▎ 摘　　要

The unique density of states of graphene at the device level is probed via tunneling spectroscopy of macroscopic metal-oxide-graphene structures. Local conductance minima from electrons tunneling into the graphene Dirac point are observed in the dI/dV spectra of both the single-junction and dual-junction configurations. Nonequally-spaced Landau levels, including the hallmark n=0 level, are observed in the presence of a magnetic field. Linear energy-momentum dispersion near the Dirac point, as well as the Fermi velocity, is extracted from both experiments. Local potential fluctuations and interface defects significantly influence these fine physical features, leading to peak broadening and anomalies comparing to the results from the ultra sharp scanning tunneling microscope tip. This study provides important implications for potential tunneling-based graphene devices in the future. (C) 2010 American Institute of Physics. [doi:10.1063/1.3460283]