Umklapp induced surface band structure of Ag/Ge(111)6 × 6

This study focuses on the electronic structure of a 6 × 6 surface which is formed by 0.2 monolayer of Ag on top of the Ag/Ge(111) 3×3 surface. The 6 × 6 periodicity was verified by low energy electron diffraction. Angle resolved photoelectron spectroscopy was employed to study the electronic structure along the Γ¯−M¯−Γ¯ and Γ¯−K¯−M¯ high symmetry lines of the 6 × 6 surface Brillouin zone. There are six surface bands in total. Out of these, three were found to be related to the 6 × 6 phase. The surface band structure of the 6 × 6 phase is significantly more complex than that of the 3×3 surface. This is particularly the case for the uppermost surface band structure which is a combination of a surface band originating from the underlying 3×3 surface and umklapp scattered branches of this band. Branches centered at neighboring 6 × 6 SBZs cross each other at an energy slightly below the Fermi level. An energy gap opens up at this point which contains the Fermi level. The complex pattern of constant energy contours has been used to identify the origins of various branches of the surface state dispersions.