Plasma probe measurements and energy selective mass spectrometry were used to characterize the composition and energetic conditions of the ion flux of a direct current, N2/Ar, unbalanced magnetron sputtering plasma in front of a graphite target, depending on the total pressure and gas composition. It is shown that the flux of ionized film-forming species consist predominantly of CxNy (x,y≤2) species. The total number of C-containing ions strongly depends on the N2 fraction in the discharge and can be increased by almost one order of magnitude scaling with the availability of N2 as the discharge gas. This finding suggests that besides C and N atoms and ions, other species, like preformed CxNy particles, play an important role during growth of fullerene-like (FL) carbon nitride (CNx) thin films. It is proposed that such clusters have a direct effect as growth templates or nucleation sites on the evolution of curved and cross-linked FL structures. The carbon target was identified as the main source of preformed C-containing species, following from the pressure dependence of the ion energy distributions of the most abundant CxNy (x,y≤2) ions. © 2003 American Institute of Physics.