Hydrogen positions in single nanocrystals revealed by electron diffraction. Impact factor: Morniroli, J. Diagonal , Barcelona Spain ; Redjaimia, A. These patterns have two main advantages with respect to the conventional selected-area electron diffraction SAED or microdiffraction patterns.

They display a much larger number of reflections and the diffracted intensity is the integrated intensity. These patterns have strong similarities with the electron precession patterns and they can be used for various applications like the identification of the possible space groups of a crystal from observations of the Laue zones or the ab-initio structure identifications.

Since this is a defocused method, another important application concerns the analysis of electron beam-sensitive materials. Successful applications to polymers are given in the present paper to prove the validity of this method with regards to these materials. Ultrashort electron bunch length measurement with diffraction radiation deflector.

In this paper, we propose a novel method to measure electron bunch length with a diffraction radiation DR deflector which is composed of a DR radiator and three beam position monitors BPMs. The deflection is found to be largely dependent on the bunch length and could be easily observed with a downstream BPM. Detailed investigations show that this method has wide applicability, high temporal resolution, and great simplicity.

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Full Text Available In this paper, we propose a novel method to measure electron bunch length with a diffraction radiation DR deflector which is composed of a DR radiator and three beam position monitors BPMs. The Rayleigh range of the laser 1. Few per cent of the injected particles are trapped in stable accelerating buckets and electrons with energies up to 35 MeV are detected on the magnetic spectrometers.

Experimental results on the scaling of the accelerator characteristics versus input parameters like injection energy, laser focus position and laser power are discussed. Three dimensional simulations are in good agreement with the electron energy spectrums observed in the experiment and indicate that substantial energy exchange between laser and electron beam only occurs in the firs TEM examination showed a heavily faulted dendritic growth structure in as-atomized powder.

An interdendritic phase possessing the C14 structure was also seen. There was also a very fine grain region consisting of the C14 structure. Upon heat treatment, the faulted structure became more defined and appeared as intercalation layers within the grains. Spherical particles rich in Zr and Ni appeared scattered at the grain boundries instead of the C14 interdendritic phase. The polycrystalline region also changed to a mixture of C14 and C15 structures. The phase stability of the C15 and C14 structures based on a consideration of atomic size factor and the average electron concentration is discussed.

Electron backscatter diffraction : Strategies for reliable data acquisition and processing. In electron backscatter diffraction EBSD software packages there are many user choices both in data acquisition and in data processing and display. In order to extract maximum scientific value from an inquiry, it is helpful to have some guidelines for best practice in conducting an EBSD investigation. The purpose of this article therefore is to address selected topics of EBSD practice, in a tutorial manner.

The topics covered are a brief summary on the principles of EBSD, specimen preparation, calibration of an EBSD system, experiment design, speed of data acquisition, data clean-up, microstructure characterisation including grain size and grain boundary characterisation. This list is not meant to cover exhaustively all areas where EBSD is used, but rather to provide a resource consisting of some useful strategies for novice EBSD users.

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Absorptive form factors for high-energy electron diffraction. The thermal diffuse scattering contribution to the absorptive potential in high-energy electron diffraction is calculated in the form of an absorptive contribution to the atomic form factor. To do this, the Einstein model of lattice vibrations is used, with isotropic Debye-Waller factors. The computed values, together with an interpolation routine, have been incorporated into a Fortran subroutine which calculates both the real and absorptive form factors for 54 atomic species.

Low temperature electron microscopy and electron diffraction of the purple membrane of Halobacterium halobium. The structure of the purple membrane of Halobacterium halobium was studied by high resolution electron microscopy and electron diffraction , primarily at low temperature. The handedness of the purple membrane diffraction pattern with respect to the cell membrane was determined by electron diffraction of purple membranes adsorbed to polylysine. A new method of preparing frozen specimens was used to preserve the high resolution order of the membranes in the electron microscope. High resolution imaging of glucose-embedded purple membranes at room temperature was used to relate the orientation of the diffraction pattern to the absolute orientation of the structure of the bacteriorhodopsin molecule.

The purple membrane's critical dose for electron beam-induced damage was measured at room temperature and at 0 C, and was found to be approximately five times greater at 0 C.

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Because of this decrease in radiation sensitivity, imaging of the membrane at low temperature should result in an increased signal-to-noise ratio, and thus better statistical definition of the phases of weak reflections. Higher resolution phases may thus be extracted from images than can be determined by imaging at room temperature.

Once the appropriate technology for taking low dose images at very high resolution has been developed, this stage will hopefully be used to determine the high resolution structure of the purple membrane. Ultrafast electron diffraction with megahertz MeV electron pulses from a superconducting radio-frequency photoinjector. Feng, L. We report ultrafast relativistic electron diffraction operating at the megahertz repetition rate where the electron beam is produced in a superconducting radio-frequency rf photoinjector.

We show that the beam quality is sufficiently high to provide clear diffraction patterns from gold and aluminium samples. With the number of electrons , several orders of magnitude higher than that from a normal conducting photocathode rf gun, such high repetition rate ultrafast MeV electron diffraction may open up many new opportunities in ultrafast science.

Kacher, Josh, E-mail: jkacherbyu gmail. Analytic model of electron pulse propagation in ultrafast electron diffraction experiments. We present a mean-field analytic model to study the propagation of electron pulses used in ultrafast electron diffraction experiments UED. We assume a Gaussian form to characterize the electron pulse, and derive a system of ordinary differential equations that are solved quickly and easily to give the pulse dynamics. We compare our model to an N-body numerical simulation and are able to show excellent agreement between the two result sets.

This model is a convenient alternative to time consuming and computationally intense N-body simulations in exploring the dynamics of UED electron pulses, and as a tool for refining UED experimental designs. High resolution electron microscopy and electron diffraction of YBa2Cu3O 7-x. Experimental high resolution electron micrographs and computer simulation experiments have been used to evaluate the visibility of the atomic constituents of YBa 2 Cu 3 O 7-x.

In practice, the detection of oxygen has not been possible in contradiction to that predicted by modelling of perfect crystalline material. Preliminary computer experiments of the electron diffraction patterns when oxygen vacancies are introduced on the Cu-O sheets separating Ba layers show the diffuse streaks characteristic of short range ordering. Local, atomic-level elastic strain measurements of metallic glass thin films by electron diffraction.

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Ebner, C. A novel technique is used to measure the atomic-level elastic strain tensor of amorphous materials by tracking geometric changes of the first diffuse ring of selected area electron diffraction patterns SAD. An automatic procedure, which includes locating the centre and fitting an ellipse to the diffuse ring with sub-pixel precision is developed for extracting the 2-dimensional strain tensor from the SAD patterns.

The thin films were deformed using MEMS based testing stages that allow simultaneous measurement of the macroscopic stress and strain. The calculated atomic-level principal strains show a linear dependence on the applied stress, and good correspondence with the measured macroscopic strains. Low-kilovolt coherent electron diffractive imaging instrument based on a single-atom electron source.

In this work, a transmission-type, low-kilovolt coherent electron diffractive imaging instrument was constructed.

It comprised a single-atom field emitter, a triple-element electrostatic lens, a sample holder, and a retractable delay line detector to record the diffraction patterns at different positions behind the sample. High-angle coherent diffraction patterns of a suspended graphene sample corresponding to 0. The ultimate goal of this instrument is to achieve atomic resolution of these materials with high contrast and little radiation damage. Weathersby, S. Ultrafast electron probes are powerful tools, complementary to x-ray free- electron lasers, used to study structural dynamics in material, chemical, and biological sciences.

High brightness, relativistic electron beams with femtosecond pulse duration can resolve details of the dynamic processes on atomic time and length scales. As the first stage of the Initiative, a mega- electron -volt MeV UED system has been constructed and commissioned to serve ultrafast science experiments and instrumentation development. The system operates at Hz repetition rate with outstanding performance. We propose a framework for indexing of grain and subgrain structures in electron backscatter diffraction patterns of polycrystalline materials. We discretize the domain of a dynamical forward model onto a dense grid of orientations, producing a dictionary of patterns.

For each measured pattern, we identify the most similar patterns in the dictionary, and identify boundaries, detect anomalies, and index crystal orientations. The statistical distribution of these closest matches is used in an unsupervised binary decision tree DT classifier to identify grain boundaries and anomalous regions.

The DT classifies a pattern as an anomaly if it has an abnormally low similarity to any pattern in the dictionary. It classifies a pixel as being near a grain boundary if the highly ranked patterns in the dictionary differ significantly over the pixel's neighborhood. Indexing is accomplished by computing the mean orientation of the closest matches to each pattern. The mean orientation is estimated using a maximum likelihood approach that models the orientation distribution as a mixture of Von Mises-Fisher distributions over the quaternionic three sphere.

The proposed dictionary matching approach permits segmentation, anomaly detection, and indexing to be performed in a unified manner with the additional benefit of uncertainty quantification. Orientation effects on indexing of electron backscatter diffraction patterns. Automated Electron Backscatter Diffraction EBSD has become a well-accepted technique for characterizing the crystallographic orientation aspects of polycrystalline microstructures.

At the advent of this technique, it was observed that patterns obtained from grains in certain crystallographic orientations were more difficult for the automated indexing algorithms to accurately identify than patterns from other orientations. The origin of this problem is often similarities between the EBSD pattern of the correct orientation and patterns from other orientations or phases.

While practical solutions have been found and implemented, the identification of these problem orientations generally occurs only after running an automated scan, as problem orientations are often readily apparent in the resulting orientation maps. However, such an approach only finds those problem orientations that are present in the scan area.

It would be advantageous to identify all regions of orientation space that may present problems for automated indexing prior to initiating an automated scan, and to minimize this space through the optimization of acquisition and indexing parameters. This work presents new methods for identifying regions in orientation space where the reliability of the automated indexing is suspect prior to performing a scan.

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This methodology is used to characterize the impact of various parameters on the indexing algorithm. Molecular structure of tetramethylgermane from gas electron diffraction. The molecular structure of Ge CH 3 4 has been determined from gas-phase electron diffraction augmented by a normal coordinate analysis. The methyl torsional barrier V 0 is estimated to be 1. Using a combination of our recently developed automated diffraction tomography ADT module with precession electron technique PED , quasi-kinematical 3D diffraction data sets of an inorganic salt BaSO 4 were collected.

The lattice cell parameters and their orientation within the data sets were found automatically.