Scanning probe microscopy study of height-selected Ag/Ge(111) nanomesas driven by quantum size effects

We present scanning tunnel microscope, noncontact atomic force microscopy, Kelvin probe force microscopy, and low-energy electron diffraction study of the morphological evolution of Ag ultrathin films (0.5-6 ML) grown at 150 K on Ge(111)-c(2×8) substrate. Although the system has been widely studied in the context of quantum confinement effects in the electronic structure of these films, no real-space imaging has been reported so far. Our results demonstrate that upon annealing to room temperature, the Ag film adopts a (111) epitaxy on top of a wetting layer. It has been found that the Ag film adopts a metastable morphology which is determined by a delicate interplay between thermodynamics and the kinetics of interlayer mass transport. The preferential population of a discrete set of the deposit heights at 6, 10, and 12 ML suggests that quantum size effects are indeed active for the Ag/Ge system. Kelvin probe force microscopy indicates that the surface potential depends monotonically on the film thickness and does not show any oscillatory behavior in correspondence to the height changes