Control of crystallographic orientation in diamond synthesis through laser resonant vibrational excitation of precursor molecules.

Crystallographic orientations determine the optical, electrical, mechanical, and thermal properties of crystals. Control of crystallographic orientations has been studied by changing the growth parameters, including temperature, pressure, proportion of precursors, and surface conditions. However, molecular dynamic mechanisms underlying these controls remain largely unknown. Here we achieved control of crystallographic orientations in diamond growth through a joint experimental and theoretical study of laser resonant vibrational excitation of precursor molecules (ethylene). Resonant vibrational excitation of the ethylene molecules using a wavelength-tunable CO2 laser steers the chemical reactions and promotes proportion of intermediate oxide species, which results in preferential growth of {100}-oriented diamond films and diamond single crystals in open air. Quantum molecular dynamic simulations and calculations of chemisorption energies of radicals detected from our mass-spectroscopy experiment provide an in-depth understanding of molecular reaction mechanisms in the steering of chemical reactions and control of crystallographic orientations. This finding opens up a new avenue for controlled chemical vapor deposition of crystals through resonant vibrational excitations to steer surface chemistry.