Valence- and Conduction-Band Structure of the Sapphire (1102) Surface

摘要

X-ray photoelectron and electron energy loss spectroscopies have been employed to investigate the valence- and conduction-band densities-of-states of the sapphire (1102) surface. The photoemission spectrum of the valence-band region has been adjusted to remove cross-section effects and compared to the recent theoretical density-of-states calculated by Ciraci and Batra. The energy loss data have been used to determine the bulk plasmon energy of sapphire, 24.0 +or- .3 eV, as well as the locations of eight regions of high conduction-band state density within 20 eV above the conduction-band minimum. One of these regions is an empty surface state 4.0 eV below the conduction-band minimum. Several high binding energy satellites in the XPS core level spectra are reported and interpreted in terms of energy losses to plasmons and interband transitions.