LAUSR

Surface layer characterization is crucial for the high-accuracy determination of the Avogadro constant using 28Si enriched spheres to redefine the kilogram. In this paper, we measured the thickness of the oxide layer (OL) and carbonaceous layer (CL) on a 28Si-enriched sphere by X-ray photoelectron spectroscopy (XPS). A mechanism for the rotation of the sphere was integrated into the XPS system to measure the thickness at different points on the surface of the sphere. A SI-traceable X-ray reflectometry system was used to determine an attenuation length for the Si 2p electrons in SiO2, which was an important parameter for the calculation of the oxide thickness on the Si sphere by XPS. The average thickness and uncertainty budget of the OL and CL were evaluated.