Segregation-mediated capping of Volmer-Weber Cu islands grown onto Ag(111)

The growth of Cu on an Ag(111) surface is studied using scanning tunneling microscopy at room temperature and for low Cu coverage ranging from 0.02 to 1.5 monolayers. Three-dimensional islands are found to grow at the Ag surface steps. During this Volmer-Weber growth, the erosion of steps and the formation of vacancy domains inside the terraces indicate that a large redistribution of Ag atoms takes place. Moreover, STM images from the top of islands reveal a (9 X 9) reconstruction which is well known to occur in the reverse case. where one Ag monolayer is deposited on Cu(111). These findings combined with molecular dynamics simulations allow us to conclude that the Cu islands are capped, from the very beginning of the growth, by one monolayer of Ag atoms diffusing from the eroded regions.