Spatially resolved absolute densities of reactive species and positive ion flux in He-O₂ RF-driven atmospheric pressure plasma jet: touching and non-touching with dielectric substrate

Atmospheric pressure plasma jets (APPJs) are operating in direct contact with dielectric substrates for many applications. Nonetheless, many studies have been focusing on free jets. In this letter, we report spatially resolved measurements of reactive species including neutral and ionic species in an He + 1% O₂ RF-driven APPJ by molecular beam mass spectrometry equipped with a dielectric sampling plate, enabling to detect species densities for APPJ operating remotely or in direct contact with a substrate. The spatially resolved distribution of O, O₂(a ¹Δ_g) and O₃ is dominated by convection and, remarkably, shows minimum differences between touching and non-touching conditions.