Electron Diffraction And Crystal Structure (original) (raw)
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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.
QED V 1.0: a software package for quantitative electron diffraction data treatment
Ultramicroscopy, 2000
A new software package for quantitative electron di!raction data treatment of unknown structures is described. No`a prioria information is required by the package which is able to perform in successive steps the 2-D indexing of digitised di!raction patterns, the extraction of the intensity of the collected re#ections and the 3-D indexing of all recorded patterns, giving as results the lattice parameters of the investigated structure and a series of data "les (one for each di!raction pattern) containing the measured intensities and the relative e.s.d.s of the 3-D indexed re#ections. The software package is mainly conceived for the treatment of di!raction patterns taken with a Gatan CCD Slow-Scan Camera, but it can also deal with generic digitised plates. The program is designed to extract intensity data suitable for structure solution techniques in electron crystallography. The integration routine is optimised for a correct background evaluation, a necessary condition to deal with weak spots of irregular shape and an intensity just above the background.
A century of X-ray crystallography and 2014 international year of X-ray crystallography
Macedonian Journal of Chemistry and Chemical Engineering, 2015
The 100th anniversary of the Nobel prize awarded to Max von Laue in 1914 for his discovery of diffraction of X-rays on a crystal marked the beginning of a new branch of science - X-ray crystallography. The experimental evidence of von Laue's discovery was given by physicists W. Friedrich and P. Knipping in 1912. In the same year W. L. Bragg described the analogy between X-rays and visible light and formulated the Bragg's law, a fundamental relation, that connected the wave nature of X-rays and fine structure of a crystal at atomic level. In 1913 the first simple diffractometer was constructed and structure determination started by the Braggs, father and son. In 1915 their discoveries were awarded by Nobel prize in physics. Since then, X-ray diffraction has been basic method for determination of three-dimensional structures of synthetic and natural compounds. The three-dimensional structure of molecule defines its physical, chemical, and biological properties. All over the p...
Low-Dose Electron Crystallography: Structure Solution and Refinement
Symmetry, 2022
There is a wealth of materials that are beam sensitive and only exist in nanometric crystals, because the growth of bigger crystals is either impossible or so complicated that it is not reasonable to spend enough time and resources to grow big crystals before knowing their potential for research or applications. This difficulty is encountered in minerals, zeolites, metal-organic frameworks or molecular crystals, including pharmaceuticals and biological crystals. In order to study these crystals a structure determination method for beam sensitive crystals of nanometric size is needed. The nanometric size makes them destined for electron diffraction, since electrons interact much more strongly with matter than X-rays or neutrons. In addition, for the same amount of beam damage, electron diffraction yields more information than X-rays. The recently developed low-dose electron diffraction tomography (LD-EDT) not only combines the advantages inherent in electron diffraction, but is also optimized for minimizing the electron dose used for the data collection. The data quality is high, allowing not only the solution of complex unknown structures, but also their refinement taking into account the dynamical diffraction effects. Here we present several examples of crystals solved and refined by this method. The range of the crystals presented includes two synthetic oxides, Sr5CuGe9O24 and (Na2/3Mn1/3)3Ge5O12, a natural mineral (bulachite), and a metal organic framework (Mn-formiate). The dynamical refinement can be successfully performed on data sets that needed less than 0.1 e−/Å2 for the entire data set
Acta Crystallographica Section A Foundations of Crystallography, 2002
Energy-®ltered Debye±Scherrer electron powder data have been successfully employed to determine the structure of nanocrystalline anatase (TiO 2). The performed structure analysis includes determining the unit cell, space group, solving the structure via direct methods from extracted intensities and re®ning the structure using the Rietveld technique. The re®ned structural parameters for space group I4 1 aamd are a = 3.872 (2), c = 9.616 (5) A Ê with titanium at 0.5, 0.75, 0.375 and oxygen at 0.5, 0.75, 0.1618 (6). The obtained structure indicates low internal stress as judged from the almost regular geometry of the TiO 6 building blocks. Striking resemblance with the anatase structure determined previously by Burdett, Hughbanks, Miller, Richardson & Smith [J. Am. Chem. Soc. (1987). 109, 3639±3646] from neutron diffraction on coarsegrained material gives strong support for the correctness of the structure determined here. The result of the present study shows that the methods originally developed for determining structures from X-ray powder data work equally well with data from electron powder diffraction. This may open the window for structural investigations on the vast number of nanocrystalline materials and thin ®lms whose structures are dif®cult to determine by X-ray diffraction since they are frequently only available in small quantities.