The Determination of Rotation Axis in the Rotation Electron Diffraction Technique

2013 ◽  
Vol 19 (5) ◽  
pp. 1276-1280 ◽  
Author(s):  
Mika Buxhuku ◽  
Vidar Hansen ◽  
Peter Oleynikov ◽  
Jon Gjønnes
Keyword(s):  
Electron Diffraction ◽  
Rotation Axis ◽  
Incident Beam ◽  
Zone Axis ◽  
Crystallographic Direction ◽  
Accurate Knowledge ◽  
Electron Diffraction Technique ◽  
Diffraction Patterns

AbstractMethods to determine the rotation axis using the rotation electron diffraction technique are described. A combination of rotation axis tilt, beam tilt, and simulated experimental diffraction patterns with nonintegers zone axis has been used. Accurate knowledge of the crystallographic direction of the incident beam for deducing the excitation error of reflections simultaneously near Bragg positions is essential in quantitative electron diffraction. Experimental patterns from CoP3 are used as examples.

Computer Indexing of Electron Diffraction Patterns Including the Effects of Lattice Symmetry

1977 ◽  
Vol 35 ◽  
pp. 22-23
Author(s):  
J. S. Lally ◽  
R. J. Lee
Keyword(s):  
Electron Diffraction ◽  
Zone Axis ◽  
Crystal Thickness ◽  
Double Diffraction ◽  
Automated Method ◽  
Lattice Symmetry ◽  
Intensity Calculations ◽  
Unknown Structure ◽  
Diffraction Patterns ◽  
Orientation Parameters

In the 50 year period since the discovery of electron diffraction from crystals there has been much theoretical effort devoted to the calculation of diffracted intensities as a function of crystal thickness, orientation, and structure. However, in many applications of electron diffraction what is required is a simple identification of an unknown structure when some of the shape and orientation parameters required for intensity calculations are not known. In these circumstances an automated method is needed to solve diffraction patterns obtained near crystal zone axis directions that includes the effects of systematic absences of reflections due to lattice symmetry effects and additional reflections due to double diffraction processes.Two programs have been developed to enable relatively inexperienced microscopists to identify unknown crystals from diffraction patterns. Before indexing any given electron diffraction pattern, a set of possible crystal structures must be selected for comparison against the unknown.

Kinematic Approximations in TED and RHEED Analysis of Reconstructed Surfaces

1990 ◽  
Vol 48 (2) ◽  
pp. 396-397
Author(s):  
L. -M. Peng ◽  
M. J. Whelan
Keyword(s):  
Electron Diffraction ◽  
Kinematic Analysis ◽  
Incident Beam ◽  
High Energy ◽  
Energy Electron ◽  
Great Success ◽  
High Energy Electron ◽  
Kinematic Approximation ◽  
Reconstructed Surfaces

In recent years there has been a trend in the structure determination of reconstructed surfaces to use high energy electron diffraction techniques, and to employ a kinematic approximation in analyzing the intensities of surface superlattice reflections. Experimentally this is motivated by the great success of the determination of the dimer adatom stacking fault (DAS) structure of the Si(111) 7 × 7 reconstructed surface.While in the case of transmission electron diffraction (TED) the validity of the kinematic approximation has been examined by using multislice calculations for Si and certain incident beam directions, far less has been done in the reflection high energy electron diffraction (RHEED) case. In this paper we aim to provide a thorough Bloch wave analysis of the various diffraction processes involved, and to set criteria on the validity for the kinematic analysis of the intensities of the surface superlattice reflections.The validity of the kinematic analysis, being common to both the TED and RHEED case, relies primarily on two underlying observations, namely (l)the surface superlattice scattering in the selvedge is kinematically dominating, and (2)the superlattice diffracted beams are uncoupled from the fundamental diffracted beams within the bulk.

Determination of hydrogen ordering within the β-RH2+xphase (R= Ho, Y) using electron diffraction techniques

2000 ◽  
Vol 33 (5) ◽  
pp. 1246-1252 ◽  
Author(s):  
Elizabeth J. Grier ◽  
Amanda K. Petford-Long ◽  
Roger C. C. Ward
Keyword(s):  
Electron Diffraction ◽  
Neutron Scattering ◽  
Diffraction Pattern ◽  
Computer Simulations ◽  
Fluorite Structure ◽  
Long Range Order ◽  
Hydrogen Atoms ◽  
Ordered Structures ◽  
Diffraction Patterns

Computer simulations of the electron diffraction patterns along the [\bar{1}10] zone axes of four ordered structures within the β-RH2+xphase, withR= Ho or Y, and 0 ≤x≤ 0.25, have been performed to establish whether or not the hydrogen ordering could be detected using electron diffraction techniques. Ordered structures within otherRH2+x(R= Ce, Tb) systems have been characterized with neutron scattering experiments; however, for HoH(D)2+x, neutron scattering failed to characterize the superstructure, possibly because of the lowxconcentration or lack of long-range order within the crystal. This paper aims to show that electron diffraction could overcome both of these problems. The structures considered were the stoichiometric face-centred cubic (f.c.c.) fluorite structure (x= 0), theD1 structure (x= 0.125), theD1astructure (x= 0.2) and theD022structure (x= 0.25). In the stoichiometric structure, with all hydrogen atoms located on the tetrahedral (t) sites, only the diffraction pattern from the f.c.c. metal lattice was seen; however, for the superstoichiometric structures, with the excess hydrogen atoms ordered on the octahedral (o) sites, extra reflections were visible. All the superstoichiometric structures showed extra reflections at the (001)f.c.c.and (110)f.c.c.type positions, with structureD1 also showing extra peaks at (½ ½ ½)f.c.c.. These reflections are not seen in the simulations at similar hydrogen concentrations with the hydrogen atoms randomly occupying theovacancies.

On the Characterisatiopn of Order-Disorder in Ion-Irradiated Pyrochlore Compounds by Electron Scattering Methods

2008 ◽  
Vol 1122 ◽  
Author(s):  
Gregory R. Lumpkin ◽  
Karl R. Whittle ◽  
Mark G. Blackford ◽  
Katherine L. Smith ◽  
Nestor J. Zaluzec
Keyword(s):  
Electron Scattering ◽  
Diffuse Scattering ◽  
Zone Axis ◽  
Irradiation Damage ◽  
Nuclear Materials ◽  
Crystalline Fraction ◽  
Selected Area Electron Diffraction ◽  
Pyrochlore Compounds ◽  
Diffraction Patterns

AbstractSelected area electron diffraction patterns are routinely used to determine the effects of irradiation damage in nuclear materials. Using zone axis orientations, the intensities of Bragg beams change from a dynamical to kinematic-like state due to the presence of amorphous domains in the material. Such changes in beam intensities, together with the increased diffuse scattering from the increasing amorphous fraction, present a major obstacle to the determination of cation or anion disorder in the crystalline fraction.

A study of the high-Cu Al–Cu–Co decagonal phase

1993 ◽  
Vol 8 (7) ◽  
pp. 1473-1476 ◽  
Author(s):  
B. Grushko
Keyword(s):  
Electron Microscopy ◽  
Scanning Electron Microscopy ◽  
Electron Diffraction ◽  
Diffuse Scattering ◽  
Nonequilibrium State ◽  
Zone Axis ◽  
Decagonal Phase ◽  
Diffraction Patterns ◽  
Scanning Electron

The decagonal phase was studied by transmission and scanning electron microscopy in an Al62Cu24Co14 alloy annealed at 550–850 °C. The electron diffraction patterns of the decagonal phase exhibited weak quasiperiodic odd-n reflections in the [1-2100] zone axis corresponding to the equilibrated structure. The relative intensities of these reflections were significantly lower in the Al62Cu24Co14 than in the Al68Cu11Co21 decagonal phase. Diffuse scattering observed previously at the same positions can be related to a nonequilibrium state of the decagonal phase.

Electron Diffraction Study of Multilayer Structures with Partially Coherent Illumination

1985 ◽  
Vol 62 ◽  
Author(s):  
N. Otsuka ◽  
C. Choi ◽  
L. A. Kolodziejski ◽  
R. L. Gunshor
Keyword(s):  
Electron Diffraction ◽  
Incident Beam ◽  
Electron Diffraction Study ◽  
Diffraction Theory ◽  
Diffraction Spot ◽  
Multilayer Structures ◽  
Intensity Calculations ◽  
Diffraction Patterns ◽  
Monochromatic Source

ABSTRACTThe effect of partial coherency on electron diffraction patterns of Cd1−xMnxTe – Cd1−yMny Te superlattices has been investigated. Observed diffraction patterns are compared with intensity calculations performed using dynamical diffraction theory with a model of an extended incoherent monochromatic source. From this study, a new method of electron diffraction for characterization of multilayer structures can be developed. Under the condition that the lateral coherent distance of the incident beam covers two adjacent layers, diffraction beams arising from the two layers give rise to an interference fringe in a diffraction spot. With this type of diffraction pattern, one can determine the refractive index of a crystal in the multilayer structure.

Global least-squares determination of Eulerian angles from single electron diffraction patterns of tilted crystals

2000 ◽  
Vol 33 (4) ◽  
pp. 1088-1101 ◽  
Author(s):  
Eva Dimmeler ◽  
Rasmus R. Schröder
Keyword(s):  
Electron Diffraction ◽  
Least Squares ◽  
Three Dimensional ◽  
Test Sample ◽  
Single Electron ◽  
Dimensional Structure ◽  
Diffraction Spot ◽  
Linear Fit ◽  
Diffraction Patterns

Three-dimensional structure determination using electron diffraction of crystalline samples necessitates the determination of the Eulerian angles of tilted samples. For experimental tilt series, even with approximately known tilt, the resolution of the final three-dimensional reconstructions is reduced as a result of the large errors of the refined tilt angles and crystal axes positions. The presented new least-squares procedure determines the orientation of the crystal with very high accuracy from a single electron diffraction pattern. Instead of evaluating the averaged pattern geometry, each diffraction spot position is individually included in an analytical non-linear fit. This procedure is very stable against potential experimental errors, as demonstrated by Monte Carlo simulations. As a test sample, a three-dimensional microcrystal of an organic crystal compound was used. Contrary to the conventional method, which produced erroneous Miller indices for some reflections, the indexing obtained with the new algorithm was more consistent for each individual pattern. Preliminary data from frozen hydrated protein crystals, the samples of which are beam sensitive and for which only a few patterns can be recorded from a single crystal, indicate that the new angle determination promises to be particularly beneficial under such conditions.

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