Optical emission spectroscopy of atmospheric pressure microwave plasmas

Abstract

The optical emission behaviors of Ar, He, and Ar+He plasmas generated in air using an atmospheric pressure microwave plasma source have been studied employing optical emission spectroscopy (OES). Emissions from various source gas species and air were observed. The variations in the intensities and intensity ratios of specific emissions as functions of the microwave power and gas flow rate were analyzed to investigate the relationship between the emission behavior and the plasma properties. We find that dependence of the emission behavior on the input microwave power is mainly determined by variations in electron density and electron temperature in the plasmas. On the other hand, under different gas flow rate conditions, changes in the density of the source gas atoms also significantly affect the emissions. Interestingly, when plasma is generated using an Ar+He mixture, emissions from excited He atoms disappear while a strong Hα signal appears. The physics behind these behaviors is discussed in detail.

Low temperature co-fired ceramics plasma generator for atmospheric pressure gas spectroscopy

“…5. The obtained emission spectra for LTCC-based plasma generator were comparable with the ones presented in the literature [24,[27][28][29]. Peaks, which corresponds to certain transitions, are broaden and rather Gaussian-like than in shape of Dirac delta function.…”

Effect of substrate bias on the promotion of nanocrystalline silicon growth from He-diluted SiH4 plasma at low temperature

“…39,40 Metastable He*, having energies sufficiently larger than the dissociation energy of SiH 4 (;10 eV), plays a vital role in the process of dissociation of SiH 4 molecules to form radicals, e.g., SiH 3 , SiH 2 , etc. Also the collision cross section between He* and SiH 4 is quite large.…”

High rate synthesis of crystalline silicon films from SiH4+He using high density microwave plasma

“…33 On the other hand, we have verified previously that in the plasmas with He as one of the source gases, number density of the excited He atoms is quite large and most of the excited He atoms are in the metastable states He ‫ء‬ , leading to the occurrences of the Penning ionization and excitation. 34,42,43 The He ‫ء‬ atoms have energies of 19.8 or 20.1 eV that are extremely larger than the dissociation energy of SiH 4 of around 10 eV. Also the cross section of collisions between the He ‫ء‬ and SiH 4 is quite large.…”

“…1͑b͒ employs a hybrid-mode resonator cavity. 33,34 The cavity was designed by taking into account the resonance frequency shift caused by plasma, such that it is resonant to the microwaves in a transverse magnetic 010-like mode before the plasma ignition and in a transverse electromagnetic ͑TEM͒like mode after the plasma ignition. 35 The 2.45 GHz microwaves generated from magnetron propagate through waveguides and coaxial cable, and are coupled into the cavity through a rod antenna.…”