N-Heterocyclic Carbene Monolayers on Metal-Oxide Films: Correlations between Adsorption Mode and Surface Functionality.

N-Heterocyclic carbene (NHC) ligands have been self-assembled on various metal and semimetal surfaces, creating a covalent bond with surface metal atoms that led to high thermal and chemical stability of the self-assembled monolayer. This study explores the self-assembly of NHCs on metal-oxide films (CuO x , FeO x , and TiO x ) and reveals that the properties of these metal-oxide substrates play a pivotal role in dictating the adsorption behavior of NHCs, influencing the decomposition route of the monolayer and its impact on work function values. While the attachment of NHCs onto CuO x is via coordination with surface oxygen atoms, NHCs interact with TiO x through coordination with surface metal atoms and with FeO x via coordination with both metal and oxygen surface atoms. These distinct binding modes arise due to variances in the electronic properties of the metal atoms within the investigated metal-oxide films. Contact angle and ultraviolet photoelectron spectroscopy measurements have shown a significantly higher impact of F-NHC adsorption on CuO x than on TiO x and FeO x , correlated to a preferred, averaged upright orientation of F-NHC on CuO x .