Low Dimensionality and Epitaxial Stabilization in Metal-Supported Oxide Nanostructures: Mnx Oy on Pd(100) Mnx Oy

This chapter presents a survey of the growth and structure of manganese oxide nanolayers on a Pd(100) substrate, investigated in two different thickness regimes through a plethora of surface science techniques (scanning tunneling microscopy, atomic force microscopy (AFM), low energy electron diffraction (LEED), SPA-LEED, X-ray photoemission spectroscopy, X-ray absorption spectroscopy (XAS), and high-resolution electron energy loss spectroscopy) and state-of-the-art theoretical tools based on density functional theory and hybrid functionals. The electronic and structural properties of the films are analyzed as a function of film thickness and growth conditions. Epitaxial (geometric) relationships that favor the growth of the different oxide phases are investigated, with special attention to the stability of the Mn3O4 (001)/MnO(001) interface and the phase stability diagram of Mn x O y /Pd(100) phases at a Mn coverage of about one monolayer. A rich variety of two-dimensional (2D) nanophases, which are novel in terms of their structural and electronic properties, have been identified, which could play an important role in mediating the epitaxial growth of MnO thicker films on Pd(100). Furthermore, the formation of O or Mn vacancies drives the transition between 2D phases with similar structural units but different lattice periodicity, indicating that ion vacancies, mixed valence states, and substoichiometry lie on the basis of the architectural flexibility in the monolayer regime. Interestingly, the latter concepts play a major role in the more complex class of functional oxides such as the manganites, of which binary manganese oxides are the simplest parent compounds.