The core-level line shapes of Si(111)-(7×7), Si(100)-(2×1), and Ge(100)-(2×1) are examined with synchrotron-radiation photoemission both before and after Cs adsorption. The Cs-induced core-level shifts are determined. The results indicate that the chemisorption bond is partially ionic, and the Si or Ge surface atoms each have an extra charge of about 0.3 electron after Cs adsorption.

• Received 29 April 1991

DOI:https://doi.org/10.1103/PhysRevB.44.10719