Intercomparison of silicon samples from the Avogadro projects

The NIST lattice comparator assesses lattice parameter differences among carefully prepared samples of monocrystalline silicon with a level of imprecision near 10/sup -8/. This instrument has recently been used to effect intercomparisons among samples from laboratories currently engaged in direct optical measurements of such lattice periods. We report lattice parameter differences among samples representative of current optical measurements in all active national measurement laboratories. These data are suggestive of the current state of the art of these determinations and the population of silicon materials presently available for such purposes.