A well-ordered 25 ML epitaxial NiO(100) film on Ag(100) as prepared by layer-by-layer growth has been characterized by high-resolution electron energy loss spectroscopy. Six different phonon branches have been identified in the X direction of the surface Brillouin zone and are compared with first-principles phonon calculations. Whereas the surface Rayleigh mode shows a strong upward dispersion of 173 cm −1 in agreement with observations for the NiO(100) single crystal, the other surface phonons and surface resonances show only smaller dispersion widths in X direction. The Wallis and the Lucas phonons are localized at 425 and 367 cm −1 at the point, respectively. Additionally, two phonons are identified that have stronger weight at the zone boundary at 194 and 285 cm −1 and that become surface resonances at the zone center. The dominant spectral feature is the Fuchs-Kliewer (FK) phonon polariton at 559 cm −1 , which is excited by dipole scattering and exhibits a rather broad non-Lorentzian lineshape. The lineshape is explained by a FK splitting resulting from the splitting of bulk optical phonons due to antiferromagnetic order. This view is supported by calculations of the surface-loss function from bulk reflectivity data.

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.

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Using high-resolution electron energy loss spectroscopy the phonon dispersion of Ag(100) has been studied at two different sample temperatures of 86 and 300 K. The dominant feature in the spectra corresponds to the Rayleigh wave. Its full dispersion is determined along the ΓX high symmetry direction in the first and second Brillouin zones. The Rayleigh phonon maximum at the X point shows a redshift with increasing temperature. This is explained based on a surface anharmonicity with an anharmonicity constant of 0.014, comparable to the value reported for Cu(100). In the vicinity of the Γ point two additional phonon features have been discovered at about 110 and 160 cm(-1), which are tentatively assigned to high density of states features from the bulk phonon bands. However, the observed steep dispersion is in contrast to theoretical calculations. Along ΓX two surface resonance branches have been observed with maximum frequencies in the range of 90-110 cm(-1) near to the zone boundary. These branches agree with helium atom scattering data where available, but are not predicted by theory.