Effect of structured electrodes and electrode materials on electron power absorption and helium metastable densitiy in microplasma jets driven by tailored voltage waveforms *

Atmospheric pressure capacitively coupled radio frequency plasmas are widely used for different applications, e.g., biomedical surface treatment and etching/deposition. The main challenge is to generate and selectively control the application relevant excited species. In this work, we use a reference microplasma COST-jet constructed using different electrode materials and structured electrodes. The jet is operated in He/N2 and He/O2 mixtures and driven by single frequency as well as tailored voltage waveforms. We use Tunable Diode Laser Spectroscopy (TDLAS) to monitor the density of He-I 2³S₁ metastables and Phase Resolved Optical Emission Spectroscopy (PROES) to study the spatio-temporal dynamics of energetics electros in the COST-Jet. The experimental results are compared to kinetic (PIC/MCC) and fluid simulation results. We demonstrate that the choice of the material and topology for the powered and grounded electrode influences the electron heating dynamics, and as a consequence the generation of metastable species. Furthermore, we show that the combination of Voltage Waveform Tailoring and structured electrodes allows us to greatly influence electron power absorption dynamics and the generation of helium metastables inside the used trenches.