Diamond Synthesis by the Microwave Plasma Chemical Vapor Deposition Method Using the Pretreated Carbon Dioxide and Hydrogen Mixed-Gas System

High-quality diamond was obtained by the microwave plasma-assisted chemical vapor deposition (plasma CVD) method using the pretreated carbon dioxide (CO 2 ) and hydrogen (H 2 ) mixed-gas system. The pretreatment method is as follows: at first, CO 2 and H 2 pass through the prereactor, where plasma is generated by microwave discharge, and then the reactant passes through the cold trap at around 185 K in order to remove water (H 2 O) produced in the plasma from CO 2 and H 2 . The residue of the pretreated CO 2 and H 2 mixed gas, which consists of CO, CO 2 and H 2 , is introduced into the main reactor where diamond is synthesized. Diamond can grow to a feed ratio of CO 2 /H 2 =25/100 sccm. Plasma diagnosis was performed using optical emission spectroscopy (OES) and gas chromatography (GC).