Monovacancy in achiral and chiral graphene nanoribbons

We have investigated the monovacancy in achiral and chiral graphene nanoribbons. Using density functional theory, we calculated the structure, total energy, and electronic structure for a series of vacancy positions from the center to an edge. The interplay between the energy gain by the self-healing and the strain energy determines the physical properties. There is an optimal reconstruction scheme for each ribbon. A mobile defect should progress towards an edge and be eliminated through the migration at the expense of rougher edge morphologies. The energy gain by the monovacancy migration is in the range of 4−5 eV per defect. Creating vacancies, not necessarily at the edge, can be utilized to engineer the edge morphology. The strength of the spin polarization correlates with the length of the sequential zigzag edge segments. The monovacancy gets involved in the spin polarization and acquires up to 1μB spin polarization. The p-orbital originated defect state mixes with the edge-related states and forms a flat defect band at the Fermi level. The defect is the main spin polarization source in ribbons with no or short zigzag edge segments. The monovacancy near an edge alters the magnetic and electronic properties of the ribbon.