Electron Paramagnetic Resonance Study on 28Si Single Crystal for the Future Realization of the Kilogram

For the future realization of the kilogram using the X-ray crystal density (XRCD) method, isotopically enriched silicon crystals grown by the floating zone method are employed. In this paper, we present quantitative electron paramagnetic resonance (EPR) measurements on ²⁸Si single crystal AVO28 to increase the reliability of mass deficit correction in the XRCD method. We detected phosphorus impurity in the crystal and determined its concentration to be 3.2(5) x 10¹² cm^-3, which is consistent with that estimated using Fourier transform infrared spectroscopy. In addition, the EPR measurements revealed that the concentrations of nine types of vacancy defects with unpaired electrons in the crystal are less than 1 x 10¹² cm^-3 at 25 K both in a dark environment and under illumination. As a result, the necessary mass deficit correction due to these vacancy defects is estimated to be 0.0(2) μg for 1-kg AVO28 spheres.