The structure and morphology of Ag (0.2 to 300 monolayers) which had been deposited at room temperature onto high-quality (001) MgO surfaces were investigated in situ. Surface X-ray diffraction and grazing-incidence small-angle X-ray scattering parallel and perpendicular to the surface were combined. Nucleation, growth and coalescence of the islands were found above 0.2 of a monolayer. The height/width ratio of the islands was equal to about 0.37 at all stages of deposition. The Ag grew with a cube-on-cube epitaxy with respect to the (001) substrate. A very unusual change in the state of strain in Ag, with increasing deposition, was observed. Below 4 to 6 monolayers (island width less than 9nm), the small Ag islands were coherent with the MgO. Below 1 monolayer (island width less than 3.5nm), they had their bulk lattice parameter, and between 1 and 4 monolayers they became more and more strained by the substrate; with an average lattice parameter that was intermediate between those of Ag and MgO. At about 4 to 6 monolayers, the islands attained a critical size and misfit dislocations were introduced at the edges. Above 30 monolayers, the film was almost continuous and the interfacial misfit dislocations re-ordered to form a square network that was oriented along <110> directions. Stacking faults appeared in the Ag at this stage. A small amount of twinned Ag also began to grow at about 4 monolayers. The unusual evolution of the strain in the Ag islands, and the introduction of misfit dislocations, were explained in terms of a 1-dimensional Frenkel-Kontorova model which involved a very weak Ag/MgO interaction and a weak corrugation of the interatomic potential.

Structure and Morphology of the Ag/MgO(001) Interface during in situ Growth at Room Temperature. O.Robach, G.Renaud, A.Barbier: Physical Review B, 1999, 60[8], 5858-71