Beyond double-resonant Raman scattering: UV Raman spectroscopy on graphene, graphite and carbon nanotubes

TL;DR

This study uses deep-UV Raman spectroscopy to analyze phonon modes in graphene, graphite, and carbon nanotubes, revealing insights into double-resonant processes and phonon density of states at various excitation energies.

Contribution

It provides new experimental data on phonon contributions and the infrared-active mode in graphite using UV Raman spectroscopy, expanding understanding beyond double-resonant scattering.

Findings

Suppression of double-resonant scattering above 4.7 eV excitation energy.

Identification of phonon contributions from LO, TO, and LA branches.

Observation of the 2D mode rise at lower excitation energies.

Abstract

We present an analysis of deep-UV Raman measurements of graphite, graphene and carbon nanotubes. For excitation energies above the strong optical absorption peak at the $M$ point in the Brillouin zone ($\approx 4.7\,\text{eV}$), we partially suppress double-resonant scattering processes and observe the two-phonon density of states of carbon nanomaterials. The measured peaks are assigned to contributions from LO, TO, and LA phonon branches, supported by calculations of the phonon dispersion. Moreover, we gain access to the infrared-active $E_{1u}$ mode in graphite. By lowering the excitation energy and thus allowing double-resonant scattering processes, we demonstrate the rise of the \textit{2D} mode in graphite with ultra-short phonon wave vectors.