LASER-POWER-RESOLVED EXCITATIONS OF ETHYLENE MOLECULES IN LASERASSISTED SYNTHESIS OF DIAMOND FILMS

摘要

Laser-power-resolved excitations of precursorrnmolecules in laser-assisted synthesis of diamond filmsrnusing a wavelength-tunable CO_2 laser were studied.rnThe wavelength of the CO_2 laser was tuned to 10.532rnμm to match a vibration mode of a precursor molecule,rnethylene (C_2H_4). The density of the incident laserrnpower was adjusted to modify diamond crystalrnorientation, optimize diamond quality, and achievernhigh-efficiency laser energy coupling. It was observedrnthat at incident laser power densities between 5×10~3rnand 1.0×10~4 W/cm~2, (100)-faceted diamond crystalsrnwere grown uniformly in the center areas of therndiamond films. Higher incident laser powers, althoughrnfurther promoted growth rate, suppressed thernuniformity of the diamond (100) facets. Best diamondrnquality was obtained within a laser power densityrnrange of 5×10~3 ～ 6.7×10~3 W/cm~2, whereas the highestrnenergy efficiency was achieved within a laser powerrndensity range of 3.3×10~3 ～ 6.7×10~3 W/cm~2. The effectsrnof the resonant laser energy coupling were investigatedrnusing optical emission spectroscopy.