Abstract
Coherent x-ray diffraction is used to investigate the mechanical properties of a single grain within a polycrystalline thin film in situ during a thermal cycle. Both the experimental approach and finite element simulation are described. Coherent diffraction from a single grain has been monitored in situ at different temperatures. This experiment offers unique perspectives for the study of the mechanical properties of nano-objects.
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GENERAL SCIENTIFIC SUMMARY Introduction and background. Polycrystalline materials exhibit highly inhomogeneous deformations under mechanical loading. The non-destructive measurement of these strain distributions at the nanometer scale is a key issue for understanding the failure mechanisms of micro- and nano-devices. X-ray diffraction is very sensitive to the location of atoms in crystals and thus to their displacement from equilibrium positions. The small coherence of most x-ray sources blurs, however, the information on the strain distribution.
Main results. Using coherent x-ray diffraction from a synchrotron source, it has been shown that the diffraction pattern from a single sub-micron gold grain in a supported film can be recorded at different temperatures. The recorded diffraction pattern contains the information on the shape of the grain as well as on the strain field inside the grain. Such experimental diffraction patterns may be compared with those calculated with the help of mechanical models.
Wider implications. With sufficient oversampling of the diffraction pattern, direct inversion will yield a complete strain mapping at the nanometre scale. Hence a method for non-destructive strain mapping in polycrystals with sub-micron grain size will be available.