Aachen PK 2003 – scientific programme

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P: Plasmaphysik

P 17: Poster III

P 17.10: Poster

Thursday, March 20, 2003, 17:30–19:15, Foyer

The role of secondary electron emission in RF plasmas — •Paulo Lima, Paulo Lima, Alec Goodyear, and Nicholas Braithwaite — The Open University, Oxford Research Unit, OX1 5HR, UK

Secondary electrons are released from surfaces where electron- ion recombination is in progress. Such emission is often used to account for uncertainty in the nature of currents recorded on probes and other electrodes, where a combination of ion collection and secondary electron emission may occur. The density and mean energy of electrons close to electrodes in self-sustaining DC and RF discharges at medium pressure can be particularly sensitive to secondary electrons (cf hollow cathode sources, filament assisted discharges, PIC simulations and probe measurements of RF capacitive plasma). Necessary conditions for secondary electrons to be efffective is that they are emitted from surfaces at potentials significantly lower than that of the bulk plasma and in sufficient quantity. The secondary yield from metals following low energy ion bombardment and recombination is not as well catalogued as that from high-energy bombardment (100s eV and above). Experiments have been done on secondary emission from surfaces exposed to low to medium pressure RF plasmas. The measurements involve a combination of DC and RF bias on test surfaces, in conjunction with temporally and spatially resolved emission spectroscopy. Optical emission can be identified that is directly associated with secondary electron release, leading to quantitative measures of the role of secondary electrons in sustaining the plasma.