Improved inflection point method of emissive probe for accurate measurement of plasma potential

The potential of the inflection point of emissive probe characteristics (V-ip) in the limit of zero emission is considered to be an accurate indication of the plasma potential. Previous method for this limit is linearly extrapolating the change of V-ip with respect to the electron emission current I-emis to the limit I-emis approximate to 0, which may result in inaccurate results since evidences showed that V-ip does not change well linearly with I-emis. The authors found in this study that, instead of I-emis, V-ip changes linearly with the probe heating current (I-ht) which is a function of the probe temperature (T-p), and the phenomenon is reasonably interpreted by the space charge voltage increasing linearly with T-p. An improved inflection point method of emissive probe, which utilizes linear extrapolating the V-ip - I-ht relation to the heating current for initial emission, is proposed for accurate measurement of plasma potential. (C) 2016 American Vacuum Society.