Kinetic hindrance during the surface oxidation of Cu(100)-c(10x2)-Ag

The influence of c(10x2)-Ag superstructure on the oxidation kinetics and oxygen adsorption-induced nanostructures on Cu(100) has been investigated as a function of O-2 exposure at 373 K by employing scanning tunneling microscopy and x-ray photoelectron spectroscopy. The oxygen adsorption-induced segregation of Cu through the Ag overlayer is found to trigger agglomeration of Ag and subsequent formation of ordered oval-shaped nanosize metallic Ag islands separated by Cu(100)-(2 root 2x root 2)R45 degrees-O surface phase. As oxygen exposure is further increased, all Ag is eventually covered by oxidized Cu. The presence of Ag delays the completion of the fully reconstructed (2 root 2x root 2)R45 degrees-O surface and the nucleation and growth of Cu2O islands by limiting Cu diffusion toward the surface. Once Cu2O grows into the bulk deeper than buried Ag, the oxidation kinetics follow that of the unalloyed clean Cu(100) surface. Similar kinds of Cu-O nanostructures are found on both clean Cu(100) and Cu(100)-c(10x2)-Ag surfaces. Details of the morphology of the Ag structures and kinetic control of the surface oxidation mechanism on Cu(100)-c(10x2)-Ag are discussed.