High-precision large-diameter single-crystal silicon spheres: their fabrication and measurements of sphericity

Achim J. Leistner; Walter J. Giardini

doi:10.1117/12.218436

8 September 1995 High-precision large-diameter single-crystal silicon spheres: their fabrication and measurements of sphericity

Achim J. Leistner, Walter J. Giardini

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Proceedings Volume 2536, Optical Manufacturing and Testing; (1995) https://doi.org/10.1117/12.218436
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

Abstract

We describe the optical grinding and polishing, and the measurement of sphericity by multiple roundness profiles, of large single crystal silicon spheres (balls) (93.6 mm diameter and 1 kg mass). The balls are used in direct measurements of volume and density in the determination of the Avogadro constant. A typical peak to valley error of sphericity achieved was < 60 nm. The arithmetic mean deviation of the error surface relative to a least square sphere was around 16 nm. The microroughness was < 0.2 nm rms when measured with a WYKO TOPO 3D noncontact surface profiler. Defects in the optical finish were negligible when compared to the total allowable uncertainty specified for the volume of the balls of 0.1 ppm.

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Achim J. Leistner and Walter J. Giardini "High-precision large-diameter single-crystal silicon spheres: their fabrication and measurements of sphericity", Proc. SPIE 2536, Optical Manufacturing and Testing, (8 September 1995); https://doi.org/10.1117/12.218436

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