We investigated the interactions of atomic and molecular chlorine with plasma-conditioned stainless steel surfaces through both experiments and modelling. The recombination of Cl during adsorption and desorption of Cl2 was characterized using a rotating-substrate technique in which portions of the cylindrical substrate surface are periodically exposed to an inductively coupled chlorine plasma and then to an Auger electron spectrometer in separate, differentially pumped chambers. After several hours of exposure to the Cl2 plasma, the stainless steel substrate became coated with a Si-oxychloride-based layer (Fe : Si : O : Cl ≈ 1 : 13 : 13 : 3) due to chlorine adsorption and the erosion of the silica discharge tube. Desorption of Cl2 from this surface was monitored through measurements of pressure rises in the Auger chamber as a function of substrate rotation frequency. Significant adsorption and desorption of Cl2 was observed with the plasma off, similar to that observed previously on plasma-conditioned anodized aluminium surfaces, but with much faster desorption rates that are most likely attributable to the smoother and non-porous stainless steel surface morphology. When the plasma was turned on, a much larger pressure rise was observed due to Langmuir–Hinshelwood recombination of Cl atoms. Recombination coefficients, γCl, ranged from 0.004 to 0.03 and increased with Cl-to-Cl2 number density ratio. This behaviour was observed previously for anodized aluminium surfaces, and was explained by the blocking of Cl recombination sites by adsorbed Cl2. Application of this variable recombination coefficient to the modelling of high-density chlorine plasmas gives a much better agreement with measured Cl2 percent dissociations compared with predictions obtained with a recombination coefficient that is independent of plasma conditions.

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A simple fluid model was developed in order to investigate the driving kinetics of neutral and charged species in high-density chlorine plasmas. It was found that the dissociation degree of Cl2 molecules is directly linked to the power balance of the discharge which controls the electron density. The model was also used to identify those reactions that could be neglected in the particle balance of charged species and those that must be included. Our results further indicate that diffusion losses need to be considered up to a pressure that depends on magnetic-field intensity and reactor aspect ratio. Finally, it is shown that the dominant charged carriers are linked to the dissociation level of Cl2 molecules.

Measurement of the rotational temperature of the second positive system of N 2 was used as a diagnostic of the gas temperature in low-pressure inductively coupled Ar, Kr and N 2 plasmas. The rotational temperatures determined from the rovibrational bands (ν , ν ) = (0, 0), (1, 0), (0, 2) and (4, 2) of the N 2 C 3 u → B 3 g system differ by about 300 K depending on the operating gas pressure in the 0.4-20 mTorr range. Important discrepancies exist between the temperatures found from each of the rovibrational bands of N 2 . This shows that the method has important intrinsic uncertainty that may be due either to errors in the transition probabilities of N 2 C 3 u → B 3 g or to inefficient thermal coupling between translational and rotational temperatures. In the case of argon, the population of the emitting C 3 u states by energy transfer from Ar 3 P 0,2 metastable atoms is also considered as a possible factor influencing the rotational structure of some rovibrational bands. Based on these measurements, it is shown that, in the range of experimental conditions studied herein, the uncertainty of the method should be carefully accounted before considering one of the rotational temperatures of the N 2 second positive system equal to the gas temperature.

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