Collector Materials Guest Commentary
Diamond-like carbon (DLC) on silicon wafers (DoS) are a unique engineering material. The collector portion (DLC) is formed by pulsed laser deposition, a form of sputtering. However, the deposited film is not a simple uniform film of sputtered amorphous carbon. Rather, the carbon film is compressed at GPa-level forces so that diamond nanocrystal can – and sometimes do – form. So, the film is a mixture of (mostly) nanometer-sized domains of graphite (sp2 bonds) and diamond (sp3 bonds). During deposition, the film grows as an aggregate of columnar structures: visualize a columnar basalt. Each column has a slightly different mix of diamond and graphite and some silicon is mixed in – usually a trace amount -- inherited from the sputtering target. The columns of DLC do show some minor (mostly negligible) variation with depth – primarily because the DLC must be annealed at intervals to mitigate the high stresses. The primary issues for the analyst stem from the fact that diamond and graphite have very different physical, chemical and electrical properties. The “random” differences in electrical properties within each column of DLC makes analyses by secondary ion mass spectrometry (SIMS) especially difficult. There are also differences in secondary ion yields between low silicon-high diamond and high(er) silicon-high graphite areas and sometimes differences in ion yield of the C with changing H concentration. However, the good news for analysts is that past work indicates that once anything is implanted in DLC it doesn’t move. Therefore, a simple model of implantation will describe the implant in the DLC. A good model is given in www.srim.org, a free online teaching program for undergraduate physics students. Details of a techniques for using SIMS to quantify the solar wind are currently available in Huss et al. 2020, Jurewicz et al. 2020a; Jurewicz et al. 2020b.
Huss, G. R., Koeman-Shields, E., Jurewicz, A. J. G., Burnett, D. S., Nagashima, K., Ogliore, R., Olinger, C. T. (2019). Hydrogen fluence in Genesis collectors: Implications for acceleration of solar wind and for solar metallicity. Meteoritics & Planetary Science, 1-26. https://doi.org/10.1111/maps.13420
Jurewicz, A. J. G., Olinger, C. T., Burnett, D. S., Guan, Y., Hervig, R., Rieck, K. & Woolum, D. S. (2020). Quantifying low fluence ion implants in diamond-like carbon film by secondary ion mass spectrometry by understanding matrix effects. Journal Analytical Atomic Spectrometry, Royal Society of Chemistry. https://doi.org/10.1039/d0ja00375a
Jurewicz, A. J. G., Rieck, K. D., Hervig, R., Burnett, D. S., Wadhwa M., Olinger, C. T., Wiens, R. C., Laming, J. M., Guan, Y., Huss, G. R., Reisenfeld, D. B., & Williams, P. (2020). Magnesium isotopes of the bulk solar wind from Genesis diamond-like carbon films. Meteoritics & Planetary Science, 1-24. https://doi.org/10.1111/maps.13439