Growth and self-assembly of MnN overlayers on Cu(0Â 0Â 1)

The growth of MnN overlayers on Cu(0 0 1) has been investigated by low energy electron diffraction and scanning tunneling microscopy with emphasis on the morphology evolution with coverage. A striking feature in the growth is the formation of the self-assembled two-dimensional superstructure at the coverage of 0.9 ML. At this coverage, the MnN nano-islands show a square shape and a well-defined size. They are regularly arrayed with a periodicity of (3.5 ± 0.1) nanometer and form a two-dimensional square superstructure. The MnN island superstructure is stabilized by an unconventional short-range mechanism. A structural model has been proposed to explain the self-assembly and the high-quality of the superstructure. To explore possible wide applications of the new self-assembly mechanism, the growths of MnN on Pd(0 0 1) and calcium nitride on Cu(0 0 1) have also been investigated. MnN overlayers on Pd(0 0 1) present a layer-by-layer-like growth behavior, and highly ordered calcium nitride nanostructure is formed on Cu(0 0 1). Simple discussion is made on the conditions under which the novel mechanism leading to the self-assembly of MnN islands can be applied to other systems. We propose that a large lattice misfit between the overlayer and the substrate, low vacancy formation energy for the substrate, moderate interfacial bonding strength, and a large elastic constant for the overlayer compared with the substrate could be important factors for the split growth and self-assembly.