Resonance ionization mass spectrometry of sputtered osmium and rhenium atoms

The mass spectrometric analysis of Os and Re was investigated by use of a pulsed primary Ar^+ ion beam to provide sputtered atoms for resonance ionization mass spectrometry. A useful yield of 10^(-2) and a detection limit of 8 ppb were demonstrated for Os concentration measurement. In situ measurements of Os concentration are obtainable by this method at the sub-part-per-million level in conducting and semiconducting materials with a full width at half maximum beam diameter of ~70 µm. An ionization scheme for Os that utilizes three resonant energy levels (including an autoionizing energy level) was investigated and found to have superior sensitivity and selectivity compared to nonresonant and one and two energy level resonant ionization schemes. An elemental selectivity for Os over Re of ≥10^3 was demonstrated. It was found that detuning the ionizing laser from the autoionizing energy level to an arbitrary region in the Ionization continuum resulted in a 5-fold decrease in signal intensity and a 10-fold decrease in elemental selectivity