The unoccupied electronic structure of the model interface Sn/Si(111)-α-√3 was measured at room temperature using angle-resolved inverse photo-emission spectroscopy. In addition to a partly occupied surface band crossing the Fermi level, there was a second unoccupied surface state located 1.5eV above EF; the existence of these two surface states was not compatible with the single adatom site used to describe the α-√3 reconstruction. These surface states receive a natural explanation, once many-body effects were introduced, in the framework of a dynamical fluctuations model, where two types of adatom site, reminiscent of a possible low-temperature (3 x 3) phase, co-existed at room temperature.

Many-Body Effects in the Electronic Structure of Sn/Si(111)-α-(3)1/2. A.Charrier, R.Pérez, F.Thibaudau, J.M.Debever, J.Ortega, F.Flores, J.M.Themlin: Journal of Physics - Condensed Matter, 2001, 13[22], L521-8