Multi-wavelength Bragg coherent X-ray diffraction imaging of Au particles

International audienceMulti-wavelength (mw) Bragg coherent X-ray diffraction imaging (BCDI) is demonstrated on a single Au particle. The multi-wavelength Bragg diffraction patterns are inverted using conventional phase-retrieval algorithms where the dilation of the effective pixel size of a pixelated 2D detector caused by the variation of the X-ray beam energy is mitigated by interpolating the raw data. The reconstructed Bragg electron density and phase field are in excellent agreement with the results obtained from conventional rocking scans of the same particle. Voxel sizes of about 6 3 nm 3 are obtained for reconstructions from both approaches. Phase shifts as small as 0.41 rad, which correspond to displacements of 14 pm and translate into strain resolution better than 10 À4 in the Au particle, are resolved. The displacement field changes shape during the experiment, which is well reproduced by finite element method simulations considering an inhomogeneous strained carbon layer deposited on the Au particle over the course of the measurements. These experiments thus demonstrate the very high sensitivity of BCDI and mw-BCDI to strain induced by contaminations. Furthermore, mw-BCDI offers new opportunities for in situ and operando 3D strain imaging in complex sample environments

Scanning X-ray diffraction microscopy of a 6 GHz surface acoustic wave

Surface acoustic waves at frequencies beyond a few GHz are promising components for quantum technology applications. Applying scanning X-ray diffraction microcopy we directly map the locally resolved components of the three-dimensional strain field generated by a standing surface acoustic wave on GaAs with wavelength $\lambda\simeq500\,$nm corresponding to frequencies near 6 GHz. We find that the lattice distortions perpendicular to the surface are phase-shifted compared to those in propagation direction. Model calculations based on Rayleigh waves confirm our measurements. Our results represent a break through in providing a full characterization of a radio frequency surface acoustic wave beyond plain imaging.Comment: 9 pages, 6 figure

electronic reprint Journal of Synchrotron Radiation X-ray diffraction from rectangular slits X-ray diffraction from rectangular slits

It is shown that for micrometre-sized beams the X-ray diffraction from slits is a source of strong parasitic background, even for slits of high quality. In order to illustrate this effect, the coherent diffraction from rectangular slits has been studied in detail. A large number of interference fringes with strong visibility have been observed using a single set of slits made of polished cylinders. For very small apertures, asymmetrical slits generate asymmetrical patterns. This pattern is calculated from the theory of electromagnetic ®eld propagation and compared with experiment in the far-®eld regime. The use of guard slits to remove Fraunhofer diffraction from the beam-de®ning slits is treated theoretically. Numerical simulations yield the optimum aperture of the guard slits with respect to the distance to the primary slits. Diffraction theory is shown to be essential to understand how to reduce the background-to-signal ratio in high-resolution experiments

Epitaxial orientation changes in a dewetting gold film on Si(111).

International audienceUsing in situ x-ray diffraction, epitaxial relationships have been measured for different Au deposits on Si(111) surfaces, under ultrahigh vacuum conditions, from room temperature to the eutectic temperature (T-e) of theAuSi binary system. Epitaxies perpendicular to the substrate have been studied for different gold coverages (2, 5, 7, and 20 monolayers). The Au(111) parallel to Si(111) out-of-plane epitaxy was found to be dominant and to present three different in-plane orientation relationships evolving with increasing temperature. These epitaxial variations are induced by the variation of the lattice-parameter misfit with temperature due to differing thermal expansion of the two materials. The temperature dependence of the epitaxial relationship is explained using the coincidence site lattice theory and a study of the "matching quality" at the interface. In addition, ab initio calculations have been performed to estimate the stability of the different configurations and compared to the experimental result

Shape changes of supported Rh nanoparticles during oxidation and reduction cycles

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