Extended fine structure analysis using electron beams

Appearance potential spectroscopy has found use primarily as a core level probe of the electronic structure of solid surfaces. The observation of extended fine structure above appearance potential edges, analogous to that observed above X-ray adsorption edges, gives promise that atomic spacings in the surface region may also be determined. Most previous studies of appearance potentials have depended on observing changes in the soft X-ray yield. Poor detection efficiencies and low flourescence yields have limited the usefulness of this approach. Using the secondary electron yield, however, we have recently succeeded in observing fine structure extending more than 400 eV above appearance potential edges. We are currently employing this approach to study the structure of SiO₂ films on Si substrates. Initial attempts at Fourier inversion and problems due to diffraction of the incident electron beam and multiple scattering effects will be discussed.