Valence- and conduction-band structure of the sapphire (11¯02) surface

Abstract

X-ray photoelectron (XPS) and electron-energy-loss spectroscopies have been employed to investigate the valence- and conduction-band densities of states of the sapphire (11¯02) 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±0.3 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.