Effects of film thickness on mechanical properties of tetrahedral amorphous carbon

The tetrahedral amorphous carbon (ta-C) films with the different thickness have been prepared on the c-Si substrate under the same deposition conditions by the filtered cathodic vacuum arc (FCVA) technology. The thickness and stress of the films have been measured with the surface profiler. The hardness, Young's modulus and critical load have been analyzed by the nano-indentor. The microstructure has been characterized with visible Raman spectroscopy. It has been shown that the stress of the films continuously decreases with the increase of thickness of the films. When the thickness surpasses 30 nm, the stress is less than 5 GPa. When the thickness is more than 300 nm, hardness and Young's modulus respectively approach to 70 GPa and 750 GPa that are close the ones of diamond crystal. The position of the asymmetric broad Raman peak gradually shifts towards the lower wavenumber with the increase of thickness.