Influence of the substrate bands on the sp-levels topology of Ag films on Ge(111)

Angle-resolved photoemission spectroscopy and first-principles calculations were employed to analyze unusual features in the electronic structure of ultrathin Ag films grown on Ge(111). The Ag sp-derived quantum well states exhibit hexagonal-like constant energy contours with different in-plane orientations near the center of the surface Brillouin zone, in striking contrast to the expectations for a free-standing Ag(111) layer. The experimental observations are explained by taking into account the effects of hybridization of the Ag states with the star-like shaped Ge band edges on constant energy planes.