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@INPROCEEDINGS{Tavabi:827185,
      author       = {Tavabi, Amir H. and Duchamp, Martial and Dunin-Borkowski,
                      Rafal and Pozzi, Giulio},
      title        = {{D}ouble crystal interference experiments},
      address      = {Weinheim, Germany},
      publisher    = {Wiley-VCH Verlag GmbH $\&$ Co. KGaA},
      reportid     = {FZJ-2017-01383},
      pages        = {711 - 712},
      year         = {2016},
      comment      = {European Microscopy Congress 2016: Proceedings},
      booktitle     = {European Microscopy Congress 2016:
                       Proceedings},
      abstract     = {In 1978, Rackham and co-workers observed remarkable and
                      unusual diffraction patterns from an object that consisted
                      of two perfectly aligned, simultaneously reflecting crystals
                      that were separated by a gap [1]. They reported that they
                      could obtain such double crystals routinely by ion
                      bombardment. However, their specimen preparation method did
                      not allow the the gap between the crystals to be controlled
                      and the maximum gap that they achieved was on the order of
                      1-2 μm. A subsequent realization of a double crystal
                      interferometer (DCI) was achieved using voids in spinel [2],
                      again with a crystal spacing of below 1 μm. In 1995, Zhou
                      and co-workers [3] presented new results by combining a Si
                      double-crystal interferometer with convergent beam electron
                      diffraction (CBED), taking advantage of a special structure
                      formed at the broken edge of a Si [111] crystal. The gap was
                      still on the order of 1 μm or below.Here, we use focused
                      ion beam (FIB) milling to build DCIs that have gaps of up to
                      8 μm and to provide better control over results that were
                      previously obtained by chance. Figure 1 shows a top view
                      scanning electron micrograph of such an interferometer. The
                      gap separation is 800 nm. Both single crystal and double
                      crystal areas have been patterned. Superimposed on the image
                      is a sketch of the ray path of a convergent beam that
                      illuminates the upper crystal, generating a transmitted beam
                      and a diffracted beam. These beams, in turn, impinge on the
                      second crystal, generating further transmitted and
                      diffracted beams that overlap in the diffraction plane,
                      resulting in the formation of interference fringes.Figure 2
                      shows a comparison of diffraction patterns recorded from a
                      single crystal (left) and two overlapped crystals (right).
                      The spacing of the interference fringes depends on the
                      electron wavelength, the excited Bragg reflection and the
                      camera length. More impressive results are obtained when the
                      orientation of the crystal is close to a zone axis. Figure 3
                      shows a comparison of a standard CBED pattern (left) with a
                      complicated system of interference fringes arising from
                      overlap of many diffracted beams (right). The interference
                      phenomena in these patterns encode information about the
                      crystal structure. The fringe spacing is inversely
                      propotional to the gap width. Therefore, for an 8 μm gap,
                      ten times more fringes are present in the overlapped discs
                      and the interferogram can be considered as a hologram, as
                      showsn in Fig. 4.As suggested by the first experimenters
                      [1], accurate lattice parameter measurements can be made
                      using a DCI when one crystal is the specimen of interest.
                      If, instead, a specimen in inserted between the crystals or
                      deposited onto the lower crystal, then it will be possible
                      to obtain an off-axis Fresnel hologram with a reduced
                      exposure time that is not affected by Fresnel diffraction
                      from the edges of a biprism wire, as is the case when an
                      electron biprism is used as an interferometric device.
                      Moreover, the reduced exposure time due to amplitude
                      division beam splitting could open the way to dynamic
                      recording and processing of holograms.},
      month         = {Aug},
      date          = {2016-08-28},
      organization  = {16th European Microscopy Congress (EMC
                       2016), Lyon (France), 28 Aug 2016 - 2
                       Sep 2016},
      cin          = {PGI-5 / ER-C-1},
      cid          = {I:(DE-Juel1)PGI-5-20110106 / I:(DE-Juel1)ER-C-1-20170209},
      pnm          = {143 - Controlling Configuration-Based Phenomena (POF3-143)},
      pid          = {G:(DE-HGF)POF3-143},
      typ          = {PUB:(DE-HGF)8 / PUB:(DE-HGF)7},
      doi          = {10.1002/9783527808465.EMC2016.5140},
      url          = {https://juser.fz-juelich.de/record/827185},
}