Vibrational properties of graphene nanoribbons by first-principles calculations

TL;DR

This study uses first-principles density functional theory to analyze the vibrational properties of graphene nanoribbons, revealing how phonon modes depend on edge type and width, and relating nanoribbon phonons to graphene's dispersion.

Contribution

It provides a detailed first-principles analysis of phonon modes in graphene nanoribbons, including the effects of edge type, width, and spin states, and introduces a mapping to graphene's phonon dispersion.

Findings

Phonon modes are fundamental oscillations and overtones with width-dependent characteristics.

Gamma-point phonon frequencies can be mapped onto graphene's phonon dispersion, resembling an unfolding process.

Spin states influence the phonon spectra of zigzag nanoribbons.

Abstract

We investigated the vibrational properties of graphene nanoribbons by means of first-principles calculations on the basis of density functional theory. We confirm that the phonon modes of graphene nanoribbons with armchair and zigzag type edges can be interpreted as fundamental oscillations and their overtones. These show a characteristic dependence on the nanoribbon width. Furthermore, we demonstrate that a mapping of the calculated Gamma-point phonon frequencies of nanoribbons onto the phonon dispersion of graphene corresponds to an "unfolding" of nanoribbons' Brillouin zone onto that of graphene. We consider the influence of spin states with respect to the phonon spectra of zigzag nanoribbons and provide comparisons of our results with past studies.