Plasma–surface interaction at atmospheric pressure: A case study of polystyrene etching and surface modification by Ar/O2 plasma jet

ion by atomic O from the polymer chain has been discussed by different research groups as the most important channel for both low pressure plasma and atmospheric pressure plasma RH þ O ! R• þ OH p 1⁄4 10 ; 10 ; 10 ; (5) where p is the estimated reaction probability for the tertiary, secondary, and primary carbon sites provided by Bhoj and Kushner. It can be seen that the tertiary H has the highest abstraction reaction probability. For the Ar/O2 RF plasma jet, atomic O is the dominant reactive species in the glow region due to the large cross-ion reaction probability. For the Ar/O2 RF plasma jet, atomic O is the dominant reactive species in the glow region due to the large crosssection of electron-impact dissociation of O2. 59 This atomic O can be further transported to the far effluent region through convection and diffusion. Although the density of atomic O in Ar þ 1% O2 plasma has not yet been measured, simulation results show that both Ar þ 1% air and Ar þ 1% O2 plasmas share similar exponential decay profiles along the nozzle-to-sample distance and only the absolute value of atomic O density in Ar þ 1% O2 plasma is slightly higher. The atomic O density profile of the same plasma jet with Ar þ 2% air feed gas in air ambient has been previously measured. It is worth noting that this O density profile was measured without a target surface; however, according to Schroder et al., the presence of a plastic (polyethylene terephthalate) target does not significantly disturb the atomic O distribution measured by TALIF. In order to evaluate the relationship between PS etching and atomic O species in the gas phase, we estimated the average O flux bombarding the PS surface from the atomic O density data in Fig. 3 by using Eq. (6) from the kinetic theory of ideal gases C 1⁄4 1 4 n v 1⁄4 1 4 n ffiffiffiffiffiffiffiffiffiffiffiffiffi 8RTgas pM r