Plasma parameters and electric field fluctuations in a cold micro-plasma jet interacting with a substrate

Abstract

Interaction of a cold atmospheric pressure micro-plasma jet with different types of substrates having a range of electrical permittivity (εr), such as conductor (copper), semiconductor (p-type silicon), insulator (Teflon and quartz), and biological (goat skin), is carried out experimentally. The electric field fluctuations, cross-phase analysis, plasma parameters [electron excitation temperature (Texc) and electron density (ne)], average propagation velocity of the plasma bullet, gas temperature (Tg), power dissipated on the substrates, and substrate temperature are investigated during the interaction. Cross phase analysis and plasma bullet velocity support the return stroke phenomenon for high εr samples, such as copper and silicon, and a surface ionization wave is generated in the case of low εr samples, such as Teflon, quartz, and biological tissue. The highest substrate current (IS) is observed for copper due to its high conductivity. Tg and ne are affected by the interaction; however, Texc is observed to change only slightly. ne is comparatively higher for high εr samples, and for all samples, it increases initially and, thereafter, decreases as we get closer to the sample's surface. Tg is comparatively higher for low εr samples and increases axially downward from the orifice of the jet, it is lower and almost constant for copper and silicon. The electric field fluctuation (EZ and Eϕ components) frequencies lie up to ∼8 kHz with a peak amplitude at ∼1 kHz, which is found to be comparatively higher for low εr samples.