Healing of a Topological Scar: Coordination Defects in a Honeycomb Lattice

A crystal structure with a point defect typically returns to its ideal local structure upon moving a few bond lengths away from the defect; topological defects such as dislocations or disclinations also heal rapidly in this regard. Here we describe a simple point defect – a two-fold atom incorporated at the growth edge of a 2D hexagonal honeycomb material – whose healing may require a defect complex with 50 or more atoms. $\mathit{\text{Topologically}}$ the two-fold atom disappears into a single ‘long bond’ between its neighbors, thereby inducing a pentagonal disclination. However, $\mathit{\text{chemically}}$ this disclination occupies as much physical space as a six-fold ring. This incompatibility of chemistry and topology can cause a ‘‘ringing’’ of the Gaussian curvature that creates an expansive healing region and may even spawn a semi-infinite grain boundary propagating outwards from the topological scar.