Structure and Properties of Ultrathin Ge-Si Superlattices

1986 ◽  
Vol 67 ◽  
Author(s):  
J. Bevk ◽  
J. P. Mannaerts ◽  
L. C. Feldman ◽  
B. A. Davidson ◽  
W. P. Lowe ◽  
...  
Keyword(s):  
Optical Transition ◽  
Growth Direction ◽  
Unit Cell ◽  
Silicon Substrates ◽  
Optical Studies ◽  
One Dimensional ◽  
X Ray ◽  
Ordered Alloys ◽  
Diffraction Patterns ◽  
Highly Strained

ABSTRACTWe report the synthesis, structural characterization, and preliminary optical studies of ultrathin Ge-Si superlattices with individual sublayers smaller than the Si unit cell, grown by MBE on (001) silicon substrates. Structures are fabricated one monolayer at a time in a configuration GeGeSiSiGeGe..., resulting in either ordered alloys or complex cell superlattices. Rutherford backscattering and channeling experiments on these highly strained heterostructures indicate excellent crystallinity with tetragonal distortion as high as 3.5%. Electron diffraction patterns exhibit characteristic superlattice reflections indicative of one-dimensional layering with periodicity of four monolayers. X-ray scans along the growth direction at the (002) position in reciprocal space reveal a strong peak not observed in random GeSi alloys. This scattering is attributed indirectly to the GeSi ordered phase. The optical transition energies measured by Schottky barrier electroreflectance correspond to those expected from homogeneous alloys of the same composition; however, the width of optical transitions is less than 30 meV at room temperature, allowing a clear resolution of the splitting of the valence band by strain. Modification of the unit cell of the diamond lattice in this way should permit the design of materials with novel opto-electronic characteristics. Preliminary Raman and photoconductivity measurements are also reported.

X-ray diffraction study of a one-dimensional GaAs–AlAs superlattice

1977 ◽  
Vol 10 (1) ◽  
pp. 1-6 ◽  
Author(s):  
A. Segmüller ◽  
P. Krishna ◽  
L. Esaki
Keyword(s):  
Elastic Strain ◽  
Lattice Mismatch ◽  
Reciprocal Lattice ◽  
Unit Cell ◽  
Scattering Data ◽  
High Angle ◽  
X Ray Diffraction ◽  
One Dimensional ◽  
X Ray ◽  
Diffraction Patterns

Low- and high-angle X-ray diffraction patterns have been obtained from one-dimensional superlattice crystals prepared artificially by alternately depositing predetermined thicknesses of GaAs and AlAs, on the (001) face of a GaAs single-crystal by molecular-beam epitaxy. The positions and intensities of several superlattice reflections obtained along the 00l, 11l and 02l reciprocal lattice rows have been recorded. The structure of the superlattice can be approximated by a model which incorporates elastic strains in the unit cell due to the lattice mismatch between GaAs and AlAs. The number of Ga and Al layers in the superlattice unit cell can be accurately determined from the low-angle scattering data while the relative intensities of the high-angle superlattice reflections are a sensitive measure of the elastic strain present in the lattice. It is shown that the elastic strain agrees with the value computed theoretically on the assumption that the strain is not relieved by dislocations at the GaAs–AlAs interfaces.

Analysis of Selected Area Diffraction Patterns With Winjade

1998 ◽  
Vol 4 (S2) ◽  
pp. 342-343 ◽  
Author(s):  
S. D. Walck ◽  
P. Ruzakowski-Athey
Keyword(s):  
Single Phase ◽  
Xrd Analysis ◽  
Analysis Program ◽  
X Ray Diffraction ◽  
Program Module ◽  
Vast Number ◽  
One Dimensional ◽  
X Ray ◽  
Diffraction Patterns ◽  
Xrd Patterns

The analysis of Selected Area Diffraction (SAD) patterns that are collected from a single phase material having sufficient crystallites to provide continuous rings is relatively straightforward. However, when this condition is not met and there may be several phases present having rings of a spotty nature, the pattern is complex and can be quite difficult to analyze manually because of the vast number of discrete spots. WinJade from MDI is an X-ray diffraction (XRD) analysis program with an Electron Diffraction Program Module (EDPM) that can be used to aid in the analysis of SAD patterns. The EDPM produces Integrated Circular Density Plots (ICDP), which are one-dimensional intensity profiles plotted as a function of equivalent XRD 20 values or crystal d-spacings. These ICDP's can be overlayed with XRD patterns or with reference lines from the NIST and JCPDS crystalline databases for direct comparisons.

X-ray powder diffraction reference patterns for Bi1−xPbxOCuSe

2016 ◽  
Vol 31 (3) ◽  
pp. 223-228 ◽  
Author(s):  
W. Wong-Ng ◽  
Y. Yan ◽  
J.A. Kaduk ◽  
X.F. Tang
Keyword(s):  
Cell Volume ◽  
Powder Diffraction ◽  
Ionic Radius ◽  
Unit Cell Volume ◽  
Unit Cell ◽  
Powder Diffraction File ◽  
X Ray ◽  
Natural Superlattice ◽  
Diffraction Patterns ◽  
Pb Substitution

The structures and powder X-ray reference diffraction patterns of the “natural superlattice” series Bi1−xPbxOCuSe (x = 0, 0.02, 0.04, 0.06, 0.08, and 0.10) have been investigated. As the ionic radius of Pb2+ is greater than that of Bi3+, the unit-cell volume of Bi1−xPbxOCuSe increases progressively from x = 0 to 0.1, namely, from 137.868(5) to 139.172(11) Å3, as expected. The structure of Bi1−xPbxOCuSe is built from [Bi2(1−x)Pb2xO2]2(1−x)+ layers normal to the c-axis alternating with [Cu2Se2]2(1−x)− fluorite-like layers. Pb substitution in the Bi site of Bi1−xPbxOCuSe leads to the weakening of the “bonding” between the [Bi2(1−x)Pb2xO2]2(1−x)+ and the [Cu2Se2]2(1−x)− layers. Powder patterns of Bi1−xPbxOCuSe were submitted to be included in the Powder Diffraction File.

X-ray powder diffraction data for compound DyNiSn

1997 ◽  
Vol 12 (3) ◽  
pp. 134-135
Author(s):  
Liangqin Nong ◽  
Lingmin Zeng ◽  
Jianmin Hao
Keyword(s):  
Powder Diffraction ◽  
Diffraction Data ◽  
Figure Of Merit ◽  
Room Temperature ◽  
Unit Cell ◽  
Powder Diffraction Data ◽  
X Ray Diffraction ◽  
Space Group ◽  
X Ray ◽  
Diffraction Patterns

The compound DyNiSn has been studied by X-ray powder diffraction. The X-ray diffraction patterns for this compound at room temperature are reported. DyNiSn is orthorhombic with lattice parameters a=7.1018(1) Å, b=7.6599(2) Å, c=4.4461(2) Å, space group Pna21 and 4 formula units of DyNiSn in unit cell. The Smith and Snyder Figure-of-Merit F30 for this powder pattern is 26.7(0.0178,63).

scholarly journals The crystal structures of two polyamides (‘nylons’)

1947 ◽  
Vol 189 (1016) ◽  
pp. 39-68 ◽  
Keyword(s):  
Crystal Structures ◽  
Unit Cell ◽  
Chain Molecule ◽  
X Ray Diffraction ◽  
X Ray ◽  
Cell Dimensions ◽  
C Fibre ◽  
Diffraction Patterns ◽  
Unit Cell Dimensions ◽  
Crystalline Forms

Detailed interpretations of the X -ray diffraction patterns of fibres and sheets of 66 and 6.10 polyamides (polyhexam ethylene adipamide and sebacamide respectively) are proposed. The crystal structures of the two substances are completely analogous. Fibres of these two polyam ides usually contain two different crystalline forms, α and β, which are different packings of geometrically similar molecules; most fibres consist chiefly of the α form. In the case of the 66 polymer, fibres have been obtained in which there is no detectable proportion of the β form. Unit cell dimensions and the indices of reflexions for the α form were determined by trial, using normal fibre photographs, and were checked by using doubly oriented sheets set at different angles to the X -ray beam. The unit cell of the a form is triclinic, with a — 4·9 A, b = 5·4 A, c (fibre axis) = 17·2A, α = 48 1/2º, β = 77º, γ = 63 1/2º for the 66 polymer; a = 4·95A, b = 5·4A, c (fibre axes) = 22·4A, α = 49º, β = 76 1/2º, γ = 63 1/2º for the 6.10 polymer. One chain molecule passes through the cell in both cases. Atomic coordinates in occrystals were determined by interpretation of the relative intensities of the reflexions. The chains are planar or very nearly so; the oxygen atoms appear to lie a little off the plane of the chain. The molecules are linked by hydrogen bonds between C = 0 and NH groups, to form sheets. A simple packing of these sheets of molecules gives the α arrangement.

X-ray powder diffraction analysis of the heteropoly-molybdate (MoO2)0.5PMo14O42

2003 ◽  
Vol 18 (3) ◽  
pp. 236-239 ◽  
Author(s):  
L. Marosi ◽  
J. Cifré ◽  
C. Otero Areán
Keyword(s):  
Catalytic Activity ◽  
Diffraction Analysis ◽  
Computer Modeling ◽  
Powder Diffraction ◽  
Rietveld Analysis ◽  
Nitrogen Atmosphere ◽  
Unit Cell ◽  
X Ray Diffraction ◽  
X Ray ◽  
Diffraction Patterns

The new heteropoly blue compound (MoO2)0.5PMo14O42, which is relevant in the context of catalytic activity of heteropoly-molybdates, was prepared by controlled thermolysis of (NH4)3PMo12O40 at 730 K in a nitrogen atmosphere. Powder X-ray diffraction analysis showed that this compound has a cubic unit cell, space group Pn3m (No. 224), with ao=11.795(2) Å, Z=2 and DXR=4.2466 g cm−3. Computer modeling and Rietveld analysis of powder diffraction patterns led to a proposed structure of the corresponding Keggin-cage unit PMo14O42.

Structural properties of molecular beam epitaxy grown Ni/Pt superlattices

1997 ◽  
Vol 12 (1) ◽  
pp. 161-174 ◽  
Author(s):  
W. Staiger ◽  
A. Michel ◽  
V. Pierron-Bohnes ◽  
N. Hermann ◽  
M. C. Cadeville
Keyword(s):  
Molecular Beam ◽  
Growth Direction ◽  
Misfit Dislocations ◽  
X Ray Diffraction ◽  
Plan View ◽  
X Ray ◽  
Transmission Electron ◽  
Superlattice Peak ◽  
Diffraction Peaks ◽  
Diffraction Patterns

We find that the [Ni3.2nmPt1.6nm] × 15 and [Ni3.2nmPt0.8nm] × 15 multilayers are semicoherent and display a columnar morphology. From both the period of the moir’e fringes and the positions of the diffraction peaks in electronic (plan-view and crosssection geometries) and x-ray diffraction patterns, one deduces that the nickel is relaxed (at least in the error bars of all our measurements), whereas the platinum remains slightly strained (≈−1%). The interfaces are sharp; no intermixing takes place giving rise to neat contrasts in transmission electron microscopy (TEM) and to high intensities of the superlattice peaks in the growth direction in both diffraction techniques. The relaxation of the interfacial misfit occurs partially through misfit dislocations, partially through the strain of platinum. A quasiperiodic twinning occurs at the interfaces, the stacking fault which forms the twin being the most often located at the interface Pt/Ni, i.e., when a Pt layer begins to grow on the Ni layer. The simulation of the θ/2θ superlattice peak intensities takes into account the columnar microstructure. It shows that the roughness is predominantly at medium scale with a fluctuation of about 12.5% for Ni layers and negligible for Pt layers.

Mechanism of the morphotropic transformation between the rutile and corundum structural types

2003 ◽  
Vol 59 (4) ◽  
pp. 456-462 ◽  
Author(s):  
H. Katzke ◽  
R. Schlögl
Keyword(s):  
Simple Model ◽  
Phase Segregation ◽  
Transformation Process ◽  
Transformation Mechanism ◽  
One Dimensional ◽  
X Ray ◽  
Structural Types ◽  
Crystallographic Shear ◽  
Diffraction Patterns ◽  
Shear Planes

The rutile/corundum structural transformation which is based on crystallographic shear is discussed in terms of a one-dimensional disorder model. The transformation process is described by a simple model based on the structural relationship between the rutile-type and corundum-type phases. The model is able to handle randomly spaced crystallographic shear planes, the so-called Wadsley defects, as well as clustered CS planes. Calculations hsow that simply modifying the probability parameters of the model can lead to phase segregation. X-ray powder diffraction patterns are calculated for the proposed transformation mechanism as a function of the stoichiometry x in MO2−x in order to show the influence of such defects on the intensities and linewidths of the Bragg reflections.

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