Growth, structure, and morphology of the Pd/MgO(001) interface: Epitaxial site and interfacial distance

The growth at room temperature of Pd on an atomically flat MgO(001) surface has been investigated by grazing incidence x-ray scattering. The structure and morphology of deposits in the range 0.2 to 183 monolayers (ML) were an alyzed in situ, in ultrahigh vacuum (UHV). The growth proceeds by nucleatio n, growth, and coalescence of islands. Channeling between islands starts ar ound 18 ML, and above 35 ML, the him is continuous and fully covers the sub strate. Pd is in cube-on-cube epitaxy on MgO(001), with an average lattice parameter between those of bulk Pd and MgO. Neither stacking faults nor twi ns were found. As growth proceeds, Pd is increasingly relaxed, but most of the Pd in the first one or two atomic planes is fully lattice matched with the substrate. The islands are coherent with the substrate up to similar to 4-5 ML of Pd deposited. Above 5 ML, interfacial misfit dislocations are in troduced at their edges. These dislocations reorder to form a square networ k above 35 ML. We have determined the epitaxial site, above oxygen ions of the substrate, and the interfacial distance (2.22 +/- 0.03 Angstrom). The e volution of the interfacial distance as a function of the amount of Pd depo sited is deduced by a quantitative analysis of the substrate crystal trunca tion rods. Similarities and differences with the Ag/MgO and Ni/MgO interfac es are discussed, and general trends on the interfacial structure and morph ology are deduced. [S0163-1829(99)14431-X].