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DF: Fachverband Dielektrische Festkörper

DF 16: Dielectric surfaces and interfaces

DF 16.2: Vortrag

Donnerstag, 29. März 2012, 12:00–12:20, EB 107

Water adsorption on LiNbO₃ Z-cut surfaces calculated from first principles — •Rebecca Hölscher, Simone Sanna, and Wolf Gero Schmidt — University of Paderborn

LiNbO₃ (LN) is a frequently used material for optical and acoustic applications due to its unusual but useful piezoelectric, pyroelectric, and photorefractive properties. As for other ferroelectric materials the surface reactivity can be changed by manipulating the polarization. This opens the possibility for the realization of molecular detectors and other devices¹. Unfortunately only few data about the structure of the surface are available. Most studies do not refer to clean surfaces in UHV conditions, but are rather performed in ambient conditions, where the adsorption of foreign species like water will modify the the LN surface properties. Here we present ab initio calculations on the adsorption of H₂O molecules and thin water films on the positive (0001) and negative (0001) surface of LN. The adsorption is modelled by means of density functional theory within the generalized gradient approximation^2,3. The adsorption site and energy are determined as a function of the H₂O coverage. Different adsorption patterns are found depending on the surface polarity. The occuring water reconstruction is shown in phase diagrams as a function of temperature and pressure which reveal that at ambient conditions a H₂O film is present at the LN Z-cut.

[1] D. Li, M.H. Zhao, J. Garra, et al., Nature Materials 7 (2008) 473. [2] W.G. Schmidt, M. Albrecht, S. Wippermann, S. Blankenburg, E. Rauls, et al., Phys. Rev. B 77 (2008), 035106. [3] S. Sanna, A.V. Gavrilenko, W.G. Schmidt, Phys. Stat. Sol. C 7 (2010) 145.