Product Code: ICAL08_M704

CO2 Laser Resonant Excitation of Propylene Molecules in Diamond Deposition using Combustion-flame Method
Authors:
Z.Q. Xie, University of Nebraska-Lincoln; Lincoln NE USA
H. Ling, University of Nebraska-Lincoln; Lincoln NE USA
Y.X. Han, University of Nebraska-Lincoln; Linciln NE USA
X.K. Shen, University of Nebraska-Lincoln; Lincoln NE USA
T. Gebre, University of Nebraska-Lincoln; Lincoln NE USA
Y.F. Lu, University of Nebraska-Lincoln; Lincoln NE USA
Presented at ICALEO 2008

CO2 laser resonant excitation of propylene molecules was investigated in propylene/oxygen (C3H6/O2) combustion diamond deposition in open air. The wavelength of the CO2 laser is 10.591 μm, while the central wavelengths of C-H and C-C vibrational modes in propylene molecules are 10.684 μm and 10.881 μm, respectively. The absorption peaks of these two modes are broadened by the high ambient pressure, which cover the CO2 laser wavelength and enable the resonant absorption. The inner cone of the C3H6/O2 flame became shorter and brighter with the CO2 laser irradiation at a laser power of 800 W. The scanning electron microscopy images showed better crystal grains in the diamond films deposited with the CO2 laser excitation. The film thickness also had an obvious increase within the same deposition time, indicating a higher growth rate of diamond films. The effect of different positions where the laser irradiated into the flames was also studied. It was found that when the laser beam was in the middle of the flame, the diamond growth had the optimal results, which was the equilibrium of two mechanisms. The laser resonant excitation is beneficial to generate some desired radicals for diamond deposition. Besides the generation of the radicals, radical dispersion to substrate is another key factor for diamond deposition in this process. Optical emission spectroscopy was used to study the effect of the resonant excitation of C3H6. Emission of C-H and C-C species was enhanced with the CO2 laser excitation, indicating that there were more active species generated.