Electronic Properties of Tetraazaperopyrene Derivatives on Au(111): Energy Level Alignment and Interfacial Band Formation

TL;DR

This study explores the electronic properties of tetraazaperopyrene derivatives on Au(111), revealing weak physisorption and hybridization effects that inform the design of low-barrier organic-metal interfaces.

Contribution

It combines experimental spectroscopy and density functional calculations to analyze energy level alignment and interfacial band formation of these derivatives on gold surfaces.

Findings

Weak physisorption indicated by unperturbed surface state

Hybridization leads to hole-like dispersive bands

Potential for designing low charge-injection barrier interfaces

Abstract

N-Heteropolycyclic aromatic compounds are promising organic electron-transporting semiconductors for applications in field effect transistors. Here, we investigated the electronic properties of 1,3,8,10-tetraazaperopyrene derivatives adsorbed on Au(111) using a complementary experimental approach, namely scanning tunneling spectroscopy and two-photon photoemission combined with state-of-the-art density functional calculations. We find signatures of weak physisorption of the molecular layers, such as the absence of charge transfer, a nearly unperturbed surface state and an intact herringbone reconstruction underneath the molecular layer. Interestingly, molecular states in the energy region of the \emph{sp}- and \emph{d}-bands of the Au(111) substrate exhibit hole-like dispersive character. We ascribe this band character to hybridization with the delocalized states of the substrate. We suggest that such bands, which effectively leave the molecular frontier orbitals largely unperturbed, to be a promising lead for the design of organic-metal interfaces with a low charge injection barrier.