Precision lattice spacing comparison measurements at the National Institute of Standards and Technology (NIST) provide traceability of x-ray wavelength and powder diffraction standards to the international system of units (SI). Here we both summarize and document key measurements from the last two decades on six lots of intrinsic float-zone silicon, including unpublished results and recent internal- consistency checks. The comparison measurements link the unknown lattice spacing of a test crystal to a standard crystal whose lattice spacing has been accurately determined by x-ray/optical interferometry in units traceable to the definition of the meter. The crystal that serves as the standard in all the comparisons is WASO 04 whose lattice spacing is known with a relative uncertainty of 5 e−9. Taking material variability into account, the lattice spacing comparisons with typical uncertainties of 1 e−8 lead to lattice spacing values with relative uncertainties of a few e−8 for the test materials. It is observed that in the case of nearly-perfect modern intrinsic float- zone silicon, the variability of the lattice spacing is sufficiently small that for most diffraction applications a recommended value may be used in most applications.
Citation: Journal of Research (NIST JRES) -
NIST Pub Series: Journal of Research (NIST JRES)
Pub Type: NIST Pubs
lattice spacing difference, lattice parameter, x-ray diffraction, silicon crystal, x-ray spectrometer, Standard Reference Material