  The pi bands of epitaxially grown graphene are studied by using high
resolution angle resolved photoemission spectroscopy. Clear deviations from the
conical dispersion expected for massless Dirac fermions and an anomalous
increase of the scattering rate are observed in the vicinity of the Dirac point
energy. Possible explanations for such anomalies are discussed in terms of
many-body interactions and the opening of a gap. We present detailed
experimental evidences in support of the gap scenario. This finding reveals a
fundamental intrinsic property of epitaxial graphene and demonstrates the
possibility of engineering the band gap in epitaxial graphene.
