Superhard behaviour, low residual stress, and unique structure in diamond-like carbon films by simple bilayer approach

Simple bilayer approach is proposed for synthesizing hard and superhard diamond-like carbon (DLC) coatings with reduced residual stress. For this, M/DLC bilayer (M = Ti and Cu) structures are grown using hybrid system involving radio frequency (RF)-sputtering and RF-plasma enhanced chemical vapor deposition techniques. Ti/DLC bilayer deposited at negative self bias of 100 V shows superhard behaviour with hardness (H) as 49 GPa. Cu/DLC bilayer grown at self bias of 100 V exhibits hard behaviour with H as 22.8 GPa. The hardness of Ti/DLC (Cu/DLC) bilayer gets changed from superhard (hard) to hard (moderate hard) regime, when the self bias is raised to 300 V. Residual stress in Ti/DLC (Cu/DLC) bilayer is found to be significantly low that varies in the range of 1 GPa–1.65 GPa (0.8 GPa–1.6 GPa). The microstructure and morphology are studied by Raman spectroscopy, scanning electron microscopy (SEM), and atomic force microscopy (AFM). SEM and AFM pictures reveal the creation of nanostructured features in the deposited bilayers. Raman, SEM, and AFM analyses are correlated with the nano-mechanical properties. Owing to excellent nano-mechanical properties, these bilayers can find their direct industrial applications as hard and protective coatings.