Initial and final state contributions of the core level shifts for Gd(0001)

Abstract

The initial state and final state contributions to the core level shift are separated by comparing the shifts of occupied and unoccupied Gd 4f levels, which exhibit the initial state shift with equal signs and the final state shift with opposite signs. For clean Gd(0001) we find a surface shift of -0.4 eV for both the unoccupied and occupied 4f level. On the other hand, with 3-4 L of oxygen the unoccupied surface 4f level is shifted by + 1.0 eV with respect to the bulk, and the occupied 4f by -1.0 eV. Therefore, the initial state effect dominates at the clean surface, while the final state effect plays a significant role at the oxidized surface. The difference is explained by metallic versus dielectric screening. © 1994.