The nature of the observed free-electron-like state in a PTCDA monolayer on Ag(111)

TL;DR

This study investigates the origin of a free-electron-like band in a PTCDA monolayer on Ag(111), revealing it results from the interaction between the Shockley surface state and adsorbed molecules, as shown by DFT calculations.

Contribution

The paper demonstrates through density functional theory that the free-electron-like band arises from the shifted Shockley surface state coupled with molecular bands.

Findings

The Shockley surface state is shifted up in energy due to molecule interaction.

The free-electron-like band has significant admixture with molecular bands.

DFT calculations explain the experimental observations.

Abstract

A free-electron like band has recently been observed in a monolayer of PTCDA (3,4,9,10-perylene tetracarboxylic dianhydride) molecules on Ag(111) by two-photon photoemission [Schwalb et al., Phys. Rev. Lett. 101, 146801 (2008)] and scanning tunneling spectroscopy [Temirov et al., Nature 444, 350 (2006)]. Using density functional theory calculations, we find that the observed free-electron like band originates from the Shockley surface state band being dramatically shifted up in energy by the interaction with the adsorbed molecules while it acquires also a substantial admixture with a molecular band.