Role of the metal/semiconductor interface in quantum size effects: Pb/Si(111)

Self-organized islands of uniform heights can form at low temperatures on m etal/semiconductor systems as a result of quantum size effects, i.e., the o ccupation of discrete electron energy levels in the film. We compare the gr owth mode on two different substrates [Si(111)-(7 X 7) vs Si(lll)-Pb(root3 X root3)] with spot profile analysis low-energy electron diffraction. For t he same growth conditions (of coverage and temperature) 7-step islands are the most stable islands on the (7 X 7) phase, while 5-step (but larger isla nds)are the most stable islands on the (root3 X root3). A theoretical calcu lation suggests that the height selection on the two interfaces can be attr ibuted to the amount of charge transfer at the interface.