Subplantation effect in magnetron sputtered superhard boron carbide thin films

Abstract Superhard amorphous boron carbide films with a film thickness of about 2 μm have been prepared by r.f.-magnetron sputtering of a boron carbide target in a pure argon discharge at a gas pressure of 1.6 × 10 −3 mbar. The flux ratio of the argon ions to boron and carbon atoms has been kept constant at 3.5, while the energy of the argon ions is varied by applying a d.c.-substrate bias. The effect of argon ion implantation measured by Rutherford back scattering is discussed. When the argon ion energy is increased, the mechanical properties show extreme values at an argon ion energy of 74 eV, which can be explained quantitalively by knock-on subplantation. Stress up to 6.7 GPa and a micro-hardness up to 72 GPa are obtained. The hardness enhancement is correlated with the increase of stress. The influence of preferential sputtering of boron or carbon from the deposited B 4 C film can be neglected.