  An efficient route to synthesize macroscopic amounts of graphene is highly
desired and a bulk characterization of such samples, in terms of the number of
layers, is equally important. We present a Raman spectroscopy-based method to
determine the distribution of the number of graphene layers in chemically
exfoliated graphene. We utilize a controlled vapor-phase potassium
intercalation technique and identify a lightly doped stage, where the Raman
modes of undoped and doped few-layer graphene flakes coexist. The spectra can
be unambiguously distinguished from alkali doped graphite, and a modeling with
the distribution of the layers yields an upper limit of flake thickness of five
layers with a significant single-layer graphene content. Complementary
statistical AFM measurements on individual few-layer graphene flakes find a
consistent distribution of the layer numbers.
