Variable unbalanced rf magnetron sputtering of graphite in pure nitrogen and a mixture of nitrogen and helium has been used to prepare carbon nitride films in a wide range of ion bombardment conditions analyzed as Co their fluxes and kinetic energies by energy-resolved mass spectrometry and probe measurements. These data were related to the chemical composition, bonding structure, density and Young's modulus of the deposited CNx films which have been studied by several analytical methods. The energy flux density supplied to the growing film by the bombarding positive ions and the bombardment energy per condensing C and N atom were determined to range from below 1 x 10(-3) to close to 5 Wcm(-2) and from about 1 up to 2 x 10(3) eV, respectively, depending on rf power density, discharge pressure and magnetron magnetic field configuration chosen. With increasing energy flux of the ion bombardment the overall [N]/[C] ratio of the films decreases exponentially from a maximum of about 1 to a final value of nearly 0.3 attributed to a bombardment activated desorption of N atoms as well as to a diminishing formation and/or an increased resputtering of N-H groups. The CNx films were found to consist of an amorphous sp(2)/sp(3) hybridized carbon matrix with N substitutions of C atoms and contributions of several C-N and N-H groups. At increasing energy flux density of the ion bombardment the matrix changes from a more graphite-like phase with large sp(2) domains to a predominantly disordered carbon structure. In low-pressure quadrupole magnetic field magnetron sputtering the film density increases with increasing bombardment energy per condensing C and N atom, but remains below that of graphite. This was accompanied by increasing Young's moduli not exceeding 120 GPa.