Superhydrophilization of Surface of Aluminum Thin Film by Atmospheric-Pressure Plasma Jet Irradiation

Abstract

An atmospheric-pressure argon (Ar) plasma jet was generated with a frequency of 10 kHz, an applied voltage of 4 kV, and an Ar gas flow rate of 10 L/min. When an aluminum (Al) thin film that was vacuum-deposited on a glass substrate was irradiated with the atmospheric-pressure Ar plasma jet in air for 60 s at an irradiation distance of 2 mm, the surface of the Al thin film was hydrophilized in a circular area with a diameter of 23 mm, which was larger than that of the plasma (6 mm). It was found that the superhydrophilization first occurred at the periphery of the irradiated area (∼5–10 mm from the center of the irradiated area) and then in the area irradiated directly by the plasma (≤∼5 mm from the center of the irradiated area) on the Al thin film. In the previous research on the atmospheric-pressure plasma jet irradiation of Al, the plasma reached Al, and it was reported that the hydrophilicity only improved in the area irradiated directly by the plasma. On the other hand, our plasma in this study did not reach Al. In spite of this, the hydrophilicity improved in the area irradiated directly by the plasma and in the periphery of the irradiated area. On the basis of the results of X-ray photoelectron spectroscopy (XPS), the hydrophobic organic compounds that adsorbed on the surface of the Al thin film are considered to have been removed by the ozone (O₃) generated by the interaction between the plasma and oxygen (O₂) molecules in air. From the O₃ concentration distribution obtained using O₃ test strips, the reason for the faster superhydrophilization in the peripheral area than in the irradiated area was found to be that the peripheral area had the higher concentration of O₃. [DOI: 10.1380/ejssnt.2018.27]