Photoemission study of surface state intensity resonance and dispersion of Be2C(100)

Abstract

We have carried out an extensive study on the surface state properties of an ionic, insulating Be2C(100) surface using angle-resolved photoemission spectroscopy. Two surface states were observed and characterized. One (S1) is derived at the Gamma-point above the valence band maximum in the fundamental gap. The other (S2) is located in the gap at the X-point. Resonance in the photoemission intensity of surface state S2 shows multiple peaks due to a surface umklapp process, similar to bulk transitions, because of large corrugation of the ionic surface. The penetration lengths deduced are about 4 Angstrom for both surface states. The dispersions of these states are very small. These two results indicate strong localization of the. surface state wave function to individual surface C atoms owing to the ionic character of this compound. That a surface state (S2) exists in a non-inverted Shockley gap is attributed to the compound structure. (C) 1999 Elsevier Science B.V. All rights reserved.