Reconstruction of the Projected Potential from a through Voltage Series of Dynamical Electron Diffraction Patterns Including Absorption

2001 ◽  
Vol 7 (S2) ◽  
pp. 914-915
Author(s):  
C. Koch ◽  
J.C.H. Spence
Keyword(s):  
Electron Diffraction ◽  
Crystal Orientation ◽  
Specimen Thickness ◽  
Experimental Realization ◽  
Crystal Potential ◽  
Scattering Effects ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Multiple Scattering Effects ◽  
Better Than

Recently several different methods have been proposed to reconstruct the projected crystal potential from electron diffraction patterns. These methods envolve either diffraction patterns at many different orientations (as many orientations as beams in the pattern) and/or images, which makes their experimental realization difficult. We propose an entirely new method for reconstructing the projected crystal potential from fully dynamical [including absorption and multiple scattering effects to all orders] diffraction patterns from only a single crystal orientation and no image at all. Knowledge of the specimen thickness is not necessary. However, it requires diffraction patterns at many different accelarating voltages, which is a parameter that can easily be varied (within a certain range) in most modern electron microscopes. Since the intensities in the electron diffraction pattern are not affected by lens abberations this method is capable of reconstructing the projected potential with a resolution far better than that of any method using HRTEM images.

Dynamical Scattering in Electron Diffraction of wet Protein Crystals

1980 ◽  
Vol 38 ◽  
pp. 42-43
Author(s):  
B. B. Chang ◽  
D. F. Parsons
Keyword(s):  
Electron Diffraction ◽  
Scattering Theory ◽  
Protein Crystals ◽  
Electron Diffraction Data ◽  
Specimen Thickness ◽  
Major Question ◽  
X Ray ◽  
Scattering Effects ◽  
Diffraction Patterns ◽  
Acceleration Voltage

The significance of dynamical scattering effects remains the major question in the structural analysis by electron diffraction of protein crystals preserved in the hydrated state. In the few cases (single layers of purple membrane and 400-600 Å thick catalase crystals examined at 100 kV acceleration voltage) where electron-diffraction patterns were used quantitatively, dynamical scattering effects were considered unimportant on the basis of a comparison with x-ray intensities. The kinematical treatment is usually justified by the thinness of the crystal. A theoretical investigation by Ho et al. using Cowley-Moodie multislice formulation of dynamical scattering theory and cytochrome b5as the test object2 suggests that kinematical analysis of electron diffraction data with 100-keV electrons would not likely be valid for specimen thickness of 300 Å or more. We have chosen to work with electron diffraction patterns obtained from actual wet protein crystals (rat hemoglobin crystals of thickness range 1000 to 2500 Å) at 200 and 1000 kV and to analyze these for dynamical effects.

A Structural Model for a Quasi-Crystalline Material Derived from TEM

1990 ◽  
Vol 48 (1) ◽  
pp. 48-49
Author(s):  
Jan-Olov Bovin ◽  
Osamu Terasaki ◽  
Jan-Olle Malm ◽  
Sven Lidin ◽  
Sten Andersson
Keyword(s):  
High Resolution ◽  
Electron Diffraction ◽  
Structural Model ◽  
Image Intensifier ◽  
Crystalline Materials ◽  
Icosahedral Phases ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Quasi Crystals

High resolution transmission electron microscopy (HRTEM) is playing an important role in identifying the new icosahedral phases. The selected area diffraction patterns of quasi crystals, recorded with an aperture of the radius of many thousands of Ångströms, consist of dense arrays of well defined sharp spots with five fold dilatation symmetry which makes the interpretation of the diffraction process and the resulting images different from those invoked for usual crystals. The atomic structure of the quasi crystals is not established even if several models are proposed. The correct structure model must of course explain the electron diffraction patterns with 5-, 3- and 2-fold symmetry for the phases but it is also important that the HRTEM images of the alloys match the computer simulated images from the model. We have studied quasi crystals of the alloy Al65Cu20Fe15. The electron microscopes used to obtain high resolution electro micrographs and electron diffraction patterns (EDP) were a (S)TEM JEM-2000FX equipped with EDS and PEELS showing a structural resolution of 2.7 Å and a IVEM JEM-4000EX with a UHP40 high resolution pole piece operated at 400 kV and with a structural resolution of 1.6 Å. This microscope is used with a Gatan 622 TV system with an image intensifier, coupled to a YAG screen. It was found that the crystals of the quasi crystalline materials here investigated were more sensitive to beam damage using 400 kV as electron accelerating voltage than when using 200 kV. Low dose techniques were therefore applied to avoid damage of the structure.

scholarly journals Collecting large datasets of rotational electron diffraction with ParallEM and SerialEM

2020 ◽  
Author(s):  
Kiyofumi Takaba ◽  
Saori Maki-Yonekura ◽  
Koji Yonekura
Keyword(s):  
Electron Diffraction ◽  
Data Collection ◽  
Large Scale ◽  
General Purpose ◽  
Task Specialization ◽  
Camera Control ◽  
Combined Use ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Automated Protocol

AbstractA semi-automated protocol has been developed for rotational data collection of electron diffraction patterns by combined use of SerialEM and ParallEM, where SerialEM is used for positioning of sample crystals and ParallEM for rotational data collection. ParallEM calls standard camera control software through an AutoIt script, which adapts to software operational changes and to new GUI programs guiding other cameras. Development included periodic flashing and pausing of data collection during overnight or day-long recording with a cold field-emission beam. The protocol proved to be efficient and accurate in data collection of large-scale rotational series from two JEOL electron microscopes, a general-purpose JEM-2100 and a high-end CRYO ARM 300. Efficiency resulted from simpler steps and task specialization. It is possible to collect 12–20 rotational series from ∼ −68º to ∼ 68º at a rotation speed of 1º /s in one hour without human supervision.

scholarly journals Microstructural Characterization by Automated Crystal Orientation and Phase Mapping by Precession Electron Diffraction in TEM: Application to Hot Deformation of a γ-TiAl-based Alloy

2019 ◽  
Vol 25 (6) ◽  
pp. 1457-1465
Author(s):  
Vajinder Singh ◽  
Chandan Mondal ◽  
P. P. Bhattacharjee ◽  
P. Ghosal
Keyword(s):  
Electron Diffraction ◽  
Hot Deformation ◽  
Crystal Orientation ◽  
Microstructural Characterization ◽  
Advanced Characterization ◽  
Precession Electron Diffraction ◽  
Phase Mapping ◽  
Diffraction Patterns ◽  
Symmetry Effect ◽  
Structure Evaluation

AbstractMicrostructural evolution of a hot deformed γ-TiAl-based Ti–45Al–8Nb–2Cr–0.2B (at.%) alloy has been studied using an advanced characterization technique called automated crystal orientation and phase mapping by precession electron diffraction carried out in a transmission electron microscope (with a NanoMEGAS attachment). It has been observed that the technique, having a capability to recognize diffraction patterns with improved accuracy and reliability, is particularly suitable for characterization of complex microstructural features evolved during hot deformation of multiphase (α2 + γ + β)-based TiAl alloys. Examples of coupled orientations and phase maps of the present alloy demonstrate that the accurate reproduction of the very fine lamellar structure (α2 + γ + γ) is feasible due to its inherent high-spatial resolution and absence of a pseudo-symmetry effect. It enables identification of salient features of γ-TiAl deformation behavior in terms of misorientation analyses (GAM, GOS, and KAM) and transformation characteristics of very fine lamellar constituent phases. Apart from conventional strain analyses from the orientation database, an attempt has been made to image the dislocation sub-structure of γ-phases, which supplements the deformation structure evaluation using this new technique.

Selected Area Electron Diffraction and its Use in Structure Determination

2010 ◽  
Vol 18 (4) ◽  
pp. 22-28
Author(s):  
William F. Tivol
Keyword(s):  
Structural Analysis ◽  
Electron Diffraction ◽  
Structure Determination ◽  
Limited Region ◽  
Selected Area Electron Diffraction ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Technical Considerations

One of the capabilities of electron microscopes is to obtain diffraction patterns, which can be analyzed to give information about the structure of the specimen. This brief review discusses some of the technical considerations in using electron diffraction patterns for structural analysis. The technique of selected-area electron diffraction uses diffraction obtained from a limited region of the specimen.

scholarly journals A Convergence of Beauty and Utility

2014 ◽  
Vol 70 (a1) ◽  
pp. C41-C41
Author(s):  
John Steeds
Keyword(s):  
Electron Diffraction ◽  
Three Dimensional ◽  
Good Control ◽  
Critical Parameters ◽  
Specimen Thickness ◽  
Meaningful Information ◽  
Local Environments ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Convergent Beam

The effective routine achievement of useful convergent beam electron diffraction (CBED) patterns was frustrated for many years until transmission electron microscopes (TEMs) were developed that overcame the practical difficulties. Because specimen thickness and orientation are two critical parameters in electron diffraction and are not under good control because of the difficulty of producing thin enough regions it was necessary to have TEMs capable of forming small focussed probes of less than 100nm diameter in local environments where the hydrocarbon level was sufficiently low to reduce carbon contamination to a reasonable level. Once these problems were overcome the importance of three-dimensional diffraction became apparent but to exploit this property it was necessary to develop TEMs with a large angular range in the diffraction plane. With appropriately designed instruments very beautiful CBED patterns could be obtained from crystalline samples and a variety of experimental techniques were exploited to extract meaningful information from them.

Measuring Electrostatic Potential Profiles across Amorphous Intergranular Films by Electron Diffraction

2005 ◽  
Vol 12 (2) ◽  
pp. 160-169 ◽  
Author(s):  
Christoph T. Koch ◽  
Somnath Bhattacharyya ◽  
Manfred Rühle ◽  
Raphaëlle L. Satet ◽  
Michael J. Hoffmann
Keyword(s):  
Electron Diffraction ◽  
Laboratory Frame ◽  
Potential Profile ◽  
Specimen Thickness ◽  
One Dimensional ◽  
Intergranular Films ◽  
Transmission Electron ◽  
Specimen Orientation ◽  
Diffraction Patterns ◽  
The One

Amorphous 1–2-nm-wide intergranular films in ceramics dictate many of their properties. The detailed investigation of structure and chemistry of these films pushes the limits of today's transmission electron microscopy. We report on the reconstruction of the one-dimensional potential profile across the film from an experimentally acquired tilt series of energy-filtered electron diffraction patterns. Along with the potential profile, the specimen thickness, film orientation with respect to the grain lattice and specimen surface, and the absolute specimen orientation with respect to the laboratory frame of reference are retrieved.

scholarly journals New Features in Crystal Orientation and Phase Mapping for Transmission Electron Microscopy

Symmetry ◽  
2021 ◽  
Vol 13 (9) ◽  
pp. 1675
Author(s):  
Edgar F. Rauch ◽  
Patrick Harrison ◽  
Muriel Véron
Keyword(s):  
Electron Diffraction ◽  
Angular Resolution ◽  
X Ray ◽  
Amorphous Phases ◽  
Transmission Electron ◽  
Tremendous Amount ◽  
Processing Algorithms ◽  
Electron Microscopes ◽  
Diffraction Patterns ◽  
Scanning Electron Microscopes

ACOM/TEM is an automated electron diffraction pattern indexing tool that enables the structure, phase and crystallographic orientation of materials to be routinely determined. The software package, which is part of ACOM/TEM, has substantially evolved over the last fifteen years and has pioneered numerous additional functions with the constant objective of improving its capabilities to make the tremendous amount of information contained in the diffraction patterns easily available to the user. Initially devoted to the analysis of local crystallographic texture, and as an alternative to both X-ray pole figure measurement and EBSD accessories for scanning electron microscopes, it has rapidly proven itself effective to distinguish multiple different phases contained within a given sample, including amorphous phases. Different strategies were developed to bypass the inherent limitations of transmission electron diffraction patterns, such as 180° ambiguities or the complexity of patterns produced from overlapping grains. Post processing algorithms have also been developed to improve the angular resolution and to increase the computing rate. The present paper aims to review some of these facilities. On-going works on 3D reconstruction are also introduced.

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