Mapping Unoccupied Electronic States of Freestanding Graphene by Angle-Resolved Low-Energy Electron Transmission

TL;DR

This study uses angle-resolved low-energy electron transmission to map the unoccupied electronic states of freestanding graphene, revealing its band structure above the vacuum level with high angular and energy resolution.

Contribution

It introduces a novel experimental technique for directly mapping unoccupied band structures of 2D materials as a function of energy and momentum.

Findings

Experimental results match theoretical predictions of resonance features.

The technique enables detailed mapping of unoccupied states.

Provides insights into graphene's electronic structure above the vacuum level.

Abstract

We report angle-resolved electron transmission measurements through freestanding graphene sheets in the energy range of 18 to 30 eV above the Fermi level. The measurements are carried out in a low-energy electron point source microscope, which allows simultaneously probing the transmission for a large angular range. The characteristics of low-energy electron transmission through graphene depend on its electronic structure above the vacuum level. The experimental technique described here allows mapping the unoccupied band structure of freestanding two-dimensional materials as a function of energy and probing angle, respectively in-plane momentum. Our experimental findings are consistent with theoretical predictions of a resonance in the band structure of graphene above the vacuum level [V. U. Nazarov, E. E. Krasovskii, and V. M. Silkin, Physical Review B 87, 041405 (2013)].