Observation of a bent crystal-lattice by x-ray interferometry.

he capability of operating a separate crystal x-ray interferometer over centimeter displacements has made it possible to observe minute strain fields of a bent crystal at the atomic scale resolution by means of phase-contrast x-ray topography. Measurement and predictive capabilities of lattice strain are key ingredients of a highly accurate measurement of the Si lattice parameter and of a determination of the number of atoms in a realization of the mass unit based on an atom mass. Here we show that the observed strain can be accurately predicted by a finite-element analysis of the crystal deformation.