Optical Measurements of Atmospheric Pressure Direct Current He/H2 Microplasma in Open Air for Surface Modification

Abstract

Gas discharge parameters of a direct current Ar+2%H2 non-thermal microplasma operated at atmospheric pressure were measured in this work. The microplasma was investigated in the normal and abnormal glow regimes, for current ranging from 10 to 130 mA, at ~ 160 - 250 V of applied voltage for a cathode formed with Cu+Mo+Fe foils, covered with mica at front face Cu foil. The microplasma goes through an opening hole traversing the dielectric and metal foils and emerging on open air. Both OH (A 2 Σ + , ν = 0 → X 2 Π, ν ' = 0) and N2(C 3 ∏u , ν = 0 → B 3 ∏g, ν ' = 2) bands were used to estimate the gas temperature, which ranges from 450 to 800 K. The electron number densities, ranging from 3.0 × 10 14 to 8.0 × 10 14 cm -3 , were determined by the Hβ line. Excitation temperatures were measured from three methods: from two Cu I and Mo I spectral lines ratio (Texc = 2 700 K) and from Boltzmann-plot of both Fe I and He I transitions (Texc = 3 000 K). The vibrational temperature was carried out from the second positive system N2 (C 3 ∏u → B 3 ∏g) for Δν = -2 and it was in the range 2500 - 3000 K for a current varying from 20 to 100 mA.