Optical Properties of Vacuum-Evaporated White Tin

Abstract

Near-normal incidence-reflectance data on vacuum-evaporated white tin films, produced in situ, are presented for incident photon energies from 2.1 to 14.5 eV. In addition, the real part of the refractive index has been measured from 14.5 to 20.5 eV by the critical-angle method. These results are combined with previously published data for white tin films and an analysis of optical data is carried out from 0.1 to 27.5 eV. Separation of the dielectric constants into contributions due to free and bound electrons indicates interband transitions at 1.2±0.1 and 24.5±0.1 eV, as found by previous workers, and a further interband transition at approximately 3 eV. Tentative identification of these transitions is made using published energy-band calculations. The energy-loss functions for surface and volume plasmons show sharp peaks at 9.2 and 13.4 eV, respectively, in agreement with electron-energy-loss measurements. Sum rules are used to interpret the effective number of electrons per atom at various incident photon energies.