How is the stacking interaction of bilayer graphene affected by the presence of defects?

Abstract

The presence of Stone–Wales, single and double vacancy defect sites in bilayer graphene was studied by means of dispersion corrected density functional theory. Based on the analysis of the formation energies computed for monolayer and bilayer graphene, monovacancies are expected to be equally frequent in both materials. In the case of the single vacancy, the formation energy is barely affected by the second layer and so does the interlayer interaction energy. However, Stone–Wales and double vacancies may be expected to be more frequent in single layer graphene because their formation energies are expected to be lower as compared to bilayer graphene. Calculations employing very large unit cells would be interesting to reduce the effect of the incommensurability of the unit cells of perfect and defective graphene, and thus confirm the latter statement. The single and double vacancies have the similar formation energy in bilayer graphene but for monolayer graphene, the 5-8-5 divacancy is more stable by at least 0.7eV, in contrast with recent results. The electronic properties of defective bilayer graphene are similar to those corresponding to monolayer graphene. Finally, we have shown that the magnetic moment of monolayer graphene with a monovacancy is smaller than that of bilayer graphene bearing the same defect, when the unit cell is optimized. Yet, if the unit cells are fixed, different outcomes can be obtained. If the unit cell of perfect graphene is employed the magnetic moment of bilayer graphene with a single vacancy is larger, but if the unit cell of monolayer graphene with a single vacancy is to be employed the magnetic moment of defective bilayer graphene becomes smaller than that of monolayer graphene with a monovacancy.