OPTICAL CHARACTERIZATION OF DIAMOND SYNTHESIZED USING CH4-CO2 GAS-MIXTURES WITHOUT SUPPLYING HYDROGEN GAS

Diamond films are the optical choice for IR window applications. Polyc rystalline diamond films were synthesized in this study by microwave-p lasma-assisted chemical vapour deposition (PACVD) using CH4 + CO2 as r eactive gases. The primary purpose of this study is to determine the e ffect of the deposition conditions on the optical properties of PACVD diamond films. Room temperature optical properties of free-standing di amond films were studied by Fourier transform IR spectroscopy. Experim ental results indicate that the refractive index of diamond films is c omparable with that of natural diamond. The scattering loss caused by the rough surface of as-grown diamond film was reduced using a two-ste p process and polishing techniques. The resulting reduction in scatter ing loss increased the transmission intensity. For low temperature dep osited diamond film the intensity of absorption due to carbon-hydrogen stretch bands was higher than that for film deposited at a high tempe rature. IR spectra are fitted with simulated spectra to determine the background absorption caused by the amorphous carbon contained in the films. Additionally, the background absorption of low temperature depo sited diamond film was found to be larger than that of a diamond film deposited at 850 degrees C.