Dipole formation at metal/PTCDA interfaces: Role of the Charge Neutrality Level

TL;DR

This paper investigates the electronic structure and dipole formation at metal/PTCDA interfaces, highlighting the role of the Charge Neutrality Level in molecular level alignment driven by charge transfer.

Contribution

It introduces a weak-chemisorption theoretical framework to analyze interface barriers and defines the Charge Neutrality Level for PTCDA based on induced interface states.

Findings

Charge Neutrality Level for PTCDA is 2.45 eV above HOMO.

Interface dipole results from electrostatic charge transfer.

Induced density of states is significant despite weak interaction.

Abstract

The formation of a metal/PTCDA (3, 4, 9, 10-perylenetetracarboxylic dianhydride) interface barrier is analyzed using weak-chemisorption theory. The electronic structure of the uncoupled PTCDA molecule and of the metal surface is calculated. Then, the induced density of interface states is obtained as a function of these two electronic structures and the interaction between both systems. This induced density of states is found to be large enough (even if the metal/PTCDA interaction is weak) for the definition of a Charge Neutrality Level for PTCDA, located 2.45 eV above the highest occupied molecular orbital. We conclude that the metal/PTCDA interface molecular level alignment is due to the electrostatic dipole created by the charge transfer between the two solids.