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  • 11
    Electronic Resource
    Electronic Resource
    Dynamical diffraction calculations for RHEED and REM (1986)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 42 (1986), S. 545-552 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The multislice formulation of the many-beam dynamical diffraction theory has been applied to the Bragg case of electron diffraction for the extended surface of a perfect crystal and also for a crystal surface with a surface step. The wavefunctions within and outside the crystal have been calculated and used to derive the standing-wave pattern in the top atomic layers of the crystal, the intensities of the reflection high-energy electron diffraction (RHEED) pattern and the contrast of the reflection electron microscopy (REM) image. Calculations made for the diffraction of 19, 40 and 80 keV electrons from (111) surfaces of Pt and Au demonstrate the channeling of electrons under the conditions of surface resonance, the perturbation of the standing-wave field in the crystal by a one-atom-high surface step and the REM contrast for a through-focus series of images of a surface step. The method is applicable to models including surface relaxations and reconstructions and any kind of local defect of the surface or of the bulk crystal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767386098756
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  • 12
    Electronic Resource
    Electronic Resource
    Errors arising from numerical use of the Mott formula in electron image simulation (1988)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 44 (1988), S. 1-6 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The Mott formula relating the electron scattering factor to that for X-rays is inaccurate in its numerical form in the small-angle region. Effects of the inaccuracy on both kinematic and dynamical diffraction have been investigated. Some artifacts arising from the inaccuracy have been found in simulated electron microscopy images. A modified form for the Mott formula, which minimizes the error, is proposed. However, for any accurate and reliable calculation only those electron scattering factors derived directly from the atomic potential can be used.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0108767387006858
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  • 13
    Electronic Resource
    Electronic Resource
    Irradiation effects in beryllia and zinc oxide (1966)
    Copenhagen : International Union of Crystallography (IUCr)
    Acta crystallographica 21 (1966), S. 192-196 
    Details
    ISSN: 0001-5520
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Geosciences
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0365110X66002603
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  • 14
    Electronic Resource
    Electronic Resource
    The effects of n-beam dynamical diffraction on electron diffraction intensities from polycrystalline materials (1969)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 25 (1969), S. 475-481 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Calculations based on n-beam dynamical diffraction theory have shown that the intensities of rings and arcs in diffraction patterns from polycrystalline materials are strongly dependent on the experimental conditions. For arc patterns from BiOCl, calculations confirm a revised formula for the intensities from very thin crystals and indicate dependences on the distributions of orientation, thickness and bending of the crystals which are sufficient to account for the wide deviations of recent experimental results from the predictions of the primary extinction formula, based on the two-beam approximation. Inferences regarding the possible errors in electron diffraction analysis of crystal structures, especially for materials containing heavy atoms, are drawn from calculations relating to the intensities of arc patterns from AgTISe2. It is suggested that n-beam calculations should be made in order to avoid serious error in the refinement stages of a structure analysis.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739469000957
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  • 15
    Electronic Resource
    Electronic Resource
    Diffraction by crystals with planar faults. I. General theory (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 83-87 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Kinematical diffraction from a crystal having planar faults is described by a systematic writing of the Patterson function and its Fourier transform for the general case of an arbitrary number of different kinds of layer, describing the faults in terms of a fault vector plus an addition, or subtraction, of scattering matter. The general series expression is readily simplified to deal with a wide variety of special cases. Particular examples include Wadsley-type shear faults associated with non-stoichiometry of oxides and the deformation and growth faults of simple close-packed structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476000156
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  • 16
    Electronic Resource
    Electronic Resource
    Refinement of the defect structure of `GeNb9O25' by high-resolution electron microscopy (1976)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 32 (1976), S. 799-805 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: It has been previously established that calculations of intensity distributions in high-resolution electron-microscope images of crystal structures can reproduce the experimental observations. The use of comparisons Of observed and computed images for structure analysis has been extended for the first time to the refinement of a defect structure in the case of crystals of nominal composition 'GeNb9O25. The results show that previously proposed models for the disordered atom configurations around 'tetrahedral' sites are not completely correct. A new model is proposed which shows good agreement between computed and observed images. This model suggests an interpretation for observations on other related structures in terms of a new type of defect.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739476001630
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  • 17
    Electronic Resource
    Electronic Resource
    Diffraction by crystals with planar faults. III. Structure analyses using microtwins (1978)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 34 (1978), S. 738-743 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The general theory for kinematical diffraction from crystals having planar faults is applied to the case of microtwinning and the related cases occurring in some minerals where there is a disordered sequence of two types of structure having small differences in composition, unit-cell dimensions and axial orientations. It is shown that, if intensities are measured for unresolved or partially resolved pairs of diffraction spots using conventional techniques, errors may well arise if the measurements are interpreted on the usual assumption that the intensities from the different crystal regions are summed incoherently. Calculations for representative cases suggest that errors, due to the neglect of the spreading of intensity maxima into continuous streaks, may amount to 20 or 30% when overlapping diffraction spots have structure amplitudes of opposite sign, but are usually much smaller, especially if the structure amplitudes are of the same sign.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739478001515
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  • 18
    Electronic Resource
    Electronic Resource
    Short-range ordering in PbMg1/3Nb2/3O3 (1979)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 35 (1979), S. 1015-1017 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: High-resolution electron-microscope images in conjunction with selected-area electron diffraction were used to investigate the short-range order in PbMg1/3Nb2/3O3. Intensity fluctuations of the [110] image indicated ordered domains extending over about 20 to 50 Å. Decomposition phases were observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739479002230
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  • 19
    Electronic Resource
    Electronic Resource
    Microdiffraction from antiphase domain boundaries in Cu3Au (1982)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 38 (1982), S. 718-724 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: Electron diffraction patterns have been obtained from regions of a thin crystal of partially ordered copper-gold alloy, Cu3Au, which have a diameter of about 15 Å and contain an antiphase domain boundary. The superlattice diffraction spots show a characteristic splitting similar to the splitting which appears in all spots, both fundamental and superlattice, when the beam irradiates a region at the edge of a crystal. By observing which of the superlattice spots are split and which are not, it is possible to deduce immediately whether the antiphase domain boundary is of the 'good' type or is one of the 'bad' types or whether more than one boundary is illuminated by the beam. The observations of split spots are in good agreement with the results of calculations made on the basis of kinematic theory. It is shown that these results remain valid in the presence of strong dynamical scattering for small specimen thicknesses.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739482001442
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  • 20
    Electronic Resource
    Electronic Resource
    Diffuse scattering in electron diffraction patterns. I. General theory and computational methods (1968)
    [S.l.] : International Union of Crystallography (IUCr)
    Acta crystallographica 24 (1968), S. 109-116 
    Details
    ISSN: 1600-5724
    Source: Crystallography Journals Online : IUCR Backfile Archive 1948-2001
    Topics: Chemistry and Pharmacology , Geosciences , Physics
    Notes: The solution of the n-beam dynamical theory of the diffraction of electrons by crystals is generalized to cover the case of diffraction by crystals containing defects and disorders, including thermal motion. The conditions and assumptions under which practical computer calculations of diffuse intensities can be made are explored on the basis of the slice approach of Goodman and Moodie, although matrix methods are equally applicable. It is shown that, if the range of correlation of the deviations from the perfect crystal lattice is small, the total diffuse scattering can be expressed in terms of dynamical factors which multiply the intensities calculated using the kinematical approximation. Simple expressions are derived for the absorption coefficients which must be applied to the sharp Bragg reflexions to take account of the energy lost from them into the diffuse scattering. The possibility that the intensity of diffuse scattering may show dependence on the range of correlation of the defects is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1107/S0567739468000148
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