On the Role of Metastable States in Low Pressure Oxygen Discharges

TL;DR

This study investigates how metastable states affect electron heating, temperature, and electronegativity in low-pressure oxygen discharges using particle-in-cell simulations, highlighting the importance of detachment processes at higher pressures.

Contribution

It demonstrates the significant influence of metastable state detachment on discharge properties across a range of low pressures, providing insights into electron heating mechanisms.

Findings

Detachment processes significantly affect discharge properties at higher pressures.

Electron heating shifts from ohmic in the bulk at low pressure to sheath regions at higher pressure.

Metastable states influence effective electron temperature and electronegativity.

Abstract

We use the one-dimensional object-oriented particle-in-cell Monte Carlo collision code {\tt oopd1} to explore the spatio-temporal evolution of the electron heating mechanism in a capacitively coupled oxygen discharge in the pressure range 10 -- 200 mTorr. The electron heating is most significant in the sheath vicinity during the sheath expansion phase. We explore how including and excluding detachment by the singlet metastable states O$_2$(a$^1 \Delta_{\rm g}$) and O$_2$(b$^1\Sigma_{\rm g}^+$) influences the heating mechanism, the effective electron temperature and electronegativity, in the oxygen discharge. We demonstrate that the detachment processes have a significant influence on the discharge properties, in particular for the higher pressures. At 10 mTorr the time averaged electron heating shows mainly ohmic heating in the plasma bulk (the electronegative core) and at higher pressures there is no ohmic heating in the plasma bulk, that is electron heating in the sheath regions dominates.