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Fast growth of diamond crystals in open air was achieved by combustion synthesis with resonant laser energy coupling. A premixed C 2 H 4 /C 2 H 2 /O 2 gas mixture was used as precursors for growth of diamond crystals. Through the resonant excitation of the CH 2 wagging mode of the ethylene (C 2 H 4 ) molecules using a CO 2 laser tuned at 10.532 μm, high-quality diamond crystals were grown on silicon substrates with a high growth rate at ∼139 μm/h. Diamond crystals with a length up to 5 mm and a diameter of 1 mm were grown in 36 h. Sharp Raman peaks at 1332 cm -1 with full width at half-maximum (fwhm) values around 4.5 cm -1 and distinct X-ray diffraction spectra demonstrated the high quality of the diamond crystals. The effects of the resonant laser energy coupling were investigated using optical emission spectroscopy.

International audienceAdvanced micro/nanofabrication of functional materials and structures with various dimensions represents a key research topic in modern nanoscience and technology and becomes critically important for numerous emerging technologies such as nanoelectronics, nanophotonics and micro/nanoelectromechanical systems. This review systematically explores the non-conventional material processing approaches in fabricating nanomaterials and micro/nanostructures of various dimensions which are challenging to be fabricated via conventional approaches. Research efforts are focused on laser-based techniques for the growth and fabrication of one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) nanomaterials and micro/nanostructures. The following research topics are covered, including: 1) laser-assisted chemical vapor deposition (CVD) for highly efficient growth and integration of 1D nanomaterial of carbon nanotubes (CNTs), 2) laser direct writing (LDW) of graphene ribbons under ambient conditions, and 3) LDW of 3D micro/nanostructures via additive and subtractive processes. Comparing with the conventional fabrication methods, the laser-based methods exhibit several unique advantages in the micro/nanofabrication of advanced functional materials and structures. For the 1D CNT growth, the laser-assisted CVD process can realize both rapid material synthesis and tight control of growth location and orientation of CNTs due to the highly intense energy delivery and laser-induced optical near-field effects. For the 2D graphene synthesis and patterning, room-temperature and open-air fabrication of large-scale graphene patterns on dielectric surface has been successfully realized by a LDW process. For the 3D micro/nanofabrication, the combination of additive two-photon polymerization (TPP) and subtractive multi-photon ablation (MPA) processes enables the fabrication of arbitrary complex 3D micro/nanostructures which are challenging for conventional fabrication methods. Considering the numerous unique advantages of laser-based techniques, the laser-based micro/nanofabrication is expected to play a more and more important role in the fabrication of advanced functional micro/nano-devices

Nitrogen-doped diamond was synthesized in open air using laser-assisted combustion flame method. A wavelength-tunable CO2 laser was used to resonantly excite the vibration modes of ammonia molecules, which were added into the diamond forming combustion flame. The wavelength of the CO2 laser was tuned to match frequencies of the NH wagging mode of the ammonia molecules. High efficiency energy coupling was achieved at laser wavelengths of 9.219, 10.35, and 10.719 μm, which are related to a rotational–vibrational transition (1084.63 cm−1), and splitting of the NH wagging mode (υ2+, 932.51 cm−1 and υ2−, 968.32 cm−1). Vibrational excitations of the ammonia molecules under these wavelengths actively intervenes the reaction courses, which steers the chemical reaction in the combustion flame and eventually promotes nitrogen concentration in the deposited diamond films. Concentration of the doped nitrogen atoms reaches up to 1.5 × 1020 atoms/cm3 in the diamond films deposited with a laser wavelength of 9.219 μm. Optical emission spectroscopy and mass spectrometry were used to study the evolution of chemical reactions with and without laser excitations.

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.