Comparison of the phase-invariant and mosaic crystal models for dynamical x-ray diffraction from metamorphic InxGa1−xAs/GaAs (001) structures

2015 ◽  
Vol 33 (2) ◽  
pp. 021204 ◽  
Author(s):  
Paul B. Rago ◽  
John E. Ayers
Keyword(s):  
X Ray Diffraction ◽  
X Ray ◽  
Mosaic Crystal

Mosaic Crystal Model for Dynamical X-Ray Diffraction from Step-Graded InxGa1-xAs and InxAl1-xAs/GaAs (001) Metamorphic Buffers and Device Structures

2017 ◽  
Vol 26 (03) ◽  
pp. 1740019
Author(s):  
P. B. Rago ◽  
J. E. Ayers
Keyword(s):  
Semiconductor Device ◽  
High Electron Mobility Transistors ◽  
High Electron ◽  
X Ray Diffraction ◽  
General Applicability ◽  
X Ray ◽  
Device Structures ◽  
Mosaic Crystal ◽  
Crystal Model ◽  
Metamorphic Buffers

In this paper we apply a mosaic crystal model for dynamical x-ray diffraction to step-graded metamorphic semiconductor device structures containing dislocations. This model represents an extension of the previously-reported phase-invariant model, which is broadly applicable and serves as the basis for the x-ray characterization of metamorphic structures, allowing determination of the depth profiles of strain, composition, and dislocation density. The new model has more general applicability and is more appropriate for step-graded metamorphic device structures, which are of particular interest for high electron mobility transistors and light emitting diodes. Here we present the computational details of the mosaic crystal model and demonstrate its application to step-graded InxGa1-xAs/GaAs (001) and InxAl1-xAs/GaAs (001) metamorphic buffers and device structures.

scholarly journals Neutron diffraction

1949 ◽  
Vol 196 (1044) ◽  
pp. 50-64 ◽  
Keyword(s):  
Neutron Diffraction ◽  
Practical Problem ◽  
Perfect Crystal ◽  
Thermal Neutrons ◽  
X Ray Diffraction ◽  
X Ray ◽  
Structure Factors ◽  
Mosaic Crystal ◽  
Mosaic Crystals ◽  
Collimated Beam

The problem of neutron diffraction by crystals is treated by analogy with X-ray diffraction, consideration being given to the perfect crystal, the mosaic crystal and the powdered block. The first part of the paper deals with a comparison between X-ray and neutron diffraction and it is shown that quantitatively the two are similar, apart from the case of the thick mosaic crystal where the very low values which are usually found for the true absorption of neutrons result in the integrated reflexion being largely independent of structure factor under practical conditions. The second part deals with the practical problem of diffracting the collimated beam of thermal neutrons from an atomic pile. Again, perfect and mosaic crystals are considered and it is also shown that the powder method, which it is desirable to use when structure factors are to be determined, will be feasible if the number of pile neutrons which hit the mono-chromatizing crystal is greater than 10 5 per sec.

Dynamical X-Ray Diffraction Analysis of a GaAs/In0.3Ga0.7As Single Quantum Well Grown on a GaAs (001) Substrate

2018 ◽  
Vol 27 (01n02) ◽  
pp. 1840010
Author(s):  
F. A. Althowibi ◽  
J. E. Ayers
Keyword(s):  
Quantum Well ◽  
Bragg Peak ◽  
Threading Dislocation ◽  
Single Quantum ◽  
X Ray Diffraction ◽  
Single Quantum Well ◽  
X Ray ◽  
Mosaic Crystal ◽  
Crystal Model ◽  
Threading Dislocation Density

We applied the mosaic crystal model to calculate the dynamical x-ray rocking curves for a coherently-strained GaAs/In0.3Ga0.7As/GaAs single quantum well grown epitaxially on a GaAs (001) substrate for a number of reflection profiles, including 004, 113, 224, 044 and 444 reflections. We show that it is possible to estimate the threading dislocation density in the quantum well, and therefore detect the pseudomorphic-metamorphic transition, using the widths or normalized intensities of the primary quantum well Bragg peak, or using the widths of the Pendellösung fringes associated with the quantum well structure.

The Use of Advanced Analytical Techniques for Characterization of the Chemical, Physical, and Crystallographic Nature of a Surface

1973 ◽  
Vol 31 ◽  
pp. 132-133 ◽  
Author(s):  
R. E. Herfert
Keyword(s):  
Surface Characterization ◽  
Analytical Techniques ◽  
X Ray Diffraction ◽  
Depth Of Penetration ◽  
X Ray ◽  
The Past ◽  
Transmission Electron ◽  
Scanning Electron

Studies of the nature of a surface, either metallic or nonmetallic, in the past, have been limited to the instrumentation available for these measurements. In the past, optical microscopy, replica transmission electron microscopy, electron or X-ray diffraction and optical or X-ray spectroscopy have provided the means of surface characterization. Actually, some of these techniques are not purely surface; the depth of penetration may be a few thousands of an inch. Within the last five years, instrumentation has been made available which now makes it practical for use to study the outer few 100A of layers and characterize it completely from a chemical, physical, and crystallographic standpoint. The scanning electron microscope (SEM) provides a means of viewing the surface of a material in situ to magnifications as high as 250,000X.

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.

Electron Microscopy of Human Gallstones

1971 ◽  
Vol 29 ◽  
pp. 296-297
Author(s):  
C. Wolpers ◽  
R. Blaschke
Keyword(s):  
Electron Microscopy ◽  
Room Temperature ◽  
Bile Pigment ◽  
X Ray Diffraction ◽  
Triclinic Crystal System ◽  
X Ray ◽  
Follow Up Study ◽  
Infra Red ◽  
Main Components

Scanning microscopy was used to study the surface of human gallstones and the surface of fractures. The specimens were obtained by operation, washed with water, dried at room temperature and shadowcasted with carbon and aluminum. Most of the specimens belong to patients from a series of X-ray follow-up study, examined during the last twenty years. So it was possible to evaluate approximately the age of these gallstones and to get information on the intensity of growing and solving.Cholesterol, a group of bile pigment substances and different salts of calcium, are the main components of human gallstones. By X-ray diffraction technique, infra-red spectroscopy and by chemical analysis it was demonstrated that all three components can be found in any gallstone. In the presence of water cholesterol crystallizes in pane-like plates of the triclinic crystal system.

High Resolution Replication of Organoclay Surfaces

1982 ◽  
Vol 40 ◽  
pp. 576-577
Author(s):  
W. W. Barker ◽  
W. E. Rigsby ◽  
V. J. Hurst ◽  
W. J. Humphreys
Keyword(s):  
Clay Mineral ◽  
Organic Molecule ◽  
Organic Molecules ◽  
X Ray Diffraction ◽  
Xrd Pattern ◽  
X Ray ◽  
Naturally Occurring ◽  
Silicate Layers ◽  
Mineral Identification

Experimental clay mineral-organic molecule complexes long have been known and some of them have been extensively studied by X-ray diffraction methods. The organic molecules are adsorbed onto the surfaces of the clay minerals, or intercalated between the silicate layers. Natural organo-clays also are widely recognized but generally have not been well characterized. Widely used techniques for clay mineral identification involve treatment of the sample with H2 O2 or other oxidant to destroy any associated organics. This generally simplifies and intensifies the XRD pattern of the clay residue, but helps little with the characterization of the original organoclay. Adequate techniques for the direct observation of synthetic and naturally occurring organoclays are yet to be developed.

Electron Microscopy of Shock Loaded Polycrystalline Beryllium

1974 ◽  
Vol 32 ◽  
pp. 506-507 ◽  
Author(s):  
J. M. Galbraith ◽  
L. E. Murr ◽  
A. L. Stevens
Keyword(s):  
Electron Microscopy ◽  
Wave Propagation ◽  
Structural Change ◽  
Single Crystal ◽  
Diffraction Pattern ◽  
Shock Loading ◽  
Slip Systems ◽  
Compression Tests ◽  
X Ray Diffraction ◽  
X Ray

Uniaxial compression tests and hydrostatic tests at pressures up to 27 kbars have been performed to determine operating slip systems in single crystal and polycrystal1ine beryllium. A recent study has been made of wave propagation in single crystal beryllium by shock loading to selectively activate various slip systems, and this has been followed by a study of wave propagation and spallation in textured, polycrystal1ine beryllium. An alteration in the X-ray diffraction pattern has been noted after shock loading, but this alteration has not yet been correlated with any structural change occurring during shock loading of polycrystal1ine beryllium.This study is being conducted in an effort to characterize the effects of shock loading on textured, polycrystal1ine beryllium. Samples were fabricated from a billet of Kawecki-Berylco hot pressed HP-10 beryllium.

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