ESR of pyro-graphite irradiated by ions—I. Low energy ion bombardments

Abstract

Paramagnetic centers in pyrolytic graphite irradiated with low energy ions were studied by ESR. Above nitrogen temperature, only one sharp line was observed in spite of inhomogeneous distribution of defects caused by the irradiation. The g-value and width of the line from the irradiated part decreased monotonously with an increase in the fluence. By annealing, no change was observed in the g-value and little change in width. With decreasing measuring temperature, the g-value remained unchanged, but the width showed a trend to decrease at low temperatures. The temperature dependence of the intensity of the line followed nearly the Curie law, especially for low fluences. At temperatures below 15 K, the line split into two for low fluences. Localized spin centers were assigned to these lines. The correlation between localized spin centers and the pockets of disorder produced by the irradiation was discussed. The extent of the wave function of spin centers was presumed to be influenced by the disorder of the surroundings. The distribution rather than the concentration of defects was found to play an important role in the localization of spins.