Stability of an ultra-thin Fe ®lm on a Cu(1 0 0) surface studied by positron-annihilation induced Auger electron spectroscopy (PAES)

The stability and intermixing of ultra-thin Fe layers grown on a Cu(1 0 0) surface has been studied as a function of ®lm thickness, growth temperature and annealing history using positron-annihilation induced Auger electron spectroscopy (PAES). Theoretical calculations and previous experimental PAES studies indicate that when a complete metal layer is formed on top of a metal substrate almost of all the PAES signal originates from the overlayer. However, in the research reported here, it was found that even after depositions in excess of 1 equivalent monolayer (eq. ML) of Fe at 173 K and 3 eq. ML at 303 K, a signi®cant fraction of the Cu PAES signal was observed. These result are consistent with the formation of Fe islands leaving regions of exposed Cu surface or with Cu mixing with or moving on top of the deposited Fe. The increase in the fraction of Cu in the top most layer observed as the sample was heated is consistent with a thermally induced increase in island height or an increase in the diffusion of Cu into or on top of the surface layer. # 2001 Elsevier Science B.V. All rights reserved.