An unbalanced magnetron uses changes in the configuration of the magnetic field, which confines the plasma close to the sputtering cathode, to allow some of it to ‘‘leak’’ out to impinge on the substrate. An isolated or insulating substrate will acquire a negative bias and be subject to an ion bombardment at that potential. The creation of biases of up to 100 V with a current of 100 mA is reported. The dependence of the surface bombardment on process parameters such as magnetron power and gas pressure has been evaluated; a general diminution of the bombardment occurs as the pressure is increased beyond 1 mTorr, but the effect becomes greater when oxygen replaces argon as the sputtering gas. The operation of the magnetron under conditions using extra electron injection is shown to result in additional ion current, whilst the bias potential is maintained. The application of such a device to the preparation of thin films of diamond-like carbon, indium–tin oxide, silicon oxide and nitride, and titanium nitride and oxide is described. The etching of a polymer using the unbalanced magnetron as an ion gun is also reported.