  Based on first-principles calculations we predict that periodically repeated
junctions of armchair graphene nanoribbons of different widths form
superlattice structures. In these superlattice heterostructures the width and
the energy gap are modulated in real space and specific states are confined in
certain segments. Orientation of constituent nanoribbons, their width and
length, the symmetry of the junction are the structural parameters to engineer
electronic properties of these quantum structures. Not only the size
modulation, but also composition modulation, such as periodically repeated,
commensurate heterojunctions of BN and graphene honeycomb nanoribbons result in
a multiple quantum well structure. We showed that these graphene based quantum
structures can introduce novel concepts to design nanodevices.
