High-angle diffraction

As the annealing temperature increases, the intensity of the high angle diffractions increases relative to the hioo reflection of MCM-41. 

The electron density distribution in the Se02Cl anion of [ (CH3)4N ][Se02Cl ] has been studied by an X-X deformation density analysis using high-angle diffraction data at 120 K (405, 406). The deformation density maps clearly reveal the presence of lone-pair (E) density (maximum of 0.40 0.04 e x at a distance of ca. 0.75 A from Se) consistent with model predictions for an approximately i )-tetrahedral Se02ClE arrangement with additional tt density in the Se-0 bonds and with a rather polar Se-Cl bond. 

A reasonably strong high-angle diffraction line is needed for the measurement of stress. The combination of (hkl) reflecting planes and wavelength A that will produce such a line varies from one kind of material to another. These combinations and the approximate 26 position of the line are listed in Table 16-1 for various materials. 

It should cause no surprise that for polymer crystals with very small sizes, a definitive structural analysis is difficult using only unoriented diffraction patterns. This is not only due to the small number of observable diffractions and their general broadening, but also to the fact that high angle diffraction rings often consist of the superimposition of several refiections of different indices. In certain special cases, eg, when a structural similarity to a known substance is suspected on the basis of chemical composition, it may be possible to make identification by comparison, but even this procedure contains possible errors. 

Macrostrain is often observed in modified surfaces such as deposited thin films or corrosion layers. This results from compressive or tensile stress in the plane of the sample surface and causes shifts in diffraction peak positions. Such stresses can easily be analyzed by standard techniques if the surface layer is thick enough to detect a few diffraction peaks at high angles of incidence. If the film is too thin these techniques cannot be used and analysis can only be performed by assuming an un-... 

Greenall, R., Fuller, W. High Angle Fibre Diffraction Studies on Conformational Transitions DNA Using Synchrotron Radiation. 151, 31-59 (1989). 

Figure 4c shows a high angle annular detector image of the same area, where the angular collection range is now 80 to 400 mrad. Support diffraction contrast has been attenuated and Pt particle contrast is significantly enhanced compared with that... 

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