Growth, atomic structure, and vibrational properties of MnO ultrathin films on Pt(111)

Abstract

Ultrathin films of MnO have been grown by reactive metal deposition in an ${\mathrm{O}}_{2}$ atmosphere on Pt(111) and studied using scanning tunneling microscopy (STM), low-energy electron diffraction, temperature programmed desorption, and high-resolution electron energy loss spectroscopy. In situ STM experiments which have been performed during film growth at elevated temperatures show that MnO grows highly ordered in a layerlike mode on Pt(111). The first MnO monolayer exhibits large, uniaxial reconstructed domains with a $(19\ifmmode\times\else\texttimes\fi{}1)$ periodicity, which results in rotational domains on the hexagonal Pt(111) substrate. Growth and structural properties of the $(19\ifmmode\times\else\texttimes\fi{}1)$ reconstruction are discussed in a model based on long-range ordering of antiphase boundaries within a uniaxially reconstructed and otherwise bulklike MnO(001) monolayer. The vibrational spectra for the MnO monolayer are dominated by a strong and narrow surface phonon peak at $368\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$, which is identified as the out-of-plane vibration of the O sublattice against the Mn sublattice based on the $^{16}\mathrm{O}$ to $^{18}\mathrm{O}$ isotope shift. After completion of the MnO monolayer, multilayer growth mode is found at higher coverages ($g1.5$ ML). The appearance of the second MnO layer is accompanied by an additional Fuchs-Kliewer phonon mode at $545\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$.