EXELFS AS A STRUCTURAL TOOL FOR STUDIES OF LOW Z-ELEMENTS

By using high and medium voltage microscopes we have been able to obtain EELS spectra showing EXELFS modulations above the K edge of low atomic number Z less-than-or-equal-to 16, elements. These modulations supply important structural information about the local atomic environment of the absorbing atoms. After recapitulating the physical foundations of EXELFS and the ways of analysing the spectra, we discuss the main steps of the experimental technique, as developed for the medium voltage transmission electron microscope. The potential of the technique is studied for four types of specimen : graphite, hexagonal boron nitride, carbon made amorphous and cubic silicon carbide. They have been chosen to illustrate the accuracy of the method, its potential for the determination of short-range order of crystallized and non-crystallized materials and to emphasize the influence of plural scattering effects on the RDF determination.