Surface states on Si(111)-(2×1)

Surface-state energy bands for a single-domain Si(111)-(2×1) surface have been studied with angle-resolved photoemission using synchrotron radiation. From the angular photoelectron distributions seen with a display-type spectrometer, we conclude that there are two surface states near the top of the valence bands Ev, one at Ev-0.7 eV around »[0.65 eV full width half maximum (FWHM)] and a second at Ev-0.15 eV (0.4 eV FWHM) along the line J»K». These states are found to be nearly dispersionless along the symmetry lines J and J»K». Their range of existence can be related to different gaps in the projected bulk bands. The lower surface state lies in a band gap above the L3 point which we find at Ev-1.5 eV. Our findings are not well described by band calculations reported to date which use buckled-surface model geometries. Our results also indicate that several discrepancies among different reported experimental results are likely due to multidomain cleavage effects. We conclude that either the geometry of Si(111)-(2×1) has not yet been determined unambiguously or that the surface states cannot be described by a bandlike model which is the basis of present calculations. © 1981 The American Physical Society.