Regensburg 2004 – wissenschaftliches Programm

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O: Oberflächenphysik

O 14: Postersitzung (Adsorption an Oberflächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Phasenübergänge, Rastersondentechniken, Struktur und Dynamik reiner Oberflächen)

O 14.67: Poster

Montag, 8. März 2004, 18:00–21:00, Bereich C

Valence Band Spectroscopy on CoO Surfaces: A Comparison of MIES and UPS(HeI) Results — •F. Schweiger, S. Rudenkiy, M. Frerichs, W. Maus-Friedrichs, and V. Kempter — Institut für Physik und Physikalische Technologien, Technische Universität Clausthal, D–38678 Clausthal–Zellerfeld, Germany

We report the growth of CoO–films on Si substrates. The characterization of the electronic and geometrical structure took place by MIES/UPS and STM/AFM, respectively. Two strategies were pursued for the preparation of the CoO films: (1) Co films (10 layers) were prepared by thermal evaporation of Co onto Si substrates. The films were characterized by XPS, and MIES/UPS(HeI). The Co film was then exposed to oxygen (2000L) at 500K under No-dqin situNo-dq control of MIES and UPS(HeI). (2) Co and O₂ (10ML in 7min at 10⁻⁶mbar) were co–deposited at 400K, and were characterized by XPS, and MIES/UPS. Although both procedures give films that display the electronic structure of bulk CoO, procedure (2), according to STM, produced a superior geometric structure. Both MIES and UPS display 5 spectral features. However, characteristic differences are seen. The same behaviour has been seen before for LaCoO₃ and NiO. By recalling that the He^* probe atom, employed for MIES, interacts far more efficiently with the diffuse O2p states of the O²⁻ anions than with the rather compact Co3d states of the Co²⁺ cations, the qualitatively different behaviour, seen in MIES and UPS, can be explained on the basis of a Co₂O₁₁ cluster model (S. Masuda et al: P.R.L. 71 (1993) 4214).