EFFECT OF STRAIN ON THE GROWTH-MECHANISM AND STRUCTURE OF ULTRA-THIN CU FILMS ON PD(110)

The growth mechanism and structure of strained ultra-thin Cu films on Pd(110) have been studied by LEED. AES and X-ray photoelectron polar intensity plots (Pips) combined with single-scattering cluster modelling. The first Cu monolayer grows largely two-dimensionally and pseudomorphic with the underlying Pd(110) substrate with an in-plane lattice expansion of 7.2%. Upon completion of the first atomic layer, growth proceeds in the form of (110)-oriented clusters of large base-to-height ratio. Polar intensity plots utilising emission from the Cu 2p(3/2) core level in the [001] azimuth combined with curved wave single-scattering cluster calculations demonstrate that the films adopt an fee stacking sequence. The possibility of a strain-induced tetragonal distortion of the fee Cu lattice is examined. The strain-induced (1 X 1)-->(1 X 2) missing-row surface-phase transformation predicted by Guillope and Legrand [Surf. Sci. 215 (1989) 577] is not observed for any film thickness in the range 1-20 eML.