Polarization-dependent water adsorption on the LiNbO3(0001) surface

The effect of ferroelectric poling on the adsorption characteristics of water at lithium niobate surfaces is investigated by ab initio calculations. Thereby we model the adsorption of H2O monomers, small water clusters, and water thin films on the LiNbO3(0001) surface. The adsorption configuration and energy are determined as a function of the surface coverage on both the positive and negative (0001) surfaces. Confirming the results of temperature programed desorption measurements [Garra, Vohs, and Bonnell, Surf. Sci. 603, 1106 (2009)], polarization-dependent adsorption energies, geometries, and equilibrium coverage are found. Our calculations predict the adsorption to occur mainly nondissociatively, independently of the coverage. The water structures formed at the surface are coverage-dependent, though. The different affinity of water to the two surfaces is explained in terms of electrostatic interactions between the substrate and polar molecules. Water adsorption accentuates the surface relaxation, thus increasing the microscopic surface roughness.