Polarization-specific adsorption of organic molecules on ferroelectric LiNbO₃ surfaces

Polarization effect on adsorption of d-cysteine molecules on ferroelectric LiNbO₃ surfaces is studied by a combination of infrared spectramicroscopy and spatially resolved x-ray absorption near edge spectroscopy. It is shown that even in the absence of any electronic excitation (optical or thermal), the adsorption is still polarization-specific with preferential d-cysteine deposition occurring on positive domains. This observation rules out molecular adsorption solely due to pyroelectric or photoinduced charge and suggests possible dipole-dipole interaction between polar d-cysteine molecules and ferroelectric polarization dipoles. The surface chemistry related to polarization-dependent variations in Li/Nb concentration is also implicated as a contributing factor in the domain-specific adsorption of d-cysteine.