Laser resonant excitation of precursor molecules in chemical vapor deposition of diamond thin films and crystals

Fast growth of diamond thin films and crystals in open air was achieved by combustion synthesis with resonant laser energy coupling. A pre-mixed C ₂H₄/C₂H₂/O₂ gas was used as precursors for chemical vapor deposition of diamond. Through the resonant excitation of the CH₂ wagging mode of the ethylene (C ₂H₄) molecules using a CO₂ laser tuned at 10.532 μm, high-quality diamond thin films and crystals were grown on various substrates with a high growth rate. The effects of the resonant laser energy coupling were investigated using optical emission spectroscopy and mass spectroscopy. Excitations of precursor molecules by different laser powers were studied. The density of the incident laser power was adjusted to modify diamond crystal orientation, optimize diamond quality, and achieve high-efficiency laser energy coupling. The wavelength-tunable CO₂ laser steers the chemical reactions and promotes proportion of intermediate oxide species, which results in preferential growth of (100)-oriented diamond. The wavelengthtunable CO₂ laser was also used to resonantly excite the vibration modes of ammonia molecules to synthesize N-doped diamond. The laser wavelength was tuned to match frequencies of the NH wagging mode of the ammonia molecules. Vibrational excitation of the ammonia molecules promotes nitrogen concentration in the deposited diamond films. This study opens up a new avenue for controlled chemical vapor deposition of crystals through resonant vibrational excitations to steer surface chemistry.