Uniformly dispersed nanocrystalline silver reduces the residual stress within diamond-like carbon hard coatings

Composite films containing silver (Ag) nanoparticles embedded in amorphous diamond-like carbon (Ag-DLC) matrix have been deposited on glass and Si (100) substrates using r.f. capacitatively coupled plasma chemical vapour deposition (rf-CVD). Ag content in the DLC films varies with the relative amount of argon in the methane and argon gas mixture during the plasma growth. The film thickness ranges from 50 nm to 105 nm. The sp2/sp3 ratio in the DLC films decreases with the incorporation of nanocrystalline silver. A considerable amount, of about 99% residual stress reduction in Ag-DLC films has been demonstrated through theoretical calculation with the help of experimental optical absorption spectra. The results are verified by experimental nano-mechanical property evolution using nano-indentation. The related residual compressive stress reduction in the Ag-DLC composite films is attributed to the addition of uniformly dispersed nanocrystalline silver nanoparticles in the DLC matrix and the corresponding relative sp2/sp3 ratio variation.