Genesis DoS Wafers: What Every SIMS Analyst Needs to Know Before Measuring Solar Wind

Genesis DoS wafers are amorphous, anhydrous, tetrahedrally-coordinated diamond-like carbon (DLC) films on silicon wafers [1, 2]. Using these wafers, excellent analytical results were achieved quickly after the Genesis return for noble gasses using laser ablation [3]. Yet, obtaining precise and accurate analyses by secondary ion mass spectroscopy (SIMS) has been problematic for a decade -even when the data from each individual analysis looked superb [4]. Here we discuss the problems of SIMS analyses of Genesis DoS and how to mitigate them. Experimental: Multiple SIMS data sets (2006present) from various DoS wafers are given to show the issues are consistent between sessions and laboratories. Data were taken at either Caltech (Cameca IMF 7f) or ASU (Cameca IMF 6f). An O2 primary beam was used. Other analytical parameters were varied. The Problem: Nicknamed DoS (for Diamond on Silicon), these DLC-coated wafers were chosen for the Genesis mission for their low backscatter during solar wind (SW) collection, relatively low number of potential mass interferences affecting analysis, retentiveness of SW in the DLC film, especially volatiles, as well as physical and chemical durability. Because it is conductive and yield beautifully-shaped SIMS depth-profiles it is extremely tempting to use for SIMS analysis. However, quantification of the results is complicated. Fluence Measurements. Fig. 1 shows 3+ years of attempting to reliably reproduce SW Mg measurments in DoS. The breakthrough was made when a minor