Are HOLZ lines kinematic in off-zone-axis orientation?

1993 ◽  
Vol 51 ◽  
pp. 692-693
Author(s):  
J. M. Zuo ◽  
A. L. Weickenmeier ◽  
R. Holmestad ◽  
J. C. H. Spence
Keyword(s):  
Structure Determination ◽  
Standard Procedure ◽  
High Order ◽  
Zone Axis ◽  
Great Promise ◽  
Line Position ◽  
Measured Intensity ◽  
Constant Intensity ◽  
Axis Orientation ◽  
Diffraction Condition

The application of high order reflections in a weak diffraction condition off the zone axis center, including those in high order laue zones (HOLZ), holds great promise for structure determination using convergent beam electron diffraction (CBED). It is believed that in this case the intensities of high order reflections are kinematic or two-beam like. Hence, the measured intensity can be related to the structure factor amplitude. Then the standard procedure of structure determination in crystallography may be used for solving unknown structures. The dynamic effect on HOLZ line position and intensity in a strongly diffracting zone axis is well known. In a weak diffraction condition, the HOLZ line position may be approximated by the kinematic position, however, it is not clear whether this is also true for HOLZ intensities. The HOLZ lines, as they appear in CBED patterns, do show strong intensity variations along the line especially near the crossing of two lines, rather than constant intensity along the Bragg condition as predicted by kinematic or two beam theory.

Crystal Structure Determination of Glycerol-Containing Lipids from Electron Diffraction Data. Use of Analog Compounds Based upon Configurational Isomers of Cyclopentane-1, 2, 3-TRIOL

1977 ◽  
Vol 35 ◽  
pp. 24-25
Author(s):  
Douglas L. Dorset ◽  
Anthony J. Hancock
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Diffraction Data ◽  
Structure Determination ◽  
Crystal Surface ◽  
Coherent Scattering ◽  
Crystal Structure Determination ◽  
Electron Diffraction Data ◽  
Polar Group ◽  
Axis Orientation

Lipids containing long polymethylene chains were among the first compounds subjected to electron diffraction structure analysis. It was only recently realized, however, that various distortions of thin lipid microcrystal plates, e.g. bends, polar group and methyl end plane disorders, etc. (1-3), restrict coherent scattering to the methylene subcell alone, particularly if undistorted molecular layers have well-defined end planes. Thus, ab initio crystal structure determination on a given single uncharacterized natural lipid using electron diffraction data can only hope to identify the subcell packing and the chain axis orientation with respect to the crystal surface. In lipids based on glycerol, for example, conformations of long chains and polar groups about the C-C bonds of this moiety still would remain unknown.One possible means of surmounting this difficulty is to investigate structural analogs of the material of interest in conjunction with the natural compound itself. Suitable analogs to the glycerol lipids are compounds based on the three configurational isomers of cyclopentane-1,2,3-triol shown in Fig. 1, in which three rotameric forms of the natural glycerol derivatives are fixed by the ring structure (4-7).

The usefulness of high index low symmetry zone axes for holz line analysis

1987 ◽  
Vol 45 ◽  
pp. 384-385
Author(s):  
C. M. Sung ◽  
D. B. Williams
Keyword(s):  
Lattice Parameter ◽  
High Order ◽  
Zone Axis ◽  
High Index ◽  
High Symmetry ◽  
Second Phases ◽  
Line Patterns ◽  
Low Symmetry ◽  
Line Analysis

Researchers have tended to use high symmetry zone axes (e.g. <111> <114>) for High Order Laue Zone (HOLZ) line analysis since Jones et al reported the origin of HOLZ lines and described some of their applications. But it is not always easy to find HOLZ lines from a specific high symmetry zone axis during microscope operation, especially from second phases on a scale of tens of nanometers. Therefore it would be very convenient if we can use HOLZ lines from low symmetry zone axes and simulate these patterns in order to measure lattice parameter changes through HOLZ line shifts. HOLZ patterns of high index low symmetry zone axes are shown in Fig. 1, which were obtained from pure Al at -186°C using a double tilt cooling holder. Their corresponding simulated HOLZ line patterns are shown along with ten other low symmetry orientations in Fig. 2. The simulations were based upon kinematical diffraction conditions.

Systematic zone-Axis orientation of NM-scale particles for microdiffraction

1990 ◽  
Vol 48 (4) ◽  
pp. 262-263
Author(s):  
E D Boyes ◽  
L Hanna
Keyword(s):  
Real Space ◽  
Dark Field ◽  
Zone Axis ◽  
High Symmetry ◽  
Lattice Imaging ◽  
Cell Level ◽  
Bright Field ◽  
Axis Orientation ◽  
Annular Dark Field ◽  
Target Designation

A VG HB501 FEG STEM has been modified to provide track whilst tilt [TWIT] facilities for controllably tilting selected and initially randomly aligned nanometer-sized particles into the high symmetry zone-axis orientations required for microdiffraction, lattice imaging and chemical microanalysis at the unit cell level. New electronics display in alternate TV fields and effectively in parallel on split [+VTR] or adjacent externally synchronized screens, the micro-diffraction pattern from a selected area down to <1nm2 in size, together with the bright field and high angle annular dark field [HADF] STEM images of a much wider [˜1μm] area centered on the same spot. The new system makes it possible to tilt each selected and initially randomly aligned small particle into a zone axis orientation for microdiffraction, or away from it to minimize orientation effects in chemical microanalysis. Tracking of the inevitable specimen movement with tilt is controlled by the operator, with realtime [60Hz] update of the target designation in real space and the diffraction data in reciprocal space. The spot mode micro-DP and images of the surrounding area are displayed continuously. The regular motorized goniometer stage for the HB501STEM is a top entry design but the new control facilities are almost equivalent to having a stage which is eucentric with nanometric precision about both tilt axes.

scholarly journals Expansion of the Laser Beam Wavefront in Terms of Zernike Polynomials in the Problem of Turbulence Testing

2021 ◽  
Vol 11 (24) ◽  
pp. 12112
Author(s):  
Alexey Rukosuev ◽  
Alexander Nikitin ◽  
Vadim Belousov ◽  
Julia Sheldakova ◽  
Vladimir Toporovsky ◽  
...  
Keyword(s):  
Spectral Analysis ◽  
Laser Radiation ◽  
Laser Beam ◽  
Standard Procedure ◽  
Higher Order ◽  
High Order ◽  
Zernike Polynomials ◽  
Taylor’S Hypothesis ◽  
Zernike Modes ◽  
Low Order

The results of a study of the wavefront distortions of laser radiation caused by artificial turbulence obtained in laboratory conditions using a fan heater are presented. Decomposition of the wavefront in terms of Zernike polynomials is a standard procedure that traditionally is used to investigate the set of existing aberrations. In addition, the spectral analysis of the wavefront dynamics makes it possible to estimate the fraction of the energy distributed between different Zernike modes. It is shown that the fraction of energy related to the low-order polynomials is higher compared to the high-order polynomials. Also, one of the consequences of Taylor’s hypothesis is confirmed—low-order aberrations are slower compared to the higher-order ones.

Appropriate zone-axis orientations for the determination of crystal polarity by convergent-beam electron diffraction

2015 ◽  
Vol 48 (3) ◽  
pp. 736-746 ◽  
Author(s):  
Katsushi Tanaka ◽  
Norihiko L. Okamoto ◽  
Satoshi Fujio ◽  
Hiroki Sakamoto ◽  
Haruyuki Inui
Keyword(s):  
Electron Diffraction ◽  
Rotation Axis ◽  
Convergent Beam Electron Diffraction ◽  
Zone Axis ◽  
Mirror Plane ◽  
Axis Orientation ◽  
Beam Electron ◽  
Polarity Determination ◽  
Point Groups ◽  
Convergent Beam

A convergent-beam electron diffraction (CBED) method is proposed for polarity determination, in which polarity is determined from the intensity asymmetry of any of thehkl–\overline h\overline k\overline l Friedel pairs appearing in a zone-axis CBED pattern with a symmetric arrangement of Bijvoet pairs of reflections. The intensity asymmetry occurs as a result of multiple scattering among Bijvoet pairs of reflections in the CBED pattern. The appropriate zone-axis orientations for polarity determination are deduced for 19 of the 25 polar point groups from symmetry considerations so as to observe Bijvoet pairs of reflections symmetrically in a single CBED pattern. These appropriate zone-axis orientations deduced for the 19 polar point groups coincide with nonpolar directions. This is because the nonpolar directions for these point groups are perpendicular to an even-fold rotation axis, which guarantees the symmetric arrangement of Bijvoet pairs of reflections with respect to the symmetry (m–m′) line in a CBED pattern taken along any of the appropriate zone-axis orientations. Them–m′ line in the CBED pattern is proved to be perpendicular to the trace of the even-fold rotation axis. On the other hand, if the nonpolar direction is either perpendicular to a mirror plane or parallel to a roto-inversion axis as in the four point groupsm, 3m1, 31m, \overline 6, the nonpolar direction cannot be used as the appropriate zone-axis orientation for polarity determination because the Bijvoet pairs of reflections are not arranged symmetrically in the CBED pattern. The validity of the CBED method is confirmed both by experiment and by calculation of CBED patterns.

Electron lattice image interpretation of V2O3 wedge shaped crystal

1978 ◽  
Vol 36 (1) ◽  
pp. 286-287
Author(s):  
M. Tanaka ◽  
A. Rocher ◽  
R. Ayroles ◽  
B. Jouffrey
Keyword(s):  
Image Interpretation ◽  
Theoretical Aspect ◽  
Zone Axis ◽  
Lattice Image ◽  
Hexagonal System ◽  
Axis Orientation ◽  
Vanadium Sesquioxide ◽  
Small Lattice ◽  
Experimental Image ◽  
Unit Cell Dimensions

The thickness dependence of a two dimensional lattice image with small lattice spacings (< 5 Å) has been discussed in the theoretical aspect by some authors(1) (2),(3) in the case of zone axis orientation. Our intention is to compare the experimental image with the theoretical one for a vanadium sesquioxide (V2O3) crystal not in the zone axis orientation but in more general orientations. This crystal, one of those which show the metal-insulator transition, is metallic and belongs to the space group at room temperature. The unit cell dimensions in the hexagonal system are a = 4.951 Å and c = 14.003 Å (4). The electron microscope used is a JEM-100C equipped with the fixed specimen stage and operated at 100 kV (Cs = 1.4 mm).Figure 1 shows a lattice image from a wedge shaped crystal. Especially remarkable is the recurrence of similar contrast in three thicknesses regions : < 50 Å,∽ 250Å,and ∽ 450Å.

scholarly journals Single-crystal structure validation with the programPLATON

2003 ◽  
Vol 36 (1) ◽  
pp. 7-13 ◽  
Author(s):  
A. L. Spek
Keyword(s):  
Crystal Structure ◽  
Single Crystal ◽  
Structure Determination ◽  
Structure Refinement ◽  
Standard Procedure ◽  
Single Crystal Structure ◽  
Crystal Structure Determination ◽  
Structure Validation

The results of a single-crystal structure determination when in CIF format can now be validated routinely by automatic procedures. In this way, many errors in published papers can be avoided. The validation software generates a set of ALERTS detailing issues to be addressed by the experimenter, author, referee and publication journal. Validation was pioneered by the IUCr journalActa Crystallographica Section Cand is currently standard procedure for structures submitted for publication in all IUCr journals. The implementation of validation procedures by other journals is in progress. This paper describes the concepts of validation and the classes of checks that are carried out by the programPLATONas part of the IUCrcheckCIFfacility.PLATONvalidation can be run at any stage of the structure refinement, independent of the structure determination package used, and is recommended for use as a routine tool during or at least at the completion of every structure determination. Two examples are discussed where proper validation procedures could have avoided the publication of incorrect structures that had serious consequences for the chemistry involved.

scholarly journals Single-pass STEM-EMCD on a zone axis using a patterned aperture: progress in experimental and data treatment methods

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Thomas Thersleff ◽  
Linus Schönström ◽  
Cheuk-Wai Tai ◽  
Roman Adam ◽  
Daniel E. Bürgler ◽  
...  
Keyword(s):  
Data Processing ◽  
Magnetic Circular Dichroism ◽  
Magnetic Moments ◽  
Scanning Transmission Electron Microscope ◽  
Zone Axis ◽  
Atomic Resolution ◽  
Magnetic Scattering ◽  
Axis Orientation ◽  
Single Pass ◽  
Scale Down

AbstractMeasuring magnetic moments in ferromagnetic materials at atomic resolution is theoretically possible using the electron magnetic circular dichroism (EMCD) technique in a (scanning) transmission electron microscope ((S)TEM). However, experimental and data processing hurdles currently hamper the realization of this goal. Experimentally, the sample must be tilted to a zone-axis orientation, yielding a complex distribution of magnetic scattering intensity, and the same sample region must be scanned multiple times with sub-atomic spatial registration necessary at each pass. Furthermore, the weak nature of the EMCD signal requires advanced data processing techniques to reliably detect and quantify the result. In this manuscript, we detail our experimental and data processing progress towards achieving single-pass zone-axis EMCD using a patterned aperture. First, we provide a comprehensive data acquisition and analysis strategy for this and other EMCD experiments that should scale down to atomic resolution experiments. Second, we demonstrate that, at low spatial resolution, promising EMCD candidate signals can be extracted, and that these are sensitive to both crystallographic orientation and momentum transfer.

A simple method for determining orientation and misorientation of the cubic crystal specimen

1994 ◽  
Vol 27 (5) ◽  
pp. 755-761 ◽  
Author(s):  
Q. Liu
Keyword(s):  
Zone Axis ◽  
Beam Direction ◽  
Simple Method ◽  
Axis Orientation ◽  
Cubic Crystal ◽  
Kikuchi Pattern ◽  
Rotation Axes ◽  
Transmission Electron ◽  
Fluorescent Screen

With the aid of a double-tilt holder, a simple method for determining orientation and misorientation of a cubic crystal specimen in a transmission electron microscope is developed. To use this method, a recognizable zone axis from one grain needs to be aligned along the beam direction, the corresponding tilt positions (α 0, β 0) of the two rotation axes must be obtained from the meter reading of the holder and the rotation position of the Kikuchi pattern around the beam direction must be measured on the fluorescent screen with the aid of apparatus for the direct measurement of a diffraction-pattern position on screen. After the input of (α 0, β 0) and the rotation positions, the orientation of the grain can be calculated using a computer program. The misorientation matrix R, rotation angle Θm , axis I m and sense can then be calculated for any selected set of two grains. The accuracy of determination of the orientation of any particular grain is about 1° and, in the case of the determination of misorientation angles between two grains within a sample, the precision is within 0.1°. This method is considered to be much simpler and more rapid than previous methods because no photographs of Kikuchi patterns need to be taken and only one zone-axis orientation needs to be adjusted along the beam direction.

Modeling and simulation of octahedral Pb inclusions in Al

1995 ◽  
Vol 53 ◽  
pp. 646-647
Author(s):  
S.Q. Xiao ◽  
S. Paciornik ◽  
R. Kilaas ◽  
E. Johnson ◽  
U. Dahmen
Keyword(s):  
Total Sample ◽  
Inclusion Size ◽  
Zone Axis ◽  
Sample Thickness ◽  
Solidification Behavior ◽  
Axis Orientation ◽  
Resolution Electron ◽  
The Matrix ◽  
High Resolution Electron Micrographs

Pb inclusions in Al have been extensively studied for their unusual melting/solidification behavior. Pb inclusions have a cube on cube parallel orientation relationship with the Al matrix and assume cuboctahedral shapes faceted on {111} and {100}. Al and Pb are both fcc structures but with very different lattice parameters: aAl = 0.405 nm, apb = 0.495 nm. Thus 5 Al spacings match approximately 4 Pb spacings giving rise to a moire pattern visible in HREM images.High resolution electron micrographs in the <110> zone axis orientation were recorded on the Berkeley ARM at an accelerating voltage of 800 kV. In this orientation the cuboctahedra project as truncated parallelograms as shown in Fig. 1. Although the four (111) interfaces revealed in Fig. 1 are imaged edge-on, the Al lattice overlaps the Pb lattice above and below, because the other four (111) interfaces are inclined. Therefore, even though the (111)Al lattice is clearly resolved, the determination of inclusion size is not straightforward because the contrast depends on defocus (Δf), particle size (s), depth of the inclusion in the matrix (z) and total sample thickness (t).

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