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Atmospheric pressure water-vapor plasma in an air-shielded environment by water flow

Atmospheric pressure plasma sources in air-shielded environment by water flow were developed for a plasma process utilizing water-derived reactive species without air contamination in the atmosphere. An atmospheric pressure plasma jet with He gas was enclosed by a cylindrical water flow preventing air contamination to the plasma without using a gas flow shield, vessel or pump. Suppression of air contamination into the plasma was confirmed by optical emission spectroscopy. Furthermore, a microwave-excited water-vapor plasma source in a space shielded by a cone-shaped water flow was developed using a coaxial waveguide with a ring-shaped slot to use a high-density hydroxyl radical without air contamination at atmospheric pressure. A water-vapor plasma without air was successfully realized by pulsed-microwave discharges. Production of a hydroxyl radical was confirmed from the optical emission from the plasma. As an application example of the water-vapor plasma in the air-shield environment, atmospheric pressure photoresist removal treatment was demonstrated and the removal rate as high as 2.2 μm min−1 was obtained.