Auger line shape analyses for epitaxial growth in the Cu/Cu, Ag/Ag and Ag/Cu systems

Abstract

A new measure of the MVV doublet Auger line shape called the R-factor has been applied to homoepitaxial layer growth on (111)Cu and on (111)Ag as well as to the heteroepitaxial growth of (111)Ag on (111)Cu. AES and TEM show that as thick (∼1500 Å) monocrystalline Cu and Ag films grow thicker, R oscillates with a period equal to one atomic layer. Polycrystalline films do not show such a periodicity. The changes in doublet line shape are interpreted as arising from the superposition of two sets of doublets slightly displaced in energy. One set is presumed to come from the flat areas of the film and the other from the edge areas of incomplete layers. The origin of the periodicity in R arises then from the atomic relaxations that can be expected at the edges of surface steps, whose density varies periodically during growth. For the initial stages of (111)Ag growth on (111)Cu, an initially high R Ag decreased to bulk values as the Ag thickened beyond one or two monolayers for both polycrystalline and monocrystalline films; but the periodicity in R Ag was detected only for monocrystalline growth. The high initial values of R Ag are interpreted as arising from changes in the energy levels of the corresponding Auger transitions with changing interatomic spacing. Since the Ag overgrowth is compressed towards the smaller lattice parameter of the Cu substrate, energy levels in the valence band of Ag might be expected to become more widely separated. Consequently a more highly resolved MVV doublet for Ag would occur, resulting in a larger R Ag.