engleski

Optical emission spectroscopy of inductively coupled RF methane plasma

Inductively coupled RF methane plasma was generated in a linear borosilicate glass tube and studied by means of optical emission spectroscopy. Plasma was created by an 8 turn coil with an EM field oscillating at 13.56 MHz. Various total pressures (up to 200 Pa) and discharge powers (100-300W) were investigated. Optical spectra in the range from 200 nm to 980 nm were measured by means of a LIBS2000+ spectrometer system with spectral resolution 0.1 nm. Optical fibre was placed to observe plasma emission along the tube. For pure methane plasma optical spectra show signatures of atomic hydrogen lines (Balmer series: n=3, 4, 5 → n=2) and molecular features H2 Fulcher band (d3Π → a3 Σg+) around 602 nm , CH (A2Δ(v’=0)-X2Π(v”=0)) band at 431 nm, H2 (g 1Σg+→ b 1Σu+) around 460 nm and H2 continuum emission (a3Σg+ → b3Σu+) from 200-600 nm. In some cases CN (B 2Σ+ - X 2Σ+) molecular band at 388 nm was observed as an impurity. Above mentioned spectral features were studied in respect to methane pressure and discharge power. Spectral simulations of main molecular bands were performed. For example, for CH band rotational and vibrational temperatures of 1500 K and 3000 K were obtained, respectively. Possible excitation mechanisms of main plasma constituents were considered and prospect for OES methane plasma diagnostics is discussed in terms of various applications.

opical emission spectroscopy; inductively coupled plasma; methane plasma

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