Analysis of valence shell electronic excitations in silicon and its refractory compounds using electron energy loss microspectroscopy

Valence shell electronic excitations in silicon, and its carbide, nitride, and oxide are studied using electron energy loss microspectroscopy in a transmission electron microscope, at 1-eV resolution with a 100-keV electron beam. This so-called ‘‘low-loss’’ region of the spectrum is normalized to scattering cross section per valence electron for each compound, and a large, sequential, variation in the cross section across the series of compounds is reported. The low-loss cross section is calculated using the Born approximation by including single-electron transitions in the target. Both band-to-band and band-to-continuum transitions are included, by using extended Hückel band calculations to obtain the valence shell crystal states, using the electron gas model for the ionization states, and using the random phase approximation to obtain differential cross sections. The calculations yield semiquantitative results, and allow for a chemical interpretation of the experimental results. The relation of the present model to that for plasmon excitation is also briefly discussed.