Characterizing the dominant ions in low-temperature argon plasmas in the range of 1–800 Torr

Abstract

The dominant ions in low-temperature rare gas plasmas can be either molecular ions or atomic ions depending on the discharge regime. In this paper, the dominant ions in low-temperature argon plasmas are characterized in a wide range of gas pressure (1–800 Torr). The channels for creation of molecular ions include atom assisted association, dissociative recombination, dissociation by atom impact (DAI), and dissociation by electron impact (DEI). The latter two were previously less often considered. It is found that the DEI reaction has a significant impact on the ion fractions, while the effect of the DAI reaction is much less important in the whole investigated gas pressure regime. As the gas pressure increases from 1 to 800 Torr, the atomic ion fraction drops rapidly in conjunction with an increase of the molecular ion fraction. This phenomenon confirms that in low-temperature argon plasmas the dominant ion will be the atomic ion in the low pressure regime but the molecular ion in the high pressure regime. The impact of power density is also investigated in combination with the DEI reaction. The results show that both the DEI reaction and the power density serve to delay the transition trend of the ion fraction, shifting the dominance of molecular ions to a higher pressure.