PREPARATION OF SMOOTH AND NANOCRYSTALLINE DIAMOND FILMS

Nanocrystalline, optically transparent films were grown on silicon and quartz substrates by remote plasma deposition, using CH4-O2-H-2 gas mixtures at temperatures ranging from 600 to 950-degrees-C. The substrate was positioned about 3 cm downstream from the plasma centre. To enhance nucleation, different diamond powders with grain sizes in the range 0.01-3 mum were used. Nucleation densities up to 3 x 10(10) nuclei cm-2 were achieved by polishing the substrate with 10 nm diamond powder. These high nucleation densities lead to a smooth surface, thus reducing light scattering. The films were characterized using scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), and Raman and visible spectroscopies. Diamond films 1 mum thick had a surface roughness of 30 +/- 10 nm; films 10 mum thick showed a surface roughness of about 200 nm, as measured by SEM and AFM. The grain size of the nanocrystalline diamond films was estimated using the Scherrer formula to be as small as 20 nm, assuming that the internal film stress is 3 GPa or lower. The optical transparency of the films on quartz substrates was improved, reaching as high as 70% at a wavelength of 880 nm.