Raman analysis of deposition pressure variations in nanocomposite Si-C-N coatings: A 4-stage model

A 4-stage model was proposed based on Raman spectroscopy due to the N2-Ar pressure variations (0.4–10 Pa) during the deposition process of Si-C-N coatings by magnetron sputtering. The stage I (0.4 Pa) was associated to amorphous carbon with high defect density followed by stage II (1 Pa) where the growth of hard nanocrystalline phases took place resulting in increased hardness. The stage III (5 Pa) was linked to increased disorder and finally the growth of the graphitic phase at 10 Pa causing again a decrease in hardness was categorized as stage IV.The model is analogous to the conventional 3-stage Ferrari–Robertson model on the growth features of carbon materials and takes a step further in proposing it for Si-C-N specific to pressure variation and introducing tetrahedral carbon and effects due to nitrogen incorporation The integral intensity of the G (graphitic), disorder (D), tetrahedral (T) and nitrogen (N) peaks namely IG, ID, IT and IN were calculated after the deconvolution of the spectra. The sp 2 domain size and defect parameters were evaluated and correlated with the hardness and different bond formation involving Si, C, and N. Image analysis revealed the atomic migration involved during the growth process leading to crystallization along with the formation of voids and defects. The deposition carried out at 1 Pa yielded the maximum hardness of 22 GPa for a domain size ∼ 25 nm and defect density of 2.25 × 10 11 cm −2 at 500 °C. These optimized Si-C-N hard coatings with previously established fracture toughness, conductivity and thermal stability serves in N/MEMS devices operating in harsh environmental conditions like aerospace. The study provides a structure—property correlation between deposition pressure and mechanical properties of Si-C-N through the 4-stage model based on Raman spectra .