Selective supply of atomic oxygen to a surface placed in room air using vacuum ultraviolet photolysis of carbon dioxide

Reactive species play important roles in plasma treatments of surfaces, including polymers, metals, water, and living tissues. To elucidate the surface reaction mechanism, it is crucial to measure the effect of each type of reactive species on the surface treatment. Accordingly, we previously developed a method to selectively supply OH or O radicals to a surface placed in room air. Ar/H2O or Ar/O-2 gas flowing through a quartz tube is irradiated with a vacuum ultraviolet lamp, causing photodissociation of H2O and O-2 to produce OH and O. The resulting gas flows to the surface from the tube end. The O density supplied to the surface, however, is only approximately 1x10(12) cm (-3) according to our simulation, which is not sufficient to determine the surface treatment effect of O atoms. Therefore, in this study, a new method is proposed, supplying O atoms with a density that is two orders of magnitude higher. Specifically, CO2 gas is used as the medium to be photodissociated instead of O-2 gas. The performance of this method is discussed herein using simulation results. The maximum O density supplied to the surface reaches 1x10(14) cm(-3) according to the simulation. Additionally, the experimental results demonstrate that the newly developed method can supply a sufficient amount of O atoms to selectively measure the effect of O atoms on the surface treatment of polypropylene (PP). In particular, the water contact angle (WCA) is considered as an index of the surface treatment. As a result, O atoms decrease the WCA of the PP surface at rates of the same order of magnitude as OH.