Matrix effects of easily ionized elements on the spatial distribution of electron number densities in an inductively coupled plasma using an optical fibre probe and a photodiode array spectrometer

Abstract

The effects of alkali and alkaline earth metals on the spatial distribution of electron number densities (n_e) in an inductively coupled plasma have been studied. An optical fibre probe was used to sample the spatial position of the plasma and the photodiode array spectrometer to detect the Hβ line. The resultant lateral profiles were subjected to an Abel inversion. An on-line intelligent background correction method was used to correct the background under the Hβ line, whose full width at half maximum was then calculated automatically. Graphs of three-dimensional spatial distributions of n_e in the presence of K, Na and Ca are compared with that of water. At an observation height of 7.2 mm above the load coil, the n_e increased with decreasing ionization potentials of the elements. At an observation height of 9.6 mm, no measurable increase of n_e is observed except for K.