SIMS direct ion imaging in the mineralogical sciences

Abstract

The use of secondary ion mass spectrometry (SIMS) has enjoyed increasing popularity in the mineralogical sciences owing to its high sensitivity to all elements in the periodic table with detection limits in the parts per million to parts per billion regime, coupled with the ability to display maps of elemental distribution at these detection levels with a spatial resolution of 1 μm. A description of the technique and its application to a wide variety of mineralogical problems has recently been reviewed.The drawback of SIMS is the rather complicated nature of quantification schemes necessitated by sample matrix effects, which refer to differences in the sensitivity for a given element in samples of different composition. These differences result from changes in the ionization efficiency and sputtering yield (sample matrix specific) as well as changes in secondary ion transmission and ion collection efficiencies (instrument specific). Therefore, the use of matrix-matched standards of known concentration is required to establish a calibration factor known as the relative sensitivity factor (RSF) which can be used to convert the experimentally measured secondary ion intensity into concentration values. Furthermore, the effect of changes in ion intensity caused by variations in primary beam current or analysis at different sample positions is removed by normalization to an ion species which represents the matrix material.