Molekular adsorption on ferroelectrics calculated from first-principles

铁电表面的物理和化学性质与极化有关。例如，水膜在不同的温度下冻结，具有相反极化的表面的化学蚀刻性能有很大的不同。铁电畴取向影响分子吸附现象。由于铁电材料中的偶极子取向可以在纳米尺度上进行切换，因此可以实现特定领域表面化学作为制造纳米级器件的途径。然而，极化依赖吸附特性的起源在很大程度上尚未探索。它暂时归因于由空间电荷层和带弯曲引起的电荷转移过程和/或静电力，表面上的外部筛选电荷，铁电衬底的热释电性质以及相反极化表面的不同原子表面结构。拟议的项目旨在通过第一性原理总能量计算来探测/验证这些影响。因此，我们将从铌酸锂表面和小分子开始，这些小分子通常存在于N2、O2、CO2和H2O等环境条件下。后来的研究将扩展到其他铁电衬底，如钛酸钡和小碳氢化合物以及液晶分子模型。除了对吸附机理（如吸附几何和反应动力学）的深入了解外，我们还对分子覆盖层对铁电衬底的电子和光学性质以及极化反转行为的影响感兴趣。

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.