XPS analysis of a 28Si-enriched sphere for realization of the kilogram

This paper describes an accurate thickness measurement of a surface layer on a
²⁸
Si-enriched sphere using X-ray photoelectron spectroscopy (XPS). We focused on the influence of crystal orientations of the core sphere on the thickness determination by XPS. The changes in the intensity of Si core sphere (I
_Si
) along the main crystallographic directions were firstly studied. The I
_Si
is enhanced along the main crystallographic directions and the enhanced intensity is expected to result in large variations in the thickness values. By avoiding the line of longitude of crystallographic planes with low plane indices, the variation in I
_Si
was reduced largely and the uncertainty due to the variation in I
_Si
was decreased.