Z-Axis Control in Active AFM Array Microcantilevers Using On-Chip Electrothermal Actuator

Atomic Force Microscopy (AFM) is one of the primary instruments used in research and industry to analyze materials and objects, being able to provide measurements of topography and material properties with nanometer-scale resolution. At the heart of the AFM is a microcantilever with a sharp probe tip, which is scanned over the surface of a sample while mapping the varying intermolecular forces that exist between the probe tip and the sample. Active AFM is a type of AFM in which for sensing the deflection of the cantilever an on-chip actuation and sensing mechanism is implemented. In conventional AFM, the deflection of the cantilever is sensed by a bulky optical sensor, which although has a very high resolution, but is not compatible with small cantilevers, or application of cantilevers in array.

In this project, we add an on-chip electrothermal actuator to our previously designed microcantilevers, equipped with on-chip piezoelectric actuation and piezoelectric differential sensing.  The piezoelectric actuation is for actuating the system at its first resonance mode, which is needed in tapping mode AFM. The demodulated signal sensed by the differential piezoelectric sensor is used to regulate the tip-sample force while imaging in constant force tapping mode AFM. The electrothermal actuator controls the tip-sample distance to regulate the tip-sample force.

For the cantilever tip, we transfer the silicon tip from commercial AFM cantilevers and attach it to our custom microfabricated microcantilever.

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