Spectral characterization of medium-pressure RF discharge in argon–oxygen mixture

Abstract

This study is devoted to the characterization of a 40 MHz RF discharge at 2 Torr pressure in argon–oxygen mixtures (0–5% O2 fraction). The electrical characteristics were used to determine the electron density ne and reduced electric field E/N in the plasma. The gas temperature Tg and number densities of Ar atoms in 1s states were determined from spectral measurements. The spectral measurements were also used to obtain the relative populations of argon 2p and atomic oxygen 35P and 33P states as a function of ne and O2 fraction.It was shown that the number density of Ar atoms in 1s states increased with the growth of O2 fraction, and the density of Ar 1s states was sufficiently high to cause the trapping of radiation originating from Ar atoms in 2p states. Argon atoms in 2p states were predominantly populated from 1s states; population from the Ar ground state was found to be important only for the 2p1 state at higher O2 fraction. The excitation of the O 5P state was caused by electron impact, while in the case of O 3P state excitation the role of electrons was negligible.