Magnetron-sputtered superhard materials

Abstract

Superhard materials such as nanocrystalline cubic boron nitride (c-BN) and β-silicon carbide ( β-SiC) as well as amorphous boron carbide (B 4C) and highly tetrahedral amorphous carbon (ta-C) are produced by radio frequency (RF) unbalanced magnetron sputtering in combination with intense ion plating in a pure argon discharge. As a result of energy and mass analysis the film-forming fluxes Φ n consist of sputtered atomic target components and the plating flux Φ Ar + of argon ions. Subplantation, ion-plating-induced increase of surface mobility and substrate-temperature-induced crystallisation are the three main parameters affecting the formation of superhard phases with strong covalent bonding. Knock-on subplantation allows the formation of B 4C with hardness up to 72 GPa at a flux ratio Φ Ar + / Φ n of 3 for a plating energy of 75 eV. Also c-BN and ta-C can be produced with similar parameters. In the case of SiC, densification is diminished by preferential sputtering of Si and consequently stochiometry and hardness are adversely affected. However, intense ion plating with a low ion energy of 25 eV and small film-forming fluxes shift the temperature of the phase transition from amorphous to nanocrystalline β-SiC from the usual value of >900 °C to about 420 °C. Furthermore, investigations of the formation of superhard materials in the ternary system boron–carbon–nitrogen are reported.