  We investigated Raman spectra of single-layer and multi-layer graphene under
ultraviolet laser excitation at the wavelength of 325 nm. It was found that
while the G peak of graphene remains pronounced in UV Raman spectra, the 2D
band intensity undergoes severe quenching. The evolution of the ratio of the
intensities of the G and 2D peaks, I(G)/I(2D), as the number of graphene layers
n changes from n=1 to n=5, is different in UV Raman spectra from that in
conventional visible Raman spectra excited at the 488 nm and 633 nm
wavelengths. The 2D band under UV excitation shifts to larger wave numbers and
is found near 2825 1/cm. The observed UV Raman features of graphene were
explained by invoking the resonant scattering model. The obtained results
contribute to the Raman nanometrology of graphene by providing an additional
metric for determining the number of graphene layers and assessing its quality.
