What can we learn on the structure and morphology of metal oxide/metal interfaces by measurement of X-ray crystal truncation rods in situ, during growth

Abstract

The crystal truncation rods (CTRs) of the substrate's surface were measured during the very first stages of insitu deposition of three fcc metals, Ag, Pd and Ni, on the MgO(001) surface. These interfaces are known to form via nucleation, growth and coalescence of islands. We show that quantitative analysis of the interferences between the waves scattered by the substrate and the wave scattered by a fraction of the metal film that is long-range correlated via the substrate, allows the determination of the adsorption site, the interfacial distance, parameters that are important for theoretical calculation. Some other parameters of the metal/oxide interface are also deduced, in particular, information concerning the morphology. We show that, in the cases of Pd and Ni, the analysis is rather straightforward because most of the signal arises from a few atomic planes that are lattice-strained by the substrate parallel to the interface. Much more complicated is the case of Ag, which is never fully strained by the substrate, whatever the amount deposited, i.e., the island's size. In the three cases, the epitaxial site is shown to be unique, above the oxygen ions of the MgO(001) surface. The evolutions of the interfacial distance during growth are compared. The results are discussed in view of the similarities and differences between the three systems, especially in view of the strongly differing lattice parameter mismatches and the strength of the metal oxide bound at the interface. General trends on the interfacial structure and morphology are deduced.