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

摘要

We present an analysis of deep-UV Raman measurements of graphite, grapheneand carbon nanotubes. For excitation energies above the strong opticalabsorption peak at the $M$ point in the Brillouin zone ($\approx4.7\,\text{eV}$), we partially suppress double-resonant scattering processesand observe the two-phonon density of states of carbon nanomaterials. Themeasured peaks are assigned to contributions from LO, TO, and LA phononbranches, supported by calculations of the phonon dispersion. Moreover, we gainaccess to the infrared-active $E_{1u}$ mode in graphite. By lowering theexcitation energy and thus allowing double-resonant scattering processes, wedemonstrate the rise of the \textit{2D} mode in graphite with ultra-shortphonon wave vectors.