Organics on TiO2 Surfaces: On-surface Reactions, Interfacial Barrier Heights of Formation and STM Imaging

Abstract

Understanding the interaction between organic molecules and surfaces is of paramount importance in diverse fields such as organic and molecular electronics, catalysis, and on-surface chemistry, among others. In particular, the growing field of organic electronics relies on the use of organic conjugated molecules as components of multilayer devices. To this aim, surfaces of titanium dioxide provide suitable conditions for the use of surface experimental techniques (ultra-high vacuum XPS, UPS, NEXAFS and STM) and their adequate combination with first-principles based calculations. TiO2(110) surfaces provide an anisotropic template consisting of alternating bridging oxygen rows and 5-fold coordinated Ti4+ rows, making possible different adsorption geometries for different organic molecules. On this basis, the Unified IDIS model, a beyond-DFT many-body approach, and an accurate Keldish-Green-based theoretical scanning tunneling microscopy formalism have been used to fully characterize the interaction between a large variety of organic molecules ¿ such as TCNQ, C60H30, perylene, C60, 2HTPP, and NiTPP ¿ and TiO2 surfaces. These molecules are prototypical electron donors and acceptors, and are in potentials of catalysis and molecular electronics as active catalysts precursors, promising candidates of organic conductors, and some of them interesting due to their hole-injection barrier recently evidenced. Within this contribution we will deeply analyze the interaction between TCNQ and perylene on the TiO2(110)-1×1 surface, the on-surface (cyclo-)dehydrogenation reaction of C60H30 on the TiO2(110)-1×1 surface, a recently discovered new C60/TiO2(110) phase, and the complex on-surface metalation process from 2HTPP towards NiTPP on the 1×1 and 1×2 TiO2(110) surfaces.