In-situ Piezoresponse Force Microscopy Cantilever Mode Shape Profiling

TL;DR

This paper explains how the frequency-dependent amplitude and phase in PFM measurements are influenced by cantilever dynamics and OBD spot location, highlighting the importance of considering these factors for accurate measurements.

Contribution

It introduces an analytical model linking cantilever mode shape changes to PFM response variations, emphasizing the impact of OBD spot position on measurement accuracy.

Findings

Frequency dependence of PFM response is explained by cantilever dynamics.

OBD spot position significantly affects measured amplitude and phase.

Common tip-near spot locations are vulnerable to dynamic artifacts.

Abstract

The frequency-dependent amplitude and phase in piezoresponse force microscopy (PFM) measurements are shown to be a consequence of the Euler-Bernoulli (EB) dynamics of atomic force microscope (AFM) cantilever beams used to make the measurements. Changes in the cantilever mode shape as a function of changes in the boundary conditions determine the sensitivity of cantilevers to forces between the tip and the sample. Conventional PFM and AFM measurements are made with the motion of the cantilever measured at one optical beam detector (OBD) spot location. A single OBD spot location provides a limited picture of the total cantilever motion and in fact, experimentally observed cantilever amplitude and phase are shown to be strongly dependent on the OBD spot position for many measurements. In this work, the commonly observed frequency dependence of PFM response is explained through experimental measurements and analytic theoretical EB modeling of the PFM response as a function of both frequency and OBD spot location on a periodically poled lithium niobate (PPLN) sample. One notable conclusion is that a common choice of OBD spot location, at or near the tip of the cantilever is particularly vulnerable to frequency dependent amplitude and phase variations stemming from dynamics of the cantilever sensor rather than from the piezoresponse of the sample.