Ultrasound-induced gradient crystals observed by high-energy X-rays

High-energy X-ray scattering (90keV) has been performed at the high-energy beamline ID15 at the European Synchrotron Radiation Facility, Grenoble, on perfect Si crystals excited by compressional ultrasound waves in the [111] direction. Two-dimensional intensity maps of the <(3)over bar 51> Bragg peak reveal a purely longitudinal distortion of the lattice with respect to the applied distortion field, which is, for the present scattering geometry, inclined by 72 degrees to the diffraction vector. A maximum gain factor of 50 for the diffracted intensity is observed for the strongest sound excitation. A quantitative analysis of the line shape by a transfer-matrix method shows the transition from the diffraction behavior of an ideal crystal towards a crystal slightly deformed by internal stresses.