Fig. 1. Schematic diagram of the cell for diamond synthesis.

Fig. 2. Optical morphology of the synthesized diamond crystals with different concentrations of CH₄N₂S additive or CH₄N₂S + Ti/Cu additives. (a) 0.2 mg CH₄N₂S additive, (b) 0.3 mg CH₄N₂S additive, (c) 0.2 mg CH₄N₂S + Ti/Cu additives, (d) 0.3 mg CH₄N₂S + Ti/Cu additives.

Fig. 3. Raman shift and FWHM of the synthesized diamond with different concentrations of CH₄N₂S additive or CH₄N₂S + Ti/Cu additives. (a) 0.2 mg CH₄N₂S additive, (b) 0.3 mg CH₄N₂S additive, (c) 0.2 mg CH₄N₂S + Ti/Cu additives, (d) 0.3 mg CH₄N₂S + Ti/Cu additives.

Fig. 4. (a), (b) FTIR spectra of the synthesized diamond crystals with different concentrations of CH₄N₂S additive or CH₄N₂S + Ti/Cu additives. The green, blue, red, and black curves represent the FTIR spectra of the synthesized diamond crystals with 0.2 mg CH₄N₂S additive, 0.3 mg CH₄N₂S additive, 0.2 mg CH₄N₂S + Ti/Cu additives, and 0.3 mg CH₄N₂S + Ti/Cu additives, respectively.

Fig. 5. PL spectra of the synthesized diamond crystals taken at room temperature, excited by the 488 nm line: (a) with 0.2 mg CH₄N₂S additive, (b) with 0.3 mg CH₄N₂S additive, (c) with 0.2 mg CH₄N₂S + Ti/Cu additives, (d) with 0.3 mg CH₄N₂S + Ti/Cu additives.