Toughness enhancement of single-crystal diamond by the homoepitaxial growth of periodic nitrogen-doped nano-multilayers

Periodic nitrogen-doped homoepitaxial nano-multilayers were grown by microwave plasma chemical vapor deposition. The residual time of gases (such as CH₄ and N₂) in the chamber was determined by optical emission spectroscopy to determine the nano-multilayer growth process, and thin, nanoscale nitrogen-doped layers were obtained. The highest toughness of 18.2 MPa∙m^1/2 under a Young’s modulus of 1000 GPa is obtained when the single-layer thickness of periodic nitrogen-doped nano-multilayers is about 96 nm. The fracture toughness of periodic nitrogen-doped CVD layer is about 2.1 times that of the HPHT seed substrate. Alternating tensile and compressive stresses are derived from periodic nitrogen doping; hence, the fracture toughness is significantly improved. Single-crystal diamond with a high toughness demonstrates wide application prospects for high-pressure anvils and single-point diamond cutting tools.