Fortran source listing for simulating three-dimensional convergent beam patterns with absorption by the Bloch wave method

1989 ◽  
Vol 12 (1) ◽  
pp. 29-55 ◽  
Author(s):  
J. M. Zuo ◽  
K. Gjonnes ◽  
J. C. H. Spence
Keyword(s):  
Three Dimensional ◽  
Bloch Wave ◽  
Wave Method ◽  
Source Listing ◽  
Convergent Beam ◽  
Beam Patterns

convergent-beam diffraction from surfaces

1987 ◽  
Vol 45 ◽  
pp. 30-33
Author(s):  
J. A. Eades ◽  
A. E. Smith ◽  
D. F. Lynch
Keyword(s):  
Reciprocal Lattice ◽  
Three Dimensional ◽  
Grazing Incidence ◽  
Three Dimensions ◽  
Plane Figure ◽  
Transmission Electron ◽  
Convergent Beam ◽  
Beam Patterns ◽  
Beam Diffraction

It is quite simple (in the transmission electron microscope) to obtain convergent-beam patterns from the surface of a bulk crystal. The beam is focussed onto the surface at near grazing incidence (figure 1) and if the surface is flat the appropriate pattern is obtained in the diffraction plane (figure 2). Such patterns are potentially valuable for the characterization of surfaces just as normal convergent-beam patterns are valuable for the characterization of crystals.There are, however, several important ways in which reflection diffraction from surfaces differs from the more familiar electron diffraction in transmission.GeometryIn reflection diffraction, because of the surface, it is not possible to describe the specimen as periodic in three dimensions, nor is it possible to associate diffraction with a conventional three-dimensional reciprocal lattice.

On the accuracy of structure-factor measurements in GaAs by CBED

1988 ◽  
Vol 46 ◽  
pp. 824-825
Author(s):  
J.M. Zuo ◽  
M. O'Keeffe ◽  
J.C.H. Spence
Keyword(s):  
Structure Factor ◽  
Phonon Scattering ◽  
Three Dimensional ◽  
Bloch Wave ◽  
Bragg Angle ◽  
Order Structure ◽  
Structure Factors ◽  
Convergent Beam ◽  
Electron Energy Loss ◽  
Low Order

By comparing the experimental intensity in convergent-beam electron diffraction (CBED) patterns along the [h,0,0], [h,h,0] and [h,h,h] systematics directions with three-dimensional Bloch-wave calculations, we have refined the low-order structure factor amplitudes of GaAs. (For Si, see) The experimental data were collected using a Philips EM400 electron microscope and a Gatan model 607 electron energy loss spectrometer (EELS) tuned to the elastic peak. By placing the scan coils of the microscope under the control of a PDP11 computer, the CBED patterns could be scanned over the EELS entrance slit. Data were collected at 120kV and -183°C to reduce phonon scattering and contamination. The angular resolution was 0.6% of the (200) Bragg angle. The refinement parameters in the calculations were high voltage (obtained from HOLZ lines), thickness (obtained from outer CBED fringes), absorption potentials (from the asymmetry of the (000) disk) and the low-order structure factors Vg (from inner peaks).

Crystal Structure Analysis of Cu-Zr Alloys by Convergent Beam Diffraction

1981 ◽  
Vol 39 ◽  
pp. 354-355
Author(s):  
A. F. Marshall ◽  
J. W. Steeds ◽  
D. Bouchet ◽  
S. L. Shinde ◽  
R. G. Walmsley
Keyword(s):  
Crystal Structure ◽  
Point Group ◽  
Intermetallic Phase ◽  
Three Dimensional ◽  
Crystal Structure Analysis ◽  
Ion Milling ◽  
Composition And Structure ◽  
Unit Cells ◽  
Sputter Deposited ◽  
Convergent Beam

Convergent beam electron diffraction is a powerful technique for determining the crystal structure of a material in TEM. In this paper we have applied it to the study of the intermetallic phases in the Cu-rich end of the Cu-Zr system. These phases are highly ordered. Their composition and structure has been previously studied by microprobe and x-ray diffraction with sometimes conflicting results.The crystalline phases were obtained by annealing amorphous sputter-deposited Cu-Zr. Specimens were thinned for TEM by ion milling and observed in a Philips EM 400. Due to the large unit cells involved, a small convergence angle of diffraction was used; however, the three-dimensional lattice and symmetry information of convergent beam microdiffraction patterns is still present. The results are as follows:1) 21 at% Zr in Cu: annealed at 500°C for 5 hours. An intermetallic phase, Cu3.6Zr (21.7% Zr), space group P6/m has been proposed near this composition (2). The major phase of our annealed material was hexagonal with a point group determined as 6/m.

Convergent-beam electron diffraction at high spatial resolution

1992 ◽  
Vol 50 (2) ◽  
pp. 1152-1153 ◽  
Author(s):  
J W Steeds
Keyword(s):  
Electron Diffraction ◽  
High Temperature Superconductors ◽  
Bloch Wave ◽  
Convergent Beam Electron Diffraction ◽  
Beam Electron ◽  
Energy Filtering ◽  
Small Probe ◽  
Transmission Electron ◽  
Electron Microscopes ◽  
Convergent Beam

That the techniques of convergent beam electron diffraction (CBED) are now widely practised is evident, both from the way in which they feature in the sale of new transmission electron microscopes (TEMs) and from the frequency with which the results appear in the literature: new phases of high temperature superconductors is a case in point. The arrival of a new generation of TEMs operating with coherent sources at 200-300kV opens up a number of new possibilities.First, there is the possibility of quantitative work of very high accuracy. The small probe will essentially eliminate thickness or orientation averaging and this, together with efficient energy filtering by a doubly-dispersive electron energy loss spectrometer, will yield results of unsurpassed quality. The Bloch wave formulation of electron diffraction has proved itself an effective and efficient method of interpreting the data. The treatment of absorption in these calculations has recently been improved with the result that <100> HOLZ polarity determinations can now be performed on III-V and II-VI semiconductors.

Performance and applications of a field-emission gun TEM/STEM

1992 ◽  
Vol 50 (2) ◽  
pp. 942-943
Author(s):  
Judith M. Brock ◽  
Max T. Otten ◽  
Marc. J.C. de Jong
Keyword(s):  
Field Emission ◽  
High Resolution Imaging ◽  
High Quality ◽  
Small Energy ◽  
High Brightness ◽  
Small Probe ◽  
Resolution Imaging ◽  
Convergent Beam ◽  
Beam Patterns ◽  
Beam Diffraction

A Field Emission Gun (FEG) on a TEM/STEM instrument provides a major improvement in performance relative to one equipped with a LaB6 emitter. The improvement is particularly notable for small-probe techniques: EDX and EELS microanalysis, convergent beam diffraction and scanning. The high brightness of the FEG (108 to 109 A/cm2srad), compared with that of LaB6 (∼106), makes it possible to achieve high probe currents (∼1 nA) in probes of about 1 nm, whilst the currents for similar probes with LaB6 are about 100 to 500x lower. Accordingly the small, high-intensity FEG probes make it possible, e.g., to analyse precipitates and monolayer amounts of segregation on grain boundaries in metals or ceramics (Fig. 1); obtain high-quality convergent beam patterns from heavily dislocated materials; reliably detect 1 nm immuno-gold labels in biological specimens; and perform EDX mapping at nm-scale resolution even in difficult specimens like biological tissue.The high brightness and small energy spread of the FEG also bring an advantage in high-resolution imaging by significantly improving both spatial and temporal coherence.

Structure Information From Electron Diffraction Intensities

1990 ◽  
Vol 48 (2) ◽  
pp. 516-517
Author(s):  
J. Gjønnes ◽  
N. Bøe ◽  
K. Gjønnes
Keyword(s):  
Computational Effort ◽  
Unit Cell ◽  
Small Unit ◽  
Structure Information ◽  
Dispersion Surface ◽  
Integrated Intensity ◽  
The One ◽  
Image Position ◽  
Convergent Beam ◽  
Beam Patterns

Structure information of high precision can be extracted from intentsity details in convergent beam patterns like the one reproduced in Fig 1. From low order reflections for small unit cell crystals,bonding charges, ionicities and atomic parameters can be derived, (Zuo, Spence and O’Keefe, 1988; Zuo, Spence and Høier 1989; Gjønnes, Matsuhata and Taftø, 1989) , but extension to larger unit cell ma seem difficult. The disks must then be reduced in order to avoid overlap calculations will become more complex and intensity features often less distinct Several avenues may be then explored: increased computational effort in order to handle the necessary many-parameter dynamical calculations; use of zone axis intensities at symmetry positions within the CBED disks, as in Figure 2 measurement of integrated intensity across K-line segments. In the last case measurable quantities which are well defined also from a theoretical viewpoint can be related to a two-beam like expression for the intensity profile:With as an effective Fourier potential equated to a gap at the dispersion surface, this intensity can be integrated across the line, with kinematical and dynamical limits proportional to and at low and high thickness respctively (Blackman, 1939).

Transmission Electron Diffraction Techniques for Nm Scale Strain Measurement in Semiconductors

1995 ◽  
Vol 405 ◽  
Author(s):  
J. Vanhellemont ◽  
K. G. F. Janssens ◽  
S. Frabboni ◽  
P. Smeys ◽  
R. Balboni ◽  
...  
Keyword(s):  
Electron Diffraction ◽  
Large Angle ◽  
Three Dimensional ◽  
Local Strain ◽  
Quantitative Information ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Dimensional Finite Element ◽  
Three Dimensional Finite Element ◽  
Convergent Beam

AbstractAn overview is given of transmission electron microscopy techniques to address strain with nm scale spatial resolution. In particular the possibilities and limitations of (large angle) convergent beam electron diffraction ((LA)CBED) and electron diffraction contrast imaging (EDCI) techniques are discussed in detail. It will be shown by a few case studies that unique and quantitative information on local strain distributions can be obtained by the combined use of both (LA)CBED and EDCI in correlation with three dimensional finite element simulations of the strain distributions in the thinned specimen.

Three-Dimensional Topological Insulators: The Case of Inverse Heusler Compound Lu2FePb

2014 ◽  
Vol 926-930 ◽  
pp. 440-443
Author(s):  
Ning Ding ◽  
Xi Feng Liu ◽  
Xiao Tian Wang ◽  
Wen Yuan
Keyword(s):  
Function Theory ◽  
Three Dimensional ◽  
Density Function Theory ◽  
Full Potential ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Wave Method ◽  
Heusler Compound ◽  
Plane Wave Method ◽  
Band Inversion

Using the full-potential linerized augumented plane-wave method based on the density function theory, we theoretically predict the Heusler compound Lu2FePb is a new three-dimensional topological insulator system. We also point out that the spin-orbit coupling is not the leading cause but an account can add further fuel to the band inversion.

Mechanical Properties of the Idealized Inverse-Opal Lattice

2018 ◽  
Vol 85 (4) ◽  
Author(s):  
Bijoy Pal ◽  
S. N. Khaderi
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Bloch Wave ◽  
Hydrostatic Compression ◽  
Inverse Opal ◽  
Wave Method ◽  
Yield Behavior ◽  
Cubic Symmetry ◽  
Hydrostatic Loading ◽  
Elastoplastic Properties

The idealized inverse-opal lattice is a network of slender struts that has cubic symmetry. We analytically investigate the elastoplastic properties of the idealized inverse-opal lattice. The analysis reveals that the inverse-opal lattice is bending-dominated under all loadings, except under pure hydrostatic compression or tension. Under hydrostatic loading, the lattice exhibits a stretching dominated behavior. Interestingly, for this lattice, Young's modulus and shear modulus are equal in magnitude. The analytical estimates for the elastic constants and yield behavior are validated by performing unit-cell finite element (FE) simulations. The hydrostatic buckling response of the idealized inverse-opal lattice is also investigated using the Floquet–Bloch wave method.

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