Molecule-Oxide Bond Formation (funCOS 3)

Knowledge-based design of organic/oxide interfaces requires detailed insights into molecule-oxide bond formation. This project aims at providing this information, combining two complementary surface spectroscopies, surface vibrational spectroscopy (IRAS, infrared reflection absorption spectroscopy) and photoelectron spectroscopy (XPS, X-ray photoelectron spectroscopy), both under UHV (ultrahigh vacuum) conditions.Starting from ordered, atomically clean oxides (MgO(100)/Ag(100), later Co3O4,CoO/Ir(100) and TiO2(110)) we will identify the interaction/reaction mechanisms of selected anchor groups (-OH, -COOH, -NH2, -CN) with specific surface sites using small test molecules. The energetics and kinetics of molecule-oxide bond formation will be studied by temperature-programmed and time-resolved experiments. In a second step, these linkers will be introduced into complex builders (5,10,15,20-Tetraphenypporphyrins, TPP; later other tetrapyrroles) to control their surface interaction. The combined spectroscopic information will provide insight into reaction mechanisms and kinetics during transformation of functional groups and into the energetics and the thermal stability of surface-linked intermediates. Also, we will follow spectroscopically the molecular orientation during film growth, the intermolecular interactions, and related ordering phenomena. Exploration of the linker concept will include multiple coordination through chelating and/or multifunctional units, with the aim of tuning orientation, formation barrier, and thermal stability. In the second project phase we will address the selectivity of molecule-oxide bond formation. Surface linking reactions will be studied with respect to their potential to address specific surface sites by appropriate anchors or anchor ensembles. On nanostructured oxide surfaces (defect structures, supported oxide or metal nanoparticles on oxides) we will aim at preparing nanostructured functional films maintaining a maximum level of control over the growth behavior. Finally, the project will address the reactivity of functional molecular films on oxides and, closely related to this subject, the transferability of knowledge to ambient conditions and nanomaterials. The influence of reactive environments (e.g. H2O, H2, CO, CO2) on surface anchoring (test molecules and substituted TPPs) will be probed in UHV by TPD (temperature programmed desorption spectroscopy) and MB methods (molecular beams), and compared to studies at near-ambient conditions by in-situ spectroscopies (PM-IRAS, polarization modulation IRAS, and, where required, HP-XPS, high pressure XPS). Reactivity studies of complex builders (e.g. with CO, NO, H2O, H2) in UHV and at higher pressure will be performed using the same methods. Finally, we will apply in-situ/operando DRIFTS (diffuse reflection infrared FT spectroscopy) to correlate bond formation and film growth on single-crystal models and on real oxide nanostructures (e.g. MgO nanocrystals).