Electron energy distribution functions in low-pressure oxygen plasma columns sustained by propagating surface waves

Electron energy distribution functions (EEDFs) were measured in a 50 mTorr oxygen plasma column sustained by propagating surface waves. Trace-rare-gas-optical-emission spectroscopy was used to derive EEDFs by selecting lines to extract "electron temperature" (T(e)) corresponding to either lower energy electrons that excite high-lying levels through stepwise excitation via metastable states or higher energy electrons that excite emission directly from the ground state. Lower energy T(e)'s decreased from 8 to 5.5 eV with distance from the wave launcher, while T(e)approximate to 6 eV for higher energy electrons and T(e)>20 eV for a high-energy tail. Mechanisms for such EEDFs are discussed.