Effect of H2 addition on diamond growth in C2H2CO2 gas system

Without using a lot of H2 as diluent gas, by substituting CO2 for H2, diamond films and particles of high quality could be obtained in the C2H2CO2 gas system. In order to clarify the role of H2 in diamond synthesis, H2 was introduced to the C2H2CO2 gas system as an additive. From the results of X-ray diffraction and scanning electron microscopy observations we found that a small amount of H2 addition led to an improvement in the crystallinity of the diamond but a decrease in the growth rate. On increasing the flow rate of H2, the morphology of films and particles gradually showed worse crystallinity and the growth of diamond was suppressed. The relative peak levels of the cathodoluminescence spectrum decreased with increasing H2 flow rate, which implied that the quality of the film decreased.