Synthesis and characterisation of freestanding diamond coatings

Abstract

Freestanding polycrystalline diamond (PCD) coatings are of immense technological importance. PCD has been grown over silicon substrates by microwave plasma assisted chemical vapor deposition (MWPACVD) process. The coatings are grown by suitable optimisation of the growth parameters of a 915 MHz microwave reactor. Thereafter, 1:1:1 solution of hydrofluoric acid (HF), nitric acid (HNO₃) and acetic acid (CH₃COOH) is used to etch out the silicon wafer from the backside of the coating. Hereby, freshly generated nucleation surface, could be characterised by scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy and stylus profilometer and could be compared with the growth side. It is found that both the nucleation side and growth side are of very high quality (full width at half maxima, i.e., FWHM < 8 cm^-1). The growth side is (111) textured, whereas, the nucleation side is very smooth with embedded detonation-nano-diamond (DND) agglomerates. These freestanding coatings are successfully laser cut into different geometrical shapes. They are found to be optically translucent having high refractive index. Cross-sectional microscopy of the laser cut edge reveals novel melting features of the CVD grown diamond columns.