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O: Oberflächenphysik

O 15: Postersitzung (Adsorption an Oberfl
ächen, Epitaxie und Wachstum, Organische Dünnschichten, Oxide und Isolatoren, Rastersondentechniken, Zeitaufgelöste Spektroskopie, Methoden)

O 15.48: Poster

Freitag, 4. März 2005, 17:00–20:00, Poster TU D

Charged and non-charged surface defects on NiO(001) investigated by AFM — •Uwe Kaiser, Nico Plock, Alexander Schwarz, and Roland Wiesendanger — Institut für Angewandte Physik, Universität Hamburg, Jungiusstr. 11, 20355 Hamburg

Surface defects of transition-metal oxides like NiO are important for their catalytic behavior as they strongly enhance the reactivity of the surface. In this study, we investigated the (001)-surface of NiO under UHV-conditions with our home-built atomic force microscope. Typical AFM-images show flat terraces of monatomic height with widths of some ten nanometers. The image quality strongly depends on the tip condition, which could be improved by repeatedly touching the surface with the tip. With such tips, it was possible to detect extended vacancy-islands and point defects down to the atomic scale. The circumferences of some of the vacancies appear elevated, while others do not show this specific feature. In some cases, very faint elevated circular contrasts on terraces can be found without the presence of a vacancy. As ionic crystals can trap charges like electrons in positively charged vacancy sites, these different contrasts can be interpreted as differently charged vacancies at or just below the surface.