Nano silicon top-layer for composite-induced multiphasic enhancement of thermal stability of hardness of diamond-like carbon nanofilm at 900 °C

The effect of 25-nm silicon top-layer on the hardness and thermal stability of 100-nm diamond-like carbon (DLC) film annealed at 750–900 °C has been investigated. The evolution of surface morphology, microstructure and reaction between C and Si was examined by high resolution scanning/transmission electron microscope, Raman and FTIR spectroscopy. The hardness of films was investigated using nano-indentation. After 750–900 °C annealing, the hardness of single carbon layer greatly decreased at 750 °C and then slightly increased at 900 °C due to the formation of SiC at the interface between the single C film and the Si substrate. In contrast, no significant variation occurred on the hardness of two-layer Si/C film under RTA at 750–900 °C. Although the higher annealing temperature resulted in higher sp2/sp3 bonding ratio as well as more sp2 bonding formation in the carbon layer to soften the structure, the added Si top-layer can protect DLC from reaction with environmental oxygen and sustain the hardness of the composite film because of the multiphasic formation with extra SiC on the surface and at the interface between the C layer and Si substrate through great interdiffusion between Si and C for extending DLC high-temperature application.