Influence Factors of Surface Roughness of Synthesized Diamond Films by Three-step Synthesis Method Using Flame Combustion

Abstract

A flame combustion method enables the synthesis of diamond using acetylene-oxygen gas in ambient atmosphere. It has various advantages over other methods. We previously synthesized diamond films on a Mo substrate surface by the flame combustion method. In this method, most diamond films delaminate as a result of thermal stress during cooling. To prevent diamond film delamination for the synthesis of good diamond films, a three-step synthesis method was proposed. However, the surface roughness of synthesized diamond films by this method became large. In previous study, to reduce the surface roughness by flame combustion and to achieve good adhesion on the Mo substrate, the flow ratio of oxygen flow rate to acetylene flow rate and synthesis time of the three-step synthesis method were varied during the synthesis of diamond. In result, the surface roughness of synthesized diamond films was reduced by this method. However, the surface roughness was not yet enough, and it is more necessary to reduce the surface roughness. In this study, to reduce further the surface roughness, the diamond seed particles as generation nuclei for the diamond synthesis were changed to small. To investigate the surface morphology and the surface roughness of synthesized diamond films, synthesized films were observed. The diamond seed particles size and the flow ratio and synthesis time of the three-step synthesis method affected the surface morphology and the surface roughness of synthesized diamond films. The surface roughness of the synthesized film was reduced further by this study. The surface roughness in the Case 3 condition was the smallest in this experiment. Furthermore, to confirm influence factors of the surface roughness of synthesized diamond films, diamond seed particles on the substrate surface after the seeding treatment and generation nuclei on the substrate in the synthetic initial stage were observed.