Determination of Defect Concentrations in 28Si Crystals Using EPR for the Realization of the Kilogram

To realize the kilogram using the X-ray crystal density method, 28Si crystals grown by the floating zone method are used. Samples prepared from AVO28 crystal and a new crystal, with surfaces etched in Tetramethylammonium hydroxide solution, were analyzed by electron paramagnetic resonance (EPR) spectroscopy. The EPR signals from vacancy defects were found to be below the detection limit of $1\times 10^{12}\ \mathrm{cm}^{-3}$ , which suggests that the corresponding corrections for the realization of the kilogram are equal $0.0(2)\ \mu \mathrm{g}$ . We conclude that the vacancy defects do not account for the discrepancy of $39(21)\ \mu \mathrm{g}$ between the kilograms realized using the two crystals.