Ultrathin films of MnO have been grown by reactive metal deposition in an O2 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 (19×1) periodicity, which results in rotational domains on the hexagonal Pt(111) substrate. Growth and structural properties of the (19×1) 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 cm-1, which is identified as the out-of-plane vib ration of the O sublattice against the Mn sublattice based on the O16 to O18 isotope shift. After completion of the MnO monolayer, multilayer growth mode is found at higher coverages (>1.5 ML). The appearance of the second MnO layer is accompanied by an additional Fuchs-Kliewer phonon mode at 545 cm-1

Ultrathin manganese oxide films grown on Pt(111) were examined in the low temperature CO oxidation reaction at near atmospheric pressures. Structural characterization was performed by X-ray photoelectron spectroscopy, Auger electron spectroscopy, high-resolution electron energy loss spectroscopy, and temperature programmed desorption. The results show that the reactivity of MnOsub>x ultrathin films is governed by a weakly bonded oxygen species, which may even be formed at low oxygen pressures (~10−6 mbar). For stable catalytic performance at realistic conditions the films required highly oxidizing conditions (CO:Osub>2 < 1:10), otherwise the films dewetted, ultimately resulting in the catalyst deactivation. Comparison with other thin films on Pt(111) shows, that the desorption temperature of weakly bonded oxygen species can be used as a benchmark for its activity in this reaction

MnO films have been grown by reactive metal deposition in an O 2 atmosphere on Pt͑111͒. The vibrational and electronic excitations between 50 meV and 7 eV have been investigated by high-resolution electron energy loss spectroscopy as function of layer thickness up to 17 ML. The vibrational spectrum of the MnO monolayer is characterized by a strong and narrow phonon at 368 cm −1 . For coverages above the monolayer the oxide film is characterized by a Wallis mode and a Fuchs-Kliewer phonon ͑382 and 547 cm −1 ͒. Whereas the Wallis mode has constant intensity and frequency, the Fuchs-Kliewer phonon intensity increases and its frequency decreases with coverage as predicted by dielectric theory. Mild annealing ͑Ͻ850 K͒ of MnO films improves the long-range ordering while higher temperatures causes dewetting and cluster formation. For thin films between 4 and 10 monolayers the losses due to electronic transitions within the Mn 3d states have been studied. Six transitions could be identified which indicate for thick films an electronic structure similar to the one found for MnO͑100͒ single crystal surface. Additionally, surface related d-d transitions have been identified.

The reaction of molecular oxygen with the Si(111)-7 x 7 surface is investigated at room temperature using in situ scanning tunneling microscopy and surface stress measurements to reveal the quantitative relationship between site-specific oxygen coverage and a decrease in tensile surface stress. This relationship is described using a modified form of the reaction model originally proposed by Dujardin et al. We show that the decrease in tensile surface stress is greatest for the faulted subunits of the 7 x 7 cell and determine the stress signatures of different reaction products, including the absence of long-lived metastable species with a unique stress signature.

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