Effect of microstructure evolution in ultra-thick diamonds on high-quality polishing

Ultra-thick diamond films (>3 mm) compliant with ISO 14704 were fabricated via Direct Current Arc Plasma Jet Chemical Vapor Deposition (DC Arc Plasma Jet CVD). Multiple characterization techniques, including X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), Electron Back Scatter Diffraction (EBSD), Optical Microscope (OM), Laser Scanning Confocal Microscopy (LSCM) and Atomic Force Microscope (AFM), were employed to systematically investigate the correlations between microstructure evolution, black defects (growth pores), and polishing quality (surface roughness) on the growth surfaces of ultra-thick diamonds. As diamond film thickness increases, the preferred orientation transitions from {111} to {110} planes. This shift primarily results from twins-induced lattice stacking variations that induce orientation dispersion, coupled with the cooperative effects of twins-induced randomization (Σ3 twins >52 %) and Ostwald Ripening. Ostwald Ripening facilitates the consumption of disadvantageously oriented grains by {110}-oriented grains. Under the OM, the area of black defects (growth pores) first increases, then decreases, and subsequently increases again, peaking at thicknesses of 1700 μm and 3000 μm. This fluctuation in defect content is directly correlated with variations in polishing quality. Through crystallographic evolution and surface integrity analysis of DC Arc Plasma Jet CVD diamond films (>3 mm), this study establishes the correlation between microstructure gradients, pore distribution, and polishing quality. These findings provide a theoretical foundation for engineering applications of ultra-thick diamond.