Extended Interplanar Linking in Graphite Formed from Vacancy Aggregates

The mechanical and electrical properties of graphite and related materials such as multilayer graphene depend strongly on the presence of defects in the lattice structure, particularly those which create links between adjacent planes. We present findings which suggest the existence of a new type of defect in the graphite or graphene structure which connects adjacent planes through continuous hexagonal $s{p}^2$ bonding alone and can form through the aggregation of individual vacancy defects. The energetics and kinetics of the formation of this type of defect are investigated with atomistic density functional theory calculations. The resultant structures are then employed to simulate high resolution transmission electron microscopy images, which are compared to recent experimental images of electron irradiation damaged graphite.

Figure 1

(a) Schematic of the $V_2^2\beta \beta$ interlayer divacancy, where the red square highlights the two under coordinated atoms that form the interlayer bond. (b) Two $V_5$ lines forming three interlayer bonds. (c) Extending $V_2^2\beta \beta$ in the armchair direction, with two $V_4$ lines forming four interlayer bonds.

Figure 2

(a) Topology of the extended defect and (b) dislocation loop representation (arrows indicate the Burgers vectors of the loop; the dark arrows are screw dislocation vectors, and the light are edge dislocation vectors).

Figure 3

(a) Optimized structure of the bonded $2\times V_3$ zigzag defect. (b) Optimized structure of the bonded $2\times V_5$ zigzag defect. (c) Optimized structure of the bonded $2\times V_3$ armchair defect.

Figure 4

(a) Simulated HRTEM image of a $V_7\mathrm{\text{−}}{V}_7$ interlayer defect viewing parallel to the line of the defect. (b) Experimental HRTEM image of irradiated graphite, reprinted with permission from C. Karthik et al., J. Nucl. Mater. 412, 321 (2011). Copyright 2011, Elsevier.