Molekular adsorption on ferroelectrics calculated from first-principles

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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.