Effects of Helium Addition to Radio-Frequency Argon Glow-Discharge Mass Spectrometry

The addition of helium to argon up to 5% significantly decreased the sputtering rate for a brass sample, while about 30% increases of copper and zinc-ion signals were observed upon the 2% helium addition. The normalized ionization efficiencies were calculated from the ratio of the ion intensity and the atom density in the plasma measured by atomic absorption spectrometry. The ionization efficiency at 4% addition of helium was 25-times higher than that for pure argon. No change in the DC self-bias voltage was observed for various additions of helium, These characteristics were compared with the oxygen addition as well as with a DC glow discharge. The differences in the ion-signal behavior between the radio frequency and DC glow discharges are discussed.