Defects in Carbon Allotropes Studied by Positron Annihilation

Slow positron beam technique has been employed to study the defects of graphite, nanophase C, as well as the structural changes in un-doped, B-doped and S-doped diamond films with annealing temperatures. The results show that the concentration of defects in nanophase C is higher than that in graphite. The vacancy concentration in the S-doped diamond film is higher than that in un-doped one. The addition of small amount of B atoms leads to the decrease of the vacancy concentration in the film. The vacancy concentration in un-doped diamond film would decrease after annealing at temperature below 600°C, while vacancy concentration will increase after annealing at temperatures above 900°C. The vacancy concentration in the 40 Ω cm B-doped diamond film decreases at annealing temperatures higher than 200°C.