  We have measured the transformation of pseudomorphic Ni films on Pd(100) into
their bulk fcc phase as a function of the film thickness. We made use of x-ray
diffraction and x-ray induced photoemission to study the evolution of the Ni
film and its interface with the substrate. The growth of a pseudomorphic film
with tetragonally strained face centered symmetry (fct) has been observed by
out-of-plane x-ray diffraction up to a maximum thickness of 10 Ni layers (two
of them intermixed with the substrate), where a new fcc bulk-like phase is
formed. After the formation of the bulk-like Ni domains, we observed the
pseudomorphic fct domains to disappear preserving the number of layers and
their spacing. The phase transition thus proceeds via lateral growth of the
bulk-like phase within the pseudomorphic one, i.e. the bulk-like fcc domains
penetrate down to the substrate when formed. This large depth of the walls
separating the domains of different phases is also indicated by the strong
increase of the intermixing at the substrate-film interface, which starts at
the onset of the transition and continues at even larger thickness. The
bulk-like fcc phase is also slightly strained; its relaxation towards the
orthomorphic lattice structure proceeds slowly with the film thickness, being
not yet completed at the maximum thickness presently studied of 30 Angstrom
(i.e. about 17 layers).
