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The density of the single crystal natural silicon sphere Avo#3 has been re-determined at the National Measurement Institute, Australia (NMIA) as part of an international collaboration to determine the value of the Avogadro constant. A systematic review of the measurement system found a significant bias was introduced by the response of the laser to frequency steps during phase-shifting interferometry,...
The density of an isotopically enriched 28Si crystal is evaluated. A transfer standard of the hollow silicon cylinder is prepared and its density is determined by the hydrostatic weighing (HW). The 28Si crystal is then compared with the hollow silicon for the determination of the density by the pressure-of-flotation (PF) measurement.
Graphene is the first example of truly two-dimensional crystals - it's just one layer of carbon atoms. It turns out that graphene is a gapless semiconductor with unique electronic properties resulting from the fact that charge carriers in graphene obey linear dispersion relation, thus mimicking massless relativistic particles. This results in the observation of a number of very peculiar electronic...
Accurate volume measurements for silicon spheres by optical interferometers play an important role in the determination of the Avogadro constant by the X-ray crystal density method. To reduce the uncertainty in the volume determination, a new vacuum chamber with a radiation shield has been developed. A new sphere temperature measurement system has been also introduced. Details of the improvements...
Within the International Avogadro Project measurements of molar mass and lattice parameter of a silicon single crystal and mass and volume of a high precision silicon sphere made of the same crystal are combined to calculate Avogadro's constant. As an overall uncertainty of 2ldr10-8 is aimed at, the determination of the volume of the Avogadro sphere requires unequalled precision in absolute interferometry...
A combined x-ray and optical interferometer capable of centimeter displacements has been realized to measure the lattice parameter of a 28Si crystal to within a 3 x 10-9 relative uncertainty. This paper relates the results of test measurements carried out to assess the capabilities of the new apparatus.
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