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Apparent corrugation variations in moiré patterns of dislocated graphene on Highly Oriented Pyrolytic Graphite and the origin of the van Hove singularities of the moiré system

Moiré patterns on Highly Oriented Pyrolytic Graphite surfaces due to dislocated graphene layers were studied. We observed that the apparent corrugations of the moiré patterns in scanning tunnelling microscopy images change as a function of tunnel junction bias. A simple geometric investigation of the atomic structure of the graphene layers generating moiré patterns revealed that different atomic arrangements due to different twist angles can result in similar geometric moiré periods such that, only a small fraction of the observed moiré periodicities may coincide with the real atomic periodicity generating the moiré system. Ab initio calculations showed that the band structure of moiré patterns exhibit the fingerprints of those of bilayer graphene system preserving the Dirac cone. Moreover, our calculations in view of the correct atomistic modelling of the moiré patterns showed that van Hove singularities in twisted bilayer graphene system with varying angles have different origins in their respective band structures. Consequently, our results shed light on the graphene like behaviour of the top most dislocated graphene layer on HOPG surfaces by showing that the layer does not act alone but the final graphene bilayer has electronic properties partially resembling graphene.