Diffusion of silver through epitaxial films of copper and nickel on silver (111): the formation of an equilibrium layer of silver

Abstract

Thick (>2000 AA) epitaxial films of nickel and copper grown on silver (111) have been annealed in ultra-high vacuum at temperatures in the range 500-600K. This annealing procedure appears to cause diffusion of silver to the outer surface to take place, with the formation of an 'equilibrium layer' of silver. The silver layer appears to be strained in each case to give an integral ratio matching with the nickel or copper, the matching being 6:7 for Ag:Ni and 8:9 for Ag:Cu. A comparative study was made for thin films of silver deposited directly on to copper (111). LEED, RHEED and Auger spectroscopy were used throughout the study. Extra non-primary satellite beams in both LEED and RHEED from thin layers of Ag on Cu or Ni are believed to result from a combination of multiple diffraction and periodic deformations in the overlayer.