Thickness measurements of oxide and carbonaceous layer on a 28Si sphere by using XPS

Surface layer characterization is crucial for high-accuracy determination of the Avogadro constant by using
²⁸
Si enriched spheres for redefinition of the kilogram. In this work, we carried out the thickness measurements of the oxide and carbonaceous layer on a
²⁸
Si-enriched sphere by x-ray photoelectron spectroscopy (XPS) for a pilot study to confirm the international equivalence of the ability to realize the kilogram from the new definition. A sphere rotation mechanism was installed into the XPS system to measure the thickness at different points on the surface. The average thickness and uncertainty budget of the oxide and carbonaceous layers were evaluated.