First-principle study of CO adsorption influence on the properties of ferroelectric tunnel junctions

Based on first principles calculations, we systematically investigated the structural, electronic and ferroelectric properties of Pt-BaTiO₃-Pt ferroelectric tunnel junctions (FTJs) with CO adsorbed on the surface of the top electrode. Changes of electrode/barrier thickness and different adsorption sites were considered. We found that although the CO molecule is not directly adsorbed on the surface of the ferroelectric thin film (FTF), the local properties of the BaTiO₃ FTFs were still significantly changed by CO adsorptions, e.g. the change of polarization bistability. Furthermore, by simulating isolated geometry, we found that the orientation of polarization induced by CO adsorptions exhibited sensitive dependence on the thickness of the adsorbed electrode. The adsorption energy was found to change with the change of both the thickness of the electrodes and the polarization orientation in the barrier, which provides a modifiable effect by virtue of the surface ambient chemicals controlling the bulk ferroelectric properties. An electronic structure analysis reveals that the work function of the adsorbed electrode is altered by the adsorption, and the effect can be reversed as the electrode thickness changes. Our findings should provide a new method to tailor the magnitude and bistability of polarization in ferroelectric thin films (FTF) as well as the top electrode surface reactivity in FTJs, which has a significant prospect of application in FTJ-based nanoscale multifunctional devices.