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Piezoresponse Force Microscopy
Piezoresponse imaging is based on the detection of tip bias induced electromechanical response of the surface. Conductive tip is brought into contact with the surface. Bias is applied to the tip, and extension and contraction of the surface are transferred to the tip and result in the cantilever deflection. Lock-in is used to detect the magnitude and phase of the response. The latter depends on polarization orientation below the tip (i.e. if the surface expands or contract under positive bias) and the former quantifies piezoelectric properties of the surface. Variation of dc bias offset on the tip allows local hysteresis and butterfly loops of the material to be obtained thus giving insight into local electromechanical properties with unrivaled spatial resolution.
Despite significant progress achieved in this field, controversy exists regarding the relative contributions of electrostatic vs. electromechanical interactions to the piezoresponse contrast. This, in turn, severely complicates quantification of the piezoresponse data in terms of effective material properties. Our group is currently involved in analysis of this problem and our recent papers on the subject will soon appear in the publications list.
