S E. Schnatterly

Optical properties of silicon and its oxides

We have measured the inelastic electron scattering spectra of a variety of Si and SiO2 thin films from the fundamental absorption threshold to well above the L-shell thresholds. We have used Kramers–Kronig analyses and sum rules to obtain the dielectric and optical response functions. We compare the optical properties of crystalline and evaporated and hydrogenated amorphous Si, amorphous evaporated SiO and SiO2, and chemical-vapor-deposition SiO2 in both the interband and the L-shell absorption regions. The interband structure in crystalline Si shows three sharp peaks that are blended into a single broad peak in the amorphous samples. At the L threshold crystalline Si also shows more structure than amorphous Si, however, the overall shape in the region well above the threshold is quite similar in the three samples. Above the SiO2 band gap the three oxide samples show strikingly similar behavior.

Local fields in high-Tc materials

Abstract Most high-temperature superconductors exhibit two-dimensional conductance; therefore the conduction electrons are localized in the third dimension, and experience the local electric field rather than the macroscopic applied field in that direction. We report model calculations which indicate that the local field leads to enhanced electron-phonon coupling in these materials which may play a role in determining the high transition temperatures.

Effective masses of the 4p excitons in solid Kr

Abstract We have measured the momentum dependent electron energy loss spectrum of solid Kr and evaluated the effective masses of the excitons for the first two principal quantum numbers of each excitonic series. We find that n = 1 excitons disperse more slowly than the n = 2 excitons of the same series indicating greater effective masses for n = 1 excitons than for n = 2 excitons within the effective mass model. For intermediate wave vectors, where the splitting of the heavy hole and light hole bands should be observable, we find no evidence for a splitting in the two bands, in conflict with band structure calculations.