A geometrical method for the determination and indexing of electron diffraction patterns (original) (raw)

Indexation of electron diffraction patterns at grain boundaries

Materials Characterization, 2021

Grain boundaries play a vital role in materials science, and they are extensively studied through experimental and numerical methods. Electron backscatter diffraction (EBSD) is commonly used to characterize crystalline materials, yet its performance is often compromised at grain boundaries. The key difficulty is to index the overlapped electron backscatter patterns, where Kikuchi bands from multiple crystal orientations coexist. Houghindexation often fails in treating overlapped EBSP, while the recently proposed dictionary indexation and sphere indexation give only one triplet of Euler angles from overlapped patterns. For all these methods, the orientation indexing precision drops for overlapped EBSP. Here we propose an integrated Digital Image Correlation (DIC) procedure to determine simultaneously and precisely multiple crystal orientations by registering the overlapped EBSP and the master pattern. The contribution ratio of each crystal orientation to the overlapped pattern is also available. Through an experimental EBSD dataset around a triple point, multiple benefits of the rich results from the method are demonstrated, such as refining grain boundaries, revealing EBSD scan errors and quantifying spatial resolution of EBSD. At the grain boundaries, the crystal orientation measurement uncertainty is 0.03°for both indexed crystal orientations, the same order for grain interiors, while their contribution ratios of uncertainty around 0.02 are obtained.

Structures of nanometre-size crystals determined from selected-area electron diffraction data

Acta Crystallographica Section A Foundations of Crystallography, 2000

The structure of a new modi®cation of Ti 2 Se, the-phase, and several related inorganic crystal structures containing elements with atomic numbers between 16 and 40 have been solved by quasi-automatic direct methods from singlecrystal electron diffraction patterns of nanometre-size crystals, using the kinematical aproximation. The crystals were several thousand times smaller than the minimum size required for single-crystal X-ray diffraction. Atomic coordinates were found with an average accuracy of 0.2 A Ê or better. Experimental data were obtained by standardized techniques for recording and quantifying electron diffraction patterns. The SIR97 program for solving crystal structures from three-dimensional X-ray diffraction data by direct methods was modi®ed to work also with two-dimensional electron diffraction data.

Orientation effects on indexing of electron backscatter diffraction patterns

Ultramicroscopy, 2005

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. This methodology is used to characterize the impact of various parameters on the indexing algorithm. r

ELD — a computer program system for extracting intensities from electron diffraction patterns

Ultramicroscopy, 1993

A computer program system, ELD, for extracting intensities from electron diffraction (ED) patterns has been developed. ELD runs on a personal computer (PC). Electron diffraction patterns are digitized using a CCD camera, and the data is transferred to the PC via a frame grabber. The lattice vectors and the shape and size of the diffraction spots are first determined, and based upon this information the strategy for extracting the electron diffraction intensities is decided by ELD. It is possible to merge several diffraction patterns taken with different exposure times, whereby both very strong and very weak reflections can be measured. Quantified electron diffraction data can be useful both for chemical applications, such as refining crystal structures, previously solved by crystallographic image processing (CIP), in materials science and for physical applications.

Introduction to electron crystallography

Crystal Research and Technology, 2011

Everything in Nature, macroscopic or microscopic, inorganic, organic or biological, has its specific properties. Most properties of matter depend on the atomic structures, and many techniques have been developed over the centuries for structure analysis. The greatest of them all, structure analysis of single crystals by X-ray diffraction, X-ray crystallography, was founded in 1912, and remains the most important technique for studying structures of periodically ordered objects at atomic resolution. Electron diffraction of single crystals was discovered fifteen years later by Thomson, Davisson and Germer. The wave property of electrons was exploited in the invention of the electron microscope by Knoll and Ruska in 1932. Since then, electron microscopes have been used in many fields as a tool for exploring and visualising the microscopic world in all its beauty. Between the first blurred images and today's sharp atomic resolution lies seventy years of untiring engineering. More recently, the unprecedented power of computers has made it possible to analyse quantitatively, and even further improve, these images. The amalgamation of electron diffraction and atomic resolution electron microscopy with crystallographic image processing has created a new powerful tool for structure analysis-electron crystallography.