TIME-RESOLVED STUDIES OF IONIZED SPUTTERED ATOMS IN PULSED RADIO-FREQUENCY POWERED GLOW-DISCHARGE MASS-SPECTROMETRY

The temporal evolution of the ionized sputtered atom population in a p ulsed radio frequency (rf) powered argon glow discharge is investigate d using mass spectrometry. Ionized sputtered atoms are found to exhibi t temporal signal profiles that differ from the temporal signal profil es of ionized discharge gas species. The signals for ionized sputtered atoms are observed to maximize approximately 1.6 ms after the termina tion of the discharge power. The temporal signal profiles of ionized s puttered atoms are influenced by the discharge working parameters, i.e ., discharge power, duty cycle, support gas composition, and sampling distance. In addition, the ion kinetic energy distributions depend on the time regime during which the ions were formed. Ionized sputtered a toms formed during the afterpeak time regime exhibit a higher average kinetic energy and narrower kinetic energy distribution than those ion s formed during the plateau time regime. These results indicate that t he Penning process dominates analyte ionization during the afterpeak t ime regime of the pulsed rf-powered glow discharge plasma. The time-de pendent nature of the ion signals permits the use of time-gated detect ion to provide discrimination against certain spectral background spec ies.