Authors:
L. S. Fan
Z. Q. Xie
J. B. Park
X. N. He
Y. S. Zhou
Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0511

L. Jiang
Department of Mechanical and Automation Engineering, Beijing Institute of Technology, Beijing 100081, People’s Republic of China

Y. F. Lu
Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, Nebraska 68588-0511

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 (&ugr;₂+, 932.51 cm⁻¹ and &ugr;₂−, 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.