Growth-mode and interface structure of epitaxial ultrathin MgO/Ag(001) films.

MgO ultrathin films are of great technological importance as electron tunneling barrier in electronics and spintronics, and as template for metallic clusters in catalysis and for molecular networks for 2D electronics. The wide band-gap of MgO allows for a very effective decoupling from the substrate. The films morphology and the detailed structure of the interface are crucial for applications, controlling the electronic transfer. Using surface x-ray diffraction, we studied the growth-mode and the structure of MgO/Ag(001) ultrathin films elaborated by reactive molecular beam epitaxy as function of the substrate temperature. We observed that deposition of about 1 monolayer results in an MgO(001) film in coherent epitaxy, with the oxygen atoms on top of silver as predicted by DFT calculations, and an interlayer distance at the interface of about 270 pm. Under well-defined conditions, a sharp MgO bilayer is formed covering a fraction of the substrate surface.