Studies of Planar Defects in Silver Plate-Like Crystals by CBED and Hrtem Techniques

1984 ◽  
Vol 41 ◽  
Author(s):  
N. Tanaka ◽  
J. M. Cowley
Keyword(s):  
Three Dimensional ◽  
Dark Field ◽  
Silver Plate ◽  
Planar Defects ◽  
Field Patterns ◽  
Unit Cells ◽  
Evaporation Technique ◽  
Diffraction Patterns ◽  
Gas Evaporation Technique ◽  
Fractional Unit

AbstractElectron diffraction patterns with <111> incidence of f.c.c. plate-like crystals prepared by gas evaporation technique show forbidden spots such as the 1/3.422 spot. The origin of the spots has been explained in terms of planar defects such as (i) fractional unit cells on (111) surfaces, (ii) repeated thin twins and (iii) stacking faults or hexagonal layers. In the present study, the defect structures are examined by CBED and HRTEM techniques. The <111> CBED pattern of the platelet shows three-fold symmetry for the whole pattern. The dark field patterns of ± 1/3. 422 discs show symmetry of. These features prove that the platelet ha-s no center of symmetry for the three dimensional crystal (3m) and irregular arrangements of twins parallel to (111) planes. The electron micrographs taken along the <110> and <211> directions can give “cross-section” images of the platelet. The images show a few repeated twins with a thickness of several nm. The dark field images taken with the forbidden spots with <111> incidence show weak step contrast. The contrast may be due to fractional unit cells. Consequently, the forbidden spots of the platelet are mostly due to the fractional unit cells.

Direct observation ofB-site cation displacements in Pb-based complex perovskite relaxor oxides

2010 ◽  
Vol 44 (1) ◽  
pp. 111-121 ◽  
Author(s):  
K. Z. Baba-Kishi
Keyword(s):  
Long Range ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Unit Cells ◽  
Annular Dark Field ◽  
Pb Ions ◽  
Diffraction Patterns ◽  
Spatial Displacements

Electron diffraction patterns recorded using a scanning transmission electron microscope (STEM) from PbMg1/3Nb2/3O3(PMN) crystallites and PbZn1/3Nb2/3O3(PZN) crystals show weak and systematic continuous diffuse streaking along the 〈110〉 directions. Detailed high-angle annular dark-field (HAADF) images recordedviaan aberration-corrected STEM show that theB-site cations in PMN and PZN undergo correlated and long-range displacements towards the Pb2+ions on the (110) planes. The planarB-site displacement measured from the centres of the octahedra is about 0.3–0.5 Å in PMN and about 0.20–0.4 Å in PZN. In the HAADF images of the PMN crystallites and PZN crystals studied, there is insufficient evidence for systematic long-range planar displacements of the Pb2+ions. The observed Pb2+ion displacements in PMN and PZN appear randomly distributed, mostly displaced along 〈110〉 towards theB-site columns. There is also evidence of possible stress-related distortion in certain unit cells of PMN. In the relaxors studied, two distinct types of displacements were observed: one is the long-range planarB-site spatial displacement on the (110) planes, correlated with the Pb2+ions, possibly resulting in the observed diffuse streaking; the other is short-range Pb2+ion displacement on the (110) planes. The observed displacement status indicates a mutual attraction between the Pb ions and theB-site cations in which theBsites undergo the largest spatial displacements towards the Pb ions along 〈110〉.

A Shift-Lattice Interpretation of Structures in the Au4Mn Region of the Au-Mn System

1996 ◽  
Vol 49 (8) ◽  
pp. 873
Author(s):  
RJD Tilley ◽  
RP Williams
Keyword(s):  
Three Dimensional ◽  
One Dimensional ◽  
Ordered Phases ◽  
The Matrix ◽  
Unit Cells ◽  
The Face ◽  
Cubic Structure ◽  
Diffraction Patterns

The structures of a number of ordered phases in the Au-Mn system derived from the face- centred cubic structure of Au4Mn have been described in a systematic manner by use of shift-lattice distributions of the manganese atoms throughout the matrix of the alloys. The simplest structures are describable in terms of one-dimensional shift lattices, but many are best treated as two- or three-dimensional shift lattices. This approach has allowed structural correlations to be presented that have not been described previously and the variation in stoichiometry of these phases to be accounted for without recourse to defect populations. The diffraction patterns of such structures are also discussed, especially incommensurate patterns from materials with 'infinitely large' crystallographic unit cells.

Surface structure of (001) Au films by high resolution transmission electron microscopy

1978 ◽  
Vol 36 (1) ◽  
pp. 246-247
Author(s):  
William Krakow
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Atomic Layer ◽  
Surface Layers ◽  
Transmission Electron ◽  
Fcc Lattice ◽  
Unit Cells ◽  
Diffraction Patterns ◽  
Fractional Unit

In nonprimitive lattices, surface layers corresponding to partially filled unit cells give rise to reflections forbidden in the bulk structure. These reflections allow detailed studies of the surface layer by high resolution transmission electron microscopy and computer modeling experiments.The occurrence of fractional unit cells at the surface of (001) oriented Au films can be demonstrated by assembling the fcc lattice by the alternate stacking of planar {100} type layers such that the atoms of,each atomic layer are embedded in the depressions of neighboring planes above and below. The stacking sequence is of the ABABAB….type with the B layers shifted an amount ao/2 in the [100] direction (Fig. 1a). The presence of an excess A or B layer gives rise to additional reflections with mixed odd and even Miller indices which are forbidden in the fcc lattice, e.g., (110). In obtaining diffraction patterns from ∼100Å thick Au films the forbidden reflections were approximately 2% of the corresponding bulk lattice reflections and easily identified (see Fig. 1b).

MoS2 deposited by ion beam assisted deposition: 2H or random layer structure?

1998 ◽  
Vol 13 (10) ◽  
pp. 3001-3007 ◽  
Author(s):  
D. N. Dunn ◽  
L. E. Seitzman ◽  
I. L. Singer
Keyword(s):  
Layer Structure ◽  
Ion Beam ◽  
Three Dimensional ◽  
Dimensional Structure ◽  
Planar Defects ◽  
Selected Area Electron Diffraction ◽  
Ion Beam Assisted Deposition ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
Dimensional Crystal

The structure of MoS2 films grown by ion beam assisted deposition is investigated using transmission electron microscopy. Films consist of stacks of S–Mo–S planes with a [001] texture; however, three-dimensional crystal symmetry is disrupted by a high density of planar defects. Selected area electron diffraction patterns show (hk0) and (00l) reflections, features similar to a random layer structure, as well as diffuse (103) reflections. It is suggested that these films do not have a true random layer structure, but rather a two-dimensional structure formed by nonrandom in-plane translations.

scholarly journals Three-dimensional nanostructure determination from a large diffraction data set recorded using scanning electron nanodiffraction

IUCrJ ◽  
2016 ◽  
Vol 3 (5) ◽  
pp. 300-308 ◽  
Author(s):  
Yifei Meng ◽  
Jian-Min Zuo
Keyword(s):  
Dimensional Space ◽  
Large Angle ◽  
Three Dimensional ◽  
Dark Field ◽  
Data Set ◽  
Angle Rotation ◽  
Diffraction Patterns ◽  
Scanning Electron ◽  
Three Dimensional Space

A diffraction-based technique is developed for the determination of three-dimensional nanostructures. The technique employs high-resolution and low-dose scanning electron nanodiffraction (SEND) to acquire three-dimensional diffraction patterns, with the help of a special sample holder for large-angle rotation. Grains are identified in three-dimensional space based on crystal orientation and on reconstructed dark-field images from the recorded diffraction patterns. Application to a nanocrystalline TiN thin film shows that the three-dimensional morphology of columnar TiN grains of tens of nanometres in diameter can be reconstructed using an algebraic iterative algorithm under specified prior conditions, together with their crystallographic orientations. The principles can be extended to multiphase nanocrystalline materials as well. Thus, the tomographic SEND technique provides an effective and adaptive way of determining three-dimensional nanostructures.

Two Investigations into Grain Boundary Structure

1977 ◽  
Vol 35 ◽  
pp. 688-691
Author(s):  
P. Humble
Keyword(s):  
Grain Boundary ◽  
Dark Field ◽  
Boundary Structure ◽  
Boundary Dislocation ◽  
Bright Field ◽  
Intrinsic Structure ◽  
Weak Beam ◽  
Grain Boundary Structure ◽  
Independent Information ◽  
Diffraction Patterns

There has been sustained interest over the last few years into both the intrinsic (primary and secondary) structure of grain boundaries and the extrinsic structure e.g. the interaction of matrix dislocations with the boundary. Most of the investigations carried out by electron microscopy have involved only the use of information contained in the transmitted image (bright field, dark field, weak beam etc.). Whilst these imaging modes are appropriate to the cases of relatively coarse intrinsic or extrinsic grain boundary dislocation structures, it is apparent that in principle (and indeed in practice, e.g. (1)-(3)) the diffraction patterns from the boundary can give extra independent information about the fine scale periodic intrinsic structure of the boundary.In this paper I shall describe one investigation into each type of structure using the appropriate method of obtaining the necessary information which has been carried out recently at Tribophysics.

Zero-loss omega-filtered REM and RHEED on the new Zeiss 912

1991 ◽  
Vol 49 ◽  
pp. 616-617
Author(s):  
J.C.H. Spence ◽  
J. Mayer
Keyword(s):  
Electron Microscopy ◽  
Materials Science ◽  
Surface States ◽  
Ccd Camera ◽  
Dark Field ◽  
Ion Pump ◽  
Magnetic Imaging ◽  
Reflection Electron Microscopy ◽  
Diffraction Patterns ◽  
Large Background

The Zeiss 912 is a new fully digital, side-entry, 120 Kv TEM/STEM instrument for materials science, fitted with an omega magnetic imaging energy filter. Pumping is by turbopump and ion pump. The magnetic imaging filter allows energy-filtered images or diffraction patterns to be recorded without scanning using efficient parallel (area) detection. The energy loss intensity distribution may also be displayed on the screen, and recorded by scanning it over the PMT supplied. If a CCD camera is fitted and suitable new software developed, “parallel ELS” recording results. For large fields of view, filtered images can be recorded much more efficiently than by Scanning Reflection Electron Microscopy, and the large background of inelastic scattering removed. We have therefore evaluated the 912 for REM and RHEED applications. Causes of streaking and resonance in RHEED patterns are being studied, and a more quantitative analysis of CBRED patterns may be possible. Dark field band-gap REM imaging of surface states may also be possible.

Imaging of platinum-shadowed macromolecular complexes in dark field

1984 ◽  
Vol 42 ◽  
pp. 146-147
Author(s):  
D.W. Andrews ◽  
F.P. Ottensmeyer
Keyword(s):  
Thin Film ◽  
Three Dimensional ◽  
Average Diameter ◽  
Dark Field ◽  
Bright Field ◽  
Field Mode ◽  
Macromolecular Complexes ◽  
Average Mass ◽  
Topological Features ◽  
Projection Images

Shadowing with heavy metals has been used for many years to enhance the topological features of biological macromolecular complexes. The three dimensional features present in directionaly shadowed specimens often simplifies interpretation of projection images provided by other techniques. One difficulty with the method is the relatively large amount of metal used to achieve sufficient contrast in bright field images. Thick shadow films are undesirable because they decrease resolution due to an increased tendency for microcrystalline aggregates to form, because decoration artefacts become more severe and increased cap thickness makes estimation of dimensions more uncertain.The large increase in contrast provided by the dark field mode of imaging allows the use of shadow replicas with a much lower average mass thickness. To form the images in Fig. 1, latex spheres of 0.087 μ average diameter were unidirectionally shadowed with platinum carbon (Pt-C) and a thin film of carbon was indirectly evaporated on the specimen as a support.

Conformational Transitions in Escherichia coli Ribosomal RNAs as Visualized by Dedicated STEM

1988 ◽  
Vol 46 ◽  
pp. 176-177
Author(s):  
J.S. Wall ◽  
V. Maridiyan ◽  
S. Tumminia ◽  
J. Hairifeld ◽  
M. Boublik
Keyword(s):  
Ionic Strength ◽  
Three Dimensional ◽  
Conformational Transitions ◽  
Dark Field ◽  
Dimensional Structure ◽  
Ribosomal Rnas ◽  
Field Mode ◽  
Freeze Dried ◽  
High Resolution Images ◽  
Low Ionic Strength

The high contrast in the dark-field mode of dedicated STEM, specimen deposition by the wet film technique and low radiation dose (1 e/Å2) at -160°C make it possible to obtain high resolution images of unstained freeze-dried macromolecules with minimal structural distortion. Since the image intensity is directly related to the local projected mass of the specimen it became feasible to determine the molecular mass and mass distribution within individual macromolecules and from these data to calculate the linear density (M/L) and the radii of gyration.2 This parameter (RQ), reflecting the three-dimensional structure of the macromolecular particles in solution, has been applied to monitor the conformational transitions in E. coli 16S and 23S ribosomal RNAs in solutions of various ionic strength.In spite of the differences in mass (550 kD and 1050 kD, respectively), both 16S and 23S RNA appear equally sensitive to changes in buffer conditions. In deionized water or conditions of extremely low ionic strength both appear as filamentous structures (Fig. la and 2a, respectively) possessing a major backbone with protruding branches which are more frequent and more complex in 23S RNA (Fig. 2a).

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.

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