Effects of Limiting Orifice (Anode) Geometries on Charged Particle Characteristics in an Analytical Radiofrequency Glow Discharge as Determined by Langmuir, Current and Voltage Probes

Abstract

Fundamental studies were performed to assess the role of limiting orifice (anode) diameter on the charged particle characteristics of a radiofrequency glow discharge (rf-GD) atomic emission source. Measurements of the electron and ion number densities, electron temperature, average electron energy and electron energy distribution function were made by using an impedance-tuned Langmuir probe. The electrical features of the rf-GD were studied by the simultaneous use of voltage and current probes. Studies were focused on the effects of the limiting orifice geometry on the rf-GD operation under various conditions of operating pressure and probe sampling position. The results show that limiting orifice diameters and discharge pressures have an important role in the excitation conditions of rf-GD sources. In addition, rf-power generator systems can greatly affect electron and ion densities, and to a lesser extent the electron temperature, average electron energy and electron energy distribution functions. Some phenomena previously reported, including conditions that produce self-absorption in atomic emission applications and the high degree of spatial specificity in MS applications, are reasonably explained.