Astronomy and Astrophysics – Astrophysics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsh13b1535v&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SH13B-1535
Astronomy and Astrophysics
Astrophysics
[7514] Solar Physics, Astrophysics, And Astronomy / Energetic Particles, [7594] Solar Physics, Astrophysics, And Astronomy / Instruments And Techniques
Scientific paper
The samples of Solar Wind (SW) delivered by the NASA Genesis mission, present significant challenges for surface analytical techniques, in part due to severe terrestrial contamination of the samples on reentry, in part due to the ultra-shallow and diffused ion implants in the SW collector materials. We are performing measurements of metallic elements in the Genesis collectors using Resonance Ionization Mass Spectrometry (RIMS), an ultra-sensitive analytical method capable of detecting SW in samples with lateral dimensions of only a few mm and at concentrations from above one ppm to below one ppt. Since our last report at 2008 AGU Fall Meeting, we have (a) developed and tested new resonance ionization schemes permitting simultaneous measurements of up to three (Ca, Cr, and Mg) elements, and (b) improved reproducibility and accuracy of our RIMS analyses for SW-like samples (i.e. shallow ion implants) by developing and implementing an optimized set of new analytical protocols. This is important since the quality of scientific results from the Genesis mission critically depends on the accuracy of analytical techniques. In this work, we report on simultaneous RIMS measurements of Ca and Cr performed on two silicon SW collector samples, (#60179 and #60476). First, we have conducted test experiments with 3×1013 at/cm2 52Cr and 44Ca implants in silicon to evaluate the accuracy of our quantitative analyses. Implant fluencies were measured by RIMS to be 2.73×1013 and 2.71×1013 at/cm2 for 52Cr and 44Ca, respectively, which corresponds to an accuracy of ≈10%. Using the same implanted wafer as a reference, we conducted RIMS analyses of the Genesis samples: 3 spots on #60179 and 4 spots on #60476. The elemental SW fluencies expected for Cr and Ca are 2.95×1010 and 1.33×1011 at/cm2 , respectively. Our measurements of 52Cr yielded 3.0±0.6×1011 at/cm2 and 5.1±4.1×1010 at/cm2 for #60179 and #60476, respectively. For 40Ca, SW fluencies of 1.39±0.70×1011 at/cm2 in #60179 and 3.6±2.5×1013 at/cm2 in #60476 were measured. Thus, only one element in each sample showed reasonable agreement with the expected values, Ca in #60179 and Cr in #60476. However the cleaning procedures applied to these samples were different: #60179 was only Megasonicated in ultra-pure water, while #60476 was subjected to longer Megasonication and an RCA cleaning procedure involving multiple rinsing steps with acid solutions. It is apparent that the surface contamination and cleaning procedures influenced the results of our measurements. We will present these experimental results and discuss procedures - including improved sample cleaning, dual-beam high resolution sputter depth profiling from front and back sides of the sample, and modeling of near-surface impurity transport - aimed at improving the accuracy of determination of elemental abundances by ion sputtering based analytical methods. This work is supported by NASA through a grant NNH08AH761 and by UChicago Argonne, LLC, under contract No. DE-AC02-06CH11357.
Burnett Don S.
King B. V.
Pellin Michael J.
Tripa Emil C.
Veryovkin I. V.
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