Silicon molar volume discrepancy: perfection of the NRLM crystal [for Avogadro constant determination]

A large discrepancy was found in the molar volume of silicon used to determine Avogadro constant. Voids are suspected to cause the difference in the molar volume. Laser scattering tomography, secco-etching, electron spin resonance and X-ray topography have been applied to Japanese silicon to detect voids but no voids were observed in the crystal.