Graphene, a monolayer of a honeycomb lattice of carbon atoms has been attracted a great amount of attention from both experimental and theoretical points of view Novoselov et al. (2006). Flat structure of graphene makes its fabrication more straightforward than carbon nanotubes. Moreover, dreams of carbon nanoelectronic approach to the reality based on planar graphene structures. This structure overcomes some difficulties of nanoelectronics based on carbon nanotubes, by using lithography, one-dimensional ribbon patterns on graphene sheets Liu et al. (2009). Experiments in graphene-based devices Ozyilmaz et al. (2007) have shown the possibility of controlling their electrical properties by the application of an external gate voltage. For achieving realistic nanoelectronic applications based on graphene nanoribbons (GNR), width of ribbon have to be narrow enough that a transport gap is opened Han el al. (2007); Li et al. (2008); Wang et al. (2008). Using a chemical process, sub-10 nm GNR field-effect-transistors with very smooth edges have been obtained in Ref.[ Li et al. (2008); Wang et al. (2008)] and demonstrated to be semiconductors with band-gap inverselyproportionaltothewidthandon/offratioofcurrentupto106 atroomtemperature. By connecting GNRs with different types of edges and widths, it is applicable to fabricate electronic devices based on graphene nanoribbons.