Chemical Control of Ferroelectric Switching in PbTiO$_3$ Films*

Stabilization of monodomain polarization in ultrathin ferroelectric films can be accomplished via surface-adsorbed ions [Fong, D. D. \emph{et al}., \emph{Phys. Rev. Lett.} \textbf{96}, 127601/1-4 (2006)]. Here, we use in-situ grazing-incidence synchrotron x-ray scattering to study the ferroelectric polarization and surface structure of PbTiO$_3$ ferroelectric thin films as a function of vapor environment above the film surface. Coherent PbTiO$_3$ films of 10 nm thickness were grown on conducting SrRuO$_3$ on (001) SrTiO$_3$ substrates. We observe that the polarization direction in the PbTiO$_3$ film can be reversed by changing between oxidizing and reducing atmospheres, and the piezoelectric butterfly loop can be traced out as a function of oxygen partial pressure. Additionally, a new surface reconstruction is observed under reducing conditions.