Refinement of crystal structural parameters using two-dimensional energy-filtered CBED patterns

Tsuda, Kenji; Tanaka, Michiyoshi

doi:10.1107/s0108767399005401

Cited by 141 publications

(93 citation statements)

References 26 publications

(11 reference statements)

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“…Dynamic simulation of the CBED patterns was performed using the Bloch-wave program ( Fig. 2 A2 and D2) (15). Agreement of the experimental patterns with the simulated ones confirmed that the sharp ZnO tips grow along the positive [0001] direction (i.e., Zn-polar direction), whereas the smooth tips grow along the negative ½0001 direction (i.e., O-polar direction).…”

Section: Resultsmentioning

confidence: 82%

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Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence

Gautam

Imura

Rout

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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Oriented assemblies of small crystals forming larger structures are common in nature and crucial for forthcoming technologies as they circumvent the difficulties of structural manipulation at microscopic scale. We have discovered two distinctive concentric assemblies of zinc oxide rods, wherein each rod has an intrinsically positive and a negative polar end induced by the noncentrosymmetric arrangement of Zn and O atoms. All the rods in a single assembly emanate out of a central core maintaining a single polar direction. Due to growth along the two polar surfaces with different atomic arrangements, these assemblies are distinct in their intrinsic properties and exhibit strong UV luminescence in the exterior of Zn-polar assemblies, unlike the O-polar assemblies. Although novel applications can be envisioned, these observations suggest that hierarchical organization with respect to internal asymmetry might be widespread in natural crystal assemblies.

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Section: Resultsmentioning

confidence: 82%

“…Simulated CBED patterns were obtained by many-beam dynamical calculations. The intensity calculation is based on the Bloch-wave formulation of dynamical theory (15). After the structural and chemical examinations, spatially resolved CL measurements on individual ZnO assemblies were carried out.…”

Section: Methodsmentioning

confidence: 99%

Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence

Gautam

Imura

Rout

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

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“…Spiral distortion is related to the rotation of the image that takes place in the magnetic electron lenses. Modern designs of magnetic electron lenses allow spiral distortion to be almost completely removed [18,19], or at least maintained below 1% if one has to work with beams subtending very large diffracting angles [20]. Our experience in dealing with HR imaging and SA diffraction reveals that the most relevant image affecting distortion can be approximated to be elliptical (Fig.…”

Section: Introductionmentioning

confidence: 96%

A practical method to detect and correct for lens distortion in the TEM

et al. 2006

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A practical, offline method for experimental detection and correction for projector lens distortion in the transmission electron microscope (TEM) operating in high-resolution (HR) and selected area electron diffraction (SAED) modes is described. Typical TEM works show that, in the simplest case, the distortion transforms on the recording device, which would be a circle into an ellipse. The first goal of the procedure described here is to determine the elongation and orientation of the ellipse. The second goal is to correct for the distortion using an ordinary graphic program. The same experimental data set may also be used to determine the actual microscope magnification and the rotation between SAED patterns and HR images.The procedure may be helpful in several quantitative applications of electron diffraction and HR imaging, for instance while performing accurate lattice parameter determination, or while determining possible metrical deviations (cell edges and angles) from a given symmetry. r

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“…124 of the 129 unique atoms (1176 in the unit cell) were found in the remarkably clean calculated potential maps ( Fig. 1) [2]. This investigation demonstrates that inorganic crystals of any complexity can be solved by electron crystallography.…”

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confidence: 70%

“…Distortion and background corrections were applied. A maximum of 91 reflections per pattern was fitted using the software package MBFIT, which provides a multi beam nonlinear least squares algorithm for zeroth order and higher order Laue zone (ZOLZ, HOLZ) reflections, fully based on dynamical diffraction theory [2]. The set of fitting parameters contains full structural information (atomic positions, anisotropic Debye-Waller-factors and low order structure factors).…”

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confidence: 99%

Three-dimensional reconstruction of quasicrystal approximant structures by electron crystallography

Zou¹,

Mo²,

Hovmöller³

et al. 2004

Acta Cryst Sect A

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Lincoln, c Beijing Laboratory of Electron Microscopy, P.O. Box 2724, 100080 Beijing, China. Email: zou@struc.su.se Keywords: Electron Crystallography; 3d Reconstruction; Quasicrystal Approximants Electron crystallography can be applied for solving structures of crystals too small for X-ray diffraction. The advantage of electron crystallography over X-ray crystallography is that the phases of the crystallographic structure factors, which are lost in X-ray diffraction, are present in HREM images. Electron crystallography has been demonstrated on many structures with one short axis [1] . However, for crystals lacking of short axes, atoms may overlap in all directions so several images from different directions must be combined in order to solve the 3D structure. We have reconstructed the 3D structure of a complex quasicrystal approximant n-AlCrFe (P6 3 /m, a = 40.687 and c = 12.546 Å). Due to the huge unit cell, it was necessary to combine crystallographic data from 13 projections to resolve the atoms. Electron microscopy images containing both amplitude and phase information were combined with amplitudes from electron diffraction patterns. 124 of the 129 unique atoms (1176 in the unit cell) were found in the remarkably clean calculated potential maps (Fig. 1) [2]. This investigation demonstrates that inorganic crystals of any complexity can be solved by electron crystallography. A method to deduce the structures of several other related approximants is presented. Hematite (a-Fe 2 O 3 ) crystallizes in the corundum type structure (spacegroup R-3c) with the magnetic ions on the threefold axis. Antiferromagnetic ordering takes place at 950 K, a magnetic phase transition occurs at » 250 K, the so called Morin transition. Below the Morin transition the magnetic moments are ordered antiferromagneticaly parallel to [111]. Above, a slightly canted antiferromagnetic arrangement with the spins perpendicular to the [111] direction is observed, which leads to a weak ferromagnetic component (Morin phase). The magnetic ordering of the Morin phase is not in agreement with the crystal symmetry, since the magnetic moments are perpendicular to the threefold axis. This break of symmetry should either result in an orthorhombic distortion of the lattice, a shift of the magnetic ions off the axis (implying static disorder) or an orbital ordering of the valence electrons. None has been reported in the literature.To investigate the points in question, electron density studies are carried out on a natural hematite. Convergent beam electron diffraction patterns were taken from the three symmetry zone axes [001], [100] and [210] (hex. setting) with the corresponding whole-and bright-pattern symmetries of 3m, 2 and m. The patterns were each measured at room temperature and 90K using a JEOL2010FEF microscope equipped with a Schottky-type field emission gun and a Wollnik-type W-Filter [1]. Distortion and background corrections were applied. A maximum of 91 reflections per pattern was fitted using the software package MBFIT, which provi...

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Refinement of crystal structural parameters using two-dimensional energy-filtered CBED patterns

Cited by 141 publications

References 26 publications

Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence

Unipolar assembly of zinc oxide rods manifesting polarity-driven collective luminescence

A practical method to detect and correct for lens distortion in the TEM

Three-dimensional reconstruction of quasicrystal approximant structures by electron crystallography

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