Observation of Raman G-band splitting in top-doped few-layer graphene

TL;DR

This study investigates how doping affects the Raman G-band in few-layer graphene, revealing layer-dependent splitting linked to electron-phonon interactions and symmetry changes.

Contribution

It provides the first detailed analysis of doping-induced G-band splitting in N-layer graphene, highlighting layer-dependent electron-phonon interaction effects.

Findings

G-band splitting occurs in even-layer graphene at high doping levels.

Splitting is absent in odd-layer graphene, indicating symmetry effects.

Different doping trends suggest multiple electron-phonon interaction regimes.

Abstract

An experimental study of Raman scattering in N-layer graphene as a function of the top layer doping is reported. At high doping level, achieved by a CHF_3 plasma treatment, we observe a splitting of the $G$ band in the spectra of bilayer and 4-layer graphene (N even), whereas the splitting is not visible in case of monolayer and trilayer graphene (N odd). The different behaviors are related to distinct electron-phonon interactions, which are affected by symmetry breaking and Fermi level position in different ways in the various N-layer graphenes. In trilayer graphene, a weakening of the electron-phonon coupling as a function of the Fermi energy induces a hardening of all zone-center in-plane optical phonon modes, like in monolayer graphene. On the other hand, in 4-layer graphene two distinct trends are observed in the G band as a function of doping, suggesting the presence of two different groups of electron-phonon interactions, like in bilayer graphene.