Bound and free self-interstitial defects in graphite and bilayer graphene: A computational study

The role of self-interstitials in the response of layered carbon materials such as graphite, bilayer graphene and multiwalled carbon nanotubes to irradiation has long remained a puzzle. Using density-functional-theory methods with an exchange and correlation functional which takes into account the interlayer van der Waals interaction in these systems without any material-specific empirical parameters, we study the energetics and migration of single- and di-interstitials in graphite and bilayer graphene. We show that two classes of interstitials, “bound” and “free,” can coexist. The latter are mobile at room and lower temperatures, which explains the experimental data and reconciles them with the results of atomistic simulations. Our results shed light on the behavior of graphite and carbon nanotubes under irradiation and have implications for irradiation-mediated processing of bilayer graphene.

Figure 1

Atomic structures of self-interstitials in graphite. (a) Top view and (b) side view. The labels S, G, and D correspond to the spiro, grafted, and dumbbell configurations, respectively. White circles highlight the interstitials. Blue (dark-gray) and red (gray) circles represent atoms in different layers. (c) The potential energy surface representing the energetics of the configurations and potential barriers (in eV) between them.

Figure 2

Atomic configurations of di-interstitials and energetics of their transformations. (a) Top view and (b) side view. The labels C, TT, BB, FD, and ISTW correspond to the crane, twin-triangle, bent-bridge, free-dimer, and inverse Stone-Thrower-Wales di-interstitials, respectively. White circles highlight the interstitial atoms. Blue (dark-gray) and red (gray) circles represent atoms in different layers. (c) The potential energy surface representing the energetics of the configurations and potential barriers (in eV) between them.