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Surface-state energy bands for a single-domain Si (111) - (21) 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 Eₕ, one at Eₕ-0. 7 eV around 0. 65 eV full width half maximum (FWHM) and a second at Eₕ-0. 15 eV (0. 4 eV FWHM) along the line JK. These states are found to be nearly dispersionless along the symmetry lines -{J^'} and JK. 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 Eₕ-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) - (21) 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.
Himpsel et al. (Sat,) studied this question.