Domain wall roughness and creep behavior in nanoscale crystalline ferroelectric oxide and polymer films

We have studied the static and dynamic properties of domain wall (DW) in nanoscale crystalline ferroelectric oxide Pb(Zr,Ti)O$_{3} $ (PZT) and poly(vinylidene-fluoride-trifluorethylene) (PVDF-TrFE) films of 20 to 40 nm thick using piezo-response force microscopy. DW roughness exponent $\zeta $ is extracted from the correlation function of DW displacement. At room temperature, $\zeta $ of PVDF-TrFE is 0.4 to 0.48, much higher than those obtained on the PZT films (0.2-0.3). Combined with the dynamic studies of the DW creep behavior, this yields an effective dimensionality of 1.5 for PVDF-TrFE films, in sharp contrast to $d_{eff} \sim $ 2.5 observed in PZT films. We have also thermally quenched the DWs after heating them at high temperatures. Thermal quench causes significant change in the DW configuration in PZT films with $\zeta $ increasing to $\sim $ 0.5 after the films are heated close to the Curie temperature $T_{C} $. On the other hand, the DWs in PVDF-TrFE films exhibit very weak temperature dependence. We attribute this distinctly different behavior to the strong anisotropy between in-plane and out-of-plane interaction in PVDF-TrFE, which is absent in PZT.