Multifrequency techniques for tuning fork based atomic force microscopes: Lateral resolution and additional separate control knobs.

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In dynamic atomic force microscopy multiple different operation modes exist, which allow to excite the cantilever in different ways. In particular the so-called multifrequency techniques have been studied recently. In the original multifrequency mode from 2004 the cantilever is excited simultaneously at two frequencies, which correspond to the 1st and 2nd eigenmodes of the cantilever. In contrast to standard single mode atomic force microscopy the multifrequency technique offers a higher information depth and each eigenmode of the oscillation can be used for a different purpose. Usually the 1st eigenmode is used for tracking the sample topography while the 2nd eigenmode delivers additional and enhanced material contrast. This can be achieved by separately adjusting and optimizing the oscillation parameters of each eigenmode. Meanwhile the multifrequency concept was adapted for different sample systems in different environments (air, liquid, and vacuum) and it was proven that multifrequecy operation is beneficial in terms of lateral resolution and signal-to-noise ratio. A systematic study for tuning fork based atomic force microscopes, however, has not been performed so far. Tuning forks are mainly used for applications in UHV at low temperatures where the maximum lateral resolution is needed. In this project we will analyze which imaging parameters will offer the best resolution/sensitivity when using the multifrequency technique. Successively, it will be studied which operation modes are most suitable and what benefits are provided with regard to the image resolution.