Extreme ultraviolet response of ionic crystals

The absorption coefficients of rubidium chloride, rubidium bromide and potassium bromide have been determined in the extreme-ultraviolet by means of transmission measurements on thin films. For this purpose an electron storage ring was used as a source of continuum radiation in the range of photon energy from 70 to 220eV. A careful comparison of experimental and theoretical response was made in order to understand the various transition processes. The conduction band of rubidium chloride was ca1culated at approximately 50,000 points in the first Brillouin zone by a combined interpolation scheme utilizing the pseudopotentia1 method and the tight binding method of Slater and Koster. Available ESCA data was used to position the conduction band minimum with respect to the onset of absorption. The resulting conduction band density of states was then compared with the first spin-orbit component of the rubidium 3d level and the chlorine 2p level. The interpretation was extended to the bromine 3d level of potassium bromide and the bromine and rubidium 3d levels of rubidium bromide. It was found that excitonic, solid-state band and atomic effects are important in determining the spectral features appearing in this region of the spectrum.U of I Onlydissertatio