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

The crystal truncation rods (CTRs) of the substrate's surface were measured during the very first stages of in situ deposition of three fcc metals, Ag , Pd and Ni, on the MgO(001) surface. These interfaces are known to form vi a 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 c orrelated via the substrate, allows the determination of the adsorption sit e, the interfacial distance, parameters that are important for theoretical calculation. Some other parameters of the metal/oxide interface are also de duced, in particular, information concerning the morphology. We show that, in the cases of Pd and Ni, the analysis is rather straightforward because m ost 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 c ase of Ag, which is never fully strained by the substrate, whatever the amo unt deposited, i.e., the island's size. In the three cases, the epitaxial s ite is shown to be unique, above the oxygen ions of the MgO(001) surface. T he evolutions of the interfacial distance during growth are compared. The r esults are discussed in view of the similarities and differences between th e three systems, especially in view of the strongly differing lattice param eter mismatches and the strength of the metal oxide bound at the interface. General trends on the interfacial structure and morphology are deduced.