Dresden 2017 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 74: Group IV: Si/Ge/SiC

HL 74.1: Talk

Thursday, March 23, 2017, 12:00–12:15, POT 06

The silicon path to a new kilogram: Impact of the isotopic composition of Si determined by high resolution mass spectrometry — •Axel Pramann and Olaf Rienitz — Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany

The planned re-definition of the SI unit kilogram will be performed via the Planck constant h and in a complementary approach via the Avogadro constant N_A applying the X-ray-crystal-density XRCD method (Avogadro-project) by counting the silicon atoms in single-crystalline Si spheres[1]. One key experiment is the mass spectrometric determination of the molar mass M of Si with lowest uncertainty by developing new analytical techniques (isotope ratio calibration) and modifying e.g. isotope dilution mass spectrometry (IDMS) in combination with a high resolution multicollector-ICP-mass spectrometer (HR-MC-ICP-MS) [2]. This resulted in u_rel(M) < 5 x 10-9 routinely, when applied to silicon material enriched in 28Si with x(28Si) > 0.9999 mol/mol. New Si crystals even higher enriched in 28Si recently produced in Russia exhibit a strong reduction of u(M). Already u_rel(M) < 1 x 10-9 can be obtained when using crystals with x(28Si) > 0.999 99 mol/mol. An estimation of the correlation between enrichment and decrease of uncertainty is given, stimulated by an uncertainty reduction of M by approximately three orders of magnitude in ten years [3].

[1] Y. Azuma et al., Metrologia, 52, 360 (2015). [2] O. Rienitz, A. Pramann, D. Schiel, Int. J. Mass Spectrom., 289, 47 (2010). [3] K. Fujii et al. Metrologia, 53, A19 (2016).