Self-healing monovacancy in low-buckled silicene studied by first-principles calculations

Abstract

A new type of monovacancy (MV), MV-1, with a planelike $s{p}^{3}$ hybridization at its defect core has been found in two-dimensional (2D) low-buckled silicene by using the first-principles study, which has never been found to exist stably in the 2D single-layer nanostructures, including other previously studied graphene, $h$-BN sheets, and single-layer ${\mathrm{MoS}}_{2}$. In addition, other two possible monovacancies (MV-2 and MV-3) with higher energies have also been found to exist in 2D low-buckled silicene. More importantly, it is found that the new type MV-1 is the most stable ground structure among the three possible MVs. And the high-energy MV-3 is unstable, easily decaying into MV-1, but metastable MV-2 could coexist with MV-1 at low temperatures less than 10 K. The diffusion coefficient of MV-1 is calculated to be $2.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}\phantom{\rule{0.28em}{0ex}}{\mathrm{cm}}^{2}/\mathrm{s}$, much higher than that of the MV in graphene. Finally, electronic structures of the defective silicene with MV-1 and MV-2 are calculated, showing both of them are metallic.