Thickness-dependent Evolution of the Ferroelectric Domain in Ultrathin BiFeO3 Films below 10 nm

Abstract

The scaling behavior of the ferroelectric domain in thick BiFeO3 has been reported to follow Kittel’s law both theoretically and experimentally. The law collapses at a certain thickness, known as the critical thickness. However, little experimental work focused on the ferroelectric domain evolution behavior in ultrathin BiFeO3 films below 10 nm. In this work, the BiFeO3 films with various thicknesses were prepared and observed with piezoresponse force microscopy (PFM) and the periodicity of the domain was extracted by a two-dimensional fast Fourier transform (2D-FFT). The reciprocal space mapping (RSM) analysis is consistent with PFM results demonstrating the 71° domain of the BiFeO3 films. It is confirmed that the critical thickness in BiFeO3 films is below 5 nm and the domain size decreases with decreasing thickness in accordance with Kittel’s law and a scaling exponent of 0.41 down to that thickness.