ATOMIC EXCITATION IN A JET-ASSISTED GLOW-DISCHARGE PLASMA PLUME

A jet-assisted glow discharge emission source has previously been shown to suffer from self-absorption when the viewing axis is orientated in line with the support gas flow. This problem can be alleviated by rotating the viewing axis 90-degrees so that the absorption path length is significantly reduced; however, in viewing side-on, line-of-sight measurements of the plasma plume can be accomplished no closer than 25 mm from the sample surface due to geometry limitations. At this axial distance from the sample, the plume shows no Ar 11 emission, which differentiates it from the negative glow. Furthermore. evidence was found that the plume possesses features similar to flowing afterglows: energy is transported from the negative glow to the plume through argon metastable atoms. The collision of two metastable argon atoms produces ionization to the ground state of the argon ion, deactivation to the ground state of the argon atom and an energetic electron (7.32-7.68 eV) which is capable of exciting sputtered atoms. A strong correlation is observed between the square of the argon metastable population and the emission intensity for Cu I and Zn I as the jet flow rate is manipulated.