Unveiling surface adsorbates under atmospheric conditions and in surface water redox reactions on TiO2 terminated surfaces and ferroelectric oxides, as studied by AP-XPS.

Electrochemistry and surface water redox reactions on Pb(Zr0.2,Ti0.8)O3 ferroelectric thin films as a function of polarization and external electric field, as studied by AP-XPS and KPFM.

The mechanical properties of materials are insensitive to space inversion, even when they are crystallographically asymmetric. In practice, this means that turning a piezoelectric crystal upside down or switching the polarization of a ferroelectric should not change its mechanical response. Strain gradients, however, introduce an additional source of asymmetry that has mechanical consequences. Using nanoindentation and contact-resonance force microscopy, this study demonstrates that the mechanical response to indentation of a uniaxial ferroelectric (LiNbO ) does change when its polarity is switched, and use this mechanical asymmetry both to quantify its flexoelectricity and to mechanically read the sign of its ferroelectric domains.

Polarization dependence of water adsorption and desorption on LiNbO 3 surfaces was demonstrated using X-ray photoelectron spectroscopy (XPS) carried out in situ under nearambient 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 zcut 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.