Fermi surfaces of surface states on Si(111)-Ag, Au

Metallic surface states on semiconducting substrates provide an opportunity to study low-dimensional electrons decoupled from the bulk. Angle resolved photoemission is used to determine the Fermi surface, group velocity, and effective mass for surface states on Si(111)√3×√3-Ag, Si(111)√3×√3-Au, and Si(111)√21 ×√21-(Ag+Au). For Si(111)√3×√3-Ag the Fermi surface consists of small electron pockets populated by electrons from a few % excess Ag. For Si(111)√21×√21-(Ag+Au) the pockets increase their size corresponding to a filling by three electrons per unit cell. The √21×√21 superlattice leads to an intricate surface umklapp pattern and to minigaps of 110 meV, giving an interaction potential of 55 meV for the √21×√21 superlattice.