FORMATION OF CARBON NITRIDE FILMS BY HIGH-ENERGY NITROGEN ION-IMPLANTATION INTO GLASSY-CARBON

Carbon nitride beta-C3N4 thin films are presently attracting increasing interest both scientifically and technologically. This is due to their expected mechanical and tribological properties, superior to those of diamond. In the present work the nitriding process of the near-surface region of glassy carbon by high-energy nitrogen ion implantation has been investigated with particular emphasis on the implantation temperature and post-annealing processes. The implantations were performed at room temperature and at 400 degrees C using 25 and 50 keV nitrogen ions up to doses of 1 x 10(18) cm(-2). The distribution of the implanted nitrogen and its bonding states have been studied by a number of complementary techniques: Auger electron spectroscopy, secondary ion mass spectrometry and X-ray photoelectron spectroscopy (XPS). The possibility of carbon nitride phase formation and the effect of implantation on the glassy carbon microstructure was assessed by Raman measurements. Volume effects were studied by measurements of the step height between the implanted and unimplanted regions. The maximum amount of nitrogen in the implanted layer obtained in the present study reaches 25-30 at.%. Annealing the RT implanted layer up to 500 degrees C does not result in a measurable diffusion of the implanted nitrogen. However, during annealing to 1000 degrees C a diffusion of the implanted nitrogen occurs. Hot implantation at 400 degrees C results in a broad and nearly homogeneous distribution of the implanted nitrogen with an average concentration of 18 at.%. XPS measurements indicate that hot implantation results in a preferred population of a rather covalent nitrogen bonding state in the implanted layer compared with that obtained after RT implantation and annealing.