For ultra-thin Co films on Cu(001), a method was presented for controlling Cu diffusion from the substrate to the overlayer by choosing various sample temperatures during and after film growth. The topography and chemical composition of the overlayer films were characterized by scanning tunnelling microscopy and photo-emission, 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 was suppressed when growing the film at a low temperature of 115K, which, however, results in a rough surface. An atomically smooth surface was recovered by moderate annealing to 555K, though without Cu impurities. Cu diffusion sets in for higher temperatures accompanied by changes in surface composition and topography.

Controlling Cu Diffusion in Co Films Grown on Cu(001). T.Allmers,, M.Donath: Surface Science, 2011, 605[21-22], 1875-80