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)root3xroot3-Ag, Si(111)root3xroot3-Au, and Si(111)root21xroot21-(Ag+Au). For Si(111)root3xroot3-Ag the Fermi surface consists of small electron pockets populated by electrons from a few % excess Ag. For Si(111)root21xroot21-(Ag+Au) the pockets increase their size corresponding to a filling by three electrons per unit cell. The root21xroot21 superlattice leads to an intricate surface umklapp pattern and to minigaps of 110 meV, giving an interaction potential of 55 meV for the root21xroot21 superlattice.