Mechanically preamplifying cantilevers

Atomic force microscopy (AFM) has led to a vast and growing number of dynamic imaging modes that link periodic interactions of the specimen and the cantilever tip to material properties and topologies. Using periodic dynamic interactions instead of static reduces tip-sample forces, tip wear (both examples for tapping mode AFM), increases measurement speed (for example, in piezoresponse imaging), or provides the ability to study higher harmonics (higher harmonic tapping mode, higher harmonic piezoresponse imaging). In this thesis a new motivation is discussed: The use of harmonic oscillators to increase the both resolution and sensitivity of the measurements. A cantilever with a tuned-fork-function has been coupled to the main cantilever, harmonically amplifying tip-sample reactions at a certain frequency. A systematic approach to design and fabricate preamplifying cantilevers is presented. The usability for higher harmonic tapping mode has been proven, the increase in performance for piezoresponse (PR) imaging characterized. An tenfold sensitivity and resolution increase compared to existing cantilevers was achieved. By using the preamplifying cantilevers, parasitic side effects, the so-called background, ever-present in PR imaging, was studied and clearly linked to electrostatic attraction between the cantilever and the sample surface with an electrostatic model. A compensation scheme has been developed to physically eliminate the electrostatic background by applying a DC bias between the cantilever and the sample. Other improvements in imaging technique derived from the model and experimentally proven include conductive coatings on the sample surface and air ionization with an alpha radiation source to discharge the sample surface. A concept for producing piezoelectric preamplifying cantilevers is presented that may enable the fabrication of lines or arrays of preamplifying sensors in an in-line tester for a production line. Preamplifying cantilevers are usable in a variety of different imaging modes, often with drastically improved resolution. They provide a starting point for the development of a material identifier with nanoscale resolution, imaging a broad variety of tip-sample interactions with unprecedented resolution.