Surface core-level shift of InSb(111)-2x2

Surface core-level photoemission of InSb(111)-2x2 was performed using a synchrotron radiation light source. There were two surface components of the In 4d core level. A higher binding component of In 4d is attributed to the surface In bonded to Sb atoms. The lower binding component with smaller intensity is due to the surface In cluster atoms. On the other hand, we were not able to observe any surface components in the Sb 4d core level. This puzzling behavior is interpreted with a different contribution of surface and bulk Madelung potential to the surface core-level shifts in relation with the atomic geometry.