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Electron Crystallography
Electron crystallography is a subset of methods in electron diffraction focusing upon detailed determination of the positions of atoms in solids using a transmission electron microscope (TEM). It can involve the use of high-resolution transmission electron microscopy images, electron diffraction patterns including convergent-beam electron diffraction or combinations of these. It has been successful in determining some bulk structures, and also surface structures. Two related methods are low-energy electron diffraction which has solved the structure of many surfaces, and reflection high-energy electron diffraction which is used to monitor surfaces often during growth. The technique date back to soon after the discovery of electron diffraction in 1927-28, and was used in many early works. However, for many years quantitative electron crystallography was not used, instead the diffraction information was combined qualitatively with imaging results. A number of advances from the 195 ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Electron Diffraction
Electron diffraction is a generic term for phenomena associated with changes in the direction of electron beams due to elastic interactions with atoms. It occurs due to elastic scattering, when there is no change in the energy of the electrons. The negatively charged electrons are scattered due to Coulomb forces when they interact with both the positively charged atomic core and the negatively charged electrons around the atoms. The resulting map of the directions of the electrons far from the sample is called a diffraction pattern, see for instance Figure 1. Beyond patterns showing the directions of electrons, electron diffraction also plays a major role in the contrast of images in electron microscopes. This article provides an overview of electron diffraction and electron diffraction patterns, collective referred to by the generic name electron diffraction. This includes aspects of how in a general way electrons can act as waves, and diffract and interact with matter. It a ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Max Knoll
Max Knoll (17 July 1897 – 6 November 1969) was a German electrical engineer and co-inventor of the electron microscope. Knoll was born in Wiesbaden and studied at the University of Munich and at the Technischen Hochschulen in Munich and Berlin-Charlottenburg, where he obtained his doctorate in the Institute for High Voltage Technology. In 1927 he became the leader of the electron research group there, where he and his co-worker, Ernst Ruska, invented the electron microscope in 1931. In April 1932, Knoll joined Telefunken in Berlin to do developmental work in the field of television design. He was also a private lecturer in Berlin. After World War II, Knoll joined the University of Munich as an extraordinary professor and director of the Institute for Electromedicine. He moved to the USA in 1948, to work at the Department of Electrical Engineering at Princeton University. In 1956 he returned to Munich and engaged in a series of experiments at the Technische Hochschule, i ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Precession Electron Diffraction
Precession electron diffraction (PED) is a specialized method to collect electron diffraction patterns in a transmission electron microscope (TEM). By rotating (precessing) a tilted incident electron beam around the central axis of the microscope, a PED pattern is formed by integration over a collection of diffraction conditions. This produces a quasi-kinematical diffraction pattern that is more suitable as input into direct methods (crystallography), direct methods algorithms to determine the crystal structure of the sample. Overview Geometry Precession electron diffraction is accomplished utilizing the standard instrument configuration of a modern Transmission electron microscope, TEM. The animation illustrates the geometry used to generate a PED pattern. Specifically, the beam tilt coils located pre-specimen are used to tilt the electron beam off of the optic axis so it is incident with the specimen at an angle, φ. The image shift coils post-specimen are then used to til ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Boris Vainshtein
Boris Konstantinovich Vainshtein (Russian: Бори́с Константи́нович Вайнште́йн, 10 July 1921 – 28 October 1996) was a Russian crystallographer. He headed the Laboratory of Protein Crystallography of the Shubnikov Institute of Crystallography RAS, and was the director of the institute, where he spent the majority of his career. Vainshtein studied at the Lomonosov Moscow State University and the Institute of Steel. In 1990 Vainshtein won the second IUCr Ewald Prize "for his contributions to the development of theories and methods of structure analysis by electron and X-ray diffraction and for his applications of his theories to structural investigations of polymers, liquid crystals, peptides and proteins". See also * Alexei Vasilievich Shubnikov Alexei Vasilievich Shubnikov (; 29March 1887 – 27April 1970) was a Soviet crystallographer and mathematician. Shubnikov was the founding director of the Institute of Crystallography (named after him ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Microstructure
Microstructure is the very small scale structure of a material, defined as the structure of a prepared surface of material as revealed by an optical microscope above 25× magnification. The microstructure of a material (such as metals, polymers, ceramics or composites) can strongly influence physical properties such as strength, toughness, ductility, hardness, corrosion resistance, high/low temperature behaviour or wear resistance. These properties in turn govern the application of these materials in industrial practice. Microstructure at scales smaller than can be viewed with optical microscopes is often called nanostructure, while the structure in which individual atoms are arranged is known as crystal structure. The nanostructure of biological specimens is referred to as ultrastructure. A microstructure's influence on the mechanical and physical properties of a material is primarily governed by the different defects present or absent of the structure. These defects can ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Transmission Electron Microscopy
Transmission electron microscopy (TEM) is a microscopy technique in which a beam of electrons is transmitted through a specimen to form an image. The specimen is most often an ultrathin section less than 100 nm thick or a suspension on a grid. An image is formed from the interaction of the electrons with the sample as the beam is transmitted through the specimen. The image is then magnified and focused onto an imaging device, such as a fluorescent screen, a layer of photographic film, or a detector such as a scintillator attached to a charge-coupled device or a direct electron detector. Transmission electron microscopes are capable of imaging at a significantly higher resolution than light microscopes, owing to the smaller de Broglie wavelength of electrons. This enables the instrument to capture fine detail—even as small as a single column of atoms, which is thousands of times smaller than a resolvable object seen in a light microscope. Transmission electron micr ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Space Group
In mathematics, physics and chemistry, a space group is the symmetry group of a repeating pattern in space, usually in three dimensions. The elements of a space group (its symmetry operations) are the rigid transformations of the pattern that leave it unchanged. In three dimensions, space groups are classified into 219 distinct types, or 230 types if chiral copies are considered distinct. Space groups are discrete cocompact groups of isometries of an oriented Euclidean space in any number of dimensions. In dimensions other than 3, they are sometimes called Bieberbach groups. In crystallography, space groups are also called the crystallographic or Fedorov groups, and represent a description of the symmetry of the crystal. A definitive source regarding 3-dimensional space groups is the ''International Tables for Crystallography'' . History Space groups in 2 dimensions are the 17 wallpaper groups which have been known for several centuries, though the proof that the list ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Point Group
In geometry, a point group is a group (mathematics), mathematical group of symmetry operations (isometry, isometries in a Euclidean space) that have a Fixed point (mathematics), fixed point in common. The Origin (mathematics), coordinate origin of the Euclidean space is conventionally taken to be a fixed point, and every point group in dimension ''d'' is then a subgroup of the orthogonal group O(''d''). Point groups are used to describe the Symmetry (geometry), symmetries of geometric figures and physical objects such as molecular symmetry, molecules. Each point group can be Group representation, represented as sets of orthogonal matrix, orthogonal matrices ''M'' that transform point ''x'' into point ''y'' according to . Each element of a point group is either a Rotation (mathematics), rotation (determinant of ), or it is a Reflection (mathematics), reflection or improper rotation (determinant of ). The geometric symmetries of crystals are described by space groups, which allow T ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
John Steeds (scientist)
John Wickham Steeds (born 9 February 1940) is a British physicist and materials scientist. He is an Emeritus Professor of Physics at the University of Bristol. Research Steeds is best known for his investigations of the microstructure of materials using electron microscopy and convergent-beam electron diffraction. Early in his career, he produced seminal work on dislocation arrangements in deformed copper crystals, which is a basis for the more recent theories of work hardening. His monograph on anisotropic elasticity theory of dislocations is a standard reference. He has led a sophisticated research effort to make, from image plane diffraction analysis ("real-space crystallography") and convergent-beam diffraction, a complete system for crystallographic structure determination in the electron microscope. He is recognised as a world expert in this technique. Significant applications include precipitate structure in steels, new phases in the contact regions of integrated circu ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Convergent Beam Electron Diffraction
Convergent beam electron diffraction (CBED) is an electron diffraction technique where a convergent or divergent beam (conical electron beam) of electrons is used to study materials. History CBED was first introduced in 1939 by Kossel and Möllenstedt. The development of the Field Emission Gun (FEG) in the 1970s, the Scanning Transmission Electron Microscopy (STEM), energy filtering devices and so on, made possible smaller probe diameters and larger convergence angles, and all this made CBED more popular. In the seventies, CBED was being used for the determination of the point group and space group symmetries by Goodman and Lehmpfuh, and Buxton, and starting in 1985, CBED was used by Tanaka et al. for studying crystals structure. Applications By using CBED, the following information can be obtained: *parameters of the crystal lattice, sample thickness *strain distribution * defects such as stacking faults, dislocations, grain boundaries, three-dimensional deformations, lattice ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Gottfried Möllenstedt
Gottfried Möllenstedt (14 September 1912 – 11 September 1997) was a German physicist and professor at the University of Tübingen, where he founded the Institute of Applied Physics in 1957, and served as rector from 1966 to 1968. Together with his doctoral student Heinrich Düker (1923–1985), in 1955 he invented the electron biprism, which is widely used in electron holography. Life Möllenstedt was the fourth of eight children of the teacher, cantor and vice-principal Johann Heinrich Möllenstedt; he had two sisters and five brothers. At first he wanted to become an aircraft engineer, but then, impressed by his teachers Walther Kossel and Eberhard Buchwald, turned to physics in 1934. Under Walther Kossel he obtained his diploma in engineering at the Gdańsk University of Technology in 1939, and received his doctorate on electron diffraction on 17 December 1940. On 11 October 1940, he married the teacher Dorothea Tanner. From 1939 to 1945 he was Kossel's research assistant ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Walther Kossel
Walther Ludwig Julius Kossel (; 4 January 1888 – 22 May 1956) was a German chemist and physicist known for his theory of the chemical bond (ionic bond/octet rule), Sommerfeld–Kossel displacement law of atomic spectra, the Kossel–Stranski model for crystal growth, and the Kossel effect. Walther was the son of Albrecht Kossel who won the Nobel Prize in Physiology or Medicine in 1910. Career Kossel was born in Berlin, and began studies at the University of Heidelberg in 1906, but was at the University of Berlin during 1907 and 1908. In 1910, he became assistant to Philipp Lenard, who was also his thesis advisor. Kossel was awarded his Ph.D. in 1910, and he stayed on as assistant to Leonard until 1913. In 1913, the year in which Niels Bohr introduced the Bohr model of the atom, Kossel went to the University of Munich as assistant to Arnold Sommerfeld, under whom he did his Habilitation. Under Sommerfeld, Munich was a theoretical center for the developing atomic theory, e ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
