Structure of mono- and bilayer FeO on Ru(0001): STM and DFT study

•STM and DFT are used to study the structure of FeO/Ru(0001).•Structural models of mono- and bilayer FeO on Ru(0001) are proposed.•The possible magnetic configurations are discussed. Scanning tunneling microscopy (STM) and density functional theory (DFT) are used to determine the structure of mono- and bilayer iron monoxide (FeO) islands and films grown on Ru(0001). The experimental results provide information on the atomic and Moiré periodicities, the height of mono- and bilayer structures, the mutual shift of their crystalline lattices and the rotation with respect to the underlying single-crystal support. Based on the determined parameters, structural models are proposed. The calculations reveal the preferred stacking configurations of Fe and O layers in both structures, their stability within different high-symmetry regions of the Moiré supercell (top, fcc, hcp), the interlayer spacings and the possible magnetic configurations.