Paper PS1+SE-MoM8
OES Imaging and Double Langmuir Probe Studies of Flow-through, Supersonic Microplasma Jet Sources

Monday, October 21, 2019, 10:40 am, Room B131

Spatially-resolved OES imaging and double Langmuir probe (DLP) measurements were carried out on flow-through supersonic microplasma jets to highlight how plasma operating conditions (e.g., pressure, current, presence of growth precursors/O₂, distance from the nozzle) affect the local gas (T_rot and T_trans) and electron (T_e) temperatures in the plasma jet plume. T_rot and T_vib were estimated using semi-empirical and rigorous quantum mechanical fits to OES spectra of the first positive group of N₂ (B³Π --> A³Σ_u⁺), and T_e was obtained via fits to DLP IV curves. Experiments on Ar jets with downstream pressures in the 10-200 Torr regime yielded estimates of T_rot = T_g and T_vib of 500-700 K and 5000-6000 K, respectively, using two independent methods. DLP data gave estimates of T_e in the 1-3 eV range, which depended on the exact location in the expanding jet plume. The transition between a pre-discharge-like operating regime at low plasma currents to true hollow cathode operation at high currents was also observed in the plasma IV characteristic and companion OES measurements. The talk will highlight OES imaging and DLP results, as well as the effect of gas additives, i.e., the presence of film deposition precursors and/or oxidants in the jet feed vs. background gas, on jet operating characteristics (T_e, T_gas, etc.).