Two-dimensional Excitonic Photoluminescence in Graphene on Cu surface

TL;DR

This study reveals unexpected sharp excitonic photoluminescence in graphene on Cu, caused by hybridization effects, opening new avenues for optoelectronic device engineering while preserving graphene's electrical qualities.

Contribution

It demonstrates the emergence of excitonic PL in graphene on Cu due to hybridization, a phenomenon not previously observed, suggesting new pathways for optoelectronic applications.

Findings

Sharp PL emission near 3.16 eV with FWHM ≤ 3 meV

PL blue-shifts with increasing temperature

PL originates from suppressed electron dispersion due to hybridization

Abstract

Despite having outstanding electrical properties, graphene is unsuitable for optical devices because of its zero band gap. Here, we report two-dimensional excitonic photoluminescence (PL) from graphene grown on Cu(111) surface, which shows an unexpected remarkably sharp and strong emission near 3.16 eV (full-width at half-maximum $\leq$ 3meV) and multiple emissions around 3.18 eV. As temperature increases, these emissions blue-shift, showing the characteristic negative thermal coefficient of graphene. Observed PLs originate from significantly suppressed dispersion of excited electrons in graphene caused by hybridization of graphene $\pi$ and Cu d orbitals of the 1st and 2nd Cu layers at a shifted saddle point 0.525(M+K) of Brillouin zone. This finding provides a new pathway to engineering novel optoelectronic graphene devices, whilst maintaining the outstanding electrical properties of graphene.