Localized Distribution of Atomic Oxygen near Barrier Surface in Sub-atmospheric Pressure O₂ Pulsed Barrier Discharge

Atmospheric-pressure cold plasma (APCP) exhibits high chemical reactivity and valuable applicability to various targets including liquids and living organisms. APCP produces high-density radicals, whereas it has the short lifetime of radicals due to frequent collisional deactivations. To address this issue, plasma generation in sub-atmospheric pressure is an effective way to extend the radical lifetime without the sacrifice of target variety. However, the behavior of radicals in sub-atmospheric pressure is still under investigation.

In this study, we measured the behavior of atomic oxygen (O) in needle-to-sphere pulsed discharge in sub-atmospheric pressure oxygen, using TALIF spectroscopy. As the pressure dependence of atomic oxygen, the O production near the cathode took a maximum at 50 kPa, while the lifetime of O atom increased as the pressure was reduced. Consequently, the flux of atomic oxygen near the cathode was maximized at 50 kPa, where the flux was five times larger than that in atmospheric pressure. The specific production of atomic oxygen near the glass surface was observed in barrier discharge, whereas that at metal-to-metal discharge did not show the localized distribution near the cathode. In contrast, there was no strong discharge emission near the cathode in barrier discharge. This suggests that the specific O production near the barrier surface can be attributed to the relatively low-energy electrons which does not contribute to discharge emission.