Nanoscale Studies of Domain Walls in Epitaxial Ferroelectric Thin Films

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Abstract

Nanoscale ferroelectric domains in epitaxial Pb(Zr0.2Ti0.8)O3 thin films were investigated using atomic force microscopy to allow the static roughness configuration and dynamic response of ferroelectric domain walls in these materials to be accessed. The observed dependence of domain size on writing time revealed a two-step switching process in which nucleation under the atomic force microscope tip is followed by radial domain growth. We obtained a non-linear dependence of domain wall velocity on the electric field, v ∝ exp−(1∕E)μ, characteristic of a creep process. The domain wall motion was analyzed both in the context of stochastic nucleation in a periodic potential as well as that of an elastic manifold in a disorder potential, in better agreement with the dimensionality of the system and the values of the dynamic exponent ∼ 0.6. Independent measurements of domain wall roughness in the same films revealed a power law growth of the correlation function of relative displacements B(L) ∝ L with ζ ∼ 0.26 at short length scales L, followed by an apparent saturation at large L. These results give rise to a clear physical picture of domain walls in ferroelectrics as elastic sheets in the presence of “random-bond” disorder, and where dipolar interactions play an important role, effectively increasing the dimensionality of the system to 2.5, in agreement with theoretical predictions.