RECONSTRUCTION AND PHYSICAL PROPERTIES OF MONOVANCACIES IN GRAPHENE NANORIBBONS

Year 2016, Volume: 12 Issue: 2, 4 - 4, 01.08.2016

Mehmet Ali Baykal Savaş Berber

Abstract

We have investigated the reconstruction, electronic and magnetic properties of
graphene nanoribbons using density functional theory structure optimization and electronic
structure calculations. In order to obtain proper edge states and their spin polarizations, we
generate wide enough edge hydrogenated graphene nanoribbons that have not only mostly
considered armchair and zigzag geometries both also other chiralities. First, the reconstruction of
monovacancies in graphene nanoribbons are investigated by directed structure optimizations to
obtain all possible reconstruction geometries that differ by the orientation of the new bonds that
are formed during the self-healing of the defect. We find that the reconstruction requires large
structural changes to accommodate the strain of the self-healing, and the straight forward
structure optimizations that start from an ideal vacancy often fails to find possible reconstructed
atomic structures. The reconstruction energies are closely related to the orientation of the new
bond and thus to the chirality of the nanoribbon. Since the reconstruction still leaves an
unsaturated bond, there is a spin polarization at the vacancy site. The magnetic ordering of this
localized spin with the spins at the edges is searched by constraining initial spins in our selfconsistent
calculations. The total energy of the ferromagnetically and antiferromagnetically
coupled edges and the vacancy is compared to obtain energetically most stable magnetic
structure for each chirality and the vacancy orientation. We find that the magnetic ordering to
depend on the chirality and the nanoribbons prefer to have antiferromagnetic coupling between
the spin polarized regions.

Keywords

Graphene Nanoribbons, Defects, Density Functional Theory, Nanomagnetism