scholarly journals Mapping of local lattice parameter ratios by projective Kikuchi pattern matching

2018 ◽  
Vol 2 (12) ◽  
Author(s):  
Aimo Winkelmann ◽  
Gert Nolze ◽  
Grzegorz Cios ◽  
Tomasz Tokarski
Keyword(s):  
Pattern Matching ◽  
Lattice Parameter ◽  
Kikuchi Pattern ◽  
Local Lattice

The limits of strain and lattice parameter measurements by CBED

1989 ◽  
Vol 47 ◽  
pp. 518-519
Author(s):  
Hamish L. Fraser
Keyword(s):  
Electron Beam ◽  
Mirror Symmetry ◽  
Local Symmetry ◽  
Lattice Parameter ◽  
Growth Direction ◽  
Surface Relaxation ◽  
Strained Layer ◽  
Axis Parallel ◽  
Local Lattice ◽  
Strained Layer Superlattice

The topic of strain and lattice parameter measurements using CBED is discussed by reference to several examples. In this paper, only one of these examples is referenced because of the limitation of length. In this technique, scattering in the higher order Laue zones is used to determine local lattice parameters. Work (e.g. 1) has concentrated on a model strained-layer superlattice, namely Si/Gex-Si1-x. In bulk samples, the strain is expected to be tetragonal in nature with the unique axis parallel to [100], the growth direction. When CBED patterns are recorded from the alloy epi-layers, the symmetries exhibited by the patterns are not tetragonal, but are in fact distorted from this to lower symmetries. The spatial variation of the distortion close to a strained-layer interface has been assessed. This is most readily noted by consideration of Fig. 1(a-c), which show enlargements of CBED patterns for various locations and compositions of Ge. Thus, Fig. 1(a) was obtained with the electron beam positioned in the center of a 5Ge epilayer and the distortion is consistent with an orthorhombic distortion. When the beam is situated at about 150 nm from the interface, the same part of the CBED pattern is shown in Fig. 1(b); clearly, the symmetry exhibited by the mirror planes in Fig. 1 is broken. Finally, when the electron beam is positioned in the center of a 10Ge epilayer, the CBED pattern yields the result shown in Fig. 1(c). In this case, the break in the mirror symmetry is independent of distance form the heterointerface, as might be expected from the increase in the mismatch between 5 and 10%Ge, i.e. 0.2 to 0.4%, respectively. From computer simulation, Fig.2, the apparent monocline distortion corresponding to the 5Ge epilayer is quantified as a100 = 0.5443 nm, a010 = 0.5429 nm and a001 = 0.5440 nm (all ± 0.0001 nm), and α = β = 90°, γ = 89.96 ± 0.02°. These local symmetry changes are most likely due to surface relaxation phenomena.

scholarly journals Lattice disorder effect on magnetic ordering of iron arsenides

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Athena S. Sefat ◽  
Xiaoping P. Wang ◽  
Yaohua Liu ◽  
Qiang Zou ◽  
Mimgming Fu ◽  
...  
Keyword(s):  
Magnetic Coupling ◽  
Magnetic Ordering ◽  
Structural Features ◽  
Lattice Parameter ◽  
Chemical Compositions ◽  
Lattice Disorder ◽  
Local Lattice ◽  
Higher Temperature ◽  
Disordered Crystal ◽  
Planar Strain

AbstractThis study investigates magnetic ordering temperature in nano- and mesoscale structural features in an iron arsenide. Although magnetic ground states in quantum materials can be theoretically predicted from known crystal structures and chemical compositions, the ordering temperature is harder to pinpoint due to potential local lattice variations that calculations may not account for. In this work we find surprisingly that a locally disordered material can exhibit a significantly larger Néel temperature (TN) than an ordered material of precisely the same chemical stoichiometry. Here, a EuFe2As2 crystal, which is a ‘122’ parent of iron arsenide superconductors, is found through synthesis to have ordering below TN = 195 K (for the locally disordered crystal) or TN = 175 K (for the ordered crystal). In the higher TN crystals, there are shorter planar Fe-Fe bonds [2.7692(2) Å vs. 2.7745(3) Å], a randomized in-plane defect structure, and diffuse scattering along the [00 L] crystallographic direction that manifests as a rather broad specific heat peak. For the lower TN crystals, the a-lattice parameter is larger and the in-plane microscopic structure shows defect ordering along the antiphase boundaries, giving a larger TN and a higher superconducting temperature (Tc) upon the application of pressure. First-principles calculations find a strong interaction between c-axis strain and interlayer magnetic coupling, but little impact of planar strain on the magnetic order. Neutron single-crystal diffraction shows that the low-temperature magnetic phase transition due to localized Eu moments is not lattice or disorder sensitive, unlike the higher-temperature Fe sublattice ordering. This study demonstrates a higher magnetic ordering point arising from local disorder in 122.

Local Lattice Parameter Determination of Strained Areas of Semiconductors Using CBED

2004 ◽  
Vol 10 (S02) ◽  
pp. 310-311
Author(s):  
Takayuki Akaogi ◽  
Kenji Tsuda ◽  
Masami Terauchi ◽  
Michiyoshi Tanaka
Keyword(s):  
Lattice Parameter ◽  
Parameter Determination ◽  
Local Lattice

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

Image Simulation of Small Pt Particles and its Application to Lattice Spacing Measurements in Catalysts

1999 ◽  
Vol 5 (S2) ◽  
pp. 200-201
Author(s):  
S.-C. Y. Tsen ◽  
P. A. Crazier ◽  
C. López Cartes ◽  
J. Liu ◽  
J.J. Calvino
Keyword(s):  
Lattice Spacing ◽  
Lattice Parameter ◽  
Image Simulation ◽  
Initial Image ◽  
Bimetallic Systems ◽  
Local Lattice ◽  
Nanophase Materials ◽  
Resolution Imaging ◽  
Small Metal Particle ◽  
Image Simulations

The technique of high resolution imaging is important for characterizing the structure of small metal particle catalysts and nanophase materials. For bimetallic systems, it is possible to use local lattice parameter measurements to identify alloy compositions in ensembles of nanometer sized metal particles [1]. However, determining alloy composition is challenging because changes in lattice parameters of only a few percent must be reliably detected. We have performed measurements of the apparent d(111) fringe spacing on both simulated and experimental HREM images from Pt particles in the size range 15 - 35 Å. A series of initial image simulations of Pt cubeoctahedrons with 17 Å (201 atoms) and 34 Å (1289 atoms) in diameter have been studied in order to understand the effect of different parameters on the accuracy of lattice spacing. The clusters were built using the Rhodius program developed by Botana et al [2]. Starting with a bulk crystal we create cubeoctahedra by applying successive cuts along either the (111) or (100) direction. A supercell size of 50Å was selected and the particles were oriented at or close to the [110]. Images were calculated by the multi-slice techniques using both the CERIUS and EMS applications. The supercell was divided into 20 slices and the following parameters were used in the calculation Eo = 400 kV, Cs = 1mm, Δf= -320 Å, focal spread = 80 Å, convergence = 0.5 mrad and atomic vibration = 0.35Å.

scholarly journals Synchrotron Bragg diffraction imaging characterization of synthetic diamond crystals for optical and electronic power device applications

2017 ◽  
Vol 50 (2) ◽  
pp. 561-569 ◽  
Author(s):  
Thu Nhi Tran Thi ◽  
J. Morse ◽  
D. Caliste ◽  
B. Fernandez ◽  
D. Eon ◽  
...  
Keyword(s):  
Surface Damage ◽  
Lattice Parameter ◽  
Bragg Diffraction ◽  
Fast Method ◽  
Extended Defects ◽  
X Ray ◽  
Single Crystal Diamond ◽  
Local Lattice ◽  
Diffraction Imaging

Bragg diffraction imaging enables the quality of synthetic single-crystal diamond substrates and their overgrown, mostly doped, diamond layers to be characterized. This is very important for improving diamond-based devices produced for X-ray optics and power electronics applications. The usual first step for this characterization is white-beam X-ray diffraction topography, which is a simple and fast method to identify the extended defects (dislocations, growth sectors, boundaries, stacking faults, overall curvature etc.) within the crystal. This allows easy and quick comparison of the crystal quality of diamond plates available from various commercial suppliers. When needed, rocking curve imaging (RCI) is also employed, which is the quantitative counterpart of monochromatic Bragg diffraction imaging. RCI enables the local determination of both the effective misorientation, which results from lattice parameter variation and the local lattice tilt, and the local Bragg position. Maps derived from these parameters are used to measure the magnitude of the distortions associated with polishing damage and the depth of this damage within the volume of the crystal. For overgrown layers, these maps also reveal the distortion induced by the incorporation of impurities such as boron, or the lattice parameter variations associated with the presence of growth-incorporated nitrogen. These techniques are described, and their capabilities for studying the quality of diamond substrates and overgrown layers, and the surface damage caused by mechanical polishing, are illustrated by examples.

The relevance of local lattice parameter measurements using CBED

1988 ◽  
Vol 46 ◽  
pp. 1006-1007
Author(s):  
Hamish L. Fraser
Keyword(s):  
Materials Science ◽  
Lattice Parameter ◽  
Physical Situation ◽  
Thin Foils ◽  
Transmission Electron ◽  
Local Lattice ◽  
The Subject ◽  
Electron Microscopes ◽  
Convergent Beam ◽  
Made In

Since the development of transmission electron microscopes in which the electron beam may be caused to be incident on the sample in the form of a convergent probe, much work has been aimed at the use of convergent beam electron diffraction (CBED) in materials science. One of the techniques afforded by CBED permits the measurement of lattice parameters on a scale more or less defined by the diameter of the probe at the sample, and so a powerful means of determining local distortions has become available. While this technique appears to be very exciting, as is shown below, the necessary use of thin foils results in the possibility of surface relaxations modifying the stress fields of a given distortion, and this raises the question of the relevance of measurements made in thin foils to the physical situation in the bulk. This question is the subject of this paper.

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