Characterization of Ar–O2 DC Discharge Employing Langmuir Probe in Conjunction With Photodetachment

Negative oxygen ions (O2- + O-) in the bulk of a dc discharge for Ar/O2 gas mixture have been determined employing Langmuir probe-assisted laser photodetachment. Electron density and temperature were obtained for the mixture at discharge powers between 2 and 15 W and pressure between 75 and 375 mtorr. Electron temperature shows very minimum dependence on pressure, while electron number density is increasing with power and decreasing as a function of pressure. Total negative ion number density showed an increasing trend as a function of power, while decreasing as the pressure was increased at a constant discharge power. Equally negative ion density was found to decrease as the O2 percentage in the mixture was increased under the same conditions of discharge pressure and power. The maximum negative ion number density was found to be about 6.5 E14 at 75 mtorr and 5.5 W of power with 25% O2 in the mixture. The electronegativity at 150 mtorr pressure and 5 W of discharge power was found to decrease from 0.21 to a minimum of 0.06 and increase again to 0.11 as the O2 partial pressure was varied from 25% to 100% with the minimum at 75% O2.