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Publication Detail
Three-dimensional Mapping of a Deformation Field inside a Nanocrystal
  • Publication Type:
    Journal article
  • Publication Sub Type:
  • Authors:
    Pfeifer MA, Williams GJ, Vartanyants IA, Harder R, Robinson IK
  • Publication date:
  • Pagination:
    63, 66
  • Journal:
  • Volume:
  • Print ISSN:
  • Keywords:
    Strain, X-ray, Diffraction, Nano, Nanocrystal
  • Notes:
    This work was completed at UCL but was started at UIUC. THe experiments were all done at the 34-ID-C beamline of the Advanced Photon Source. The two UCL authors (Harder, Robinson) did most of the interpretation of the images, the graphics and the preparation of the manuscript. Authors Pfeifer and Williams were PhD students who measured the data and phased it to obtain the 3D image. Former group member Vartaniants provided theoretical guidance. The beamline, essential to this important development, was fundraised and built by Robinson.
Coherent X-ray diffraction imaging is a rapidly advancing formof microscopy: diffraction patterns, measured using the latest thirdgeneration synchrotron radiation sources, can be inverted to obtain full three-dimensional images of the interior density within nanocrystals1–3. Diffraction from an ideal crystal lattice results in an identical copy of this continuous diffraction pattern at every Bragg peak. This symmetry is broken by the presence of strain fields, which arise from the epitaxial contact forces that are inevitable whenever nanocrystals are prepared on a substrate4. When strain is present, the diffraction copies at different Bragg peaks are no longer identical and contain additional information, appearing as broken local inversion symmetry about each Bragg point. Here we show that one such pattern can nevertheless be inverted to obtain a ‘complex’ crystal density, whose phase encodes a projection of the lattice deformation. A lead nanocrystal was crystallized in ultrahigh vacuum from a droplet on a silica substrate and equilibrated close to its melting point. A three-dimensional image of the density, obtained by inversion of the coherent X-ray diffraction, shows the expected facetted morphology, but in addition reveals a real-space phase that is consistent with the three-dimensional evolution of a deformation field arising from interfacial contact forces. Quantitative threedimensional imaging of lattice strain on the nanometre scale will have profound consequences for our fundamental understanding of grain interactions and defects in crystalline materials4. Our method of measuring and inverting diffraction patterns from nanocrystals represents a vital step towards the ultimate goal of atomic resolution single-molecule imaging that is a prominent justification for development of X-ray free-electron lasers5–7.
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