EXELFS ANALYSIS OF AMORPHOUS AND CRYSTALLINE SILICON-CARBIDE

Core-shell ionization edges from thin specimens of cubic silicon carbide (c-SiC) are studied by means of electron energy-loss spectroscopy (EELS) in a transmission electron microscope (TEM). Special attention is paid to the investigation of extended energy-loss fine structures (EXELFS) to study local order effects around silicon atoms as a function of disorder in SiC. Two forms of SiC were used: c-SiC for the crystalline form, and friction-induced amorphous silicon carbide (a-SiC) for the disordered form. EXELFS are generated by the elastic backscattering of outgoing electron waves by neighbouring atoms. Results show that both Si-K and Si-L edges contain structural information. EXELFS at the Si-K edge can be used to calculate the radial distribution function (RDF) in the same way as extended X-ray absorption fine structures (EXAFS). EXELFS at the Si-L edge can be isolated by digital filtering. The high signal-to-noise ratio at the Si-L edge permits the effect of larger interatomic distances to be observed, and thus the EXELFS technique is of promise for studying the effect of disorder in Si-based ceramic materials with a high spatial resolution (nanometre scale).