Michael Borys

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New results are reported from an ongoing international research effort to accurately determine the Avogadro constant by counting the atoms in an isotopically enriched silicon crystal. The surfaces of two 28 Si-enriched spheres were decontaminated and reworked in order to produce an outer surface without metal contamination and improved sphericity. New(More)
The Avogadro constant links the atomic and the macroscopic properties of matter. Since the molar Planck constant is well known via the measurement of the Rydberg constant, it is also closely related to the Planck constant. In addition, its accurate determination is of paramount importance for a definition of the kilogram in terms of a fundamental constant.(More)
Spheres made of a silicon single crystal with a mass of about 1 kg are used as density standards and in the context of a project for the determination of the Avogadro constant. The status of the mass determination of such silicon spheres at the PTB is presented. Special facilities and procedures used for the mass determination in air are described. Results(More)
The acoustic output of a harmonic scalpel was experimentally determined, and both the airborne ultrasound and the ultrasound transmitted in water were taken into account. The sound pressure level of airborne ultrasound was measured with a microphone and an artificial head, so that the free-field value and the sound level at the entrance at the bottom of the(More)
Within the International Avogadro Project, two spheres of highly enriched <sup>28</sup>Si crystals have been produced to perform new determination of Avogadro constant N<sub>A</sub>. The mass of the oxide layer of the spheres has to be measured as one of the critical tasks. For this purpose, a method consisting of precise thickness measurements and density(More)
The first results of gravimetric measurements of the growth of the oxide layer on single-crystal silicon spheres are presented and compared with a theoretical model and with measurements of the surface layer based on X-ray and ellipsometric methods. From the results, conclusions can be drawn about the quantitative influence of the growth of the oxide layer(More)
The initial determination of Avogadro's constant based on measurements of <sup>28</sup>Si material ended up with an overall uncertainty of 3&#x00D7;10<sup>-8</sup>. The results were clouded by an unexpected effect: the surface of both silicon spheres were contaminated by small amounts of copper (Cu) und nickel (Ni). Although the contaminations were(More)
In 2011, the first determination of the Avogadro constant with <formula formulatype="inline"><tex Notation="TeX">${}^{28}$ </tex></formula>Si material was published with an overall relative uncertainty of <formula formulatype="inline"><tex Notation="TeX"> $3 \times 10^{-8}$</tex></formula>. The results were based on measurements of a very pure single(More)