The similar crystalline structure of diamond and cubix boron nitride suggests the synthesis of superhard thin films containing boron, carbon and nitrogen. BCN thin films have been prepared by reactive r.f.-magnetron sputtering of a hexagonal boron nitride target in an argon/acetylene atmosphere of a constant pressure of 2 × 10-2 mbar. A deposition temperature of 600°C leads to nearly hydrogen-free BCN films. At a flow ratio of 0.05