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

►Cu diffusion in ultrathin Co films on Cu(001) is controlled. ►Experimental parameter is the sample temperature during and after film growth. ►Room-temperature growth cannot prevent Cu diffusion on the timescale of hours. ►Sharp interfaces with no diffusion obtained by low-temperature growth plus annealing. ►Cu diffusion at higher temperatures changes surface composition and topography.