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Electron Diffraction in Transmission Electron Microscopes
Published in Dong ZhiLi, Fundamentals of Crystallography, Powder X-ray Diffraction, and Transmission Electron Microscopy for Materials Scientists, 2022
The zone axis is antiparallel to the electron beam direction. If the zone axis direction is just slightly deviated from the antiparallel direction of the electron beam due to the orientation variation of the crystal under study, a diffraction pattern can still be observed. If the electron beam in the microscope travels downward, the zone axis points upward. Students should not forget that the right-hand rule is employed when choosing g⇀1 and g⇀2 from an electron diffraction pattern, so that g⇀1×g⇀2 is pointing upwards.
Application of Advanced Aberration-Corrected Transmission Electron Microscopy to Material Science: Methods to Predict New Structures and Their Properties
Published in Alina Bruma, Scanning Transmission Electron Microscopy, 2020
Conventional TEM (CTEM) uses electrons focused by electromagnetic lenses into a fine electron beam. Due to the high accelerating voltage use in the electron microscope, the short wavelength of the accelerated electrons (around 2 pm for a 300-kV accelerating voltage) made the resolution of an electron microscope significantly high to solve structural problems in various materials. The classical set of TEM techniques for primary material characterization was electron diffraction (ED), bright-field (BF) imaging and high-resolution TEM (HRTEM). At the same time, energy-dispersive x-ray spectroscopy (EDXS) offers local chemical information. ED patterns collected from main crystallographic zone axes give basic information about the crystal structure. The angles between diffraction spots, showing the presence or absence of certain reflections, can be used to determine the crystal structure (unit cell parameters, extinction conditions, space groups) and can be correlated with data obtained from XRD (Fultz and Howe 2013).
Interfacial Disorder in InAs/GaSb Heterostructures Grown by Molecular Beam Epitaxy
Published in M. O. Manasreh, Antimonide-Related Strained-Layer Heterostructures, 2019
M. E. Twigg, B. R. Bennett, P. M. Thibado, B. V. Shanabrook, L. J. Whitman
In order to use HRTEM in measuring changes in composition, such as those occurring at an interface, one needs to be able to image along a zone axis that includes reflections which are particularly sensitive to changes in atomic number. From a simple geometrical point of view, imaging with the electron beam direction parallel to the [001] zone axis allows one to view the cations and anions in separate columns (as shown in Fig. 3), thereby allowing one atomic species to be distinguished from another. The {200} reflections of the [001] zone axis are particularly useful because the strength of each {200} reflection is proportional to the difference between the cation and anion scattering factors [46,47]. Therefore, a {200} reflection is strong for zinc blende materials with a large difference in atomic number between cation and anion, such as InAs or GaSb, the components of our SL layers. Similarly, {200} reflections would be expected to be weak for zinc blende materials with a small difference between cation and anion atomic number, such as GaAs or InSb, which are responsible for the bonding at InAs/GaSb interfaces [48–52].
Nanosized oxide phases in oxide-dispersion-strengthened steel PM2000
Published in Philosophical Magazine, 2021
Yuan Wang, Jian Lin, Bocong Liu, Yifeng Chen, Dehui Li, Hui Wang, Yinzhong Shen
The TEM micrographs of carbon replica samples that were prepared from PM2000 steel (Figure 4(a)) show large particle P1 with a 65 nm diameter along with many nanosized particles, including particle P2. The chemical composition of particle P1 was 20.92Al, 0.02Ti, 0.10Fe, 18.16Y, 60.76O (atomic percent). This composition indicates that particle P1 belongs to a Y–Al oxide phase with chemical formula YAlO3. Figure 4(b) shows the selected-area electron diffraction (SAED) pattern of particle P1. This pattern matched the diffraction pattern from yttrium aluminum oxide (YAlO3, orthorhombic P Bravais lattice, space group: Pbn* with the lattice parameters a/b/c = 5.179/5.329/7.37 Å, JCPDS file 08–0147/33-0041) in the zone axis of [201] [24]. Based on the pattern indexing and EDX analysis, particle P1 was identified to be the YAlO3 phase. Previous research has shown the presence of the YAlO3 phase in the as-rolled PM2000 steel with the observed YAlO3 particle size ranging from 35 to 84 nm in diameter [9].
Atomic-scale study of precipitates (NbC and Cu-rich phase) at the twin boundary in the long time ageing austenitic stainless steel
Published in Philosophical Magazine, 2020
Xingyuan San, Dan Zhang, Xinshuang Guo, Xingkun Ning
Figure S1 shows the typical morphology of the matrix of the Super304H austenitic stainless steel. The matrix contains the twin lamellae, and the SAED pattern can be well indexed as an fcc lattice (lattice constant a = 0.37 nm) along the [1–10] zone axis. Figure S2a is a bright-field TEM of the Cu-rich phases in the matrix (as indicated by the white arrows). The energy filtered transmission electron microscopy (EFTEM) mapping shows that the NbC tends to precipitate at the TBs (Figure S2b). However, these Cu-rich precipitated phases are observed obscurely because of the strain field contrast. Figure 1 shows the HAADF-STEM image of an edge-on twin boundary along the [1–10] direction. The STEM-EDS mapping is shown in the inset of Figure 1. At the TB, there are dense Cu-rich phases and Nb elements. In Figure S2c, little nanosized NbC precipitates were observed at the TBs in the austenitic matrix of the Super304H steel, which means that the nanosized Nb-rich phases easily nucleates at the TBs during ageing process. The EDS maps in Figure S2d further verified there is no fine-scale precipitation of NbC at the TBs in the unaged alloy. Obviously, TBs as a diffusion source and defect site make the precipitated phase nucleated easily.
Formation of radioactive cesium microparticles originating from the Fukushima Daiichi Nuclear Power Plant accident: characteristics and perspectives
Published in Journal of Nuclear Science and Technology, 2019
Toshihiko Ohnuki, Yukihiko Satou, Satoshi Utsunomiya
Fragments of nuclear fuel bearing U were discovered by Ochiai et al. [23]. These researchers analyzed CsMPs samples collected at Ottozawa located ~4 km west of FDNPP and found Fe oxide nanoparticles of ~100 nm size that were attached to the CsMP surface (indicated by the white square in Figure 5(a)). Two U oxide nanoparticles of ∼10 and ∼30 nm in size were present (see Figure 5(b)) The Fe oxide and U oxide nanoparticles were identified as magnetite (Fe3O4) and uraninite (UO2+X), respectively (Figure 5(c)), with epitaxial growth between magnetite and uraninite being evident (Figure 5(c)). For a portion of the U oxide nanoparticle, the high-resolution high-angle annular dark field (HR-HAADF)-STEM image (Figure 5(c)) displayed an enhanced contrast every 4 or 5 atomic columns, both in the a and b axes (Figure 5(d)). This was due to the overlying or underlying Fe atoms being in the same orientation along the projected zone axis because magnetite and uraninite are both isometric with unit cell parameters of 0.83958 [38] and 0.54682 nm [39], respectively.