Substrate-molecule decoupling induced by self-assembly—Implications for graphene nanoribbon fabrication

Xinqian Li,Daniel M Packwood

doi:10.1063/1.5025101

Abstract

Interactions between organic molecules and metal surfaces are often very strong, resulting in the loss of well-defined frontier orbitals on the molecule due to electronic hybridization with the surface. In this paper, we use theoretical calculations to show that the interaction between graphene nanoribbon precursor molecules and copper surfaces is weakened upon molecular self-assembly. This phenomenon, which we abbreviate as SAID (Self-Assembly Induced Decoupling), increases the adsorption distance of the molecules to the surface, and results in a partial recovery of frontier molecular orbital electron density. The SAID phenomenon opens a new topic in the field of organic-metal interface physics, and may have broader implications for thin film devices and catalysis.

Highlights

Innovations in the field of organic electronics and catalysis require a fundamental understanding of the organic molecule-metal surface interface.1 Even in the absence of chemical linking groups, aromatic organic molecules such as benzene often adsorb strongly to metal surfaces via van der Waals interactions
For the case of organic molecules adsorbed to metal surfaces via van der Waals interactions, tentative evidence for a weakened surface-molecule interaction upon molecular self-assembly can be found by considering the mechanism of certain on-surface chemical reactions
While an isolated Br2BA molecule on Cu[111] shows major broadening in the density of states around the HOMO and LUMO peaks, the sharpness of these peaks is partially recovered when two Br2BA molecules assemble into a chain-like alignment

Summary

Introduction

Innovations in the field of organic electronics and catalysis require a fundamental understanding of the organic molecule-metal surface interface.1 Even in the absence of chemical linking groups, aromatic organic molecules such as benzene often adsorb strongly to metal surfaces via van der Waals interactions. This result, as well as the observation of increased adsorption distance and a smaller work function change for the case of two Br2BA molecules in a chain-like alignment, supports the idea that self-assembly can result in a decoupling of van der Waals-adsorbed molecules from a surface.

Results

Conclusion