Enhanced chemical vapor deposition of diamond by wavelength-matched vibrational excitations of ethylene molecules using tunable CO₂ laser irradiation

Wavelength-matched vibrational excitations of ethylene (C₂H ₄) molecules using a tunable carbon dioxide (CO₂) laser were employed to significantly enhance the chemical vapor deposition (CVD) of diamond in open air using a precursor gas mixture of C2 H4, acetylene (C ₂H₄), and oxygen (O2). The CH2 -wag vibration mode (7) of the C2 H4 molecules was selected to achieve the resonant excitation in the CVD process. Both laser wavelengths of 10.591 and 10.532 μm were applied to the CVD processes to compare the C₂H₄ excitations and diamond depositions. Compared with 10.591 μm produced by common CO₂ lasers, the laser wavelength of 10.532 μm is much more effective to excite the C2 H4 molecules through the CH2 -wag mode. Under the laser irradiation with a power of 800 W and a wavelength of 10.532 μm, the grain size in the deposited diamond films was increased by 400% and the film thickness was increased by 300%. The quality of the diamond crystals was also significantly enhanced.