Electronic structure of Ag-induced √3X √3 and √21X √21 superstructures on the Si(111) surface studied by angle-resolved photoemission spectroscopy and scanning tunneling microscopy -: art. no. 205316

Polarization-dependent angle-resolved photoemission spectroscopy was used to analyze the electronic band structure of the Si(111)-root 21 X root 21(R +/- 10.89 degrees)-Ag surface induced by adding submonolayer Ag atoms on top of the Si(111)-root3 X root3-Ag surface at 140 K, together with a refinement of the electronic states of the initial root3 X root3-Ag substrate itself. The surface-state band crossing the Fermi level on the the root3 X root3-Ag surface was found to have similar dispersions in both <()over bar>-(K) over bar and <()over bar>-(M) over bar directions around the <()over bar> point of the root3 X root3 surface Brillouin zone, and consist mainly of components parallel to the surface with no measurable polarization dependence. The five intrinsic surface-state bands observed on the root3 X root3-Ag surface basically remained in the root 21 X root 21-Ag structure, but shifted down in energy position from the Fermi level by about 0.4 eV. This is due to electron transfer from the Ag adatoms to the substrate, suggesting that the Ag adatoms in the root 21 X root 21-Ag phase sit on a nearly unaltered root3 X root3-Ag substrate, and do not make any orbital hybridization with the substrate. Only one parabolic band crossing the Fermi level was found on the root 21 X root 21-Ag surface, for which distribution in real space is observed by bias-dependent scanning tunneling microscopy, This result is in contrast to two metallic bands on the root 21 X root 21 phase induced by Au or Cu adatoms on the root3 X root3-Ag substrate reported in previous papers.