ANALYSES OF EELS FINE-STRUCTURES OF DIFFERENT SILICON-COMPOUNDS

Electron energy loss spectra of different silicon compounds, in partic ular, silicon carbide, dioxide, and oxycarbide, are analysed experimen tally as well as theoretically. For this purpose features measured of both the low-loss region and the SiL(23) inner-shell excitation are co mpared with results of corresponding calculations. In the theoretical treatment the features of the low-loss region are interpreted as super positions of plasmon and interband excitations. On the basis of the en ergy eigenvalues E(m) and the occupation densities of the occupied val ence states attained by MNDO (modified neglect of diatomic overlap) ca lculations the scattering function Im {-1/epsilon(E)} in the low-loss region is simulated. The low-loss features attained both experimentall y and theoretically agree quite well. The fine structure of the Sit,, ionization edge is interpreted using densities of unoccupied states ob tained by MNDO calculations, too. The density of states calculated dep ends on the chemical bonding as experimentally proved. The calculation s enable predictions concerning the electronic structure of the silico n compounds under investigation, whereas the limits of LCAO (linear co mbination of atomic orbitals) methods have to be considered if inelast ic electron scattering processes are described.