Investigation of active species in low-pressure capacitively coupled N2/Ar plasmas

Abstract

In this paper, a self-consistent fluid model is developed focusing on the plasma parameters in capacitively coupled 20% N2–80% Ar discharges. Measurements of ion density are performed with the help of a floating double probe, and the emission intensities from Ar(4p) and N2(B) transitions are detected by an optical emission spectroscopy to estimate their relative densities. The consistency between the numerical and experimental results confirms the reliability of the simulation. Then the plasma characteristics, specifically the reaction mechanisms of active species, are analyzed under various voltages. The increasing voltage leads to a monotonous increase in species density, whereas a less homogeneous radial distribution is observed at a higher voltage. Due to the high concentration of Ar gas, Ar+ becomes the main ion, followed by the N2+ ion. Besides the electron impact ionization of neutrals, the charge transfer processes of Ar+/N2 and N2+/Ar are found to have an impact on the ionic species. The results indicate that adopting the lower charge transfer reaction rate coefficients weakens the Ar+ ion density and yields a higher N2+ ion density. However, the effect on the species spatial distributions and other species densities is limited. As for the excited-state species, the electron impact excitation of background gases remains overwhelming in the formation of Ar(4p), N2(B), and N2(a′), whereas the N2(A) molecules are mainly formed by the decay of N2(B). In addition, the dissociation of N2 collided by excited-state Ar atoms dominates the N generation, which are mostly depleted to produce N+ ions.

Kinetic Modeling Analysis of Ar Addition to Atmospheric Pressure N2–H2 Plasma for Plasma-Assisted Catalytic Synthesis of NH3

“…We first attributed the observation to our low degree of ionization and an abundance of side reactions enabled by the highly collisional environment at atmospheric pressure. But Liang et al and Bogaerts also found that the production of gas-phase N radicals by the dissociative recombination reactions of N 2 + is insignificant at low pressure and higher electron number density in Ar–N 2 plasma. In our model of an atmospheric pressure Ar–N 2 –H 2 plasma, we found that N 2 + is mostly depleted by collision with H 2 molecules to produce gas-phase N 2 H + rather than neutralization by electrons or charge transfer with Ar, and gas-phase N 2 H + can subsequently play a minor role in consuming NH 3 via the gas-phase reaction N 2 H + + NH 3 → NH 4 + + N 2 .…”

“…The Ar contributing factor never exceeds 1, indicating that electron-impact dissociation of N 2 always dominates. In cases when Ar is the dominant gas component in the plasma, N 2 dissociation by excited Ar has been found to surpass electron-impact dissociation. , Our model predicts that the Ar contributing factor is maximized at E/N = 80 Td, when the mean electron temperature is 2.7 eV, and decreases with high n e .…”

“…We first attributed the observation to our low degree of ionization and an abundance of side reactions enabled by the highly collisional environment at atmospheric pressure. But Liang et al 31 and Bogaerts 21 also found that the production of gas-phase N radicals by the dissociative recombination reactions of N 2…”

Numerical simulation of inductively coupled Ar/O₂ plasma

“…产生的离子和中性粒子的温度远小于电子，因此在模型中采用"冷流体"近似， 即假设重粒子的温度为室温(293 K) [14,[23][24][25][26][27][28] ，并在放电过程中保持不变. 此外， 模型中利用所有重物质的质量分数之和为1进行约束，并且假设背景气体为理想 气体.…”

Benchmarking and validation of a hybrid model for electropositive and electronegative capacitively coupled plasmas

“…This hybrid model is established based on the framework of multi-physics analysis of plasma sources (MAPS), which is a comprehensive modeling platform developed by Prof. Wang and his group. MAPS consists of various models, such as the global model [39][40][41], fluid model [42][43][44] and PIC/MCC model [45][46][47], which could qualitatively demonstrate physical mechanisms in lowtemperature plasmas. This newly developed hybrid model, which enjoys low computational cost while maintaining great accuracy, makes MAPS more valuable and powerful in quantitative predictions for physical phenomena, as well as in improvement in equipment design.…”