Low-Energy Electron Reflectivity of Graphene on Copper and other Substrates

TL;DR

This study investigates how low-energy electrons reflect off graphene on copper and other substrates, revealing oscillations linked to interlayer states, with theoretical models matching experimental observations across different substrate orientations.

Contribution

It provides a combined experimental and theoretical analysis of electron reflectivity in graphene on various substrates, highlighting the role of interlayer states and substrate orientation effects.

Findings

Oscillations in reflectivity are observed and reproduced theoretically.

Number of minima correlates with the number of graphene layers.

Differences in spectra are due to substrate band structures.

Abstract

The reflectivity of low energy electrons from graphene on copper substrates is studied both experimentally and theoretically. Well-known oscillations in the reflectivity of electrons with energies 0 - 8 eV above the vacuum level are observed in the experiment. These oscillations are reproduced in theory, based on a first-principles density functional description of interlayer states forming for various thicknesses of multilayer graphene. It is demonstrated that n layers of graphene produce a regular series of n-1 minima in the reflectance spectra, together with a possible additional minimum associated with an interlayer state forming between the graphene and the substrate. Both (111) and (001) orientations of the copper substrates are studied. Similarities in their reflectivity spectra arise from the interlayer states, whereas differences are found because of the different Cu band structures along those orientations. Results for graphene on other substrates, including Pt(111) and Ir(111), are also discussed.