Thermal stability of a-C:H:SiOx thin films in hydrogen atmosphere

Highlights: • a-C:H:SiO_x films were deposited by plasma-chemical method with bipolar substrate bias. • Thermal stability of a-C:H:SiO_x thin films in hydrogen atmosphere was studied. • Graphitization of films in hydrogen occurs at higher temperatures than in air. • Film annealed in hydrogen reduces H sorption up to 600 °C. -- Abstract: a-C:H:SiO_x thin films were deposited by the plasma assisted chemical vapor deposition method, using polyphenylmethylsiloxane as a precursor. The thermal stability of a-C:H:SiO_x films deposited on stainless steel substrates was investigated after thermal annealing of samples in a hydrogen atmosphere for 4 h at temperatures ranging from 300 to 700 °C. The sample analysis by optical and atomic force microscopy, nanoindentation, glow discharge optical emission spectrometry and Raman spectroscopy is reported here. Characterization of the mechanical properties of films (hardness, modulus, endurance capability, elastic recovery) was accomplished using the nanoindentation method. The investigation revealed that the above mechanical characteristics of a-C:H:SiO_x films are very good up to 600 °C in hydrogen compared to un-doped diamond-like coatings. The hardness of the as-deposited a-C:H:SiO_x films (11–13 GPa) showed no decrease after annealing at 600 °C. It is shown that the properties of films begin to change after annealing in hydrogen at a temperature of 200 °C more than during annealing in an air atmosphere. It is demonstrated that graphitization of a-C:H:SiO_x films in hydrogen occurs at higher temperatures than in air.