Electronic Structure of the √3 × √3-α and 3×3 Periodicities of Sn/Ge(111)

Angle-resolved photoemission shows that the $\sqrt{3}\times \sqrt{3}$ and the $3\times 3$ surfaces have almost identical surface band structures with two dispersive bands, one of which crosses the Fermi level. The close resemblance between the electronic structures strongly points to a common atomic structure which is further supported by the two Sn $4d$ core-level components observed for both the $\sqrt{3}\times \sqrt{3}$ and the $3\times 3$ surfaces. The existence of two surface state bands on the $\sqrt{3}\times \sqrt{3}$ surface calls for the reevaluation of the $T_4$ model for Sn/Ge(111) and other related group IV adatom surfaces.