Water Affinity and Surface Charging at the z‑Cut and y‑Cut LiNbO₃ Surfaces: An Ambient Pressure X‑ray Photoelectron Spectroscopy Study

Polarization dependence of water adsorption and desorption on LiNbO₃ surfaces was demonstrated using X-ray photoelectron spectroscopy (XPS) carried out in situ under near-ambient conditions. Positive and negative (0001) faces (z-cut) of the same crystal were compared for the same temperature and pressure conditions. Our results indicate a preferential adsorption on the positive face of the crystal with increasing water pressure and also higher desorption temperature of the adsorbed molecular water at the positive face. Adsorption measurements on the (1100) face (y-cut) showed also strong affinity to water, as observed for the z-cut positive surface. We found a direct relation between the capacity of the surface to discharge and/or to screen surface charges and the affinity for water of each face. XPS spectra indicate the presence of OH groups at the surface for all the conditions and surfaces measured