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O: Fachverband Oberflächenphysik

O 33: Oxides and Insulators: Epitaxy and Growth

O 33.3: Vortrag

Dienstag, 27. März 2007, 16:15–16:30, H41

Structural and vibrational properties of ultrathin MnO films on Pt(111): An HREELS, STM and LEED study — S. Sachert¹, B. Bochmann¹, Ch. Hagendorf¹, K. Kostov², and •W. Widdra¹ — ¹Martin-Luther-Universität Halle-Wittenberg, Institute of Physics , Halle — ²Bulgarian Academy of Science, Sofia, Bulgaria

The atomic structure and the vibrational properties of ultrathin MnO films on Pt(111) have been studied using high-resolution electron energy loss spectroscopy (HREELS), scanning tunneling microscopy (STM), and low-energy electron diffraction (LEED). The formation of several Mn oxide structures during Mn deposition in an O₂ atmosphere has been investigated as a function of film thickness up to 6 ML, substrate temperature and subsequent annealing cycles up to 1200 K. Within the monolayer, three different Mn_xO_y structures with Mn/O ratios between 1 and 2 have characterized by HREELS, STM, LEED, and thermal oxygen desorption : The MnO monolayer grown in an oxygen atmosphere of about 8x10⁻⁸ mbar is characterized by a strong optical phonon at 364 cm⁻¹, a (19x1) superstructure which is stable up to 1100 K. Annealing in p_O2=1x10⁻⁶ mbar converts this phase to a hexagonal structure with a lattice constant of 0.42 nm and MnO₂ stoichiometry. It shows two characteristic vibrations at 580 and 716 cm⁻¹, is stable up to 840 K and identified as single O-Mn-O layer of MnO(111). Reduction of this phase in CO or annealing above 840 K in UHV results in a third oxide structure with two strong phonons at 332 and 391 cm⁻¹. This oxide is stable up to 1000K.