are formed to relieve the accumulated lattice strain. In addition, if the cooling rates are increased further, the accentuated thermal stresses can give rise to more pronounced deformation processes, comprising the formation of dislocation slip bands, as confirmed by the extensive slip bands revealed by the X-ray reflection topographs.

Characterization of Defect Structures in 3C-SiC Single Crystals Using Synchrotron White Beam X-ray Topography

1996 ◽  
Vol 423 ◽  
Author(s):  
W. Huang ◽  
M. Dudley ◽  
C. Fazi
Keyword(s):  
Single Crystals ◽  
Stacking Faults ◽  
Interference Microscopy ◽  
Defect Structures ◽  
Growth Sector ◽  
X Ray ◽  
Partial Dislocations ◽  
White Beam ◽  
Transmission And Reflection

AbstractDefect structures in (111) 3C-SiC single crystals, grown using the Baikov technique, have been studied using Synchrotron White Beam X-ray Topography (SWBXT). The major types of defects include complex growth sector boundary structures, double positioning twins, stacking faults on { 111 } planes, inclusions and dislocations (including growth dislocations and partial dislocations bounding stacking faults). Detailed stacking fault and double positioning twin configurations are determined using a combination of Nomarski interference microscopy, SEM and white beam x-ray topography in both transmission and reflection geometries. Possible defect generation phenomena are discussed.

Structure and optical non-linearity of PbO.2B2O3

1996 ◽  
Vol 52 (2) ◽  
pp. 260-265 ◽  
Author(s):  
D. L. Corker ◽  
A. M. Glazer
Keyword(s):  
Room Temperature ◽  
Three Dimensional ◽  
Asymmetric Distribution ◽  
X Ray Diffraction ◽  
Acta Cryst ◽  
X Ray ◽  
Dimensional Network ◽  
Non Linear ◽  
Linear Optical ◽  
Atomic Coordinates

The crystal structure of lead tetraborate, PbO.2B2O3, has been refined using single-crystal X-ray diffraction data (Mo Kα radiation, λ = 0.71069 Å). Crystal data at room temperature: Mr = 362.43, orthorhombic, P21 nm (C 7 2v ), a = 4.251 (2), b = 4.463 (3), c = 10.860 (3) Å, V = 206.04 Å3 with Z = 2, μ = 402.6 cm−1, Dx = 5.88 Mg m−3, F(000) = 316, final R = 0.022, wR = 0.025 over 655 reflections with I > 2.5σ(I). Atomic coordinates are in general agreement with those previously reported for the isostructural compound, SrO.2B2O3, by Perloff & Block [Acta Cryst. (1966), 20, 274–279]. All the borons are tetrahedrally coordinated with a three-dimensional network formed from O atoms that are common to either two or three tetrahedra. The tetrahedra show deformation because the B—O bonds involving the two-coordinated O atoms are much shorter than those involved with three-coordinated O atoms. The Pb atoms are situated in empty tunnels running along [010] left by the network of tetrahedra. The Pb atoms display a highly asymmetric distribution of Pb—O bonding, with the five shortest bonds covering the range 2.483 (5)–2.664 (5) Å, being all situated to one side of the Pb atom. Preliminary investigations of the non-linear optical behaviour of lead tetraborate are also discussed. The results indicate that doping with barium should lead to a new non-linear optical material that is both phase-matchable and has a high optical non-linearity.

scholarly journals Sir Aaron Klug OM. 11 August 1926—20 November 2018

2020 ◽  
Vol 68 ◽  
pp. 273-296
Author(s):  
R. A. Crowther
Keyword(s):  
Electron Microscopy ◽  
Molecular Biology ◽  
Royal Society ◽  
Zinc Fingers ◽  
Three Dimensional ◽  
Transfer Rna ◽  
Biological Structure ◽  
X Ray ◽  
X Ray Crystallography ◽  
Atomic Structures

Aaron Klug made outstanding contributions to the development of structural molecular biology. An early interest in viruses, stemming from work with Rosalind Franklin, prompted him to think deeply about extracting the information contained in electron micrographs. As a result, he proposed a method for making three-dimensional maps of biological specimens from the projected images given by micrographs. For this development and its application to complex molecular assemblies, he was awarded the 1982 Nobel Prize in Chemistry. The recent revolution in biological structure determination, whereby atomic structures can now be determined from micrographs of frozen hydrated specimens, derives from this initial breakthrough. With colleagues, Aaron applied X-ray crystallography and electron microscopy to determine the structures and thereby understand the functions of many biological assemblies, including viruses, transfer RNA, chromatin and zinc fingers. He also made important forays into the pathogenesis of Alzheimer's disease and related dementias. Aaron was director of the MRC Laboratory of Molecular Biology in Cambridge from 1986 to 1996 and President of the Royal Society from 1995 to 2000.

Nanoscale stability of two- and three-dimensional defects in Cu/Ag–Mo thin films

2017 ◽  
Vol 50 (1) ◽  
pp. 152-171 ◽  
Author(s):  
G. Csiszár ◽  
A. Makvandi ◽  
E. J. Mittemeijer
Keyword(s):  
Thin Films ◽  
Heat Treatment ◽  
Texture Evolution ◽  
Three Dimensional ◽  
X Ray Diffraction ◽  
Twin Boundaries ◽  
X Ray ◽  
Transmission Electron ◽  
Before And After ◽  
Columnar Grain

A comparative study of the thermal stability of nanocrystalline Cu–Mo and Ag–Mo alloy thin films was performed. Phase decomposition, texture evolution, grain coarsening and segregation of Mo to planar faults of both films, before and after heat treatment, were studied using X-ray diffraction measurements and (high-resolution) transmission electron microscopy with energy-dispersive spectroscopy. The evolution of stress/strain in the thin films was traced by in situ X-ray diffraction measurements. The segregation of Mo solute atoms at twin boundaries in both films already occurs at room temperature. By first segregation and then precipitation of Mo atoms at grain boundaries, the columnar grain microstructure is preserved upon heat treatment. In the case of Ag–Mo thin films, the twin boundaries are also more or less preserved at elevated temperature, but in the case of Cu–Mo thin films the annihilation of twin boundaries takes place concomitantly with the precipitation of Mo in columnar grain interiors.

scholarly journals MicroED data collection and processing

2015 ◽  
Vol 71 (4) ◽  
pp. 353-360 ◽  
Author(s):  
Johan Hattne ◽  
Francis E. Reyes ◽  
Brent L. Nannenga ◽  
Dan Shi ◽  
M. Jason de la Cruz ◽  
...  
Keyword(s):  
Data Collection ◽  
Three Dimensional ◽  
Limiting Factor ◽  
Structural Studies ◽  
X Ray ◽  
X Ray Crystallography ◽  
Atomic Structures ◽  
Single Well ◽  
Diffraction Patterns ◽  
Three Dimensional Models

MicroED, a method at the intersection of X-ray crystallography and electron cryo-microscopy, has rapidly progressed by exploiting advances in both fields and has already been successfully employed to determine the atomic structures of several proteins from sub-micron-sized, three-dimensional crystals. A major limiting factor in X-ray crystallography is the requirement for large and well ordered crystals. By permitting electron diffraction patterns to be collected from much smaller crystals, or even single well ordered domains of large crystals composed of several small mosaic blocks, MicroED has the potential to overcome the limiting size requirement and enable structural studies on difficult-to-crystallize samples. This communication details the steps for sample preparation, data collection and reduction necessary to obtain refined, high-resolution, three-dimensional models by MicroED, and presents some of its unique challenges.

Studies of Interface Demarcation and Structural Defects in Ga Doped Ge Single Crystals Using Synchrotron White Beam X-Ray Topography

1996 ◽  
Vol 437 ◽  
Author(s):  
H. Chung ◽  
B. Raghothamachar ◽  
W. Zhou ◽  
M. Dudley ◽  
D. C. Gillies
Keyword(s):  
Single Crystals ◽  
Reciprocal Lattice ◽  
Dislocation Cell ◽  
Structural Defects ◽  
Interface Plane ◽  
Lattice Vector ◽  
Synchrotron Source ◽  
X Ray ◽  
Correct Orientation ◽  
White Beam

AbstractSynchrotron White Beam X-ray Topography (SWBXT) has been applied to the characterization of marked growth interfaces in Ga doped Ge single crystals. The techniques employed in interface demarcation include modifications of the cold zone temperature, mechanical pulsing and Peltier pulsing. As revealed by our observations, the visibility of growth interfaces is a sensitive function of diffraction conditions. A combination of the correct orientation of the active reciprocal lattice vector with respect to the interface plane and the necessary strain sensitivity controlled by the rocking curve width of the reflection are proved to be important for interface visibility. This can easily be achieved by using synchrotron radiation since the tunability of the synchrotron source provides great flexibility in the choice of proper diffraction conditions. Structural defects such as small-angle tilt boundaries and dislocation cell structures were also observed. The formation mechanism of these defects will be discussed. Direct evidence of dislocations present in the seed crystal propagating into the as-grown crystal through the melt-back interface during crystal growth was also obtained.

Ribosome Structural Organization

1974 ◽  
Vol 32 ◽  
pp. 332-333
Author(s):  
James A. Lake
Keyword(s):  
Ribosomal Proteins ◽  
Structural Organization ◽  
Three Dimensional ◽  
Small Subunit ◽  
Structural Studies ◽  
X Ray Diffraction ◽  
Specific Antibodies ◽  
X Ray ◽  
E Coli ◽  
Complete Sequences

The understanding of ribosome structure has advanced considerably in the last several years. Biochemists have characterized the constituent proteins and rRNA's of ribosomes. Complete sequences have been determined for some ribosomal proteins and specific antibodies have been prepared against all E. coli small subunit proteins. In addition, a number of naturally occuring systems of three dimensional ribosome crystals which are suitable for structural studies have been observed in eukaryotes. Although the crystals are, in general, too small for X-ray diffraction, their size is ideal for electron microscopy.

Arsenic segregation in polysilicon

1983 ◽  
Vol 41 ◽  
pp. 154-155 ◽  
Author(s):  
P.E. Batson ◽  
C.R.M. Grovenor ◽  
D.A. Smith ◽  
C. Wong
Keyword(s):  
Incident Beam ◽  
Silicon Wafers ◽  
Chemical Polishing ◽  
Bright Field Image ◽  
Beam Size ◽  
Stem Analysis ◽  
Bright Field ◽  
Twin Boundaries ◽  
X Ray ◽  
Line Scan

In this work As doped polysilicon was deposited onto (100) silicon wafers by APCVD at 660°C from a silane-arsine mixture, followed by a ten minute anneal at 1000°C, and in one case a further ten minute anneal at 700°C. Specimens for TEM and STEM analysis were prepared by chemical polishing. The microstructure, which is unchanged by the final 700°C anneal,is shown in Figure 1. It consists of numerous randomly oriented grains many of which contain twins.X-ray analysis was carried out in a VG HB5 STEM. As K α x-ray counts were collected from STEM scans across grain and twin boundaries, Figures 2-4. The incident beam size was about 1.5nm in diameter, and each of the 20 channels in the plots was sampled from a 1.6nm length of the approximately 30nm line scan across the boundary. The bright field image profile along the scanned line was monitored during the analysis to allow correlation between the image and the x-ray signal.

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