Two-dimensional manganese oxide nanolayers on Pd(100): The surface phase diagram

Two-dimensional manganese oxide layers have been grown on Pd(100) and have been characterized by means of scanning tunnelling microscopy, low energy electron diffraction and x-ray photoelectron spectroscopy (XPS). The complex surface phase diagram of MnO_x on Pd(100) is reported, where nine different novel Mn oxide phases have been detected as a function of the chemical potential of oxygen μ_O. Three regions of the chemical potential of oxygen can be identified, in which structurally related oxide phases are formed, often in coexistence at the surface. The different regions of μ_O are reflected in the oxidation states of the respective Mn oxide nanolayers as revealed by the Mn 2p and O 1s XPS binding energies. The MnO_x nanolayers form two-dimensional wetting layers and it is speculated that they mediate the epitaxial growth of MnO on Pd(100) by providing structurally graded interfaces.