Probing the experimental phonon dispersion of graphene using12C and13C isotopes

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 intravalley phonon.

Probing carbon isotope effects on the Raman spectra of graphene with differentC13concentrations

“…The focus of this work is to understand the effect of isotopic substitution on the position and linewidth of the main Raman features (D, G, G * , and 2D bands). The analysis of the 2D Raman peak as a function of the 13 C concentration and laser energy allowed us to conclude that the slopes of the electronic and phonon dispersions near the K point are not affected by the isotope enrichment of the graphene samples. Finally, we present results of the phonon mean free path as a function of the isotopic ratio.…”

“…Other authors have suggested that the G band resonance is closely related to the optically allowed electronic transition in twisted bilayer graphene [18,19]. Bernard et al [13] identified several weak Raman peaks in isotope-enriched graphene, ascribed to the double-resonance Raman process, and obtained phonon dispersion for these mixed isotopic materials [13].…”

“…For instance, Miyauchi et al [10] used pure 12 C and 13 C SWNTs and assigned phonon-assisted peaks in the photoluminescence spectra of nanotubes. In the case of SWCNTs, a redshift of the G band when the 13 C concentration is increased * brunorc@fisica.ufmg.br † fantini@fisica.ufmg.br has been reported [10], and a dependence of the G band linewidth on the isotope concentration was observed [14]. Studies of bilayer graphene, where one layer is composed of 12 C atoms and the other of 13 C atoms, were performed, thus allowing the investigation of interlayer interactions in the Raman scattering process [11,15].…”

“…In the case of SWCNTs, a redshift of the G band when the 13 C concentration is increased * brunorc@fisica.ufmg.br † fantini@fisica.ufmg.br has been reported [10], and a dependence of the G band linewidth on the isotope concentration was observed [14]. Studies of bilayer graphene, where one layer is composed of 12 C atoms and the other of 13 C atoms, were performed, thus allowing the investigation of interlayer interactions in the Raman scattering process [11,15]. It was also observed in twisted bilayer graphene that the G band intensity is enhanced in regions of the sample where the separation in energy of the van Hove singularities in the density of states, which are induced by the twisted electronic band structure, match the laser excitation energy [15].…”

“…Significant efforts have been devoted to produce and study isotope-enriched graphene-related materials [4][5][6][7][8][9][10][11][12][13]. For instance, isotope labeling provided direct evidence that the growth mechanism of graphene is substrate dependent and, furthermore, shed light on the rational design of chemical vapor deposition (CVD) synthesis methods [4][5][6][7][8].…”