Inverse corrugation and corrugation enhancement of Pb superstructures on Cu(111) and (110)

Contrary to intuitive expectation, a monatomic hexagonal close-packed Pb film on Cu(111) shows an ''inverse'' corrugation, i.e. the Pb atoms in on-top adsorption sites appear lowest in scanning tunneling microscopy (STM) images, as well as in effective medium theory (EMT) simulations. On small subsurface Cu islands on a Pb(111) substrate, which are also covered by a monatomic Pb film, the corrugation of this film was found to be strongly dependent on the thickness of the Cu island (the thinner the island, the larger the corrugation). EMT simulations reproduce this enhanced corrugation qualitatively and thus further confirm the formation of these subsurface Cu islands. On a p(8 x 1) superstructure of Pb/Cu(110), similarly, the lowest coordinated Pb atoms also show the lowest apparent height in STM images.