Characterization of diamond thin films deposited by a CO2 laser-assisted combustion-flame method

Diamond thin films were deposited by a CO₂ laser-assisted O₂/C₂H₂/C₂H₄ combustion-flame process. The effect of the deposition parameters, in particular the laser wavelength and power, on the film surface morphology, microstructure and phases present was the primary focus of the work. The laser power was set at 100, 400 and 800 W while the wavelength was varied and set at 10.591 µm in the untuned condition and set at 10.532 µm to resonantly match the CH₂-wagging vibrational mode of the C₂H₄ molecule when in the tuned condition. When the laser was coupled to the combustion flame during deposition the diamond film growth was enhanced as the lateral grain size increased from 1 µm to greater than 5 µm. The greatest increase in grain size occurred when the wavelength was in the tuned condition. Scanning transmission electron microscopy images from focused-ion beam cross-sectioned samples revealed a sub-layer of smaller grains less than 1 µm in size near the substrate surface at the lower laser powers and untuned wavelength. X-ray diffraction results showed a more intense Diamond (111) peak as the laser power increased from 100 to 800 W for the films deposited with the tuned laser wavelength. Micro-Raman spectra showed a diamond peak nearly twice as intense from the films with the tuned laser wavelength.