Molekular adsorption on ferroelectrics calculated from first-principles
Overview
The physical and chemical properties of ferroelectric surfaces are polarization dependent. For example, water films freeze at different temperatures and the chemical etching properties of surfaces with opposite polarization are strongly different. The ferroelectric domain orientation affects molecular adsorption phenomena. As the dipole orientation in ferroelectric materials can be switched at the nanoscale, domain-specific surface chemistries as a route towards the fabrication of nanoscale devices may thus be realized. However, the origin of the polarization dependent adsorption characteristics is largely unexplored. It has been tentatively attributed to charge transfer processes and/or electrostatic forces induced by space charge layers and band bending, to external screening charges on the surface, to the pyroelectric properties of the ferroelectric substrate as well as to the different atomic surface structure of oppositely polarized surfaces. The proposed project aims at probing/verifying these effects by means of first-principles total-energy calculations. Thereby we will start with lithium niobate surfaces and small molecules typically expected in ambient conditions such as N2, O2, CO2, and H2O. Later the investigations shall be extended to other ferroelectric substrates such as barium titanate and small hydrocarbons as well as models for liquid crystal molecules. Apart from a thorough understanding of the adsorption mechanisms, e.g., adsorption geometries and reaction kinetics, we are interested in the impact of the molecular overlayer on the electronic and optical properties as well as on the polarization reversal behavior of the ferroelectric substrate.
Key Facts
- Project type:
- Research
- Project duration:
- 01/2013 - 12/2020
- Funded by:
- DFG
- Website:
-
DFG-Datenbank gepris
More Information
Results
Within the framework of this DFG project, it was shown that the polarization of ferroelectric surfaces has a major influence on molecular adsorption. For smaller molecules this concerns e.g. the desorption temperature or the molecular order and correlation functions in water layers which are not in direct contact with the surface. In the case of larger molecules, such as in liquid crystals, there may be a change in molecular orientations. In this case, the influence of polarization-dependent surface stoichiometry and the local bonding conditions induced by it outweigh the influence of long-range electric fields. Application-relevant is in particular the first-time calculation of complete surface phase diagrams for the relevant lithium niobate crystal orientations under ambient conditions. «Intrinsic LiNbO3 point defects from hybrid density functional calculations» Phys. Rev. B 89, 094111 (2014) Y Li, WG Schmidt, S Sanna (Siehe online unter https://doi.org/10.1103/PhysRevB.89.094111) «Modeling LiNbO3 Surfaces at Ambient Conditions» J. Phys. Chem. C 118, 10213 (2014) R. Hölscher, WG Schmidt, S Sanna (Siehe online unter https://doi.org/10.1021/jp502936f) «Temperature dependent LiNbO3(0001): Surface reconstruction and surface charge» Appl. Surf. Sci. 301, 70 (2014) S Sanna, R Hölscher, WG Schmidt (Siehe online unter https://doi.org/10.1016/j.apsusc.2014.01.104) «Defect complexes in congruent LiNbO3 and their optical signatures» Phys. Rev. B 91, 174106 (2015) Y Li, WG Schmidt, S Sanna (Siehe online unter https://doi.org/10.1103/PhysRevB.91.174106) «Liquid Crystal (8CB) Molecular Adsorption on Lithium Niobate Z-Cut Surfaces» J. Phys. Chem. 119, 9342 (2015) C Braun, S Sanna, WG Schmidt (Siehe online unter https://doi.org/10.1021/acs.jpcc.5b00894) «Modeling atomic force microscopy at LiNbO3 surfaces from first-principles» Comput. Mater. Sci. 103, 145 (2015) S Sanna, C Dues, WG Schmidt (Siehe online unter https://doi.org/10.1016/j.commatsci.2015.03.025) «Polaronic deformation at the Fe2+/3+ impurity site in Fe:LiNbO3 crystals» Phys. Rev. B 91, 094109 (2015) A Sanson, A Zaltron, N Argiolas, C Sada, and M Bazzan, WG Schmidt, S Sanna (Siehe online unter https://doi.org/10.1103/PhysRevB.91.094109) «Surface induced vibrational modes in the fluorescence spectra of PTCDA adsorbed on the KCl(100) and NaCl(100) surfaces» Phys. Chem. Chem. Phys. 18, 32891 (2016) A Paulheim, C Marquardt, M Sokolowski, M Hochheim, T Bredow, H Aldahhak, E Rauls and WG Schmidt (Siehe online unter https://doi.org/10.1039/C6CP05661J) «LiNbO3 surfaces from a microscopic perspective» J. Phys.: Condens. Matter 29, 413003 (2017) S Sanna, WG Schmidt (Siehe online unter https://doi.org/10.1088/1361-648X/aa818d)Selected Publications