Pseudomorphic-to-bulk fcc phase transition of thin Ni films on Pd(100)

Abstract

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 bulklike 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 30Å (∼ 17 layers).

Core and Valence Band Photoemission Study of Highly Strained Ultrathin NiO Films on Pd(100)

“…Following again such deposition route, we have recorded the He I and He II excited spectra of a 1 MLE thick Ni layer deposited on Pd(100) prior and after the exposure to oxygen. It is to be outlined, however, that the c(4 × 2) ML obtained by this procedure is only short-range ordered and with a partial dissolution of Ni metal into the Pd selvedge . The corresponding VB data are reported in Figure together with the spectrum of a bulklike 14 MLE thick Ni film on Pd(100).…”

Composition, structure and stability of surfaces formed by Ni deposition on Pd(111)

“…In related studies of Ni films deposited on Pd substrates, Granozzi and coworkers investigated Ni ultrathin films on Pd(100) [22][23][24] and Kleiman's group studied Ni thin film growth on Pd(111) [25,26] using LEED, X-ray photoelectron diffraction (XPD) and X-ray photoelectron spectroscopy (XPS). After depositing Ni on Pd(111) at room temperature, the (1 × 1) LEED pattern showed a diffuse background, reported to arise from a random distribution of Ni atoms.…”

Growth morphology of ultra-thin Ni films on Pd(100)

“…This distortion, due to the resulting pseudomorphic growth and the lattice misfit, is characterized by a large tensile strain, m = 10.5%, in the Ni overlayer. While there are few previous reports [11][12][13] which have focused on the structure of the strained Ni films, there is almost no information regarding the evolution of the structural morphology in this system. For RT growth, the existing diffraction studies [11][12][13] show the formation of a tetragonally distorted structure, induced by the Ni epitaxial growth.…”