Mechanical properties of hydrogen-free a-C:Si films

Abstract

Hydrogen-free a-C:Si films with Si concentration between 3 and 50 at.% were prepared by magnetron sputtering of pure graphite and silicon. In contrast to a-C the a-C:Si films do not delaminate even from steel substrates and remain stable after vacuum annealing up to 780 °C. Mechanical properties (microhardness, intrinsic stress) and film structure (electron diffraction (ED), Raman spectra) were investigated in dependence on discharge power, Ar pressure and substrate bias. For lower silicon concentrations (below ∼15 at.%) both microhardness and intrinsic stress of films on biased substrates exceeds the value observed at grounded bias. In the range 38–43 at.% of Si the microhardness of a-C:Si films almost does not depend on the substrate bias and reaches values of 45–55 GPa corresponding to the hardest a-C films prepared by magnetron sputtering under the same conditions. The intrinsic stress is lower than that in a-C films. ED indicates a disappearing graphite-like layer structure and gradual transition to structure formed by the SiC (sp 3) bonds as the silicon concentration increases. These structural changes are reflected in Raman spectroscopy.