Abstract:Highlights STEM probe intensity depth profile is simulated to reveal the probe channeling in the BaSnO3/LaAlO3 bilayer. Defocus of a probe and atomic column arrangements in the bilayer modify channeling in a specimen. Depth of channeling is determined by specifics of examined materials unlike depth of field. Measured and simulated HAADF-and LAADF-STEM images of the BaSnO3/LaAlO3 bilayer visualize the MD network.
AbstractA study of the STEM probe channeling in a heterostructured crystalline specimen is pre… Show more
“…Channeling of the electron beam as it travels through a crystal has long been understood to have a strong effect on image contrast, and significant work has been undertaken to better understand the subtleties of its behavior. − In atomic columns that are not coherent or that have close neighboring columns, the channeling behavior can be particularly complex. A recent study combining multislice simulation and experimental HAADF-STEM showed that channeling can cause unintuitive contrast in noncoherently stacked heavy atomic columns based on crystal thickness and lateral separation of atomic sites . Other studies have shown that light species, such as oxygen, in columns near heavy atomic columns can affect the radial intensity profile and even the shape of the heavy atomic column. − Here, we show experimentally that cation sites in a distorted perovskite oxide crystal can appear to be displaced by several picometers from their true positions in HAADF-STEM due to coherently displaced oxygen atoms in the same atomic columns.…”
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confidence: 53%
“…A recent study combining multislice simulation and experimental HAADF-STEM showed that channeling can cause unintuitive contrast in noncoherently stacked heavy atomic columns based on crystal thickness and lateral separation of atomic sites. 12 Other studies have shown that light species, such as oxygen, in columns near heavy atomic columns can affect the radial intensity profile and even the shape of the heavy atomic column. 13−15 Here, we show experimentally that cation sites in a distorted perovskite oxide crystal can appear to be displaced by several picometers from their true positions in HAADF-STEM due to coherently displaced oxygen atoms in the same atomic columns.…”
Measurement of picometer-scale atomic displacements by aberration-corrected STEM has become invaluable in the study of crystalline materials, where it can elucidate ordering mechanisms and local heterogeneities. HAADF-STEM imaging, often used for such measurements due to its atomic number contrast, is generally considered insensitive to light atoms such as oxygen. Light atoms, however, still affect the propagation of the electron beam in the sample and, therefore, the collected signal. Here, we demonstrate experimentally and through simulations that cation sites in distorted perovskites can appear to be displaced by several picometers from their true positions in shared cation− anion columns. The effect can be decreased through careful choice of sample thickness and beam voltage or can be entirely avoided if the experiment allows reorientation of the crystal along a more favorable zone axis. Therefore, it is crucial to consider the possible effects of light atoms and crystal symmetry and orientation when measuring atomic positions.
“…Channeling of the electron beam as it travels through a crystal has long been understood to have a strong effect on image contrast, and significant work has been undertaken to better understand the subtleties of its behavior. − In atomic columns that are not coherent or that have close neighboring columns, the channeling behavior can be particularly complex. A recent study combining multislice simulation and experimental HAADF-STEM showed that channeling can cause unintuitive contrast in noncoherently stacked heavy atomic columns based on crystal thickness and lateral separation of atomic sites . Other studies have shown that light species, such as oxygen, in columns near heavy atomic columns can affect the radial intensity profile and even the shape of the heavy atomic column. − Here, we show experimentally that cation sites in a distorted perovskite oxide crystal can appear to be displaced by several picometers from their true positions in HAADF-STEM due to coherently displaced oxygen atoms in the same atomic columns.…”
mentioning
confidence: 53%
“…A recent study combining multislice simulation and experimental HAADF-STEM showed that channeling can cause unintuitive contrast in noncoherently stacked heavy atomic columns based on crystal thickness and lateral separation of atomic sites. 12 Other studies have shown that light species, such as oxygen, in columns near heavy atomic columns can affect the radial intensity profile and even the shape of the heavy atomic column. 13−15 Here, we show experimentally that cation sites in a distorted perovskite oxide crystal can appear to be displaced by several picometers from their true positions in HAADF-STEM due to coherently displaced oxygen atoms in the same atomic columns.…”
Measurement of picometer-scale atomic displacements by aberration-corrected STEM has become invaluable in the study of crystalline materials, where it can elucidate ordering mechanisms and local heterogeneities. HAADF-STEM imaging, often used for such measurements due to its atomic number contrast, is generally considered insensitive to light atoms such as oxygen. Light atoms, however, still affect the propagation of the electron beam in the sample and, therefore, the collected signal. Here, we demonstrate experimentally and through simulations that cation sites in distorted perovskites can appear to be displaced by several picometers from their true positions in shared cation− anion columns. The effect can be decreased through careful choice of sample thickness and beam voltage or can be entirely avoided if the experiment allows reorientation of the crystal along a more favorable zone axis. Therefore, it is crucial to consider the possible effects of light atoms and crystal symmetry and orientation when measuring atomic positions.
“…HR-TEM and HR-STEM images are obtained from the same area, and the thickness difference between two images originates from a characteristic of HR-STEM imaging that it highly reflects an atom array on the top of the sample. 16 By contrast, bare LMRO has a relatively thin reduced surface layer of ∼11.9 nm (Figure 4f−h), which would be the reason that the reduced surface is not observed in the low-magnification EELS map in Figure 3e. Although it has a reduced surface layer, its phase has a mixed form of R3̅ m and C2/m in which the portion of R3̅ m is higher than the inside (Figure 4i,j).…”
Practical application of lithium-and manganese-rich layered oxide cathodes has been hindered despite their high performance and low cost owing to high gas evolution accompanying capacity loss even in a conservative voltage window. Here, we control the surface structure and primary particle size of lithium-and manganese-rich layered oxide cathodes not only to enhance the electrochemical performance but also to reduce gas evolution. Sulfur-coated Fm3̅ m/R3̅ m double reduced surface layers and Mo doping dramatically reduce gas evolution, which entails the improvement of electrochemical performance. With the optimization, we prove that it is competitive enough to conventional high-nickel cathodes in the aspects of gas evolution as well as electrochemical performance in the conservative voltage window of 2.5−4.4 V. Our findings provide invaluable insights on the improvement of electrochemical performance and gas evolution properties in lithium-and manganese-rich layered oxide cathodes.
“…The behavior of electron channeling across hetero-interfaces and multilayers controls the image contrast of interfacial misfit dislocation networks in STEM-based images (Perovic et al, 1993 a , 1993 b ; Kourkoutis et al, 2011; Oveisi et al, 2019). The interpretation of HAADF-STEM images of overlapping crystals can become quite complicated since the image appearance and contrast depend on a variety of electron optical and specimen parameters (Yun et al, 2020). Fig.…”
Section: The Development Of Stem Imaging Theorymentioning
Although scanning transmission electron microscopy (STEM) images of individual heavy atoms were reported 50 years ago, the applications of atomic-resolution STEM imaging became wide spread only after the practical realization of aberration correctors on field-emission STEM/TEM instruments to form sub-Ångstrom electron probes. The innovative designs and advances of electron optical systems, the fundamental understanding of electron–specimen interaction processes, and the advances in detector technology all played a major role in achieving the goal of atomic-resolution STEM imaging of practical materials. It is clear that tremendous advances in computer technology and electronics, image acquisition and processing algorithms, image simulations, and precision machining synergistically made atomic-resolution STEM imaging routinely accessible. It is anticipated that further hardware/software development is needed to achieve three-dimensional atomic-resolution STEM imaging with single-atom chemical sensitivity, even for electron-beam-sensitive materials. Artificial intelligence, machine learning, and big-data science are expected to significantly enhance the impact of STEM and associated techniques on many research fields such as materials science and engineering, quantum and nanoscale science, physics and chemistry, and biology and medicine. This review focuses on advances of STEM imaging from the invention of the field-emission electron gun to the realization of aberration-corrected and monochromated atomic-resolution STEM and its broad applications.
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