Monte Carlo Analysis of Electron Swarm Parameters in Nitrogen under Radio-Frequency Electric Fields

Monte Carlo simulations of electron swarms in N₂ gas [1] in boundary-free space under 13.56 MHz RF electric fields were performed to investigate production of reactive species, N radical and metastable excited N₂. The waveforms of mean electron energy 〈ε〉, drift velocity W, and collision frequency ν_k of the kth kind of collision were observed at various gas pressures around 133 Pa at an amplitude of the RF field 10000 V/m. The rise and fall of 〈ε〉 have an asymmetry unlike those of W. ν_k (ν_ion of ionization, ν_meta of excitation to the metastable state, ν_dis of dissociation of N₂, and ν_vib of vibrational excitation) varying synchronously with 〈ε〉 show changes particular to the energy range that each collision cross section lays. The waveform of ν_meta, its associating threshold is the lowest in the electronic excitations, is similar to that of 〈ε〉. ν_ion, the ionization threshold is the highest in the collisional processes, rises steeply when the high-energy tail of the electron energy distribution function (EEDF) reaches the threshold. ν_dis, the associating collision cross section ranges only around 10–12 eV, varies with a trapezoid-like waveform with a plateau where ν_dis is insensitive to the increase of 〈ε〉. ν_vib shows a two-peak waveform linked with the RF response of the EEDF.

[1] Y. Ohmori, M. Shimozuma and H. Tagashira, J. Phys. D: Appl. Phys. 21 724-729 (1988)