Nano-polishing and subsequent optical characterization of CVD polycrystalline diamond films

We have polished some CVD polycrystalline diamond films of diameter 15 mm using the vibrational thermochemical polishing technique. The surface morphology of the films were measured by optical microscopy and scanning electron microscopy before and after polishing. The initial roughness of the as-grown films as determined by stylus profilometry was in the neighborhood of 25 μm for the growth side and 7 μm for the substrate side. Polishing for several hours at temperatures between 900°C and 750°C thinned the surface roughness down to 2.2 nm. Confocal Raman spectroscopy was used to optically characterize the films at various stages of polishing. Non-diamond carbon bands were located at 1205 cm and a split band at 1353 cm^-1 and 1453 cm^-1 after initial polishing. The microcrystalline graphite band at 1580 cm^-1 appeared at intermediate stages of polishing, These bands vanished with persistent polishing, leaving the surface entirely diamond-like after the final fine polishing at 750°C. Photoluminescence of defect centers revealed that the only detectable impurities in the samples were nitrogen with zero-phonon lines at 2.156 eV and 1.945 eV and silicon with a zero-phonon line at 1.681. eV, accompanied by their respective phonon replicas. The defect centers are virtually uniformly distributed throughout the films