This thesis describes the characterisation of acetylene-argon plasmas by mass and energy spectrometry as well as infra-red absorption and electrical techniques under conditions favourable to diamond-like carbon deposition. The neutral, positive ionic species and energy distributions measured in an ICP at the rf biased electrode are the first such measurements reported with this mixture under various bias and pressure conditions suited to DLC growth. These are compared to measurements taken in a CCP reactor at a remote location with respect to the driven electrctrode.