  Piezoresponse Force Spectroscopy (PFS) has emerged as a powerful tool for
probing polarization dynamics on the nanoscale. Application of a dc bias to a
nanoscale probe in contact with a ferroelectric surface results in the
nucleation and growth of a ferroelectric domain below the probe apex. The
latter affects local electromechanical response detected by the probe.
Resulting hysteresis loop contains information on local ferroelectric
switching. The self-consistent analysis of the PFS data requires (a) deriving
the thermodynamic parameters of domain nucleation and (b) establishing the
relationships between domain parameters and PFM signal. Here, we analyze the
effect of screening at the domain wall on local polarization reversal
mechanism. It is shown that the screening control both the domain nucleation
activation energy and hysteresis loop saturation rate.
