Simultaneous dual-element analyses of refractory metals in naturally occurring matrices using resonance ionization of sputtered atoms
The combination of secondary neutral mass spectrometry (SNMS) and resonance ionization spectroscopy (RIS) has been shown to be a powerful tool for the detection of low levels of elemental impurities in solids. Drawbacks of the technique have been the laser-repetition-rate-limited, low duty cycle of the analysis and the fact that RIS schemes are limited to determinations of a single element. These problems have been addressed as part of an ongoing program to explore the usefulness of RIS/SNMS instruments for the analysis of naturally occurring samples. Efficient two-color, two-photon (1+1) resonance ionization schemes were identified for Mo and for four platinum-group elements (Ru, Os, Ir, and Re). Careful selection of the ionization schemes allowed Mo or Ru to be measured simultaneously with Re, Os, or Ir, using two tunable dye lasers and an XeCl excimer laser. Resonance frequencies could be switched easily under computer control, so that all five elements can be rapidly analyzed. In situ measurements of these elements in metal grains from five meteorites were conducted. From the analyses, estimates of the precision and the detection limit of the instrument were made. The trade-off between lower detection limits and rapid multielement RIS analyses is discussed.
©1995 American Vacuum Society (Received 21 October 1994; accepted 25 January 1995) The authors thank Paul Carpenter and John Armstrong for their assistance with the SEM and electron probe analyses. Joel Blum is thanked for providing the Ni-Os-Re standard and George Rossman for the laurite sample. This work was supported by the U.S. Department of Energy, BES-Materials Sciences, under Contract No. W-31-109-ENG-38 (ANL) and by NASA Grant No. NAGW 3592 (Caltech).
Published - CALjvsta95.pdf