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Production sequence of Si-spheres and interferometrical determination of the sphere volume



In air-conditioned rooms, the technology and specific strategies for the polishing of plane and spherical workpieces of brittle materials like silicon crystals, Zerodur and other glasses are developed. We develop strategies for polishing rare metal alloys, primarily for use in metrology.


One of our special tasks is the production of silicon balls highest precision for the definition of the kilogram. To this end, an elaborate production chain was developed with a special polishing process.
All targets have been achieved or are well below:
- Form deviation of less than 100 nm (minimum procedural defect so far: 16.3 nm)
- Surfaces free of contamination (no process-related or diffused
  adhering metals)
- Roughness less than 1 nm (standard at about Ra = 0.2 nm)
- Near-surface crystal structure also undisturbed (no so-called "sub-surface damage".)
- Oxide uniformly, only a few nanometers thick

1-kg silicon sphere,
diameter 90 mm
Pt-Ir masses

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