Pulsed reactive magnetron sputtering of high-temperature Si–B–C–N films with high optical transparency

• Pulsed reactive dc magnetron sputtering onto floating substrates was used.
• Multifunctional Si–B–C–N films with ultra-high thermal stability were prepared.
• Hard, highly transparent films exhibited high oxidation resistance up to 1600 °C.
• High-quality defect-free films with smooth surfaces were produced.

Multifunctional Si–B–C–N films with exceptionally high thermal stability are becoming increasingly attractive because of their potential applications in coating technologies, and in high-temperature electronics and optoelectronics. In the present work, amorphous Si–B–C–N films were deposited onto SiC and Cu floating substrates using pulsed dc magnetron co-sputtering of a single (B4C)25Si75 target in a 50% Ar + 50% N2 gas mixture. High-quality defect-free films with smooth surfaces (average roughness Ra = 4 nm) were produced. The films, possessing a composition (in at.%) of Si30–32B10–12C2–4N49–51, exhibited a hardness of 22 GPa, an effective Young's modulus of 170 GPa and an elastic recovery of 75%. The oxidation resistance of the Si–B–C–N films in air was found to be very high up to 1600 °C. The film materials retained their amorphous structure after annealing in inert gases (He and Ar) up to 1600 °C. Annealing of the as-deposited films in He from room temperature to 1400 °C led to a slight decrease in the refractive index from 1.92 to 1.91 and to an accompanying increase in the extinction coefficient from 3 × 10− 4 to 3 × 10− 3 (both at the wavelength of 550 nm).