NITROGEN-DRIVEN SP(3) TO SP(2) TRANSFORMATION IN CARBON NITRIDE MATERIALS

The coordination of carbon as a function of nitrogen concentration in energetically deposited carbon nitride films has been systematically s tudied. A structural transformation from primarily sp(3)-bonded to sp( 2)-bonded carbon and a density decrease from 3.3 to 2.1 g/cm(3) were o bserved as the nitrogen concentration increases from 11 to 17 %. Calcu lations on nitrogen-substituted carbon clusters indicate that there is a preference to form sp(2)-bonded carbon when the nitrogen concentrat ion is larger than 12%. The implications for these results to the synt hesis of superhard carbon nitride materials are discussed.