An experiment in X-ray interferometry: accuracy and resolution in Si d/sub 220/ determination

The authors analyze the resolution and the accuracy obtained in an experiment carried out to measure the silicon lattice spacing with scanning X-ray interferometry equipment. This study was prompted by the observation of a discrepancy in comparing results obtained by the authors with those obtained by other research groups. With the previous apparatus used by the authors, compensation and correction for systematic errors required considerable effort during interferometer coupling and experiment execution. With the use of a new X-ray/optical interferometer, cosine and Abbe´s errors are expected to remain below 10/sup -7/, even if, in the worst case, trajectory misalignment and offset occur. Contribution to the error budget of the crystal temperature and diffraction effects in the optical interferometer have also been considered and reduced to acceptable levels. Experimental tests and a theoretical analysis show that improvements are possible and that the desired accuracy can be obtained. A new set of lattice spacing measurements with the new apparatus is being carried out to reduce the overall uncertainty to a few parts in 10/sup -8/.<>