Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 15: Methods: Scanning Probe Techniques II

O 15.2: Talk

Monday, March 26, 2007, 14:30–14:45, H41

Measuring energy dissipation in torsional resonance mode AFM using frequency modulation — •Ayhan Yurtsever, Alexander M. Gigler, and Robert W. Stark — Ludwig-Maximilians-Universität München, Germany

The atomic force microscope (AFM) may be used as a tool to probe hardness, elastic and viscous properties of the surface at the nanoscale. In-plane properties such as friction or shear stiffness of the sample can be measured with a lateral force modulation microscopy or by analyzing torsional vibrations. The torsional resonance mode (TR mode) allows shear force microscopy with standard cantilevers [1]. The torsion about the cantilevers long axis actuates a pendulum-like oscillation of the tip apex parallel to the sample surface with typical amplitudes of 0.2 nm to 2.0 nm. In this study, the dynamics of the torsionally vibrated cantilever are analysed by the transfer function method and finite element analysis (FEA). The results explain the fundamental mechanism for the topography feedback in TR-mode. Experimentally, we measure the energy dissipation and the frequency shift in torsional resonance mode AFM using frequency-modulation on a PMMA surface. To regulate the FM detection scheme, we utilized a Nanosurf (Liestal, Switzerland) Phase-Loop-Lock controller/detector (PLL). By monitoring the changes in the resonance frequency and excitation amplitude required to keep the oscillation amplitude constant, we were able to measure both frequency shift and dissipation caused by the tip-sample interaction.

[1] L. Huang, C. Su, Ultramicroscopy 100 (2004) 277-285