Silicon molar volume discrepancy: Studies of the NRLM crystal

A relatively large discrepancy was found in the molar volume of silicon cry stals used to determine the Avogadro constant by means of the X-ray and cry stal density (XRCD) method. Voids are suspected to cause the difference in the molar volume. Infrared laser scattering tomography, Secco-etching, elec tron spin resonance, and X-ray topography have been applied to the silicon crystal of the National Research Laboratory of Metrology to detect voids, H owever, no voids were observed in the crystal.