Fingerprint of fractional charge transfer at metal/organic interface

TL;DR

This study identifies a fractional charge transfer at the metal/organic interface, characterized by specific spectroscopic fingerprints, supported by experimental and first-principles computational evidence.

Contribution

It provides clear spectroscopic signatures of fractional charge transfer at a physisorbed organic/metal interface, clarifying bonding mechanisms.

Findings

Fingerprint of fractional charge transfer detected

Non-rigid core-level shifts observed

Unoccupied states show significant changes

Abstract

Although physisorption is a widely occurring mechanism of bonding at the organic/metal interface, contradictory interpretations of this phenomenon are often reported. Photoemission and X-ray absorption spectroscopy investigations of nanorods of a substituted pentacene, 2,3,9,10-tetrafluoropentacene, deposited on gold single crystals reveal to be fundamental to identify the bonding mechanisms. We find fingerprints of a fractional charge transfer from the clean metal substrate to the physisorbed molecules. This phenomenon is unambiguously recognizable by a non-rigid shift of the core-level main lines while the occupied states at the interface stay mostly unperturbed, and the unoccupied states experience pronounced changes. The experimental results are corroborated by first-principles calculations.