ON THE PRESENCE OF MOLECULAR NITROGEN IN NITROGEN-IMPLANTED AMORPHOUS-CARBON

Hard amorphous carbon (ta-C) films were implanted with 20 keV N+ ions into saturation at two different temperatures. Monitoring the composit ion ratio [N]/[C] using in situ elastic recoil detection analysis, sat uration levels [N]/[C] of 0.35 and 0.16 have been found for implantati ons at room temperature and 400 degrees C, respectively. Raman and x-r ay photoelectron spectroscopy analyses of the implanted films indicate the presence of N-2 molecules inside room-temperature implanted sampl es, but not for the case of implantation at 400 degrees C, Cross-secti on transmission electron microscopy images show the presence of near-s urface voids, interpreted as remnants of Nz-filled bubbles, in the for mer case. Annealing experiments show that about 50% of the total N inv entory consists of nitrogen only weakly trapped inside the carbon matr ix in room-temperature implanted films, this fraction being significan tly reduced in samples held at 400 degrees C during implantation. (C) 1997 American Institute of Physics.