Investigation of the 'double cross' splitting mechanism of single-crystal diamond under nanoindentation via molecular dynamics simulation.

Elucidating the mechanical response of diamond is a difficult task due to its ultrahard nature. Here, we applied a molecular dynamics (MD) method to investigate the mechanical response of single-crystal diamond under nanoindentation. There was no obvious "pop in" phenomenon on the load-depth curve, and the elastic modulus deduced from the curve was 1128 GPa, which was similar to the value obtained from experimental measurements. Results from computed tomography (CT) and the coordination number showed that the distribution of the mismatched C atoms around the deformation zone took the form of a 'double cross.' The atoms around the indenter tip could be divided into two zones, a translation zone and a lattice distortion zone, based on their movements. Subsequent first-principles calculations revealed that the C-atom displacement barrier varied significantly with direction, which resulted in shear stress between the two zones and the formation of the double-cross splitting. Graphical Abstract The displacement of the atoms around the indenter tip.