**3.1.6. Secondary ion mass spectrometry**

Secondary ion mass spectroscopy (SIMS) is a method9 for the characterization of solid surface elemental composition and isotope distribution. The technique can be applied to all ele‐ ments and allows quantitative analysis of solid surfaces, including monolayers. Energetic ion bombardment of a solid surface (primary ions, e.g. Ar+ , Cs+ , O2+, … ) causes that atoms of the sample are shifted from their original states as positive and negative ions which are termed as secondary ions. These ions are then analyzed by mass spectrometer (e.g. quadrupole mass spectrometer) to determine the composition of the surface of sample [66],[67]. The applica‐

<sup>9</sup> The method was originally developed in the 1950s and 1960s by HERZOG et al and HONIG et al to analyze metals and oxides [69], but the basis of SIMS can be traced back to the beginning of the twentieth century with the first experimen‐ tal evidence of secondary ions given by JJ THOMSON in 1910 [68].

tions of SIMS can be broadly subdivided into static and dynamic SIMS. Static SIMS (SSIMS) is used to investigate the composition of the outermost monolayer on any solid. Dynamic SIMS (DSIMS) examines the concentration profile as the function of depth [68],[69],[70].

**Fig. 3.** Main components of SIMS [68] and schematic representation of ion microprobe imaging time-of-flight secon‐ dary ion mass spectrometry with reflectron-based mass analyser [69].

The mass filter of mass spectrometer of SIMS instruments defines the type of instruments [68], [70]:


**Fig. 4.** Schematic representation of magnetic sector and quadrupole SIMS instruments [70].

Secondary ion emission begins when the primary ions energy exceeds some threshold level. This energy ranges from 30 to 80 eV and is much higher than the energies for sputtering of neutral particles. The most important features of the method are very low sensitivity limit for majority of elements, the possibility to determine the concentration profile, the possibility of isotope analysis and the identification of all the elements and isotopes starting from hydro‐ gen [66].

The SIMS method is often used for the measurement of deuterium/hydrogen (D/H) ratio and hydroxyl (OH) content in anhydrous minerals and melt inclusions in Martian meteorites [71] and lunar materials (apatite grains, glass beds, melt inclusions and agglutinates in soils) [72]. The method is widely used to investigate biological apatites and collagen apatite composites [73] and the analysis of micrometer-sized samples like, e.g. interplanetary dust, presolar grains and small inclusions in meteorites, has become more and more important in cosmochemis‐ try [74]. The method is also utilized for U-Th-Pb dating of apatites as common accessory in igneous rocks (**Chapter 8**), based on the radioactive decay of U and Th [75],[76],[77].
