Response of a laterally vibrating nanotip to surface forces

Abstract

The torsional eigenmodes of atomic force microscope (AFM) cantilevers are highly sensitive toward in-plane material properties of the sample. We studied the effect of viscosity and lateral contact stiffness on the detuning, amplitude, and phase response numerically. To verify the theoretical considerations, a torsion mode AFM was operated in frequency modulation. During approach and retract cycles, we observed a negative detuning of the torsional resonant frequency close to the sample surface depending on the tilt angle between the tip and the sample. Thus, the tilt has a significant effect on the imaging process in torsional resonance mode.