Study of nitrogen implanted amorphous hydrogenated carbon thin films by variable-energy positron annihilation spectroscopy

Hard amorphous hydrogenated carbon (a-C:H) films deposited by self-bias glow discharge were implanted at room temperature with 70 keV nitrogen ions at fluences between 2.0 and 9.0x10(16) N/cm(2). The implanted samples were analyzed by positron Doppler broadening annihilation spectroscopy to determine the voids distribution. For samples implanted with 2.0X10(16) N/cm(2) the defect distribution is broader than the vacancies depth profile predicted by Monte Carlo simulation. For higher fluences we observed a reduction of the defect density. These results are discussed in terms of a competition between two processes: ion induced defects and structural modifications induced in the films due to ion implantation. (C) 1997 American Institute of Physics.