Diamond synthesis by plasma chemical vapor deposition in liquid and gas

The characteristics of diamond synthesis by 2.45 GHz microwave plasma chemical vapor deposition (CVD) under pressures greater than atmospheric pressure were investigated. The deposits on Si substrates were identified by scanning electron microscopy and Raman spectroscopy. The growth rate of diamond was found to be 250 μm/h at 300 kPa, which is ten times greater than that of the conventional low-pressure CVD method. In order to make high-speed deposition of diamond effective, the diamond growth rates for gas-phase microwave plasma CVD were compared to those from the in-liquid plasma CVD method. The growth rate was found to increase as system pressure increased, displaying the same tendency of that in-liquid plasma CVD. The amounts of input microwave energy per unit volume of diamond in the gas-phase and in-liquid plasma CVD methods were also compared. The amount of input microwave energy per unit volume of diamond was found to be 0.6 to 1 kWh/mm3.