| Atmospheric pressure dielectric barrier discharge (APDBD) possesses various advantages, such as simplification of experimental set-up, free of complicated vacuum system, wide range of applied power, can producing large amounts of reactive species and do not cause high substrate temperature, So it would be explored for various applications in material field in future. In this work, Ar and CH4 were applied as assisted gas and reactive gas, respectively.Nano-scale diamond-like carbon (DLC) films were successfully prepared and meanwhile the deposition processes were in-situ diagnosed by optical emission spectrometry (OES) instrument.Optical emission spectrometry is an excellent diagnostic technique, which is real-time, in-situ, non-invasive and has good temporally and spacially resolved performance. In this work, with Ar as working gas, plasma parameters of the APDBD were characterized, including electron excited temperature,electron density and vibrated temperature.The value of electron temperature and electron density were studied as a function of applied voltages,Ar flow rates, axial positions and radial positions, respectively. In addition, the OES diagnostic on CH4 plasma formed in APDBD plasma gun was also performed.Furthermore, the electrical performance of the APDBD plasma gun was also investigated preliminarily,,including current and voltage waveform, Lissajous figure and current-voltage curve.The main achievements of this work can be concluded as follows:(1)An obvious C-H peak appeared at the range from 2800cm-1 to 3000cm-1 in FTIR spectrum; a broad peak ranging from 1100 cm-1to 1700 cm-1, along with a shoulder peak positioned around 1360 cm-1 occurred in Raman spectrum, which was the noticeable feature of DLC; the DLC film, with 70nm thickness and clusters appearance, was continuous, dense and its average roughness was about 5.9nm; except Ar atom and N2 second positive system spectra lines in the OES result, some other spectra lines of typical particals also appeared, including 314nm CH (X2âˆâ†C2∑+), 386nm-390nm CH (X2âˆâ†B2∑-), 430-433nm CH (X2âˆâ†A2â–³),Ha (2pâ†3d),656.3nm Hr(2pâ†421.2 nm CH+, C2 (X3âˆâ†A3âˆ) and H2 (X1Σgâ†G1Î u). (2) In terms of the plasma formed in APDBD plasma gun, the range of the electron excited temperature increased from 4000K to 8000K. With the applied voltage and Ar flow rate increasing, the relative intensities of the spectra lines increased, while they would decrease as the axial position descended; the variation trends of the electron temperature and the electron density, both as a function of applied voltage, axial position and radial position, were nearly consistent. They both decreased when the applied voltage was elevated or the radial position was descended, and when the radial positions ranged from 0 mm to 2.5 mm, they varied unobviously and both of them achieved the maximum value at 3.5 mm radial position. But the effects of the Ar flow rate on the electron temperature and the electron density were different, namely, an increase in Ar flow rate would contribute to an enhancement in electron density but a reduce in electron temperature; also, the vibrated temperature calculated by N2 ( C3Î u→B3Î g) second positive system was about 2500K.(3) The discharge happened before zero voltage, which was the mian characteristic of the electrical performance. As the applied voltage was elevated gradually, a distortion appeared in current-voltage waveform, the number of discharge pulse increased progressively, the discharge happened in ahead and the Lissajous figure tended to standard parallelogram appearance increasingly. And no phenomenon appeared in current-voltage curve which could indicate the conversion fromαmode discharge toγmode discharge. |
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