Molecular electrodes enable faster switching in ferroelectric thin films

Abstract

The presence of unscreened polarization at the surface of ferroelectric thin films can impair their functional response. One recently proposed way to improve screening is by using “molecular electrodes”: molecules with chemically resonant bonds (i.e., energy-equivalent internal distributions of chemical bonds), such that their internal charge distribution can adapt to different depolarizing fields. However, while molecular electrodes can provide for a good electrostatic screening, we do not know what their dynamic response is, and in particular, whether they allow for agile switching of ferroelectric polarization. Here, we compare the switching dynamics of BaTiO3 (BTO) epitaxial thin films with and without a surface layer of para-aminobenzoic acid (pABA), a molecular electrode with a bipolar screening capacity. We test the domain-writing dynamics by running the biased tip of a piezoresponse force microscope across the surface of the ferroelectric films at increasing scanning speeds and studying the continuity and width of the written domains. Our results reveal orders-of-magnitude enhancement of the writing speed when the BTO surface is functionalized. pABA molecules thus emerge as a useful paradigm in electrodes, providing superior screening and localized writing capability of chemisorbed charge, but with much faster dynamics.