The mechanical enhancement of chemical vapor deposited diamond film by plasma low-pressure/high-temperature treatment

Direct-current (DC) arc plasma jet has been utilized to anneal chemical vapor deposited (CVD) polycrystalline diamond produced by the same device. Intense heating pulses around several target temperatures were achieved under constant plasma state and chamber pressure (∼5 kPa), which ensured this plasma low-pressure/high-temperature (LPHT) treatment succeed without diamond graphitization. The treatment significantly improves the fracture strengths of the diamond samples. The enhancement is ideally proportional to the temperature and the largest increase is up to 96.38%. Fractographic analysis has been done by scanning electron microscope (SEM), and the transgranular fracture/intergranular fracture ratio increases as the temperature increases. Raman spectra indicate that there exists huge compressive stress (>1.6 GPa) at the grain boundaries after the treatment so that the boundary strength is greatly enhanced. The interacting relationship between the interface graphitization and the compressive stress might play a crucial role in preventing the interface from further graphitization. This suggests that the plasma LPHT treatment can be improved by using higher temperature or longer time.