Frequency shift, damping, and tunneling current coupling with quartz tuning forks in noncontact atomic force microscopy

A combined experimental and theoretical approach to the coupling between frequency-shift (Delta f), damping, and tunneling current (I-t) in combined noncontact atomic force microscopy/scanning tunneling microscopy using quartz tuning forks (QTF)-based probes is reported. When brought into oscillating tunneling conditions, the tip located at the QTF prong's end radiates an electromagnetic field which couples to the QTF prong motion via its piezoelectric tensor and loads its electrodes by induction. Our approach explains how those I-t-related effects ultimately modify the Delta f and the damping measurements. This paradigm to the origin of the coupling between I-t and the nc-AFM regular signals relies on both the intrinsic piezoelectric nature of the quartz constituting the QTF and its electrodes design.