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Author: search.filters.author.Khlayboonme, S. T.Subject: search.filters.subject.Chemical vapor deposition

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    Plasma impedance tuning effect on nanostructure of diamond films
    (2013-10-25)
    Thowladda, Warawoot
    ;
    Khlayboonme, S. T.
    The morphology and structure of nanocrystalline diamond films as well as the plasma chemistry were studied by altering the plasma impedance. These impedances related to electron density were altered via the matching system. Two films were grown by the microwave plasma under different values of the plasma impedance, resulting in low and high electron densities in the plasma. By the use of measurements of plasma impedance and optical emission, the lowering of an inductive component of the impedance, indicating an increasing electron density, encouraged H-radical concentration present in the plasma. As the plasma was changed to the high electron density, Raman spectra of the films showed the sp<sup>3</sup> Raman peak shifted from 1325 to 1328.5 cm<sup>-1</sup> with narrower broadening. This behavior arose from an increase in grain size, corresponding to images from a field emission scanning electron microscope. Raman spectra of G-peak position and white light reflectometry showed a reduction in sp<sup>2</sup> carbon content of the film. The G-peak shifted from 1564 to 1541 cm<sup>-1</sup> and refractive index increased from 1.84 to 2.16. The formation of the films related to the concentrations of H and CH3 radicals. The plasma impedance affected the radical concentrations. © (2013) Trans Tech Publications, Switzerland.
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    Nanocrystalline diamond films deposited by two-step approach from CH4/H2 microwave plasma: The influence of reactor pressure
    (2013-08-30)
    Khlayboonme, S. T.
    ;
    Thowladda, W.
    The morphology, growth rate and atomic-bonding structure of nanocrystalline diamond films deposited on Si substrates were investigated under various pressures of the reactor. The films were deposited by CH<inf>4</inf>/H<inf>2</inf> microwave plasma with two-step deposition and H<inf>2</inf>-plasma cleaning processes. The pressures of 1, 2, 5, 9, and 25 kPa were used for deposition. In situ gas-phase species, including electron density, were monitored by an optical spectrometer and impedance analyzer. The films were characterized by SEM, Raman microscope, and white light reflectrometer. When the pressure increased, the surface smoothness and diamond grain size increased, amorphous carbon content decreased, and the intensity ratio of CH/H<inf>β</inf> for the growth step increased. The growth rate was in proportional to the ratio of CH/H<inf>β</inf> for the nucleation step but in inverse proportion to the electron density. The growth rates decreased from 370 nm/h for 1 kPa to 320 nm/h for 2 kPa. After that, the growth rate rapidly increased to 460 nm/h for 9 kPa, but it gradually decreased to 450 nm/h for 25 kPa. The film refractive indices were 2.16 for 5 kPa, 2.21 for 9 kPa, and 2.38 for 25 kPa. The films grown under 1 and 2 kPa showed highly light absorption. © (2013) Trans Tech Publications, Switzerland.