Scanning tunneling spectroscopy studies of angle-dependent van Hove singularities on twisted graphite surface layer

Slightly misoriented surface graphene layer on highly ordered pyrolytic graphite (HOPG) can result in Moire patterns (MP). Two van Hove singularity (VHS) peaks in the density of states are observed with scanning tunneling spectroscopy on a series of the MPs with different periods on HOPG surface, flanking the Fermi energy. The energy difference between the two VHS peaks (Delta E-VHS) is linearly proportional to the sine of interlayer rotation angle. A similar relation between Delta E-VHS and MP periods has recently been reported on twisted graphene layers. Compared to the case of twisted graphene layers, the Fermi velocity of MPs on a HOPG surface is found to be larger, and the interlayer hopping is enhanced. (C) 2013 AIP Publishing LLC.