We report scanning tunneling microscopy and spectroscopy investigation of graphene nanoribbons grown on an array of bunched steps of a 6H-SiC(0001) substrate. Our scanning tunneling microscopy images of a graphene nanoribbons on a step terrace feature a (sqrt(3)x sqrt(3))R30 pattern of aromatic rings which define our armchair nanoribbons. This is in agreement to a simulation based on density functional theory. As another signature of the one-dimensional electronic structure, in the

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... scanning tunneling spectroscopy spectra we find well developed, sharp Van Hove singularities.