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.

HREM Profile Image Interpretation In MgO Cubes

1985 ◽  
Vol 43 ◽  
pp. 64-65
Author(s):  
M. A. O'Keefe ◽  
J. C. H. Spence ◽  
J. L. Hutchison ◽  
W. G. Waddington
Keyword(s):  
Image Interpretation ◽  
Order Structure ◽  
Specimen Thickness ◽  
Crystal Thickness ◽  
Lattice Image ◽  
Axis Orientation ◽  
Structure Factors ◽  
Experimental Image ◽  
Simulated Images ◽  
Contrast Image

For the most credible interpretation of HREM images, it is desirable to match computed and experimental images against the variation of some parameter, usually either specimen thickness or defocus (and preferably both). MgO smoke forms in perfect crystalline cubes, so that the thickness, T, of a cube in <110> zone axis orientation can accurately be determined by geometry at each co-ordinate X (normal to the wedge edge) in the image. Figure 1 shows such an experimental 90° MgO wedge lattice image recorded in an exact <110> orientation using a JEOL 200CX. Dynamical multislice calculations for the thickness dependence of the inner beams important for imaging are shown (c) scaled to the abscissa of the experimental image (the crystal thickness, T, at any point is twice the X value shown). Analysis of this image by means of simulated images (not shown) shows the thin-crystal “structure” image changing to one containing vertical (220) fringes at A (due to strong second-order (111) x (111) interference), to a re verse-contrast image at C, to one with horizontal (002) fringes at B (from strong (111) x (111) interference), and to a “structure“-like image at D. Matching with simulated images provides a rare possibility for guantitative structure analysis by HREM, since the complex low order structure factors can be adjusted in the dynamical calculation until the contrast reversals and other turning points occur at the observed thicknesses.

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.

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.

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.

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).

High-resolution transmission electron microscopy: A structural and chemical probe of semiconductor systems

1987 ◽  
Vol 45 ◽  
pp. 332-333
Author(s):  
A. Ourmazd
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Structural Information ◽  
Image Interpretation ◽  
Lattice Image ◽  
Semiconductor Interfaces ◽  
Transmission Electron ◽  
Lattice Images ◽  
The Individual

High Resolution Transmission Electron Microscopy (HRTEM) is now a powerful probe for the structural analysis of semiconductor systems. Lattice images can be obtained in a number of orientations, in at least three of which the individual atomic columns can be resolved. However, there exits an important class of problems, whose resolution requires chemical as well as structural information. The identification of individual atomic columns in compound semiconductors, and the atomic configuration of semiconductor/semiconductor interfaces are two important examples.In general, most reflection used to form a lattice image are not particularly sensitive to chemical changes in the sample. The information content of a typical lattice image is therefore strongly dominated by structural details. On the other hand, reflections such as the (200), which are normally forbidden in the diamond structure, come about in the zinc-blende system because of the chemical differences between the occupants of the two sublattices, and are thus highly chemically sensitive. In the “kinematical” thickness region, where simple image interpretation is possible, such reflections are relatively weak and their contribution to the lattice image is dominated by the stronger and chemically insensitive, allowed reflections.

Towards an exit wave in closed analytical form

1999 ◽  
Vol 55 (2) ◽  
pp. 212-215 ◽  
Author(s):  
D. Van Dyck ◽  
J. H. Chen
Keyword(s):  
Analytical Form ◽  
Zone Axis ◽  
Axis Orientation ◽  
Accurate Expression

A simple but sufficiently accurate expression is obtained for the exit wave of a crystal in zone-axis orientation. The exit wave at each atom column can be parametrized with only one parameter, which is a function of the projected `weight' of the column.

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