Berlin 2005 – scientific programme

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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 15.43: Poster

Friday, March 4, 2005, 17:00–20:00, Poster TU D

Combined Normal and Torsional NC-AFM Measurements: PTCDA on KBr(001) — •Tobias Kunstmann, Andreas Schlarb, and Rolf Möller — Universität Duisburg-Essen, D-45141 Essen, Germany

Dissipative lateral forces provide the main contribution to friction. To measure these forces the tip has to move parallel to the surfaces. This can be achieved either by using the "q-plus sensor" [1], or torsional modes of a cantilever [2]. The normal and torsional modes of a commercially available cantilever have been excited simultaneously. For our measurements we have used the frequency shift ( df ) of the normal mode to control the tip sample distance. Additionally the energy dissipated in the normal mode has been recorded. The frequency shift and the damping of the lateral oscillation were measured independently providing the conservative as well as the dissipative lateral forces. The experiments have been performed on PTCDA on a KBr(001) surface. While the dissipation in normal mode does not show a difference between plain KBr and PTCDA-crystallites, the dissipation for the torsional mode shows a significant increase on top of the PTCDA islands.

This work was funded by the SFB616 "Energy dissipation at surfaces" of the Deutsche Forschungsgemeinschaft.

[1] F.J.Giessibl et al., Proc. Nat. Acad of Sci. US 99 (19), 12006 (2002)

[2] O. Pfeiffer et al., Phys. Rev. B 65 (16), 161403 (2002)