Effect of cantilever-sample interaction on piezoelectric force microscopy

We report on the evidence for the cantilever-sample (CS) capacitive force contribution to the piezoelectric force microscopy (PFM). In addition, we present that positioning of the tip near the edge of the sample surface can significantly reduce this spurious contribution for any combinations of tip cantilever and film. As proof of both the existence of CS interaction and its reduction, the domains formed by the application of voltage pulses through the tip are observed by PFM at two different positions, i.e., sample center and edge. In accordance with the model that a piezoresponse consists of a piezoelectric vibration of the film and an electrostatic force induced vibration of cantilever, the domain contrasts are characterized by dot structure in the amplitude and negligible contrast in the phase images when the tip is placed in the center of the sample surface. However, reducing the CS interaction by placing the tip near the sample edge yields domain contrasts showing ring structure in the amplitude and a clear 180° phase shift in the phase images. Accompanying resolution enhancement in phase images results in smaller size of domains (bits) produced by identical voltage pulses as is evidenced from bit size estimation. Additional evidence for reduction of CS interaction is obtained from piezoresponse hysteresis measurement.