Modification of surface states in ultrathin films via hybridization with the substrate: A study of Ag on Ge

The Shockley surface state of Ag(111) develops unusual band dispersion relations for Ag films of decreasing thicknesses on Ge(111), as observed by angle-resolved photoemission. Its parabolic dispersion in the thick-film limit shifts toward higher binding energies and splits into multiple bands with dispersions that reflect the valence band structure of Ge including the heavy-hole, light-hole, and split-off bands. The results are explained in terms of a hybridization interaction between the Ag surface state and the Ge substrate states.