Adsorption and Intermolecular Interaction of Cobalt Phthalocyanine on CoO(111) Ultrathin Films: An STM and DFT Study

TL;DR

This study combines STM and DFT to analyze how cobalt phthalocyanine molecules adsorb on ultrathin CoO films, revealing flat adsorption, weak chemical bonding, and the dominance of van-der-Waals forces in determining molecular geometry and interactions.

Contribution

It provides detailed insight into the adsorption geometry and intermolecular interactions of CoPc on CoO(111) using combined experimental and theoretical methods.

Findings

CoPc molecules lie flat on CoO surface.

Weak cobalt-oxygen chemical bonds dominate adsorption energy.

Van-der-Waals forces significantly influence molecular geometry and interactions.

Abstract

We investigate the adsorption of cobalt phthalocyanine (CoPc) molecules on a thin layer of cobalt oxide grown on Ir(100). To that end we compare the results of low-temperature scanning tunneling microscopy (STM) with those of ab-initio density functional theory (DFT) calculations and reveal the adsorption geometry. We find that the CoPc molecules lie flat on the surface and that their central cobalt atom forms a chemical bond to a substrate oxygen ion. However, this bond contributes only modestly to the adsorption energy, while van-der-Waals forces dominate the potential landscape and determine to a large extend the geometry as well as the distortion of substrate and molecule. Furthermore they lead to attractive molecule-molecule interactions at higher molecular coverages. The DFT calculations predict energetic positions of the molecular orbitals which are compared to scanning tunneling spectroscopy (STS) measurements.