Nitrogen implantation into amorphous carbon films: sims and positron annihilation analyses

Hard amorphous hydrogenated carbon lms deposited by self-bias glow discharge were implanted at room temperature with 70 keV-nitrogen ions at uences between 2.0 and 9:0 10 N/cm. The implantation energy was chosen so that the projected range plus range straggling (Rp+ Rp) was smaller than the lm thickness. The implanted samples were analyzed by Raman scattering, Secondary ion mass spectrometry (SIMS) and positron annihilation spectroscopy, using the Doppler broadening technique with the determination of the shape parameter (S parameter). Depth pro les of implanted species agree well with the predictions of the Monte Carlo code, Transport of Ions in Matter (TRIM-90). For samples implanted with 2 10 N/cm the S parameter follows the vacancies depth pro le predicted by the simulation. For higher uences we observed a reduction in the measured value of S. The rst result was interpreted as being due to the point defects generated during the ion stopping, whereas the PAS results for higher uences were due to the structural modi cations (increase of disorder and of the number, or size, of the graphitic domains) induced in the carbon lms by the incident ions combined with the point defects generated by the atomic collisions.