During the last few years a large number of methods have been attempted to produce C 3 N 4 films. Many of these have involved the use of ion bombardment, silicon substrates and, through the use of CH x precursors, significant concentrations of atomic hydrogen. Under these conditions it is well known that silicon can be etched from the substrate, enter the gas phase and be incorporated in the growing film, indeed such effects have been reported by a variety of groups. There is at least one report of the formation of CNSi crystals with silicon concentrations up to ∼10%, with the indication that the presence of silicon may help to stabilise the beta structure. In this work we report the preparation of deposits of CNSi x using RF chemical vapour deposition (CVD) in a graphite hollow cathode. The concentration of silicon incorporated in the deposit was controlled, primarily, by varying the amount of silicon exposed to the plasma inside the hollow cathode. The experimental conditions used are similar to those used previously to prepare C 3 N 4 deposits. However, in this case substrates other than silicon were used to avoid additional inclusion of this element from the substrate. The films were analysed using energy dispersion spectroscopy (EDS), X-ray diffraction, scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. The variation of the film properties as a function of the experimental parameters, such as plasma power, substrate temperature, exposed area of the silicon source material and methane concentration in the gas mixture, is described.