Abstract
A pulsed microwave-excited atmospheric pressure plasma jet MWAPPJ in helium, has been investigated by optical emission spectroscopy OES. Beside helium spectral lines various excited species such as atomic oxygen OI, hydrogen H α line, N2 + ion and nitrogen molecule species N2 (C3Πu) which are responsible for metal surface activation. The rotational T rot and vibrational temperature T vib were evaluated using optical emission spectroscopy and their dependences on the pulsed microwave parameters such as duty factor (20–70%) and a repetition rate (4 to 90 kHz) are investigated. Spectroscopic measurements show that, T rot, T vib and relative emission intensity of excited species greatly increases with increasing pulse duty factor. Meanwhile they show weak dependences as repetition frequency increased. Surface characterization of the examined stainless steel samples were performed through contact angle, Atomic force microscope AFM and X-ray photoelectron emission spectroscopy XPS. The contact angle decreased from 71° to 20° after pulsed MWAPPJ helium plasma at duty factor of 70% treatment for 30 s, which it is mainly due to incorporation of oxygen-containing functional groups as inferred from XPS results.
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