Deformed Surface Oxides: Uncommon Structure of a (6x1) NiO Surface Oxide on Rh(111)

We have investigated the formation of a nickel, oxide monolayer on Rh(111) by scanning tunneling microscopy (STM), high-resolution electron energy loss spectroscopy (HREELS), and density functional theory (DFT) calculations. This monolayer displays a corrugated (6 X 1) superstructure, with a formal Ni(5)O(5) stoichiometry. The interplay between polarity and interface energy leads to the formation of a structure with pronounced troughs, which may be regarded as a building deformation, containing building blocks derived from nonpolar (100) and polar (111) NiO surface terminations. The calculations also show that the (6 X 1) Ni(5)O(5) phase has a higher thermodynamic stability than the related octopolar NiO bulk terminations.