Experimental Phonon Band Structure of Graphene using C$^{12} and C$^{13}$ Isotopes

TL;DR

This study experimentally maps the phonon band structure of graphene using isotope labeling and Raman spectroscopy, revealing detailed dispersion relations and phonon processes.

Contribution

It introduces a method combining isotope variation and Raman spectroscopy to accurately measure graphene's phonon dispersion.

Findings

Identified 15 distinct Raman lines in graphene monolayers.

Mapped detailed phonon dispersion relations across the Brillouin zone.

Detected a double phonon process involving inter- and intra-valley phonons.

Abstract

Using very uniform large scale chemical vapor deposition grown graphene transferred onto silicon, we were able to identify 15 distinct Raman lines associated with graphene monolayers. This was possible thanks to a combination of different carbon isotopes and different Raman laser energies and extensive averaging without increasing the laser power. This allowed us to obtain a detailed experimental phonon dispersion relation for many points in the Brillouin zone. We further identified a D+D' peak corresponding to a double phonon process involving both an inter- and intra-valley phonon.