Electron diffraction advantages

The term exp(-2k2c ) in (6-9) accounts for the disorder of the solid. Static disorder arises if atoms of the same coordination shell have slightly different distances to the central atom. Amorphous solids, for instance, possess large static disorder. Dynamic disorder, on the other hand, is caused by lattice vibrations of the atoms, as explained in Appendix 1. Dynamic disorder becomes much less important at lower temperatures, and it is therefore an important advantage to measure spectra at cryogenic temperatures, especially if a sample consists of highly dispersed particles. The same argument holds in X-ray and electron diffraction, as well as in Mossbauer spectroscopy. 

The use of blank-disc CBED patterns for solving crystal stmctures by electron diffraction (in conjunction with direct methods for the phase problem) would seem to have many advantages ... 

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. 

Electron diffraction has a main advantage with respect to the other diffraction techniques it can be performed at a microscopic and nanoscopic scales in correlation with the image of the diffracted area. The various types of electron diffraction pattern have many applications both in the fields of structure and microstructure characterizations. 

Obviously, it is possible to use X-ray diffraction for structure refinement of tabular shaped microcrystals. However, oblique texture electron diffraction patterns have the following advantages firstly, they can provide data from the full 3D diffraction pattern in a single exposure, secondly, there is a possibility of obtaining almost perfectly oriented samples, which, owing to the minimization of their overlapping, produce diffraction patterns with good resolution of reflections. Extremely small crystals can and should be used - thinner than what is needed for X-ray powder diffraction. 

CBED is formed by focusing electrons to form a small probe at the specimen (fig. 1). Compared to selected area electron diffraction, CBED has two main advantages for studying perfect crystals and the local structure ... 

The future for electron diffraction is very bright for two reasons. First, electron diffraction pattern can be reeorded seleetively from individual nanostrueture at sizes as small as a nanometer using the electron probe forming lenses and apertures, while eleetron imaging provides the selectivity. Second, electrons interact with matter mueh more strongly than X-ray and Neutron diffraction. These advantages, eoupled with quantitative analysis, enable the structure determination of small, nonperiodic, structures that was not possible before. 

Advanced materials stmcture analysis by electron diffraction in a TEM presents a lot of advantages over conventional X-Ray diffraction the size of studied crystallites in TEM can be very small (even tens of Angstroms), therefore individual phases in Industrial powders (nm size) can be examined. 

Electron diffractometry system with the combination of the precession technique can be very perspective experimental instrumentation for precise structural investigations. The technique can now be adapted in a commercial TEM (previously applied uniquely to electron diffraction cameras) taking advantage of the small beam size and can measure reflections in the ED pattern with same required precision for structure analysis. 

Electron energy-loss spectroscopy (EELS) is nowadays widely used to obtain the information with respect to chemical composition, oxidation state and electronic structure of solids. Since all catalytic processes concern the exchange of electrons between the reactants, EELS is extremely valuable in catalysts investigations [9, 49-57], EELS in an electron microscope exhibits the advantage of high spatial resolution in area of interests with simultaneous structure determination by electron diffraction and imaging. 

For optimal use of the electron-diffraction method in large amplitude-motion studies, it is important to take advantage of the knowledge concerning potential functions as obtained by spectroscopical methods. Some features of the spectroscopically obtained findings are given in the next section. 

The torsional motion of biphenyl and related compounds is a typical large amplitude motion. The accumulated knowledge from a series of molecules in this group has led to a fairly good qualitative description of the motion. Unfortunately the quantitative description leaves much to be desired. Taking advantage of the improvements in the electron-diffraction method and applying suitable combinations with other methods, there are reasons to believe that this deficiency should be remedied. 

Professor Tadakoro s recent book(l ) illustrates the considerable advantages and benefits to be gained by coupling infra-red spectroscopy with fibre x-ray diffraction. The increasing availability of Fourier transform infra-red spectrometers allows the same thick samples, suitable for x-ray work, to be used in the spectrometer thus ensuring that both sets of information emanate from the same structure. The delightful selected area electron diffraction patterns obtained from polysaccharides by Dr. Chanzy (2), which exhibit such remarkable resolution and definition, indicate the importance and value of the modern application of electron micro-... 

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