Dual-Frequency Resonance-Tracking Atomic Force Microscopy

TL;DR

This paper introduces a dual-frequency resonance-tracking method for atomic force microscopy that enables stable operation at resonance in cases where phase locked loops are infeasible, expanding capabilities for material property analysis.

Contribution

The novel dual-excitation amplitude detection technique allows resonance tracking without phase locked loops, applicable to non-acoustic and phase-dependent driving scenarios like PFM.

Findings

Enables resonance tracking in PFM with variable drive phase

Allows reliable electromechanical property measurements in biological and inorganic materials

Demonstrates effectiveness on lead zirconate-titanate, collagen, and lithium niobate

Abstract

A dual-excitation method for resonant-frequency tracking in scanning probe microscopy based on amplitude detection is developed. This method allows the cantilever to be operated at or near resonance for techniques where standard phase locked loops are not possible. This includes techniques with non-acoustic driving where the phase of the driving force is frequency and/or position dependent. An example of the later is Piezoresponse Force Microscopy (PFM), where the resonant frequency of the cantilever is strongly dependent on the contact stiffness of the tip-surface junction and the local mechanical properties, but the spatial variability of the drive phase rules out the use of a phase locked loop. Combined with high-voltage switching and imaging, dual-frequency, resonance-tracking PFM allows reliable studies of electromechanical and elastic properties and polarization dynamics in a broad range of inorganic and biological systems, and is illustrated using lead zirconate-titanate, rat tail collagen, and native and switched ferroelectric domains in lithium niobate.