Precision Comparison of the Lattice Parameters of Silicon Monocrystals

National Institute of Standards and Technology, Gaithersburg, MD 20899-0001 The lattice spacing comparator estabMshcd MC the National InMitute of Standards and Technology to measure the lattice spacing differences between nearly perfect crystals i^ described in detail, t^tticc spacing differences are inferred from the measured differcrrces in Br3g;g Hngics for different crystals. The comparator is a vna crystal spectrometer uficd in the nearly nondispersive geometry. It has two s-ray sources, two detectors, and a ilevicc which permits rcmiUe interchange of the second crystal sample. .\ sensitive heterodyne interferometer which it calibrated with an optical polygon is used to measure the Bragg an^es. The crystals are manufactured with nearly equal rhicknesscs so that the recorded profiles exhibit pcndclhisung oscillatinifs which permit more precise division of the x-ray profiles. The difference in lattice spacing between silicon •umpks used at Physikalisch-TcchnischcBundcsansiait (PTB) and NIST has been measured with a relittive uncertainty of 1 x I0~*. This measurement Ls consisitcnt with absolute lattice spacing measurements made at PTB and NIST, Components of uncertainty associated with systematic effects due to misaligt^ments arc derived and estimated.