Epitaxial Growth of Ultrathin δ-Like MοN Films on Ru(0001)

Growth of ultrathin, single-crystalline, molybdenum-nitride films on Ru(0001) has been investigated by means of X-ray photoelectron spectroscopy (XPS), low energy electron diffraction, and helium ion scattering spectroscopy. The films were prepared in a multistep, sequential process. First, samples were exposed to saturation doses of low kinetic energy nitrogen ions. Second, the samples were exposed to varied doses of molybdenum vapor. Finally, the samples were heated in the renewed presence of low kinetic energy nitrogen ions. Through this process, an annealing temperature of 700 K was found to result in well-ordered, hexagonal films that appear to initially grow layer-by-layer, and in registry with the Ru(0001) support. XPS-characterized chemical-states and relative integrated peak intensities for Mo 3d and N 1s photoelectrons are consistent with those expected for MoN nitride formation. Films annealed above T = 700 K in UHV decompose via a presumptive N-2 recombinative desorption mechanism, which leaves the film in a purely metallic Mo-Ru configuration by T = 1100 K.