Regensburg 2004 – scientific programme

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O: Oberflächenphysik

O 9: Rastersondentechniken I

O 9.9: Talk

Monday, March 8, 2004, 17:45–18:00, H36

Damping mechanisms in dynamic force microscopy — •Andre Schirmeisen, Hendrik Hölscher, and Harald Fuchs — Physikalisches Institut und CeNTech, Universität Münster, Wilhelm-Klemm-Str.10, 48149 Münster

Dynamic force microscopy (DFM) in ultrahigh vacuum (UHV) is a powerful tool to measure interatomic forces with molecular resolution. However, apart from conservative forces the DFM is also capable of measuring dissipative tip sample interactions. A considerable dispute has arisen, as to what the underlying physical mechanisms are for the observed energy dissipation. Atomic instabilities, electric damping mechanisms and even feedback artefacts have been argued to govern the dissipation. We performed force and energy dissipation spectroscopy experiments on HOPG in UHV, where our instrument is operated in two different dynamic modes: The constant excitation (CE) and constant amplitude (CA) mode. First, we show that spectroscopy measurements from both modes yield equivalent quantitative results, which allows us to exclude artefacts induced by the amplitude feedback system inherent only to the CA mode. Secondly, we present a series of spectroscopy experiments acquired with different oscillation amplitudes, which allows us extract the velocity dependence of the dynamic friction coefficient. In fact, we will show that the velocity dependence is negligible and we will argue that hysteretic mechanisms based on atomic instabilities govern the energy dissipation in our case.