Measurement of the \{220\} lattice-plane spacing of a $^{28}$Si crystal

TL;DR

This paper precisely measures the 00b0 lattice-plane spacing of a 00b0Si crystal using x-ray and optical interferometry, confirming quantum mechanics predictions and aiding in defining the atomic mass unit.

Contribution

It provides a highly accurate measurement of the 00b0Si lattice spacing, supporting fundamental constants and the redefinition of the kilogram.

Findings

Measured 00b0Si lattice spacing with 3.5b710^{-9} accuracy

Confirmed the difference between 00b0Si and natural Si matches quantum mechanics

Used the crystal to determine Avogadro constant by atom counting

Abstract

The spacing of the \{220\} lattice planes of a $^{28}$Si crystal was measured by combined x-ray and optical interferometry to a $3.5\times 10^{-9}$ relative accuracy. The result is $d_{220}=(192014712.67 \pm 0.67)$ am, at 20.0 $^\circ$C and 0 Pa. This value is greater by $(1.9464 \pm 0.0067)\times 10^{-9} d_{220}$ than the spacing in natural Si, a difference which confirms quantum mechanics calculations. Subsequently, this crystal has been used to determine the Avogadro constant by counting the Si atoms, a key step towards a realization of the mass unit based on a conventional value of the Planck or the Avogadro constants.