Influence of intramolecular polar bonds on interface energetics in perfluoro-pentacene on Ag(111)

Abstract

We investigated the structural and electronic properties of vacuum sublimed perfluoro-pentacene (PFP) thin films on Ag(111) substrates using x-ray standing waves (XSW), x-ray diffraction (XRD) and ultraviolet photoelectron spectroscopy (UPS). XSW results reveal a flat adsorption geometry of the monolayer PFP/Ag(111) with a relatively large bonding distance of $3.16\text{ }\text{\AA{}}$ for both, the carbon and fluorine atoms. Multilayers PFP/Ag(111) adopt a herringbone structure with the molecular long axis parallel to the substrate and a vertical lattice spacing of $3.06\text{ }\text{\AA{}}$ as evidenced by XRD. The strong intramolecular polar bond character of the fluorine-carbon bonds in PFP leads to an orientation dependent ionization energy (IE) that is experimentally observed by UPS for the monolayer-multilayer transition: The inclined molecular plane orientation in the multilayer herringbone arrangement leads to an increase of the PFP IE by $>0.4\text{ }\text{eV}$ compared to the flat lying monolayer.