Fabrication and characterization of self-organized MnN superstructures on Cu(001) surfaces

Abstract

A two-dimensional ordered manganese nitride superstructure is prepared by self-organization on the Cu(001). Square MnN islands of a uniform size arrange with a $(3.5\ifmmode\pm\else\textpm\fi{}0.1)$-nanometer periodicity. This structure can be reproducibly fabricated in ultrahigh vacuum chambers by means of atomic nitrogen exposure, Mn deposition, once again atomic nitrogen exposure, and subsequent annealing. Stoichiometry of the island has been determined by in situ x-ray photoelectron spectroscopy as a manganese mononitride. In-plane lattice constant of the nanoisland is $\ensuremath{\sim}8%$ larger than that of Cu(001). Deposition of a monolayer manganese upon the MnN superstructure with subsequent annealing up to $690\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ gives rise to the same superstructure at the topmost layer. In this case, ``MnCu'' alloy interlayer is formed between the surface MnN and Cu substrate. The band structures of these films were studied by angle-resolved ultraviolet photoelectron spectroscopy, and the bands due to MnN are identified. The atomic model and formation mechanism of the superstructure are discussed in terms of the strain relief of the lattice in the MnN layers.