A convergent beam method for determination of structure factor phases and amplitudes from center disk intensity

2022 ◽  
pp. 133-136
Author(s):  
C R Birkeland ◽  
R Høier ◽  
R Holmestad ◽  
K Marthinsen
Keyword(s):  
Structure Factor ◽  
Beam Method ◽  
Convergent Beam

Determination of structure factor phase invariants from non-systematic many-beam effects in convergent-beam patterns

1988 ◽  
Vol 26 (1-2) ◽  
pp. 25-30 ◽  
Author(s):  
R. Høier ◽  
J.-M. Zuo ◽  
K. Marthinsen ◽  
J.C.H. Spence
Keyword(s):  
Structure Factor ◽  
Convergent Beam ◽  
Beam Patterns

Optimized Structure Parameter Determination From CBED

1990 ◽  
Vol 48 (2) ◽  
pp. 492-493
Author(s):  
Knut Marthinsen ◽  
Ragnvald Høier ◽  
Lars Nils Bakken
Keyword(s):  
Structure Factor ◽  
Intensity Variation ◽  
Computer Time ◽  
Parameter Determination ◽  
Unknown Parameters ◽  
Experimental Conditions ◽  
Line Intensities ◽  
The Many ◽  
Convergent Beam

The application of convergent beam electron diffraction (CBED) for structure symmetry determination is now well established. Application of quantitative CBED in crystal structure studies is so far much less developed. However, the 2-dimensional dynamical intensity distributions in the disks depend strongly on the structure factor magnitudes and phases for the reflections involved. This is particularly the case in the general non-systematic many-beam case where a quantitative determination of structure factor magnitudes and phases from CBED in general has to be based on full dynamical many-beam calculations. It has been shown however that for carefully chosen experimental conditions it is possible to find line intensities which can be analysed on a kinematic basis. The 1-dimensional intensity variation along a systematic row has also been utilized to determine a structure factor phase with high accuracy. However, an optimal use of the CBED patterns should utilize the general 2-dimensional intensity distribution. The number of unknown parameters in a full many-beam simulation will in principle be large, the computer time large even on supercomputers and an effective algorithm for searching in the many-parameter room is therefore highly needed.

On the determination of enanttomorphs from non-systematic many-beam effects in CBED patterns

1989 ◽  
Vol 47 ◽  
pp. 484-485
Author(s):  
K. Marthinsen ◽  
R. Høier
Keyword(s):  
Structure Factor ◽  
High Accuracy ◽  
Convergent Beam Electron Diffraction ◽  
Bragg Condition ◽  
Sign Problem ◽  
Three Phase ◽  
Convergent Beam ◽  
Diffraction Effects ◽  
Beam Diffraction

A convergent beam electron diffraction (CBED) method which makes it possible to determine structure factor magnitudes and phases with high accuracy has recently been suggested. It is based on detailed simulations of non-systematic many-beam diffraction effects in the disks. Basis for the phase determination is an asymmetry which may appear in a line h with respect to the Bragg condition of the coupled reflection g near a three-beam condition. Approximate analytical three-beam solutions show that the sign and size of this asymmetry depends on the structure factor phases Θh of the reflections h involved through a term cos(Φ) where Φ is the three phase structure invariant, Φ = Θh + Θg + Θh-g. The magnitude of the phase invariant is thus in principle available, but not the sign. The aim of the present work has been to discuss the origin of the sign problem and the possibilities of distinguishing +/−Φ.

scholarly journals Non-systematic Three-beam Effects in Dynamical Electron Diffraction and Their Use in Determination of Amplitude and Phase of Structure Factors

1988 ◽  
Vol 41 (3) ◽  
pp. 449 ◽  
Author(s):  
K Marthinsen ◽  
H Matsuhata ◽  
R Hfier ◽  
J Gjfnnes
Keyword(s):  
Electron Diffraction ◽  
Structure Factor ◽  
Bloch Wave ◽  
Critical Voltage ◽  
Dispersion Surface ◽  
Structure Factors ◽  
Three Phase ◽  
Convergent Beam ◽  
Diffraction Condition

The treatment of non-systematic multiple-beam effects in dynamical diffraction is extended. Expressions for Bloch wave degeneracies are given in the centrosymmetrical four-beam case and for some symmetrical directions. These degeneracies can be determined experimentally either as critical voltages or by locating the exact diffraction condition at a fixed voltage. The accuracy when applied to structure factor determination is comparable with the systematical critical voltage, namely 1% in UfT The three-beam case 0, g, h is treated as well in the non-centrosymmetrical case, where it can be used for determination of phases. It is shown that the contrast features can be represented .by an effective structure factor defined by the gap at the dispersion surface. From the variation in the gap with diffraction condition, a method to determine the three-phase structure invariant I\J = 9 + _ h + h _ 9 is given. The method is based upon the contrast asymmetry in the weaker diffracted beam and can be applied in Kikuchi, convergent beam or channelling patterns. Calculations relating to channelling in backscattering are also presented.

Symmetry breaking in convergent-beam diffraction

1989 ◽  
Vol 47 ◽  
pp. 480-481
Author(s):  
D.J. Eaglesham
Keyword(s):  
Symmetry Breaking ◽  
Point Group ◽  
X Ray Diffraction ◽  
Multiple Diffraction ◽  
Space Groups ◽  
Atomic Displacements ◽  
Small Probe ◽  
Phase Sensitive ◽  
Convergent Beam

Convergent Beam Electron Diffraction is now almost routinely used in the determination of the point- and space-groups of crystalline samples. In addition to its small-probe capability, CBED is also postulated to be more sensitive than X-ray diffraction in determining crystal symmetries. Multiple diffraction is phase-sensitive, so that the distinction between centro- and non-centro-symmetric space groups should be trivial in CBED: in addition, the stronger scattering of electrons may give a general increase in sensitivity to small atomic displacements. However, the sensitivity of CBED symmetry to the crystal point group has rarely been quantified, and CBED is also subject to symmetry-breaking due to local strains and inhomogeneities. The purpose of this paper is to classify the various types of symmetry-breaking, present calculations of the sensitivity, and illustrate symmetry-breaking by surface strains.CBED symmetry determinations usually proceed by determining the diffraction group along various zone axes, and hence finding the point group. The diffraction group can be found using either the intensity distribution in the discs

Computer simulations for the TEM bend contour technique

1996 ◽  
Vol 54 ◽  
pp. 134-135
Author(s):  
Vladimir Yu. Kolosov ◽  
Anders R. Thölén
Keyword(s):  
Computer Simulations ◽  
Real Space ◽  
Advantages And Disadvantages ◽  
Short Overview ◽  
Diffraction Contrast ◽  
Beam Method ◽  
Convergent Beam ◽  
Contour Technique

In this paper we give a short overview of two TEM applications utilizing the extinction bend contour technique (BC) giving the advantages and disadvantages; especially we consider two areas in which the BC technique remains unique. Special attention is given to an approach including computer simulations of TEM micrographs.BC patterns are often observed in TEM studies but are rarely exploited in a serious way. However, this type of diffraction contrast was one of the first to be used for analysis of imperfections in crystalline foils, but since then only some groups have utilized the BC technique. The most extensive studies were performed by Steeds, Eades and colleagues. They were the first to demonstrate the unique possibilities of the BC method and named it real space crystallography, which developed later into the somewhat similar but more powerful convergent beam method. Maybe, due to the difficulties in analysis, BCs have seldom been used in TEM, and then mainly to visualize different imperfections and transformations.

scholarly journals Convergent beam method in X-ray diffractometry to determine single crystal cuts' orientation

2005 ◽  
Vol 61 (a1) ◽  
pp. c485-c485
Author(s):  
A. V. Lyuttsau ◽  
M. A. Kumakhov ◽  
N. S. Ibraimov ◽  
S. V. Nikitina ◽  
A. E. Bulkin ◽  
...  
Keyword(s):  
Single Crystal ◽  
X Ray ◽  
Beam Method ◽  
Convergent Beam

scholarly journals ANALISIS KEBIJAKAN PENDIRIAN SEKOLAH DASAR DI KABUPATEN BATU BARA

2021 ◽  
Vol 11 (2) ◽  
pp. 102-107
Author(s):  
Regina Sipayung ◽  
◽  
Din Oloan Sihotang ◽  
Johannes Sohirimon Lumban Batu ◽  
◽  
...  
Keyword(s):  
Data Collection ◽  
Structure Factor ◽  
Interview Data ◽  
Communication Process ◽  
Study Group ◽  
National Education ◽  
School Conditions ◽  
Bureaucratic Structure

This study uses a descriptive methodology with interview data collection techniques, observation and documentation studies. The results showed that of the 17 schools that were established and categorized since 2018 it was found that 37% of the schools did not meet the study group requirements because there were less than 20 students. Then, judging from the communication process, the socialization of the requirements for the establishment of schools has not been carried out properly, information regarding the determination of school conditions is only conveyed to the school establishment committee. The readiness of resources has not been met and the disposition process still needs attention. The bureaucratic structure factor is still not clear, the standard operational procedures of the Batu Bara District Education Office have been guided by Kepmendiknas No. 060/U/2002. Based on the conclusion of this study, it was found that the Education Office of Batu Bara Regency had implemented policies in accordance with the Ministry of National Education. Number 060/U/2002, but needs to do some repairs. Keywords: Policy, School Establishment, Edwards

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