Design and fabrication of a flexural harmonic AFM probe with an exchangeable tip

While harmonic probes are essential characterization tools in dynamic mode Atomic Force Microscopy, precise fabrication of harmonic probes is a challenge, and their replacement is relatively expensive. This paper reports the design, fabrication and evaluation of harmonic AFM probes with exchangeable tips that address these issues. The probe comprises a cantilever of non-uniform geometry that carries an exchangeable tip held by a liquid meniscus. The cantilever and the liquid meniscus interface are designed so that the tip is held firmly and the tip exchange can be performed with precise control over its position and orientation. A systematic approach is proposed for the design and fabrication of probes with specified eigen-frequencies. The approach consists of adopting an appropriate initial geometry, and iteratively modifying its dimensions so that the specified eigen-frequencies are achieved. To correct for errors in fabrication of the designed probe, an iterative fabrication scheme is also proposed. To facilitate implementation of this scheme, a simple lumped parameter model is developed for the overall probe. The proposed approach is employed to design and fabricate a harmonic probe with exchangeable tip whose first two flexural eigen-frequencies are in the ratio 1:4. Finally, the fabricated probe is evaluated, and the ratio of eigen-frequencies is found to match the desired harmonic ratio to an accuracy of over 99.8%. © 2017, Springer-Verlag GmbH Germany.