Investigating arrangements of doping B atoms affecting electrical structures of graphene nanoribbons from DFTB simulations

Abstract

Self-consistent charge-density functional tight binding simulations are performed to study the effects of different doping positions for B atoms on electrical structures in armchair graphene nanoribbons passivated with H atoms at ribbon edges. Fourteen different doping modes of the two B atoms in the ribbon matrix are demonstrated. The variations of the structural, thermal stability and electrical structures of the fourteen modes are elucidated. The band gap of the B atoms doped in armchair graphene nanoribbons (B-AGNRs) decreases significantly. In the meanwhile, with doping the B atoms at different positions, the B-AGNRs present metallicity or semi-conductivity. Band structures and density of states are also affected by the arrangements of these doping atoms. The molecular orbitals on HOMO and LUMO energy levels show that the B atoms and their surrounding C atoms forms the Π bond, and the size and directivity of the Π bond change corresponding to different doping positions of the B atoms. Accompany with the formation of covalent bonds between the B and C atoms, Mulliken populations on the B atoms change significantly when they are located at the edge and the bulk positions of the B-AGNRs. These findings on electrical level provide us understanding in adjusting the electronic states of the graphene nanoribbons through doping to meet various requirements for electronic devices based on those nanoribbons.