Measurements outside resonance with piezoresponse force microscopy

In this work, we report the advantages of following a protocol to perform measurements of piezoresponse force microscopy (PFM) away from the tip-sample contact resonance. The protocol established in this work is based on Soergel's work [J. Phys. D: Appl. Phys. 44 (2011) 464003]. PFM measurements out-of-plane were carried out in the range of 10-100 kHz. The experimental background, that affects the domain contrast during PFM measurements, was reduced by analyzing the X-signal from the lock-in amplifier (LIA) during a frequency sweep measurement on a glass slide (non-piezoelectric). Optimal contrast in X-signal was attained through set the phase of the LIA to reach a null contrast in the Y-signal. Then, the X-Y and R-Θ signals are stored using the optimal conditions established for LIA. The protocol described was applied to a sol-gel BiFeO3 film and a reference sample of periodically poled lithium niobate.