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)sqrt3xsqrt3-Ag, Si(111)sqrt3x sqrt3-Au, and Si(111)sqrt21xsqrt21-(Ag+Au). For Si(111)sqrt3xsqrt3-Ag the Fermi surface consists of small electron pockets populated by electrons from a few percent excess Ag. For Si(111)sqrt21xsqrt21-(Ag+Au) the added Au forms a new, metallic band. The sqrt21xsqrt21 superlattice leads to an intricate surface umklapp pattern and to minigaps of 110 meV, giving an interaction potential of 55 meV for the sqrt21xsqrt21 superlattice.