An effect of the extended cascade on the Raman spectra of ion-irradiated graphite

Raman spectra of graphite were measured under Ne+, Kr+ and Xe+ ions irradiation at ion flux of 1.7X10(15) ions/m(2) at room temperature. The peak intensity ratio of the disorder-induced peak with respect to the Raman active E-2g2, mode peak of the first order Raman spectrum is proportional to the square root of the ion irradiation time in the beginning of the irradiation. However, the ratio saturated around 150 s for each ion irradiation. The saturation was explained by creation of vacancy cluster due to the overlap of the irradiation-induced cascades for the direction parallel to the surface. (C) 2000 Elsevier Science Ltd. All rights reserved.