Effects of ion implantation on electron centers in hydrogenated amorphous carbon films

Electron spin resonance (ESR) and Raman spectra measurements are carried out on a-C:H and a-C:H:N films both as grown and implanted with W and Ni ions with doses ranged from 0.5×1015 to 1.2×1016 cm2. The as-grown films have small concentration of paramagnetic centers with a spin density Ns of 1017 cm3. Upon implantation a significant increase in Ns of (0.522)×1019 cm3 centers with g(Si) = 2.0055 and g(C) = 2.0025 was observed. These defects are ascribed to dangling bonds in the silicon substrate and in the carbon film, respectively. The correlation between variation of Ns value with implantation dose and behavior of D and G band position and their intensity ratio in the visible Raman spectra is observed. The effects are attributed to changes in the sp2sp3 systems and hydrogen loss due to ion induced annealing of the carbon films at high ion doses. The temperature and concentration dependencies of the ESR line shape and linewidth are explained using the mechanism of motional narrowing over the temperature range 4.2300 K. Low temperature anisotropy of the g value is found in the ESR spectra and is explained as arising from the dipoledipole interaction in the infinitely thin films.