Reliably Counting Atomic Planes of Few-Layer Graphene (n > 4)

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 us:dill in the, range n > 4 where few methods exist. We compare out results with atomic force microscopy (AFM) measurements and Fresnel equation calculations. Then, we apply out method to unambiguously identify n of FLG devices on SiO2 and find that the mobility (mu approximate to 2000 cm(2) V-1 s(-1)) is independent of layer thickness for n > 4. Our findings suggest that electrical transport in gated FLG devices is dominated by carriers near the FLG/SiO2 interface and is thus limited by the environment even for n > 4.