Modifications of the electronic structure of Ni/Cu(001) as a function of the film thickness

We report angle-dependent near-edge x-ray-absorption fine-structure measurements of tetragonal Ni films [0.6--14.4 monolayers (ML)] grown on a Cu(001) surface. The analysis of the Ni L3,2 white-line intensities show that the density of $3d$ holes (nₕ) increases almost by 20% from a submonolayer to a 5 ML thick film, clearly showing that a constant value of nₕ cannot be used in sum rules to estimate spin and orbital momentum contributions to the local magnetic moment by magnetic circular dichroism. Therefore, caution must be exercised before claiming an enhancement of spin and orbital magnetic moment at lower film coverages. Also, a difference in the number of d holes having in- and out-of-plane symmetries and modifications in the near-edge features was observed.