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  • Digitale Medien  (44)
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  • Digitale Medien  (44)
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  • 1
    Digitale Medien
    Digitale Medien
    Holotomography: Quantitative phase tomography with micrometer resolution using hard synchrotron radiation x rays (1999)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 75 (1999), S. 2912-2914 
    Details
    ISSN: 1077-3118
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Because the refractive index for hard x rays is slightly different from unity, the optical phase of a beam is affected by transmission through an object. Phase images can be obtained with extreme instrumental simplicity by simple propagation provided the beam is coherent. But, unlike absorption, the phase is not simply related to image brightness. A holographic reconstruction procedure combining images taken at different distances from the specimen was developed. It results in quantitative phase mapping and, through association with three-dimensional reconstruction, in holotomography, the complete three-dimensional mapping of the density in a sample. This tool in the characterization of materials at the micrometer scale is uniquely suited to samples with low absorption contrast and radiation-sensitive systems. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.125225
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  • 2
    Digitale Medien
    Digitale Medien
    A position-sensitive detector for neutron diffraction topography (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 28-33 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The first test of a position-sensitive photomultiplier in a thermal neutron diffraction topography experiment is reported: a spatial resolution was obtained of ∼200 μm in FWHM over a sensitive area of size ∼8 × 8 mm (∼1600 pixels) and a detection efficiency of the order of 15% when using a 0.25 mm thick ZnS–LiF (NE 426) scintillator. The advantages of this detector, its foreseeable improvements, and the scientific problems it could help to solve are discussed.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889887008343
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  • 3
    Digitale Medien
    Digitale Medien
    Neutron topography as a tool for studying reactive organic crystals: a feasibility study (1990)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 23 (1990), S. 186-198 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The feasibility of using neutron topography as a non-destructive imaging technique for the study of X-ray sensitive organic single crystals, with a view to applying it to the study of reactivity in such crystals, has been tested. Crystals studied range from relatively X-ray insensitive protonated and deuterated pyrene crystals to relatively highly X-ray sensitive 2,4-hexadiynylene bis(p-toluenesulfonate) (PTS) monomer crystals. The latter crystals are readily polymerized in an X-ray beam. Results indicate that neutron topographic imaging provides little advantage over X-ray topography for either the X-ray insensitive or X-ray sensitive crystals studied here. It was concluded that this is mainly due to limitations in spatial resolution attributed to geometric effects inherent to the technique. However, for X-ray sensitive crystals, neutron topography can provide useful information, in a non-destructive way, in the form of rocking-curve data, and as such can be regarded as a useful `ally' technique to the analogous X-ray techniques. It is expected that in the case of extreme X-ray sensitivity, provided geometric losses can be minimized, neutron topography may be the only technique capable of non-destructively revealing bulk defect structures and strain distributions.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889890000371
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  • 4
    Digitale Medien
    Digitale Medien
    Three-dimensional imaging of crystal defects by `topo-tomography' (2001)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 34 (2001), S. 602-607 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A new technique, `topo-tomography', suitable for the characterization of the three-dimensional defect structure in bulk crystals, is proposed. The technique consists of the combination of diffraction topography and microtomography. It is applicable to high-quality single crystals, provided that the `direct image' is the dominant contrast mechanism. In this case, crystal defects give rise to locally enhanced intensity compared with the perfect-crystal matrix. The additional intensities sum along the diffracted-beam direction and yield projections of the local Bragg reflectivity. Like in the case of absorption tomography, the three-dimensional distribution of this reflectivity can be reconstructed from a large number of projections. The first experimental results of this technique, applied to a synthetic diamond crystal, are presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S002188980101086X
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  • 5
    Digitale Medien
    Digitale Medien
    A simple remote-controlled film holder for synchrotron X-ray topography snapshots (1988)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 21 (1988), S. 991-992 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889888008696
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  • 6
    Digitale Medien
    Digitale Medien
    Visualization of inverted ferroelectric domains in LiNbO3 by X-ray topography (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 106-108 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: A nondestructive method to visualize inverted ferroelectric domains in periodically poled LiNbO3 by X-ray topography is reported. It is shown that, when an electric field is applied to the sample, a strong contrast revealing the inner structure of the domains can be observed, even in white-beam mode.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889897011813
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  • 7
    Digitale Medien
    Digitale Medien
    Two- and Three-Beam X-ray Diffraction Imaging of Domains in Magnetite (1998)
    Copenhagen : International Union of Crystallography (IUCr)
    Applied crystallography online 31 (1998), S. 726-732 
    Details
    ISSN: 1600-5767
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: The X-ray diffraction topographic imaging process for ferrimagnetic domains in magnetite Fe3O4 at room temperature is investigated, in two- and three-beam cases, for incident synchrotron radiation beams differing in angular divergence and energy spread. In the usual two-beam configuration, domain or wall contrast is obtained from the difference in Bragg conditions, or from the slight difference in the direction of the beams diffracted by neighbouring domains, revealed by the large crystal-to-film distance that can be used at a third-generation synchrotron radiation facility. A three-beam Umweganregung case involving the weak 171 and the strong 131 reflections shows unusual domain contrast on the 171 topographs, even on images involving energy or angle integration; this contrast is particularly evident on white-beam topographs. The high angular sensitivity this implies is associated with the difference in dispersion relation between the two reflections.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0021889898004403
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  • 8
    Digitale Medien
    Digitale Medien
    New Features of Dislocation Images in Third-Generation Synchrotron Radiation Topographs (1996)
    Chester : International Union of Crystallography (IUCr)
    Journal of synchrotron radiation 3 (1996), S. 173-184 
    Details
    ISSN: 1600-5775
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Geologie und Paläontologie , Physik
    Notizen: Some aspects of the dislocation contrast observed at third-generation synchrotron radiation set-ups are presented. They can be explained by taking into account angular deviation effects on the beam propagation, which are visible because of the `almost plane-wave' character of these sources. In particular, we show how the evolution of the direct image width of a dislocation as a function of the sample-to-film distance can allow a complete determination of the Burgers vector, i.e. in sign and modulus. In addition, experimental results obtained in monochromatic beam topography are compared with simulated images calculated assuming plane-wave illumination and are demonstrated to show a satisfactory agreement. The utility of the weak-beam technique in enhancing the spatial resolution is demonstrated and a criterion for the selection of experimental conditions depending upon the required spatial resolution, signal-to-noise ratio and exposure time is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0909049596002269
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  • 9
    Digitale Medien
    Digitale Medien
    Neutron diffraction investigation of the nuclear and magnetic extinction in MnP (1986)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 42 (1986), S. 47-55 
    Details
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: The absolute values of the reflecting powers ρ are measured for the 200 and 2 ± τ, 0, 0 set of magnetic and nuclear reflections in the helimagnetic phase of a good-quality crystal of MnP as a function of its thickness. Severe and very different extinction effects are observed for the magnetic and nuclear reflections (ymagnetic ̃0.4, ynuclear ̃0.02 for the largest thickness). This corresponds to the spectacular result that the magnetic reflecting powers ρ± are twice as big as the nuclear one ρN, in spite of the fact that the scattering cross sections |F±|2 are about ten times smaller than the nuclear |FN|2. The nuclear results appear consistent with dynamical theory while the magnetic ones are not. They can be explained by Zachariasen's type II secondary extinction model based on the chirality domain pattern. The same measurements were performed in the ferromagnetic phase, yielding yferro ∼ 0.03. A model using the relative sizes of the ferromagnetic and chirality domains is presented.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108767386099919
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  • 10
    Digitale Medien
    Digitale Medien
    Extinction effects in polarized neutron diffraction from magnetic crystals. I. Highly perfect MnP and YIG samples (1991)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 47 (1991), S. 770-775 
    Details
    ISSN: 1600-5724
    Quelle: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Thema: Chemie und Pharmazie , Geologie und Paläontologie , Physik
    Notizen: Wavelength-dependent flipping-ratio data obtained with polarized neutrons are analysed with the help of two extinction models: Kato's [Acta Cryst. (1980), A36, 763–769, 770–776] statistical dynamical theory (SDT) and the random elastic deformation (RED) approach [Kulda (1987). Acta Cryst. A43, 167–173; (1991). Acta Cryst. A47, 775–779]. Because the crystals used were nearly perfect, Pendellösung oscillations are present in all cases and the extinction theories are thus tested under extreme conditions. Both treatments give fair agreement with the experimental data in the short-wavelength range and there is no significant difference between them in terms of the goodness of fit, but the parameters involved in the RED approach have a more straightforward physical meaning. There are, however, inconsistencies in the values of the SDT parameters obtained, as well as probable deviations at large wavelength and crystal thickness, which could be related to a new validity condition for SDT.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1107/S0108767391006840
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