Surface-adsorbed polar molecules
can significantly alter the ferroelectric properties of oxide thin
films. Thus, fundamental understanding and controlling the effect
of surface adsorbates are crucial for the implementation of ferroelectric
thin film devices, such as ferroelectric tunnel junctions. Herein,
we report an imprint control of BaTiO<sub>3</sub> (BTO) thin films
by chemically induced surface polarization pinning in the top few
atomic layers of the water-exposed BTO films. Our studies based on
synchrotron X-ray scattering and coherent Bragg rod analysis demonstrate
that the chemically induced surface polarization is not switchable
but reduces the polarization imprint and improves the bistability
of ferroelectric phase in BTO tunnel junctions. We conclude that the
chemical treatment of ferroelectric thin films with polar molecules
may serve as a simple yet powerful strategy to enhance functional
properties of ferroelectric tunnel junctions for their practical applications