Two-dimensional electron gas formed on the indium-adsorbed Si(111)√3 x √3-Au surface

Electronic structure of the In-adsorbed Si(111)root 3 x root 3-Au surface was investigated by core-level and angle-resolved photoelectron spectroscopy. On the Si(111)root 3 x root 3-Au surface, In adsorbates were reported to remove the characteristic domain-wall network and produce a very well-ordered root 3 x root 3 surface phase. Detailed band dispersions and Fermi surfaces were mapped for the pristine and In-dosed Si(111)root 3 x root 3-Au surfaces. After the In adsorption, the surface bands shift toward a higher binding energy, increasing substantially the electron filling of the metallic band along with a significant sharpening of the spectral features. The resulting Fermi surface indicates the formation of a perfect isotropic two-dimensional electron-gas system filled with 0.3 electrons. This band structure agrees well with that expected, in a recent density-functional theory calculation, for the conjugate-honeycomb trimer model of the pristine Si(111)root 3 x root 3-Au surface. Core-level spectra indicate that In adsorbates interact mostly with Si surface atoms. The possible origins of the electronic structure modification by In adsorbates are discussed. The importance of the domain wall and the indirect role of In adsorbates are emphasized. This system provides an interesting playground for the study of two-dimensional electron gas on solid surfaces.