Thermal stability of multilayer tetrahedral amorphous carbon films

Using the filtered cathodic vacuum arc(FCVA) deposition technique with a process of changing substrate bias, a stable thick multilayer ta-C film was prepared. The multilayer films with a good adhesion consisted of alternating sp2-rich sublayers Ai and sp3-rich sublayers Bi(i=1,2,3). The sublayers thickness ratio dAi/dBi was about 1.0, and the total thickness of the multilayer film was about 1 m. The calculated compressive stress of sublayers by the Stoney formula revealed an alternating wave change. After anealling at 500 ℃ in vacuum, the Raman spectra suggested the multilayer film had a non-changed sp3-rich microstructure. The nanoindentation measurement showed an increasing hardness and Youngs modulus of the multilayer film after annealing. The nanoscratch test showed the favourable scratch resistance and adhesive properties of multilayer film. The results indicate that the multilayer ta-C film has some excellent mechanical properties and thermal stability. The multilayer film is proper for the optical protective coatings for aeronautics and space applications.