Prediction and Characterization of Graphitic Structures at Diamond Grain Boundaries

and sp3-hybridized bonds have been drawing increasing attention because of their potential for applications in electronic devices. In this work we investigate the formation of sp2-bonded domains included different low-energy diamond grain boundaries with 21 distinct surface orientations. To this end, we rely on an efficient constrained global-structure prediction algorithm, using energy and forces from density-functional theory and density-functional tight-binding, to identify low-energy interface reconstructions at grain boundaries. Our extensive simulations show that graphitic networks always stem from flattening and reconstruction of corrugated hexagonal layers with (111) orientation. The most stable sp2 insertions are found between parallel diamond surfaces. When these surfaces contain a (110) axis, we distinguish two classes of recurring reconstructions, while only one type is observed for diamond surfaces containing a (100) axis. We also study mixed sp2- and sp3-bonds as insertions at tilt grain boundaries, where bond distortion and bending of the graphitic planes, constrained by the grain geometry, have destabilizing effects. Finally, we study the electronic properties of these structures. While graphene adsorbed on diamond has usually a finite band gap, mixed diamond-graphene phases are mostly metallic, with localized states at the edges of the graphene-like stripes.

Automated summary

This work investigates the formation of sp2-bonded domains at different low-energy diamond grain boundaries and identifies the low-energy interface reconstructions using a constrained global-structure prediction algorithm. The simulations show that graphitic networks arise from the flattening and reconstruction of corrugated hexagonal layers with (111) orientation, and the most stable sp2 insertions occur between parallel diamond surfaces. The study also reveals the destabilizing effects of bond distortion and bending of graphitic planes at tilt grain boundaries. The electronic properties of these structures are also studied.