Formation of image-potential states at the graphene/metal interface

TL;DR

This study models the formation of image-potential states at graphene/metal interfaces, revealing how these states evolve with distance and interaction strength, and explaining experimental observations.

Contribution

It introduces an analytical model that describes the evolution of image-potential states at the graphene/metal interface, matching experimental data and providing physical insights.

Findings

The model reproduces experimental energies and wave functions.

It explains the evolution from free-standing graphene states to metal surface states.

It clarifies the differences in binding energy and lifetime of states in moire superlattices.

Abstract

The formation of image-potential states at the interface between a graphene layer and a metal surface is studied by means of model calculations. An analytical one-dimensional model-potential for the combined system is constructed and used to calculate energies and wave functions of the image-potential states at the Gamma-point as a function of the graphene-metal distance. It is demonstrated how the double series of image-potential states of free-standing graphene evolves into interfacial states that interact with both surfaces at intermediate distances and finally into a single series of states resembling those of a clean metal surface covered by a monoatomic spacer layer. The model quantitatively reproduces experimental data available for graphene/Ir(111) and graphene/Ru(0001), systems which strongly differ in interaction strength and therefore adsorption distance. Moreover, it provides a clear physical explanation for the different binding energy and lifetime of the first (n=1) image-potential state in the valley and hill areas of the strongly corrugated moire superlattice of graphene/Ru(0001).