Substrate dependent bonding distances of PTCDA - A comparative XSW study on Cu(111) and Ag(111)

TL;DR

This study compares the adsorption geometries of PTCDA molecules on Cu(111) and Ag(111) substrates using X-ray standing wave techniques, revealing substrate-dependent differences in molecular and oxygen atom positions.

Contribution

It provides a detailed, element-specific analysis of PTCDA adsorption geometry on two different metal surfaces, highlighting substrate-dependent distortions.

Findings

Carbon core adsorbs in a planar configuration on both substrates.

Oxygen atoms show substrate-dependent distortions and positions.

Distinct adsorption heights for PTCDA on Cu(111) and Ag(111).

Abstract

We study the adsorption geometry of 3,4,9,10-perylene-tetracarboxylic-dianhydride (PTCDA) on Ag(111) and Cu(111) using X-ray standing waves. The element-specific analysis shows that the carbon core of the molecule adsorbs in a planar configuration, whereas the oxygen atoms experience a non-trivial and substrate dependent distortion. On copper (silver) the carbon rings resides 2.66 A (2.86 A) above the substrate. In contrast to the conformation on Ag(111), where the carboxylic oxygen atoms are bent towards the surface, we find that on Cu(111) all oxygen atoms are above the carbon plane at 2.73 A and 2.89 A, respectively.