Effect of substrate bias on microstructure and properties of tetrahedral amorphous carbon films

The microstructure and properties of tetrahedral amorphous carbon (ta-C) films deposited by the filtered cathodic vacuum arc technology have been investigated by visible Raman spectroscopy, AFM and nano-indentor. The Raman spectra are fitted with a single skewed Lorentzian lineshape described by the BWF function defining coupling coefficient, which characterizes the degree of asymmetry and is correlated with the sp³ content. When the substrate bias is -80 V, the sp³ content is the most and simultaneously the coupling coefficient is the least, followed by the minimum root mean square surface roughness (R_q=0.23 nm) and the highest hardness (51.49 GPa), Young's modulus (512.39 GPa), and critical scratching load (11.72 mN). As the substrate bias is increased or decreased, the sp³ content and other properties lower correspondingly.