In situ stiffness adjustment for AFM probes

Abstract

The choice on which cantilever to use for Atomic Force Microscopy (AFM) depends on the type of the experiment being done. Usually, the cantilevers have to be exchanged when a different stiffness is required and the entire alignment has to be repeated. In the present work, we have developed a method to adjust the stiffness of the AFM cantilever in situ, without having to exchange the cantilever. The adjustment is achieved by changing the effective length of the cantilever by electrostatic pull-in. By applying a voltage between the cantilever and an electrode (with an insulating layer at the point of contact), the cantilever snaps to the electrode, reducing the cantilever’s effective length. The working principle of this concept is demonstrated with a proof-of-concept experiment. The electrode was positioned close to a commercially available cantilever with a robotic nano-manipulator. To confirm the change in stiffness, the resonance frequency of the cantilever was measured for varying electrode positions. The results match the theoretical expectation. For the cantilever that was tested, we obtained stiffness tuning from 0.2 N/m to 27 N/m, covering two orders of magnitude in one cantilever. This proof-of-concept is the first step towards a micro fabricated prototype, that integrates the electrode positioning system and cantilever that can be used for actual AFM experiments.