Van der Waals Interaction Activated Strong Electronic Coupling at the Interface between Chloro Boron-Subphthalocyanine and Cu(111).

Shashank S Harivyasi,Oliver T Hofmann,Oliver L A Monti,Egbert Zojer,Nahid Ilyas

doi:10.1021/acs.jpcc.8b03675

Shashank S Harivyasi, Oliver T Hofmann + Show 3 more

Open Access

https://doi.org/10.1021/acs.jpcc.8b03675

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Abstract

In this article, we investigate the interface between shuttlecock-shaped chloro boron-subphthalocyanine molecules and the Cu(111) surface. We highlight how molecular planarization induced by van der Waals forces can fundamentally alter the interface properties and how it can enable a particularly strong hybridization between molecular and metal states. In our simulations, we start from a situation in which we disregard van der Waals forces and then introduce them gradually by rescaling the interaction parameter, thereby “pulling” the molecule toward the surface. This reveals two adsorption regimes with significantly different adsorption distances, molecular conformations, and adsorbate-induced changes of the work function. Notably, the above-mentioned massive hybridization of electronic states, also observed in photoelectron spectroscopy, is obtained solely for one of the regimes. We show that this regime is accessible only as a consequence of the planarization of the molecular backbone resulting from the van der Waals attraction between the molecule and the surface. The results of this study indicate that for certain metal–molecule combinations unusually strong interfacial electronic interactions can be triggered by van der Waals forces creating a situation that differs from the usually described cases of physisorptive and chemisorptive interactions.

Highlights

In organicelectronic devices, molecules are often in direct contact with metal electrodes
The results of this study indicate that for certain metal−molecule combinations unusually strong interfacial electronic interactions can be triggered by van der Waals forces creating a situation that differs from the usually described cases of physisorptive and chemisorptive interactions
The ClB-SubPc/Cu(111) interface provides valuable insight into how changes in an adsorbate geometry induced by the van der Waals attraction to a substrate can change the electronic coupling between substrate and adsorbate, pushing the interface into a significantly different coupling regime

Summary

Introduction

In organic (opto)electronic devices, molecules are often in direct contact with metal electrodes. This makes a comprehensive understanding of metal−organic interfaces a prerequisite for improving device performance. The present study focuses on understanding peculiarities of the interfacial interactions and the electronic structure that may arise from adsorption-induced geometry changes in certain nonplanar molecules. We present a detailed computational study of the adsorption of chloro boronsubphthalocyanine (ClB-SubPc) on Cu(111) and corroborate it with an assessment of the interfacial electronic structure via photoelectron spectroscopy. The system serves as a prototypical example for the hitherto rarely discussed[11] scenario in which the electronic structure of an interface is fundamentally altered by changes of molecular conformation that are, in turn, enabled by the van der Waals (vdW) forces between the molecule and the substrate

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