Molecular UHV-FTIR studies of adsorbate covered TiO2-microparticle surfaces

该项目旨在通过基于原子力显微镜和光谱技术的分子控制吸附质结构的取向、厚度和迁移率，研究颗粒与氧化基底之间的接触力。作为模型体系，SiO2和TiO2将被使用，因为它们的表面改性对颗粒粉末的流动性能有很高的兴趣。该方法基于这样的假设：超高真空（UHV）和清洁的液相允许在不受环境污染影响的情况下调整颗粒的界面化学。此外，AFM胶体探针技术作为一种力分析方法，允许在两种介质中量化这种界面结构对颗粒接触区相互作用的影响。作为有机吸附剂，将使用有机膦酸，因为它们对所考虑的颗粒的表面特性裁剪具有很大的兴趣，并且能够制备不同顺序和化学功能的单层。水在裸露或化学修饰的表面上的吸附是在超高真空或有机液相的界面上进行的。特高压分析装置包括用于分析吸附质化学的x射线光电子能谱仪（XPS）和用于测量裸露和吸附质覆盖表面上接触力的特高压原子力显微镜（UHV- afm）。特别感兴趣的是作为化学性质和温度函数的吸附层的迁移率和有序性。利用大气原子力显微镜研究了毛细管桥的形成及其作为表面化学和温度的函数对接触力的影响。为了避免大气吸附的影响，实验将在极性有机相中进行，并控制水的活度。因此，在亲水界面上，不同数量的水可用于毛细管桥的冰状水层的温度依赖相互作用。通过原位FTIR光谱和原位表面等离子体共振对这些水层的厚度和结构进行表征。

The project aims at the study of contact forces between particles and oxidic substrates based on the molecular control of the adsorbate structure concerning the orientation, thickness and mobility via AFM based and spectroscopic techniques. As model systems, SiO2 and TiO2 will be used as their surface modification is of high interest for the flow properties of particle powders.The methodology is based on the hypothesis that ultrahigh vacuum (UHV) and also clean liquid phases allow for the adjustment of the interfacial chemistry of particles without the influence of environmental contaminations. Furthermore the AFM colloidal probe technique as a force analytical method allows in both media the quantification of the influence of this interface structure on the interaction in the contact zone of the particles.As organic adsorbates organophosphonic acids will be used, as they are of large interest for the tailoring of surface properties of the considered particles and enable the preparation of monolayers of different ordering and chemical functionality. The adsorption of water on bare or chemically modified surfaces is done at the interface to ultrahigh vacuum or an organic liquid phase.The UHV analytical setup includes an X-ray photoelectron spectrometer (XPS) for the analysis of the adsorbate chemistry and an UHV-AFM which allows the measurement of contact forces on bare and adsorbate covered surfaces. A particular interest is the mobility and ordering of the adsorbate layers as a function of the chemical properties and temperature. By means of atmospheric AFM the formation of capillary bridges and their influence on contact forces as a function of surface chemistry and temperature is investigated. To avoid the influence of atmospheric adsorbates, the experiments will be performed in an apolar, organic phase with a controlled activity of water. Hence at hydrophilic interfaces different amounts of water will be available for the temperature dependent interaction involving ice-like water layers of capillary bridges. Via in-situ FTIR spectroscopy and in-situ surface plasmon resonance these water layers will be characterized concerning their thickness and structure.