  Dependency of energy bandgap (Eg) of bilayer armchair graphene nanoribbons
(AGNRB) on their widths, interlayer distance (D) and edge doping concentration
of boron/nitrogen is investigated using local density approximation and compare
to the results of monolayer graphene nanoribbons (AGNRM). Although Eg of AGNRB,
in general, is smaller than that of AGNRM, AGNRB exhibits two distinct groups,
metal and semiconductor, while AGNRM displays purely semiconducting behavior.
Eg of AGNRB, moreover, is highly sensitive to D, indicating a possible
application in tuning Eg by varying D. Finally, edge doping of both AGNR
systems reduces Eg by 11-17%/4-10% for AGNRM/AGNRB, respectively.
