At the surface of the new kilogram
New instrumentation to analyze the surface of silicon spheres
Surface effects, such as the forming of oxide and contamination layers, have a notable influence on the mass and the volume of the silicon spheres used (the surface layers altogether have a mass of approx. 100 µg).
By combining X-ray fluorescence and photoelectron spectroscopy, it is pos-sible to determine both the chemical composition and the mass deposition at the surface of the sphere(s) by means of a single apparatus. In this way, PTB can characterize the surface with the highest accuracy.
The core piece of this apparatus is a sample manipulator which only has minimum contact (three-point contact) with the sphere and allows measurement at any point on the surface. The instrumentation is equipped with a monochromatic Al X-ray source. By means of silicon oxide reference samples, it is possible to determine the oxygen mass deposition and thus the silicon oxide layer thickness over the total surface of the sphere with extremely small uncertainties. In addition, it becomes possible to determine contaminations which may occur during the production process or when handling the spheres.
Contact
Michael Kolbe
Department 7.1 Radiometry with Synchrotron Radiation
Phone: +49 (0)30 3481-7131
michael.kolbe(at)ptb.de
Scientific publication
R. Fliegauf, B. Beckhoff, E. Beyer, E. Darlatt, I. Holfelder, P. Hönicke, G. Ulm, M. Kolbe: Surface characterization of silicon spheres by combined XRF and XPS analysis for determination of the avogadro constant. Proc. of 2016 Conference on Precision Electromagnetic Measurements (CPEM 2016), DOI: 10.1109/CPEM.2016.7540797