Transformation of diamond (sp3) to graphite (sp2) bonds by ion-impact

The formation of point defects in diamond induced by an energetic displacement of a carbon atom out of its lattice site and the relaxation of the thereby disrupted crystal are studied by molecular dynamics simulations with the Tersoff potential. The displacement energy for Frenkel pair creation is calculated to be 52 eV, in agreement with experiments. It is found that the (100) split interstitial, with a bonding configuration which resembles graphite, is the most stable defect, and the disrupted region around it is rich in sp(2)-like (graphitic) bonds. This region extends several nanometers and is likely to be the elementary electrically conductive cell experimentally found in radiation-damaged diamond.