Piezoresponse/ Piezoforce Microscopy (PFM)

Piezoresponse force microscope (PFM) is a variant of the atomic force microscope (AFM). In PFM, the conductive AFM tip is in contact with the surface of the ferroelectric or piezoelectric material under investigation. Voltage is applied between the sample surface and the AFM tip, and establish an external electric field in the sample. Due to the electrostrictive or "inverse piezoelectric" effect of this ferroelectric or piezoelectric material, the sample will locally expand or contract according to the electric field. For example, if the initial polarization of the electrical domain of the tested sample is perpendicular to the sample surface and parallel to the applied electric field, the electrical domain will expand vertically. Since the AFM tip is in contact with the sample surface, this domain expansion will cause the AFM cantilever to bend upwards, and the deflection increases compared to before the electric field is applied. Conversely, if the initial electric field polarization is antiparallel to the applied electric field, the electric field field will shrink, resulting in a reduction in the deflection of the cantilever beam. In such a case, the change in the deflection of the cantilever is directly related to the expansion or contraction of the electrical domain of the number of samples, so it is directly proportional to the applied electric field. The resulting deflection probe cantilever is detected by a standard split photodiode detector, and then demodulated with a lock-in amplifier. This method can simultaneously obtain high-resolution ferroelectric domain and topographic.