Localization of metallicity and magnetic properties of graphene and of graphene nanoribbons doped with boron clusters

Abstract

As a possible way of modifying the intrinsic properties of graphene, we study the doping of graphene by embedded boron clusters with density functional theory. Cluster doping is technologically relevant as the cluster implantation technique can be readily applied to graphene. We find that B clusters embedded into graphene and graphene nanoribbons are structurally stable and locally metallize the system. This is done both by the reduction of the Fermi energy and by the introduction of boron states near the Fermi level. A linear chain of boron clusters forms a metallic “wire” inside the graphene matrix. In a zigzag edge graphene nanoribbon, the cluster-related states tend to hybridize with the edge and bulk states. The magnetism in boron-doped graphene systems is generally very weak. The presence of boron clusters weakens the edge magnetism in zigzag edge graphene nanoribbon, rather than making the system appropriate for spintronics. Thus, the doping of graphene with the cluster implantation technique might be a viable technique to locally metallize graphene without destroying its attractive bulk properties.

Keywords:

• graphene
• graphene nanoribbons
• metallization
• boron cluster
• ion implantation
• localized states
• edge magnetism
• density functional theory

Acknowledgments

J.K. acknowledges financial support from the DFG [project KU 2347/2-2]. The computations were partly performed at the computation facility of Çankaya University, at the ULAKBİM High Performance Computing Center at the Scientific and Technological Research Council of Turkey and at The Center for Information Services and High Performance Computing (ZIH) of the TU Dresden. A.Q. acknowledges financial support by the National Research Foundation (NRF) [Grant specific unique reference number (UID) 85972] and the Department of Science and Technology (DST) of South Africa, as well as by the Gauteng node of the National Institute of Theoretical Physics (NITheP). This work is partly supported by the German Research Foundation (DFG) within the Cluster of Excellence “Center for Advancing Electronics Dresden.”

Notes

1 The optimized lattice parameters of the corresponding unit cells in their (magnetic) ground states are given as follows: graphene: A = 2.460, B = 2.459, C = 10 Å, graphene supercell: A = 21.972, B = 8.458, C = 10 Å, graphene+isolated-BD supercell: A = 22.140, B = 17.043, C = 10 Å, graphene+BD supercell: A = 22.140, B = 8.522, C = 10 Å, For all AGNRs A = 4347 Å, C = 10 Å, 9-AGNR, 9-AGNR+H: B = 8.509 Å, 9-AGNR+BD, 9-AGNR+BD+H: B = 8.522 Å, For all ZGNRs B = 3537 Å, C = 10 Å, 10-ZGNR: A = 7.416 Å, 10-ZGNR+H: A = 7.383 Å, 10-ZGNR+BD, 10-ZGNR+BD+H: A = 7.511 Å,

2 Optimized k-point meshes for the different systems at their (magnetic) ground states are; graphene: 10 x 10 x 3, graphene supercell: 3 x 3 x 3, graphene+isolated-BD supercell: 3 x 3 x 3, graphene + BD supercell: 3 x 5 x 2, 9-AGNR: 2 x 5 x 3, 9-AGNR + H: 3 x 3 x 3, 9-AGNR + BD: 2 x 5 x 3, 9-AGNR + BD + H: 3 x 3 x 3, 10-ZGNR: 4 x 3 x 3, 10-ZGNR + H: 3 x 2 x 3, 10-ZGNR + BD: 3 x 3 x 3, 10-ZGNR + BD + H: 5 x 2 x 3.

3 The centre-to-centre separation of the clusters for the different systems in x-,y-directions are; graphene + isolated-BD supercell: 22.14 Å, 17.04 Å, graphene + BD supercell: 22.14 Å, 8.52 Å, 9-AGNR+BD+H: 8.52 Å  in y-direction, 10-ZGNR+BD+H: 7.38 Å  in x-direction.