Interface Characteristics at an Organic/Metal Junction: Pentacene on Cu Stepped Surfaces

TL;DR

This study uses density functional theory to analyze how pentacene molecules adsorb on stepped copper surfaces, revealing preferences for surface orientation, the impact of van der Waals interactions, and charge transfer characteristics.

Contribution

It provides detailed insights into the adsorption behavior of pentacene on various copper vicinal surfaces, highlighting the role of vdW interactions and surface structure in adsorption energies and orientations.

Findings

Pentacene prefers to adsorb parallel to the surface near steps.

Van der Waals interactions significantly increase adsorption energies by about 2 eV.

Pentacene transfers approximately one electron upon adsorption.

Abstract

The adsorption of pentacene on Cu(221), Cu(511) and Cu(911) is investigated using density functional theory (DFT) with the self-consistent inclusion of van der Waals (vdW) interactions. Cu(211) is a vicinal of Cu(111) while Cu(511) and (911) are vicinals of Cu(100). For all the three surfaces, we found pentacene to prefer to adsorb parallel to the surface and near the steps. The addition of vdW interactions resulted in an enhancement in adsorption energies, with reference to the PBE functional, of around 2 eV. With vdWs inclusion, the adsorption energies were found to be 2.98 eV, 3.20 eV and 3.49 eV for Cu(211), Cu(511) and Cu(911) respectively. These values reflect that pentacene adsorbs stronger on (100) terraces with a preference for larger terraces. The molecule tilts upon adsorption with a small tilt angle on the (100) vicinals (about a few degrees) as compared to a large one on Cu(221) where the tilt angle is found to be about 20o. We find that the adsorption results in a net charge transfer to the molecule of ~1 electron, for all surfaces.