The Avogadro constant NA is used as one of the several possible routes to redefinition of the kilogram in metrology today. Usually in order to accurately determine NA, the volume of a perfect single crystal silicon sphere of nearly 1 kg mass should be measured with a high relative uncertainty, i.e. about 1×10^-8. However, the oxide layer grown on the surface of the silicon sphere causes a remarkable systematic difference between the measured and real diameters. A novel ellipsometer has been developed to determine the thickness of the oxide layer accurately and automatically. The arrangement of this instrument is suitable for measuring the layer on the sphere surface. What's more, the measuring is faster by optimizing the parameters and developing the algorithm of calculating the thickness and refractive index of the oxide layer. The preliminary simulation result has present. Thus, the uncertainty of the diameter measurement caused by the oxide layer can be observably reduced. And the further improving of this ellipsometer is discussed in the end.

Date Published: 28 November 2007
PDF: 7 pages
Proc. SPIE 6834, Optical Design and Testing III, 683443 (28 November 2007); doi: 10.1117/12.756865

Published in SPIE Proceedings Vol. 6834:
Optical Design and Testing III
Yongtian Wang; Theo T. Tschudi; Jannick P. Rolland; Kimio Tatsuno, Editor(s)