The first part of this paper uses a contamination layer model to discuss the effects of electrode contamination upon electron temperatures estimated from Langmuir probe measurements. The model assumes that the contamination layer is equivalent to a parallel capacitor and resistor. It predicts two main features associated with electrode contamination. One of them, the so-called "frequency dependence," concerns the sweep-rate of the probe voltage and is well understood. The other is that the effect of a contaminated electrode is decreased as the density of the ambient plasma is decreased and this will be called "density dependence." We present several experimental results which verify the above predictions. This paper also presents some other experimental results which may be useful in improving the accuracy of Langmuir probe measurements. Finally the effects of electrode contamination upon electron density estimates and energy distribution measurements are briefly discussed.
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