TABLE OF CONTENTS (Edited by A. George)
Y. Okada
June 1998
The highly perfect crystalline structure of extremely pure silicon single crystals is the starting point for many metrological applications. The determination of Avogadro's number, or of the ratio of Planck constant and the neutron mass are typical experiments based on an exact knowledge of the lattice spacing of a reference crystal.
At ordinary pressure, silicon crystallises in the diamond structure, with an fee Bravais lattice and a two-atom basis. The chemical bond is purely covalent, each atom being tetrahedrally coordinated and its valence electrons occupying sp 3 hybrid orbitals. Silicon transforms to several other phases at higher pressures as shown in Datareview 3.3.
Of concern here are absolute methods for lattice parameter measurements of single crystals. The absolute methods allow us to measure the lattice parameters in the metric system or with respect to a fixed x-ray emission wavelength, taken as a secondary standard. Up to now only two such methods have reached an accuracy ?a/a in the order of 10 -7: the Bond method [1] and simultaneous x-ray and optical interferometry (xROI) [2].
The accuracy of the Bond method is limited by that of the x-ray wavelength used. Top values are obtained with the best known CuK ? 1) line, with ??/ ? = 3 10 -7. In xROI what is measured...
