Atomic scale investigations of the electronic properties of graphene are playing a crucial role in understanding and tuning the exotic properties of this material for its potential device applications. Scanning tunneling microscopy (STM) and spectroscopy (STS) are unique techniques for atomic scale investigations and have been extensively used in graphene research. In this article, we review recent progresses in STM and STS studies of the electronic properties of suspended graphene as well as graphene supported by different substrates including graphite, metals, silicon carbide, silicon dioxide and boron nitride.
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