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A simple collisional–radiative model for the Paschen 1s and 2p levels is proposed for low-temperature argon discharges. This model can predict the population distribution of 1s and 2p levels over a wide discharge pressure range 1–105 Pa and ionization ratio range 10−6–10−3. The modelling results are found to be in good agreement with observed optical emissions from several different types of argon discharges at 1, 100 and 105 Pa. By using the model, the dominant kinetic processes of 1s and 2p levels are investigated for an electron beam plasma, an inductively coupled plasma, a capacitively coupled plasma and a microwave microplasma. A kinetic diagram is given, which can be used to identify the kinetic state of 1s and 2p levels in many low-temperature argon discharges reported in the literature. This model is also useful for obtaining discharge parameters from optical emissions in low-temperature argon discharges.

This article reviews a variety of methods to obtain the electron temperature and density by the emission line ratios for low-temperature plasmas containing argon or nitrogen gas. Based on the collisional–radiative model of excited particles, the underlying principle of each of these methods is described, along with the criterion on how to select an appropriate line-ratio method according to the discharge conditions. Limitations on the application of each line-ratio technique are also discussed.

Effects of gas flow rate on the length of atmospheric pressure plasma jets have been investigated using a capillary dielectric barrier discharge configuration. For the discharge in only downstream region, three distinguishable modes of plasma jet length versus argon gas flow rate, namely, laminar, transition, and turbulent jet mode, have been identified. For the case of discharge in both downstream and upstream regions, the curve of length versus flow rate has significant “dent” in the laminar jet mode for pure helium, neon, and argon flow gas spraying into air ambient.

We have investigated the interactions of Cl and Cl2 with an anodized Al surface in an inductively coupled chlorine plasma. The cylindrical substrate is rapidly rotated within a differentially pumped wall and is exposed to the plasma 35% of the time through a conical skimmer. On the opposite side of the substrate, a second skimmer and differential pumping allows the surface and desorbing products to be analyzed by Auger electron spectroscopy (AES), line-of-sight mass spectrometry (MS), and through pressure rise measurements. In a 600W Cl2 plasma at 5mTorr, the surface becomes covered with a layer with the overall stoichiometry of about Al2Si2O10Cl3, with Si being the result of the slow erosion of the quartz discharge tube. The surface layer composition (specifically Cl coverage) does not change as a function of the delay time (1ms–10min) between plasma exposure and AES characterization. In contrast to AES measurements, the MS signals from Cl2 desorption, resulting from recombination of Cl atoms, decrease by about a factor of 10 over the 1–38ms probed by varying the substrate rotation frequency. Substantial adsorption and desorption of Cl2 are also observed with the plasma off. Cl recombination coefficients (γCl) derived from an analysis of the time-dependent MS signals range from 0.01 to 0.1 and increase with increasing Cl-to-Cl2 number density ratio, suggesting a competition for adsorption sites between Cl2 and Cl.