Ultralow-load indentation hardness and modulus of diamond films deposited by hot-filament-assisted CVD

Abstract

Diamond films, ranging in thickness to approximately 35 μm, were grown on Si(100) substrates using hot-filament-assisted CVD. Two different CH₄:H₂ ratios were employed during deposition, and the effects on the film morphology and ultralow-load indentation hardness and modulus were investigated. Films deposited from a single, linear filament exhibited a nonuniform deposition thickness profile that can be described by a simple exponential function. Films deposited at lower methane concentrations, 0.11% CH₄ in H₂, had larger crystallite sizes of ∼5–8 μm, an average hardness of 31 GPa, and an average modulus of 541 GPa. A higher CH₄ concentration of 0.99% in H₂ resulted in the formation of finer crystallites of approximately 0.5 μm, an average hardness of 65 GPa, and an average modulus of 875 GPa. While these values lie on the low end or outside of the range reported for single crystal diamond, this study has demonstrated that CVD diamond films can be synthesized with ultrahigh or near ultrahigh hardness.