Trace Elements in Presolar Dust Grains
T. Berg1,4, J. Maul1, N. Erdmann2, P. Bernhard1, F. Schertz1, S. Schuppler3, P. Nagel3, Ch. Sudek4, U. Ott4 and G. Schönhense1
1Institut für Physik, Universität Mainz, Staudingerweg 7, 55128 Mainz, Germany
Typical presolar dust grains, e.g. silicon carbide (SiC), have sizes between ~100nm and some μm. With this given constraint of small amounts of material available, the mass spectrometric methods of choice, secondary ion mass spectrometry (SIMS)  and resonance ionization mass spectrometry (RIMS) , have a crucial disadvantage: They are destructive. Furthermore, the analysis of only a small number of isotopes is possible in most cases. Thus, it proves useful to characterize the chemical composition of the sample in a nondestructive way prior to isotopic analysis in order to identify single grains with high contents of interesting trace elements. Following, the isotopic ratios of this specific element can be analyzed by state-of-the-art instruments like the "NanoSIMS 50" at the Max-Planck-Institut für Chemie (Mainz) or "Charisma" at Argonne National Laboratory (USA) with highest efficiency.
Fig. 1: Scanning electron microscopic images of presolar silicon carbide (a) and spinel (b) extracted from the Murchison meteorite.
We developed a novel approach to solving this challenge by combining nondestructive parallel screening of a large number of presolar particles (up to thousands) utilizing imaging near edge X-ray absorption fine structure (NEXAFS) measurements with imaging mass spectrometry. In a first step, the lateral distribution of the chemical elements present in the sample is analyzed by applying NEXAFS for nondestructive screening. This supports the preselection of single grains of interest, which are then accessed in subsequent mass spectrometric analysis. Utilizing time-of-flight secondary ion mass spectrometry (TOF-SIMS) we demonstrated that it is possible to recover single particles with sizes in the μm range after transfer of the sample. Further we carried out analysis of preselected particles with isotopic resolution.
Fig. 2: SEM vs Spectroscopic PEEM (a) Scanning electron microscopic (SEM) image of the investigated sample area (upper part) and "spectrally unmixed" image series representing the lateral distribution of Cr, C and Si in the same sample area. (b) NEXAFS-spectra that were extracted from the marked sample areas and served as input for the spectral unmixing algorithm
The results were published in:
Coupling of imaging NEXAFS with secondary ion mass spectrometry for the chemical and isotopic analysis of presolar cosmic grains
The Search for Trace Elements in Presolar Dust Grains: A Glance at the Time Prior to the Solar System
 "Carbon, nitrogen, magnesium, silicon and titanium isotopic compositions of single interstellar silicon carbide grains from the Murchison carbonaceous chondrite", P. Hoppe, S. Amari, E. Zinner, T. Ireland, and R.S. Lewis, Astrophys. J. 430(1994)870-890. "Barium isotopes in individual presolar silicon carbide grains from the Murchison meteorite", M.R. Savina et al., Geochim. Cosmochim. Acta 67(2003)3201-3214.
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