Effects of oxygen and nitrogen addition on the optical properties of diamond-like carbon films

Diamond-like carbon (DLC) films were synthesized using the rf-plasma CVD technique with the addition of small amounts of nitrogen and oxygen to the gas mixture of CH4 and H2. The pressure, the rf-power, and the CH4/H2 ratio were 430 mtorr, 80 W, and 1:1, respectively, in the deposition process. The transmittances of the DLC films deposited with and without the addition of nitrogen or oxygen were compared with each other in the visible light and ultraviolet light regions. FTIR analyses were performed to study the bond structures. The transmittance of the DLC film measured by UV/VIS spectrometry increased with increasing nitrogen content from 6.3 to 17.4%. The transmittance of the DLC film in the UV region was much more enhanced by oxygen addition than by nitrogen addition. Nitrogen addition increased the optical band gap of DLC, while 2% oxygen addition decreased it to 0.5.