Improvements in quantification accuracy of inorganic time-of-flight secondary ion mass spectrometric analysis of silicate materials by using C60 primary ions.

Time-of-flight secondary ion mass spectrometry is a very useful tool for the comprehensive characterization of samples by in situ measurements. A pulsed primary ion beam is used to sputter secondary ions from the surface of a sample and these are then recorded by a time-of-flight mass spectrometer. The parallel detection of all elements leads to very efficient sample usage allowing the comprehensive analysis of sub-micrometre sized samples. An inherent problem is accurate quantification of elemental abundances which mainly stems from the so-called matrix effect. This effect consists of changes in the sputtering and ionization efficiencies of the secondary neutrals and ions due to different sample compositions, different crystal structure or even different crystallographic orientations. Here we present results obtained using C60 molecules as a new primary ion species for inorganic analyses. The results show an improvement in quantification accuracy of elemental abundances, achieving relative errors as small as the certified uncertainties for the analyzed silicate standards. This improvement is probably due to the different sputter mechanism for C60+ primary ions from that for single atomic primary ions such as Ga+, Cs+ or Ar+. The C60+ cluster breaks up on impact, distributing the energy between its constituent carbon atoms. In this way it excavates nano-craters, rather than knocking out single atoms or molecules from the surface via a collision cascade, leading to a more reproducible sputter process and much improved quantification.