Experimental investigation on the floating potential of cylindrical Langmuir probes in non-Maxwellian electron distributions

[Chen and Arnush Phys. Plasmas 8, 5051 (2001)] theoretically showed that the floating potential is not constant but a function of electron density and the potential difference between the floating potential and the plasma potential differs significantly from the plane probe approximation. The electron energy distribution functions (EEDFs) in an inductively coupled plasma are measured to investigate the effect of the EEDF on the floating potential at argon pressures of 2 and 10 mTorr with respect to rf power. It is found that the measured EEDFs at 2 mTorr were bi-Maxwellian EEDFs with a high-energy tail and the potential differences were governed by the high electron temperatures. In the case of 10 mTorr, the measured EEDFs were nearly Maxwellian EEDFs at 10 mTorr and the potential difference agrees qualitatively with the theory of Chen and Arnush assuming that the electron energy distribution is a Maxwellian EEDF. (c) 2005 American Institute of Physics.