  We demonstrate a reliable technique for counting atomic planes (n) of
few-layer graphene (FLG) on SiO2/Si substrates by Raman spectroscopy. Our
approach is based on measuring the ratio of the integrated intensity of the G
graphene peak and the optical phonon peak of Si, I(G)/I(Si), and is
particularly useful in the range n>4 where few methods exist. We compare our
results with atomic force microscopy (AFM) measurements and Fresnel equation
calculations. Lastly, we apply our method to unambiguously identify n of FLG
devices and find that the mobility (~2000 cm2 V-1 s-1) is independent of layer
thickness for n>4.
