Controlling Cu diffusion in Co films grown on Cu(001)

For ultrathin Co films on Cu(001) we present a way of controlling Cu diffusion from the substrate to the overlayer by choosing different sample temperatures during and after film growth. The topography and chemical composition of the overlayer films are characterized by scanning tunneling microscopy and photoemission, respectively. For room-temperature growth, considerable Cu diffusion from the substrate through a 15 monolayer-thick Co film was identified on the timescale of hours. The diffusion is suppressed when growing the film at a low temperature of 115 K, which, however, results in a rough surface. An atomically smooth surface is recovered by moderate annealing to 555 K, though without Cu impurities. Cu diffusion sets in for higher temperatures accompanied by changes in surface composition and topography.