Map of growth rate of diamond film synthesized by use of flame CVD

Optimum conditions for the flame synthesis of diamond films have been studied by examining effects of the equivalence ratio, ejection velocity, and velocity gradient on the growth rates and morphologies of diamond films. Important factors that can affect growth rates and morphologies of diamond films deposited in the flame are confirmed to be temperature, flow, and species concentration fields. By use of a flat flame burner, these influences are well understood because the flat acetylene/hydrogen/oxygen flame is stabilized in a well-defined stagnation flow field, which can be regarded as one-dimensional field. It is found that the maximum growth rate can be obtained when the equivalence ratio is from 2.45 to 2.50. It has also been confirmed that the growth rate is nearly the same when the velocity gradient is kept constant. This result indicates that the velocity gradient is one of the important parameters that can govern the growth rate of diamond film. Furthermore, in order to obtain universal, optimum conditions for the flame synthesis of diamond films, an attempt has been conducted to make a map of the growth rates, as functions of equivalence ratio and velocity gradient. Although growth rates increase with increasing velocity gradient, excessively high velocity gradients cause decrease in growth rates. It is found that the maximum growth rate can be obtained when the equivalence ratio is around 2.50 and velocity gradient is 4000 s⁻¹.