Influence of the substrate nature on the properties of nanocrystalline diamond films

Nanocrystalline diamond/amorphous carbon (NCD/a-C) nanocomposite films have been deposited by microwave plasma CVD from CH₄/N₂ mixtures on a variety of substrates such as polycrystalline diamond, cubic boron nitride, silicon, titanium nitride, and Ti–6Al–4V. The study aimed to investigate the influence of the chemical nature of the substrate, the surface roughness, and the pretreatment of the substrate on the nucleation, the bulk structure, and the mechanical and tribological properties of the NCD/a-C films. The present paper is especially devoted to the bulk structure of the films. By means of X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) it is shown that the bulk properties of the films are not affected by the properties of the substrate although these have a strong influence on the nucleation behaviour. XRD measurements show that – irrespective of the substrate used – the films contain diamond nanocrystallites of 3–5 nm diameter. From the Raman spectra it can be inferred that the crystallite/matrix ratio does not vary. The XPS measurements, finally, show that there are no great changes in the sp²/sp³ ratio of the matrix. These findings are discussed in view of possible growth mechanisms of NCD/a-C nanocomposite films.