Noncontact Atomic Force Microscopy - Yale School of Engineering ...

Tu-1530
The Effective Quality Factor in Dynamic Force Microscopes with
Fabry-Perot Interferometer Detection
Hendrik Hölscher 1 , Peter Milde 2 , Ulrich Zerweck 2 , Lukas M. Eng 2 , Regina Hoffmann 3
1 Institute for Microstructure Technology (IMT), Forschungszentrum Karlsruhe, Karlsruhe, Germany
2 Institut für Angewandte Photophysik, Technische Universität Dresden, Germany
3 Physikalisches Institut and DFG-Center for Functional Nanostructures, Universität Karlsruhe, Germany
Recently, the self-oscillation of microfabricated silicon resonators by photo-induced
forces has become a focus of current research in order to reach the quantum ground state
[1]. Having these results in mind, it is interesting to note that the experimental set-up
used in these studies is similar in design to the standard instrumentation of lowtemperature
ultra-high vacuum atomic force microscopes (LT-UHV-AFM) using
interferometer detection [2,3].
In order to quantify the relevance of photo-induced forces for NC-AFM
experiments, we analyzed the oscillation behavior of a microfabricated cantilever in a
LT-UHV-AFM with a Fabry-Perot interferometer. We observed that photo-induced
forces depend on the cantilever-fiber distance and that they lead to a profound change of
the effective quality factor of the cantilever. Depending on the slope of the interference
signal, the effective quality factor of the cantilever is increased or decreased. The overall
effect increases with the laser power of the laser diode and decreases for higher
temperatures. The Q-factor of the cantilever, however, is an essential parameter when the
energy dissipation between tip and sample is measured with a dynamic force microscope.
Hence, the effect addressed here has to be taken into account whenever the cantilever
oscillation is measured with an interferometer at low temperatures.
a) b) c)
Figure 1: (a) Schematic set-up of the interferometer used for the detection of the cantilever
vibration in dynamic force microscopy (b) The resulting interference intensity is periodic and has
a positive or negative slope. (c) Depending on the slope and the temperature the resonance curves
change dramatically due to a change of the effective Q-factor of the cantilever.
[1] C. Höberger-Metzger and K. Karrai, Nature 432, 1002 (2004).
[2] D. Rugar, H. J. Mamin, and P. Guethner, Appl. Phys. Lett. 55, 2588 (1989).
[3] A. Moser et al., Meas. Sci. Technol. 4, 769 (1993).
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