Pulsed glow discharges for analytical applications
Résumé
Non equilibrium plasmas such as glow discharges have become a commonly used tool in direct surface and interface analysis of solid materials. The application of pulsed glow discharges to material analysis has been studied by several research groups over the last 20 years. Two European projects, EMDPA and GLADNET currently work on the analytical applications of glow discharges, giving a particular attention to pulsed discharges. This review demonstrates the advantages of pulsed discharge operation by showing how the specific excitation and ionisation processes observed during the plasma ignition phase and the afterglow can be used for analytical applications. In the first part of the review the dominant physical processes occurring during the plasma ignition and the afterglow of a pulsed plasma are reviewed. For both phases, the evolution of the population of electrons and sputtered atoms is discussed and related to the excitation and ionisation processes. In view of the complexity of the processes occurring and the variety of experimental conditions presented in the published papers, we have made some effort to point-out and compare the relevant features of the various experimental set-ups used. In the second part of this review, analytical applications of pulsed discharges for both mass spectrometry and optical emission techniques are presented and discussed. In particular the importance of time resolved signal acquisition is pointed out. The question of why pulsed discharges have not yet been introduced in routine analysis despite their obvious advantages over the continuous mode is discussed. Finally the first exciting results of the application of a pulsed glow discharge to surface and interface analysis of polymer multi-layers are shown.