Laser-assisted vibrational control of precursor molecules in diamond synthesis

Control of chemical reactions is the essence of chemistry, producing designed outcomes while suppressing unwanted side products. Laser-assisted molecular vibrational control has been demonstrated to be a potential approach to influencing the outcome of a chemical reaction. In this article, we reviewed recent progress in the laser control of diamond synthesis through vibrational excitation of precursor molecules in a laser-assisted combustion chemical vapor deposition process. Significantly promoted diamond deposition rate (139 μm/h) and crystalline quality were achieved by resonantly exciting the Q-branch (ΔJ = 0) of the CH2-wagging mode (v7 mode 949.3 cm−1) of C2H4 molecules. Resonant excitation of the fundamental vibrational modes is more effective in promoting diamond growth than random vibrational excitation. Control of diamond crystallographic orientation was also realized by resonantly exciting the R branch (ΔJ = 1) of the CH2-wagging mode of C2H4 molecules and resulted in the preferential growth of {1 0 0}-oriented diamond crystals. Nitrogen-doped diamond films with a nitrogen concentration of 1.5 × 1020 atoms/cm3 were synthesized by resonantly exciting the rotational-vibrational transition (J = 5 → J′ = 6, K = 0) of the N-H wagging mode (v2 mode) in ammonia molecules. The findings demonstrate the feasibility of laser-assisted vibrational control in steering chemical reactions and controlling reaction outcomes.