Interface control of surface photochemical reactivity in ultrathin epitaxial ferroelectric films

Asymmetrical electrical boundary conditions in (001)-oriented Pb(Zr _0.2TiO_0.8)O₃ (PZT) epitaxial ultrathin ferroelectric films are exploited to control surface photochemical reactivity determined by the sign of the surface polarization charge. It is shown that the preferential orientation of polarization in the as-grown PZT layer can be manipulated by choosing an appropriate type of bottom electrode material. PZT films deposited on the SrRuO₃ electrodes exhibit preferential upward polarization (C) whilst the same films grown on the (La,Sr)CoO ₃-electrodes are polarized downward (C^-). Photochemical activity of the PZT surfaces with different surface polarization charges has been tested by studying deposition of silver nanoparticles from AgNO₃ solution under UV irradiation. PZT surfaces with preferential C orientation possess a more active surface for metal reduction than their C^- counterparts, evidenced by large differences in the concentration of deposited silver nanoparticles. This effect is attributed to band bending at the bottom interface which varies depending on the difference in work functions of PZT and electrode materials.