Ultraviolet Raman spectroscopy of graphene and transition-metal dichalcogenides

Abstract

Here, we overview Raman spectroscopy of graphene and transition-metal dichalcogenides as a function of laser excitation energy , especially in the ultraviolet (UV) region. The double resonance G (or 2D) band of graphene is calculated for the laser energy range up to 7 eV. The intensity of the G band is proportional to for eV. We also discuss electronic Raman spectra and the asymmetric Breit–Wigner–Fano lineshape of the G band in graphene for UV light. Finally, transition-metal dichalcogenide materials show a strong optical absorption of the UV light at the M point at which we expect a two-dimensional van Hove singularity of density of states. The double-resonance Raman spectra for the UV light can be assigned to a combination or overtone phonons at the M point. Equi-energy contour of initial (blue line) and intermediate (red line) states in a double-resonance Raman process for (a) eV and (b) eV. In the case of eV, the blue and red lines are almost overlapped on each other. Gray-shaded areas are possible phonon wave vectors for the double-resonant Raman process that are measured from the center of the Brillouin zone.