Synopsis: Graphene Doesn’t Mind a Pair of Defects

Scanning tunneling microscopy and spectroscopy experiments show how missing carbon atoms affect graphene’s electronic and magnetic properties.
Synopsis figure
M. M. Ugeda et al., Phys. Rev. B (2012)

With its one-atom-thick, stable lattice structure and high electronic mobility, graphene is anticipated as a possible replacement material for silicon in conventional semiconductor electronics. Tinkering with graphene’s pristine surface, either by introducing foreign molecules or creating defects, is a promising way to control graphene’s properties and functionality. For example, defects can be introduced by knocking out carbon atoms with ion irradiation.

Now, writing in a Rapid Communication in Physical Review B, Miguel M. Ugeda at the Autonomous University of Madrid, Spain, and collaborators report the impact of a common type of defect—a double vacancy, where two neighboring carbon atoms are missing—on graphene’s electronic structure and properties. Based on scanning tunneling microscopy and spectroscopy experiments, as well as ab initio calculations, they infer that the structure surrounding double vacancies is a planar structure with no dangling bonds, and is thus less chemically active than other types of vacancy defects.

On the other hand, the presence of double vacancies does, according to the authors, strongly modify graphene’s electronic structure, creating new electronic states. As a consequence, double vacancies are expected to limit the electron mobility of graphene by acting as traps for charge carriers around the defects. Ugeda et al.’s calculations also show that double vacancies aren’t magnetic like single vacancies, so they do not contribute to the magnetism that has been observed in irradiated graphene systems. – Hari Dahal


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