Damage accumulation in diamond during ion implantation

Single-crystalline diamond plates were implanted by He+ ions with a set of energies and fluences that ensure uniform radiation damage (RD) in a 670-nm-thick layer. Implantation is carried out at a wide range of fluences, which allows one to cover the range of RD levels from very low to complete graphitization of diamond. Using the measurement data on the bending of diamond plates and the surface swelling of the ion-implanted material, we calculate the mechanical stress and the density of diamond for various levels of RD. Diamonds with various levels of RD are investigated by the Raman scattering and optical transmission methods. We establish that, above the graphitization threshold, the diamond phase almost completely disappears as the RD level increases, while the fraction of sp(2) material sharply increases. Such a material is unexpectedly ductile. It cannot be restored to diamond even by annealing under a pressure corresponding to thermodynamic stability of diamond.