This paper reports efforts to achieve low-temperature synthesis of SI-C films by ion beam sputtering in a reactive gas with concurrent ion irradiation. Two argon ion beams were employed, with one sputtering a silicon target to provide a Si flux, and the other bombarding the Si or graphite substrate on which films grow. Pure methane gas was introduced into the system with a partial pressure up to 1.8 x 10(-2) Pa. The energy of the sputtering beam was around 1 keV, whilst the bombarding beam energies were altered from 0 to 500 eV. By using Rutherford backscattering spectroscopy and X-ray diffraction, it was shown that films were produced in the amorphous state with a range of C/Si ratios covering the stoichiometric composition. X-ray photoelectron spectroscopy analysis showed a binding energy shift caused by ion beam bombardment. The discussion focusses on the dependence of the film composition on the deposition conditions, and the effects of ion bombardment and methane partial pressure on the sticking probability via a surface reaction between methane molecules, silicon atoms and bombarding ions.