Effect of microstructure on the mechanical properties of carbon nanofilms deposited on the Si(100) at high temperature under ultra high vacuum

Carbon nanofilms were deposited on the Si(100) wafers at substrate temperatures from room temperature (RT) to 700 °C by ultra-high-vacuum ion beam sputtering. The effect of substrate temperature on the evolution of microstructure and mechanical properties of carbon nanofilms was investigated using Raman spectra, X-ray diffraction, scanning electron microscopy (SEM) and nanoindentation. The correlation between microstructure and mechanical properties was discussed. Raman results showed that I_D/I_G ratio increased with substrate temperature from RT to 500 °C due to graphitization effect with more sp² bonds and then decreased with temperature from 500 to 700 °C owing to the new SiC phase formation. In addition, the C and Si reaction was found at 600 °C with an asymmetrical Raman shift wavenumbers at 900-1050 cm^{- 1} and finished at 700 °C with the enhanced asymmetrical band as well as no C peak. A nanoweb-like morphology of the crystalline SiC formation was also observed on the surface of film. The evolution of both hardness and Young's modulus of films had the similar trend as the microstructure. They were 15.01 GPa and 185.11 GPa at RT, respectively, and decreased with substrate temperature to 4.50 GPa and 60.53 GPa at 500 °C, and then increased with temperature to 32.53 GPa and 200.82 GPa at 700 °C. The much enhanced hardness and Young's modulus at 700 °C are attributed to the SiC formation as well as nanoweb-like morphology.