Fig. 1. Raman spectra at the center of sample 1 to 16

Fig. 2. Photos of the diamond film deposition and after double-sided polishing. (a) Deposition; (b) double-sided polishing

Fig. 3. Optical microscope photos of the diamond film in different positions. (a) Edge; (b) middle; (c) center

Fig. 4. Raman spectra and XRD spectra of the diamond film. (a) Raman spectra; (b) XRD spectra

Fig. 5. Photos of the diamond film deposition and after double-sided polishing. (a) Deposition; (b) double-sided polishing

Fig. 6. Optical microscope photos of the diamond film in different positions. (a) Edge; (b) middle; (c) center

Fig. 7. XRD spectrum of the diamond film

Fig. 8. Raman spectrum and PL spectrum of the diamond film. (a) Raman spectrum; (b) PL spectrum

Fig. 9. UV-VIS-NIR transmittance spectrum and Fourier transform infrared spectrum of the diamond film. (a) UV-VIS-NIR transmittance spectrum; (b) Fourier transform infrared spectrum

Fig. 10. Optical emission spectra and variation curves at different power densities. (a) Optical emission spectra; (b) C₂, H_α, H_β, and CH peak intensities and variations in I_(C2)/I_(Hα), I_(CH)/I_(Hα), and I_(Hβ)/I_(Hα) ratio variation curves

Fig. 11. Optical emission spectra and variation curves at different methane volume fractions. (a) Optical emission spectra; (b) C₂, H_α, H_β, and CH peak intensities and variations in I_(C2)/I_(Hα), I_(CH)/I_(Hα), and I_(Hβ)/I_(Hα) ratio variation curves

Fig. 12. Optical emission spectra and ratio variation curves at different oxygen flows. (a) Optical emission spectra; (b) C₂, H_α, H_β, and CH peak intensities and variations in I_(C2)/I_(Hα), I_(CH)/I_(Hα), and I_(Hβ)/I_(Hα) ratio variation curves