Mechanical chemical polishing of large-size single-crystal diamond substrates with a sol-gel polishing tool

To process large-size single-crystal diamond (SCD) substrates efficiently, we proposed a method that utilises mechanical action to induce a chemical reaction for SCD polishing. In this study, a novel semi-fixed abrasive polishing tool suitable for high-speed polishing was fabricated using the sol-gel technique. A single-diamond abrasive and a mixed abrasive of diamond and CuO were selected for the SCD (100) plane polishing. After polishing for 2.5 h, the surface roughness of the SCD was reduced from approximately Ra 80 nm to approximately Ra 9 nm. The material removal rate (MRR) was measured quantitatively, and it was found that the mixed abrasive polishing performance was superior. In addition, the amorphous carbon content on SCD surface/subsurface after mixed abrasive polishing was significantly lower than single-diamond abrasive diamond abrasive. These results indicate that the scratching of the SCD surface by diamond abrasives induced the transformation of the carbon into amorphous carbon, which could then react with CuO powder. The wear debris morphology indicates that the surface material of the SCD was peeled off with a slice shape during single-diamond abrasive polishing, while it was removed with a slag-shape by the chemical reaction and slightly crushed during the mixed abrasive polishing. The material removal process for the mixed abrasive polishing was CDia→MechanicalCAmo→CuOCu+CO, which is a mechanical chemical polishing process. Experiments confirmed that the synergistic effects of the mechanical action and chemical reaction could increase the MRR and produce a smoother surface and less damage to the subsurface of the SCD, which provides inspiration for the processing of large-size SCD substrates.