Growth and Ag-encapsulation of Pt islands on Ag(111) at room temperature

• STM was used to characterize the structures formed by low coverages of Pt on the Ag(111) surface. • Ag atoms migrate from the substrate to cover Pt islands at room temperature. • Coverage of the Pt islands is accompanied by the growth of monolayer pits in the Ag(111) surface. The growth of Pt islands at submonolayer coverages on Ag(111) at room temperature were investigated with scanning tunneling microscopy. A two-step mechanism for growth of the islands is proposed. First, Pt replaces Ag substrate atoms through a place-exchange process. Next, Pt adatoms nucleate at substitutional Pt sites and Pt islands subsequently grow from these sites. At room temperature, Ag atoms migrate to cover Pt islands, creating vacancy pits on the terraces and bays on the step edges. Ag atoms nucleate at corner sites of the Pt islands, and the layer of Ag atoms on the Pt islands grow from these sites.