Kinetics of the conversion of broken diamond(sp3)bonds to graphitic(sp2)bonds

The thermally driven structural modification of diamond damaged by low-temperature Xe ion implantation are studied by following the changes in its electrical resistivity as function of annealing temperature and time while it gradually converts to graphite. The conduction mechanism in damaged and in partially graphitized diamond is well described by the variable-range-hopping mechanism, allowing the extraction of a number of hopping sites at different stages of annealing from the temperature dependence of the resistivity. It is found that conversion of broken, metastable diamond bonds to graphitic bonds sets in already at an annealing temperature of 420 K with an activation energy of about 0.7 eV, thus giving an estimate of the height of the barrier which separates broken ${\mathrm{sp}}^3$ bonds from graphitic bonds.