Quantitative analysis of the nucleation and growth of ferroelectric domains during the polarization reversal in thin films of vinylidene fluoride and trifluoroethylene copolymer

To study microscopically the kinetics of polarization reversal in vinylidene fluoride and trifluoroethylene copolymers, the piezoresponse force microscope was modified to apply voltage pulses for the purpose of time-slicing and to obtain time-resolved measurements. Reversed domains were clearly distinguished and found to change with pulse duration. It was discovered that there were predetermined nucleation sites, each with respective nucleation times. This situation allowed for the determination of the nucleation rate and growth speed separately. Thus, for the first time, the microscopic model for the kinetics of polarization reversal was established from an experimental basis. The dependence of the nucleation rate and the growth speed on the electric field strength were also investigated, and both nucleation and growth processes were shown to have almost the same activation field strengths as the switching time. This phenomenon explains the time-field equivalence in the switching characteristics holding for a wide range of electric fields.