Chemisorption of Pentacene on Pt(111) with a Little Molecular Distortion

We investigated the adsorption of pentacene on the (111) surface of platinum, which is an archetypal system for a junction with a low charge-injection barrier. We probed the structural and electronic configurations of pentacene by scanning tunnelling microscopy (STM), X-ray photoemission spectroscopy (XPS), and near-edge X-ray absorption fine structure (NEXAFS) spectroscopy measurements. We simulated the interface by means of ab initio methods based on the density functional theory (DFT) framework, while including the dispersion forces. We found that the molecules adsorb at the bridge site of the close-compact atom rows with the long axis parallel to the substrate's <110> directions, in a slightly distorted geometry, driven by the good match between the position of the carbon atoms of the molecule and the underlying lattice of the surface. Most importantly, a chemical bond is formed at the interface, which we attribute to the high chemical reactivity of the Pt substrate.