Electron diffraction microdiffraction

Electron Diffraction (SAED), Microdiffraction, Convergent-Beam Eleetron Diffraetion (CBED), Large-Angle Convergent-Beam Eleetron Diffraetion (LACBED) and electron precession. They produee spot, ring, disk or line patterns at microseopie or nanoseopie seales in eorrelation with the image of the diffracted area. An overview of the main applieations is given. 

Convergent-Beam eleetron Diffraction and Microdiffraction) become available on analytical transmission electron microscopes. Most of the electron diffraction techniques use a stationary incident beam, but some specific methods like the precession method take advantage of a moving incident beam. 

This demonstrates that electron microdiffraction may compete with other diffraction techniques but is not easy to use. Nowadays synchrotron radiation is probably more convenient, in most cases, for the observation of very weak sublattice reflections even from small crystallites however not as small as with electron microdiffraction. 

J. Spence and J. M. Zuo, Electron Microdiffraction , Plemun Publishing, 1992. An advanced text on quantitative analysis of CBED with useful examples, tables and computer simulation programs for electron diffraction analysis. 

The preparation and structure of magnesium polyphosphide, MgP4, have been described. The compound was prepared by the reaction of gaseous phosphorus with the phosphide MgaP2 at 600 °C in a sealed silica tube. Evidence for a primitive monoclinic cell was obtained from electron microdiffraction. Refinement of X-ray powder diffraction data showed that the compound is isostructural with... 

M. Tanaka, M. Terauchi, K. Tsudaand K. Saitoh, Convergent Beam Electron Diffraction IV , JEOE Etd, Tokyo and earlier volumes. An outstanding collection of CBED patterns and application examples, including detailed description of the techniques used for analysis. J. Spence and J. M. Zuo, Electron Microdiffraction , Plenum Publishing, 1992. An advanced text on quantitative analysis of CBED with useful examples, tables and computer simulation programs for electron diffraction analysis. 

Both the electron microdiffraction and the CBED diffraction methods give a large amount of information concerning the structure of small regions of materials and powders [5]. This includes ... 

The second model of the structure is based on the works of Allman and Tailor who identified structures of the minerals (hydrotalcite and manasseite) [28,29] and showed that magnesium and aluminium ions are located in octahedral voids of hydroxide layer. Anions X and water molecules form another layer. Using this approach, Serna assumed on the basis of electron microdiffraction data and X-ray diffraction patterns of powders that the structure of LADH-CO3 obtained by the hydrolysis of aluminium-tri-(sec-butoxide) in hthium carbonate is based on closely packing two-dimensional layer (30 ]. Two thirds of the octahedral voids in this layer are occupied by aluminium cations located in a manner similar to that of gibbsite. The remaining one third of voids is occupied by lithium cations. On... 

The crystallographic structure of the platelets can be determined by electron microdiffraction. In Fig. 2.30a, the prevailing diffraction pattern is shown. It originates from a-iron single crystals and shows the (111) orientation, which was found to constitute the basal plane of many platelets. There is no indication of... 

In the two cases, the antiwear films are polycrystalline, as clearly pointed out by electron diffraction patterns. Indexations of these last ones reveal that microcrystals are mainly carbonate phases, respectively strontianite and calcite. In the case of the OCABS film, electron microdiffraction patterns carried out between well-identified nanocrystallites demonstrate the existence of an amorphous phase responsible for the cohesion of the film. This phase, not identified by ATEM, probably corresponds to (amorphous) calcium oxide species recently detected by TOE SIMS analyses [46]. 

Various electron diffraction techniques are available on modem transmission electron microscopes. Selected-Area Electron Diffraction (SAED) and Microdiffraction are performed with a parallel or nearly parallel incident beam and give spot patterns. Convergent-Beam Electron Diffraction (CBED) and Large-Angle Convergent-Beam Electron Diffraction (LACBED) are performed with a focused and defocused convergent beam... 

TEM and associated techniques such as EELS are powerful tools in investigations of heterogeneous catalysts. Electron diffraction can provide structural information in phase constitutions by electron crystallographic analysing methods. Microdiffraction offers the possibility in studying small particles down to several nanometers. In combination with electron... 

A comparative study has been made by optical and electron microscopy of the anisotropic texture of several cokes from caking coals and pitches carbonized near their resolidification temperature. A simple technique made it possible to examine, by both methods, the same area of each sample and to identify the corresponding zones of the two very similar images. The anisotropy observed in polarized light appears in electron microscopy as differences in contrast resulting not from inequalities in electron absorption, but, as revealed by microdiffraction and dark Reid examinations, from diffraction phenomena depending on the general orientation of the carbon layers within each anisotropic area. 

The atomic structure of the films was studied by transmission electron microscopy (TEM) using a JEM lOOC electron microscope in the microdiffraction mode. The diffraction patterns were obtained at a low electron beam intensity using the CCD high-sensitive registration system to prevent the films from radiation damage by the electron beam. 

The crystalline conformations and cell wall morphologies of typical fungal polysaccharides have been derived from x-ray fiber diffraction studies and microdiffraction analysis in the electron microscope. The recording of suitable diffraction data requires deincrustration and crystallization inducing treatments (7 ). From the recorded data it is possible to gain some idea of the intimate relation of various crystalline polysaccharides in the cell wall, although it is sometimes necessary to complement these studies with... 

The amorphous nature of these powders was confirmed by several techniques, including X-ray powder diffraction and electron-beam microdiffraction, differential scanning calorimetry, and transmission electron micrography, which reveal the powder microstructure. Moreover, the material shows a surface area as high as 120 m2 g-l (by the BET gas adsorption isotherm method), i.e., 150 times larger than a commercially available 5 pm-diameter iron powder. 

Due to aperture restrictions, selected area methods are only applicable for examining areas of perhaps 0.5 Xm or more in diameter. It is also possible to obtain spot patterns from much smaller areas—down to as little as a nanometer or so in diameter—by using a focused incident electron beam, rather than an aperture, to limit the sample area under examination. Such microdiffraction patterns are somewhat more complex due to the nonparallel illumination, but they may also contain more information. For example, so-called convergent-beam electron diffraction (CBED) patterns provide three-dimensional information about the compounds crystal chemistry and can be used as a sensitive fingerprint for a given atomic structure. ... 

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