Density Determination of Silicon Spheres Using an Interferometer With Optical Frequency Tuning

摘要

An absolute density measurement was performed for two 1-kg silicon spheres, which were named S4 and S5. The volumes of the spheres were measured by an interferometer equipped with a direct optical frequency tuning system. Thicknesses of the oxide layer on the surfaces of the spheres were measured by using an ellipsometer to evaluate its effect on their volumes. The accuracy of the ellipsometric measurements was evaluated using silicon disks characterized by X-ray reflectometry and X-ray photoelectron spectroscopy. The masses of the spheres were compared with that of the national prototype of the kilogram through a secondary 1-kg standard. The relative combined standard uncertainty in the density was estimated to be 3.4 10-8 to 3.7 10-8