Crystallography is the branch of science devoted to the study of molecular and crystalline structure and properties. The word crystallography is derived from the Ancient Greek word κρύσταλλος ( krústallos ; "clear ice, rock-crystal"), and γράφειν ( gráphein ; "to write"). In July 2012, the United Nations recognised the importance of the science of crystallography by proclaiming 2014 the International Year of Crystallography.
24-708: Crystallographic Information File ( CIF ) is a standard text file format for representing crystallographic information, promulgated by the International Union of Crystallography (IUCr). CIF was developed by the IUCr Working Party on Crystallographic Information in an effort sponsored by the IUCr Commission on Crystallographic Data and the IUCr Commission on Journals. The file format was initially published by Hall, Allen, and Brown and has since been revised, most recently versions 1.1 and 2.0. Full specifications for
48-474: A single crystal, but are poly-crystalline in nature (they exist as an aggregate of small crystals with different orientations). As such, powder diffraction techniques, which take diffraction patterns of samples with a large number of crystals, play an important role in structural determination. Other physical properties are also linked to crystallography. For example, the minerals in clay form small, flat, platelike structures. Clay can be easily deformed because
72-596: Is a broad topic, and many of its subareas, such as X-ray crystallography , are themselves important scientific topics. Crystallography ranges from the fundamentals of crystal structure to the mathematics of crystal geometry , including those that are not periodic or quasicrystals . At the atomic scale it can involve the use of X-ray diffraction to produce experimental data that the tools of X-ray crystallography can convert into detailed positions of atoms, and sometimes electron density. At larger scales it includes experimental tools such as orientational imaging to examine
96-781: Is a freely accessible repository for the structures of proteins and other biological macromolecules. Computer programs such as RasMol , Pymol or VMD can be used to visualize biological molecular structures. Neutron crystallography is often used to help refine structures obtained by X-ray methods or to solve a specific bond; the methods are often viewed as complementary, as X-rays are sensitive to electron positions and scatter most strongly off heavy atoms, while neutrons are sensitive to nucleus positions and scatter strongly even off many light isotopes, including hydrogen and deuterium. Electron diffraction has been used to determine some protein structures, most notably membrane proteins and viral capsids . The International Tables for Crystallography
120-404: Is an eight-book series that outlines the standard notations for formatting, describing and testing crystals. The series contains books that covers analysis methods and the mathematical procedures for determining organic structure through x-ray crystallography, electron diffraction, and neutron diffraction. The International tables are focused on procedures, techniques and descriptions and do not list
144-435: Is crucial in various fields, including metallurgy, geology, and materials science. Advancements in crystallographic techniques, such as electron diffraction and X-ray crystallography, continue to expand our understanding of material behavior at the atomic level. In another example, iron transforms from a body-centered cubic (bcc) structure called ferrite to a face-centered cubic (fcc) structure called austenite when it
168-404: Is heated. The fcc structure is a close-packed structure unlike the bcc structure; thus the volume of the iron decreases when this transformation occurs. Crystallography is useful in phase identification. When manufacturing or using a material, it is generally desirable to know what compounds and what phases are present in the material, as their composition, structure and proportions will influence
192-471: Is the primary method for determining the molecular conformations of biological macromolecules , particularly protein and nucleic acids such as DNA and RNA . The double-helical structure of DNA was deduced from crystallographic data. The first crystal structure of a macromolecule was solved in 1958, a three-dimensional model of the myoglobin molecule obtained by X-ray analysis. The Protein Data Bank (PDB)
216-470: Is used by materials scientists to characterize different materials. In single crystals, the effects of the crystalline arrangement of atoms is often easy to see macroscopically because the natural shapes of crystals reflect the atomic structure. In addition, physical properties are often controlled by crystalline defects. The understanding of crystal structures is an important prerequisite for understanding crystallographic defects . Most materials do not occur as
240-463: Is usually followed by beam diagnostics and higher-energy accelerators. The key component of a photoinjector is a photocathode , which is located inside the cavity of electron gun (usually, a 0.6-fractional cell for optimal distribution of accelerating field). Extracted electron beam suffers from its own space-charge fields that deteriorate the beam brightness. For that reason, photoelectron guns often have one or more full-size booster cells to increase
264-1092: The diffraction patterns of a sample targeted by a beam of some type. X-rays are most commonly used; other beams used include electrons or neutrons . Crystallographers often explicitly state the type of beam used, as in the terms X-ray diffraction , neutron diffraction and electron diffraction . These three types of radiation interact with the specimen in different ways. It is hard to focus x-rays or neutrons, but since electrons are charged they can be focused and are used in electron microscope to produce magnified images. There are many ways that transmission electron microscopy and related techniques such as scanning transmission electron microscopy , high-resolution electron microscopy can be used to obtain images with in many cases atomic resolution from which crystallographic information can be obtained. There are also other methods such as low-energy electron diffraction , low-energy electron microscopy and reflection high-energy electron diffraction which can be used to obtain crystallographic information about surfaces. Crystallography
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#1733093822654288-421: The symmetry of the crystal in question. The position in 3D space of each crystal face is plotted on a stereographic net such as a Wulff net or Lambert net . The pole to each face is plotted on the net. Each point is labelled with its Miller index . The final plot allows the symmetry of the crystal to be established. The discovery of X-rays and electrons in the last decade of the 19th century enabled
312-403: The beam energy and reduce the space-charge effect. The gun's accelerating field is RF (radio-frequency) wave provided by a klystron or other RF power source. For low-energy beams, such as ones used in electron diffraction and microscopy, electrostatic acceleration (DC) is a suitable. The photoemission on the cathode is initiated by an incident pulse from the driving laser . Depending on
336-601: The determination of crystal structures on the atomic scale, which brought about the modern era of crystallography. The first X-ray diffraction experiment was conducted in 1912 by Max von Laue , while electron diffraction was first realized in 1927 in the Davisson–Germer experiment and parallel work by George Paget Thomson and Alexander Reid. These developed into the two main branches of crystallography, X-ray crystallography and electron diffraction. The quality and throughput of solving crystal structures greatly improved in
360-420: The driving laser is often designed to control the pulse structure, and consequently, the distribution of electrons in the extracted bunch. For example, a fs -scale laser pulse with an elliptical transverse profile creates a thin "pancake" electron bunch, that evolves into a uniformly filled ellipsoid under its own space-charge fields. A more sophisticated laser pulse with a comb-like longitudinal profile generates
384-771: The format are available at the IUCr website. Many computer programs for molecular viewing are compatible with this format, including Jmol . Closely related is mmCIF , macromolecular CIF, which is intended as an successor to the Protein Data Bank (PDB) format . It is now the default format used by the Protein Data Bank . Also closely related is Crystallographic Information Framework , a broader system of exchange protocols based on data dictionaries and relational rules expressible in different machine-readable manifestations, including, but not restricted to, Crystallographic Information File and XML . Crystallographic Crystallography
408-425: The material of the photocathode , the laser wavelength can vary from 1700 nm ( infrared ) down to 100-200 nm ( ultraviolet ). Emission from the cavity wall is possible with laser wavelength of about 250 nm for copper walls or cathodes. Semiconductor cathodes are often sensitive to ambient conditions and might require a clean preparation chamber located behind the photoelectron gun. The optical system of
432-398: The material's properties. Each phase has a characteristic arrangement of atoms. X-ray or neutron diffraction can be used to identify which structures are present in the material, and thus which compounds are present. Crystallography covers the enumeration of the symmetry patterns which can be formed by atoms in a crystal and for this reason is related to group theory . X-ray crystallography
456-429: The physical properties of individual crystals themselves. Each book is about 1000 pages and the titles of the books are: Photoinjector A photoinjector is a type of source for intense electron beams which relies on the photoelectric effect . A laser pulse incident onto the cathode of a photoinjector drives electrons out of it, and into the accelerating field of the electron gun . In comparison with
480-421: The platelike particles can slip along each other in the plane of the plates, yet remain strongly connected in the direction perpendicular to the plates. Such mechanisms can be studied by crystallographic texture measurements. Crystallographic studies help elucidate the relationship between a material's structure and its properties, aiding in developing new materials with tailored characteristics. This understanding
504-467: The relative orientations at the grain boundary in materials. Crystallography plays a key role in many areas of biology, chemistry, and physics, as well new developments in these fields. Before the 20th century, the study of crystals was based on physical measurements of their geometry using a goniometer . This involved measuring the angles of crystal faces relative to each other and to theoretical reference axes (crystallographic axes), and establishing
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#1733093822654528-557: The second half of the 20th century, with the developments of customized instruments and phasing algorithms . Nowadays, crystallography is an interdisciplinary field , supporting theoretical and experimental discoveries in various domains. Modern-day scientific instruments for crystallography vary from laboratory-sized equipment, such as diffractometers and electron microscopes , to dedicated large facilities, such as photoinjectors , synchrotron light sources and free-electron lasers . Crystallographic methods depend mainly on analysis of
552-518: The source for a free-electron-laser experiment. High-brightness electron beams produced by photoinjectors are used directly or indirectly to probe the molecular, atomic and nuclear structure of matter for fundamental research, as well as material characterization. A photoinjector comprises a photocathode, electron gun (AC or DC), power supplies, driving laser system, timing and synchronization system, emittance compensation magnets. It can include vacuum system and cathode fabrication or transport system. It
576-465: The widespread thermionic electron gun, photoinjectors produce electron beams of higher brightness, which means more particles packed into smaller volume of phase space ( beam emittance ). Photoinjectors serve as the main electron source for single-pass synchrotron light sources , such as free-electron lasers and for ultrafast electron diffraction setups. The first RF photoinjector was developed in 1985 at Los Alamos National Laboratory and used as
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