Electronegativity of low-pressure high-density oxygen discharges

Abstract

We use a global (volume averaged) model to study the presence of negative ions and metastable species in low-pressure high-density oxygen discharges. We find the negative oxygen ion O − to be the dominant negative ion in the discharge, the density of the negative ion O − 2 to be small and the density of the negative ion O − 3 to be negligible in the pressure range of interest, 1-100 mTorr. Dissociative attachment of the oxygen molecule in the ground-state O 2 (3 − g) and the metastable oxygen molecule O 2 (a 1 g) are the dominating channels for the creation of the negative oxygen ion O −. At low pressure (<5 mTorr) recombination involving O − and O + ions is the main loss channel for O − ions. At higher pressure, the detachment on O(3 P) becomes the main loss channel for the O − ion. The creation of O − 2 is mainly through dissociative attachment of ozone O 3. Ozone is almost entirely created through detachment by the collision of O − with the metastable oxygen molecule O 2 (a 1 g). The creation of O − 2 is thus greatly influenced by this detachment process and neglecting the detachment has a significant influence on the density of O − 2 ions. At low pressure (<10 mTorr) the O − 2 ion is mainly lost through recombination while at higher pressure the charge transfer to form O 2 is the dominating loss process.

Control of plasma properties in capacitively coupled oxygen discharges via the electrical asymmetry effect

“…The former is beyond the scope of a one-dimensional model and we thus assume a constant density of O 2 (a 1 g ) in the whole chamber of 10% of O 2 density (corresponding to the data of Gudmundsson et al [46] at the chamber center) as Bronold et al did in [48]. For the collisions, which only have rate constant κ available, we adopt Nanbu's method [62] based on Direct Simulation Monte Carlo.…”

“…This has been our motivation of conducting a combined experimental, numerical and analytical investigation of CCRF discharges in pure oxygen. Oxygen discharges, being one of the simplest electronegative plasma system, provide an interesting scenario for theoretical modeling (see for example [41][42][43][44][45][46][47][48][49][50]52] and references therein) and experimental diagnostics [49,50,[52][53][54][55][56][57] of electronegative plasmas. In contrast to the previous work of the EAE in oxygen discharges with only numerical simulation [36], our complementary approach here certainly promises a more comprehensive description of the discharge properties.…”

1-D fluid model of atmospheric-pressure rf He+O2 cold plasmas: Parametric study and critical evaluation

“…As a result HeþO 2 plasmas are typically operated with reduced amount of oxygen and maximum process efficacy is often encountered at oxygen concentrations below 1%. 44,45 In the last decades, global models have been used to study low-pressure electronegative plasmas [46][47][48][49] and in recent years these models have been extended to the study electronegative atmospheric-pressure discharges. [15][16][17][18] In these models it is customary to assume that the input power is mainly coupled to the electrons 50 with various approximations regarding the power coupled to ions in the sheath.…”

Particle-in-cell Monte Carlo and fluid simulations of argon-oxygen plasma: Comparisons with experiments and validations

“…Table I shows the oxygen reaction set considered in the 2D fluid simulation of pure oxygen plasma in ICPs. 3,15,[17][18][19] We consider four charged species ͑electrons, positive oxygen ions O 2 + , negative oxygen ions O − , and positive oxygen ions O + ͒, two metastable species ͑O 2 a and O D ͒, and background oxygen atoms and molecules ͑O and O 2 ͒. We assume that the background molecular oxygen density is constant and the temperature of all species except the electrons is 0.026 eV.…”