Pseudomorphic growth of Ni films on Cu(001): a quantitative LEED analysis

Abstract

We present LEED structure determinations of ultra-thin epitaxial Ni films on Cu(001) for coverages of 3, 5 and 11 ML. From full dynamical intensity analyses, a tetragonal distortion of all films can be deduced, in good accordance with FMR results. The structural parameters of the 5 and 11 ML films are practically identical. So, obviously there are no structural changes at about 7 ML, where the orientation of the magnetization is reported to switch from in-plane to out-of-plane. The film growth is pseudomorphic with an in-plane lattice parameter a p = 2.53 A ̊ at coverages of 3 and 5 ML. This value, which is slightly reduced with respect to the copper bulk, was recently also found to produce the best fit for a similarly prepared clean Cu(100) surface. With further increasing coverage, a p tends to approach the value of the nickel bulk (2.49 Å) but does not fully reach it even at 11 ML ( a p = 2.51 A ̊ ). The films at 5 and 11 ML (and probably also in the regime between) show considerable tetragonal distortions. The top Ni layer shows an outward relaxation of 8% relative to the distances between deeper layers, which, due to the tetragonal distortion, are reduced compared to the ideal value of the nickel bulk.