8 September 1995 High-precision large-diameter single-crystal silicon spheres: their fabrication and measurements of sphericity
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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, 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); doi: 10.1117/12.218436; https://doi.org/10.1117/12.218436
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KEYWORDS
Polishing

Surface finishing

Silicon

Crystals

Abrasives

3D metrology

Optical spheres

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