Annular Bright Field Imaging Research Articles

Sample Tilt Effects on Atom Column Position Determination in ABF-STEM Imaging

The determination of atom positions from atomically resolved transmission electron micrographs is fundamental for the analysis of crystal defects and strain. In recent years annular bright-field (ABF) imaging has become a popular imaging technique owing to its ability to map both light and heavy elements. Contrast formation in ABF is partially governed by the phase of the electron wave, which renders the technique more sensitive to the tilt of the electron beam with respect to the crystal zone axis than high-angle annular dark-field imaging. Here we show this sensitivity experimentally and use image simulations to quantify this effect. This is essential for error estimation in future quantitative ABF studies.

Misalignment Induced Artifacts in Quantitative Annular Bright-Field Imaging

Journal Article Misalignment Induced Artifacts in Quantitative Annular Bright-Field Imaging Get access Peng Gao, Peng Gao Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo, JapanElectro Microscopy Laboratory, School of Physics, Center for Nanochemistry, and Collaborative Innovation Center for Quantum Matter, Peking University, Beijing, China Search for other works by this author on: Oxford Academic Google Scholar Akihito Kumamoto, Akihito Kumamoto Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo, Japan Search for other works by this author on: Oxford Academic Google Scholar Ryo Ishikawa, Ryo Ishikawa Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo, Japan Search for other works by this author on: Oxford Academic Google Scholar Nathan Lugg, Nathan Lugg Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo, Japan Search for other works by this author on: Oxford Academic Google Scholar Naoya Shibata, Naoya Shibata Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo, Japan Search for other works by this author on: Oxford Academic Google Scholar Yuichi Ikuhara Yuichi Ikuhara Institute of Engineering Innovation, School of Engineering, The University of Tokyo, Tokyo, Japan Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 22, Issue S3, 1 July 2016, Pages 888–889, https://doi.org/10.1017/S1431927616005286 Published: 25 July 2016

Atomic mechanism of polarization-controlled surface reconstruction in ferroelectric thin films.

At the ferroelectric surface, the broken translational symmetry induced bound charge should significantly alter the local atomic configurations. Experimentally revealing the atomic structure of ferroelectric surface, however, is very challenging due to the strong spatial variety between nano-sized domains, and strong interactions between the polarization and other structural parameters. Here, we study surface structures of Pb(Zr0.2Ti0.8)O3 thin film by using the annular bright-field imaging. We find that six atomic layers with suppressed polarization and a charged 180° domain wall are at negatively poled surfaces, no reconstruction exists at positively poled surfaces, and seven atomic layers with suppressed polarization and a charged 90° domain wall exist at nominally neutral surfaces in ferroelastic domains. Our results provide critical insights into engineering ferroelectric thin films, fine grain ceramics and surface chemistry devices. The state-of-the-art methodology demonstrated here can greatly advance our understanding of surface science for oxides.

Unravelling the complex nanostructure of La0.5-xLi0.5-xSr2xTiO3 Li ionic conductors.

The origin of the intricate nanostructure of La0.5-xLi0.5-xSr2xTiO3 (0.0625 ≤ x ≤ 0.25) perovskite-type Li ion conductors has been investigated. Reciprocal space electron diffraction analysis and aberration-corrected STEM by combining annular bright field (ABF) and high angle annular dark field (HAADF) imaging methods have been used to elucidate the complex local atomic arrangements which cannot be adequately described by average crystal structure models. Two different local crystal structures endotaxially-related at the nanoscale without compositional phase separation associated, constituting the crystals. Self-organization of the two different ordered regions arises as a consequence of the competition between two distortive forces in the crystal lattice: octahedral tilting and second-order Jahn-Teller distortion of TiO6 octahedra. Changes in the distribution of A species suggest different Li ion conduction pathways for the two structures and this scenario has difficult long-range Li mobility. The detailed study performed may be helpful in understanding the local structural changes affecting Li and their relation to the conductivity in LLTO-derived ionic conductors.

B11-P-07Phase-contrast characteristics of annular bright-field imaging in STEM

Noises have great influence on the phase reconstruction of holograms, especially in the gas atmosphere observations. Under noisy conditions, abrupt phase imperfections sometimes occur in a digitally reconstructed phase image, resulting in inaccurate information. In the presentation, computer simulation of electron holography under noisy and low electron luminance conditions will be accomplished and show the efficiency of the proposed restoration processing method [1]. The interference pattern of a CeO2 particle is shown in Fig. (a). One of Poisson noise holograms with λ=8 is shown in Fig. (b). The hologram after adding Gaussian noise is shown in Fig. (c). The hologram with about 25 thousands electrons is shown in Fig. (d). The reconstructed phase image from the noisy electron hologram is shown in Fig. (e). The reconstructed phase image from the corrected interference fringes under noisy situation is shown in Fig. (f). The reconstructed phase image obtained from the corrected interference fringes under noisy and low luminance situation is shown in Fig. (g). The corrected phases show that the method of phase imperfections restoration contributes to the correctly phase reconstruction of the hologram with a quit weak wave intensity and noisy circumstance. [1] W. Li and T. Tanji. Microscopy, 62 (6): 583-588 (2013) Figure: Holograms and reconstructed phase images (a) (b)

Sample tilt effects on atom column position determination in ABF–STEM imaging

The determination of atom positions from atomically resolved transmission electron micrographs is fundamental for the analysis of crystal defects and strain. In recent years annular bright-field (ABF) imaging has become a popular imaging technique owing to its ability to map both light and heavy elements. Contrast formation in ABF is partially governed by the phase of the electron wave, which renders the technique more sensitive to the tilt of the electron beam with respect to the crystal zone axis than high-angle annular dark-field imaging. Here we show this sensitivity experimentally and use image simulations to quantify this effect. This is essential for error estimation in future quantitative ABF studies.

Atomic resolution ptychographic phase contrast imaging of polar-ordered structures in functional oxides

Scanning transmission electron microscopy (STEM) imaging has traditionally relied on (mostly) incoherent imaging using electrons scattered to high angles [1,2]. This gives strong contrast for imaging heavier atoms, but is only an incomplete technique for in ferroelectrics or polar-ordered functional oxides, since the oxygens are invisible in the presence of the dominant scattering from the heavy cations. In recent years, however, there has been a resurgence in the use of low angle scattered electrons using modes like annular bright field imaging [3] and standard bright field imaging [4,5]. This allows the direct imaging of oxygen atoms, which can be used for a full quantification of the local polarization [5], as has previously been performed using negative CS imaging using high resolution TEM [6].

Atomic scale elemental mapping of light elements in multilayered perovskite coatings

Spherical aberration corrected transmission electron microscopes offer unprecedented capabilities in materials structural characterization down to atomic resolution. Electron energy loss spectroscopy (EELS) – spectrum imaging (SI) and annular bright field (ABF) imaging allow to simultaneously identify both the position and nature of the atomic species in a crystalline material. These techniques, along with conventional high-resolution transmission electron microscopy are particularly useful in heterostructures interfaces like epitaxial multilayers characterization, for identifying possible atomic interdiffusion at sub-nanometric scale. This paper presents the structural and compositional microanalysis down to atomic resolution of an epitaxial BaTiO3/SrRuO3/SrTiO3 ferroelectric heterostructure using complex complementary analytical electron microscopy techniques. The atomic arrangement of both heavy and light atomic species across the interfaces in the BaTiO3/SrRuO3/SrTiO3 heterostructures is revealed.

ChemInform Abstract: Atomic‐Scale Structure Evolution in a Quasi‐Equilibrated Electrochemical Process of Electrode Materials for Rechargeable Batteries

AbstractReview: 188 refs.

Research Update: Interface-engineered oxygen octahedral tilts in perovskite oxide heterostructures

Interface engineering of structural distortions is a key for exploring the functional properties of oxide heterostructures and superlattices. In this paper, we report on our comprehensive investigations of oxygen octahedral distortions at the heterointerface between perovskite oxides SrRuO3 and BaTiO3 on GdScO3 substrates and of the influences of the interfacially engineered distortions on the magneto-transport properties of the SrRuO3 layer. Our state-of-the-art annular bright-field imaging in aberration-corrected scanning transmission electron microscopy revealed that the RuO6 octahedral distortions in the SrRuO3 layer have strong dependence on the stacking order of the SrRuO3 and BaTiO3 layers on the substrate. This can be attributed to the difference in the interfacial octahedral connections. We also found that the stacking order of the oxide layers has a strong impact on the magneto-transport properties, allowing for control of the magnetic anisotropy of the SrRuO3 layer through interface engineering. Our results demonstrate the significance of the interface engineering of the octahedral distortions on the structural and physical properties of perovskite oxides.

Atomic‐Scale Structure Evolution in a Quasi‐Equilibrated Electrochemical Process of Electrode Materials for Rechargeable Batteries

Lithium-ion batteries have proven to be extremely attractive candidates for applications in portable electronics, electric vehicles, and smart grid in terms of energy density, power density, and service life. Further performance optimization to satisfy ever-increasing demands on energy storage of such applications is highly desired. In most of cases, the kinetics and stability of electrode materials are strongly correlated to the transport and storage behaviors of lithium ions in the lattice of the host. Therefore, information about structural evolution of electrode materials at an atomic scale is always helpful to explain the electrochemical performances of batteries at a macroscale. The annular-bright-field (ABF) imaging in aberration-corrected scanning transmission electron microscopy (STEM) allows simultaneous imaging of light and heavy elements, providing an unprecedented opportunity to probe the nearly equilibrated local structure of electrode materials after electrochemical cycling at atomic resolution. Recent progress toward unraveling the atomic-scale structure of selected electrode materials with different charge and/or discharge state to extend the current understanding of electrochemical reaction mechanism with the ABF and high angle annular dark field STEM imaging is presented here. Future research on the relationship between atomic-level structure evolution and microscopic reaction mechanisms of electrode materials for rechargeable batteries is envisaged.

Quantitative evaluation of annular bright-field phase images in STEM.

A phase reconstruction method based on multiple scanning transmission electron microscope (STEM) images was evaluated quantitatively using image simulations. The simulation results indicated that the phase shift caused by a single atom was proportional to the 0.6th power of the atomic number Z. For a thin SrTiO3 [001] crystal, the reconstructed phase at each atomic column increased according to the specimen thickness. The STEM phase images can quantify the oxygen vacancy concentration if the thickness is less than several nanometers.

走査型透過電子顕微鏡によるリチウム分布のイメージング

Recently, lithium atomic columns have been visualized by a new method of scanning transmission electron microscopy (STEM) called as annular bright field (ABF) imaging. We show that the number of lithium atoms in individual columns can be countable by quantitative analysis and the atoms at the surface layer can be detectable by using large convergent electron beam. We also show local structural transformation accompanied by the displacement of lithium ions for LiV2O4 crystals by in-situ ABF observation. We briefly present operand TEM observation of the lithium ion battery, consisting of LiMn2O4 cathode nanowire, ionic liquid electrolyte and Li4Ti5O12 anode.

Dislocation imaging for orthopyroxene using an atom-resolved scanning transmission electron microscopy.

Dislocations, one-dimensional lattice defects, appear as a microscopic phenomenon while they are formed in silicate minerals by macroscopic dynamics of the earth crust such as shear stress. To understand ductile deformation mechanisms of silicates, atomic structures of the dislocations have been examined using transmission electron microscopy (TEM). Among them, it has been proposed that {100}<001> primary slip system of orthopyroxene (Opx) is dissociated into partial dislocations, and a stacking fault with the clinopyroxene (Cpx) structure is formed between the dislocations. This model, however, has not been determined completely due to the complex structures of silicates. Scanning transmission electron microscopy (STEM) has a potential to determine the structure of dislocations with single-atomic column sensitivity, particularly by using high-angle annular dark field (HAADF) and annular bright field (ABF) imaging with a probing aberration corrector.[1] Furthermore, successive analyses from light microscopy to atom-resolved STEM have been achieved by focused ion beam (FIB) sampling techniques.[2] In this study, we examined dislocation arrays at a low-angle grain boundary of ∼1° rotation about the b-axis in natural deformed Opx using a simultaneous acquisition of HAADF/ABF (JEM-ARM200F, JEOL) equipped with 100 mm2 silicon drift detector (SDD) for energy dispersive X-ray spectroscopy (EDS). Figure1 shows averaged STEM images viewed along the b- axis of Opx extracted from repeating units. HAADF provides the cation-site arrangement, and ABF distinguishes the difference of slightly rotated SiO4 tetrahedron around the a- axis. This is useful to distinguish the change of stacking sequence between the partial dislocations. Two types of stacking faults with Cpx and protopyroxene (Ppx) structures were identified between three partial dislocations. Furthermore, Ca accumulation in M2 (Fe) site around the stacking faults was detected by STEM-EDS. Interestingly, Ca is distributed not only in these stacking faults but also Opx matrix around the faults. jmicro;63/suppl_1/i17/DFU063F1F1DFU063F1Fig. 1. (a) HAADF and (b) ABF of Opx view of [010] direction with inset simulation images and models of its unit cell (a = 0.52, c = 1.83 nm).

Local structure of Pb(Zr0.53Ti0.47)O3

High-angle annular dark-field (HAADF) and annular bright-field (ABF) images recorded from the Pb(ZrxTi1−x)O3morphotropic phase boundary (PZTmpb) showB-site displacements along the 〈110〉 directions and prominent distortions in the oxygen cages surrounding both theBsites and the Pb environments. The measured range ofB-site displacements is about 0.25–0.4 Å. Oxygen cage distortions appear to be variable in shape and dimensions at the unit-cell level. Comparison of the observed displacements with the structural projections based on the established monoclinic space groupCm(Cs3) shows a good overall agreement. A qualitative match betweenCm(Cs3) and the reported observations is inconclusive because of inaccuracy in the measurements, originating from imprecise identification of atomic column centres inherent in the HAADF and ABF images. In most of the observed cases,B-site displacements in HAADF images, and oxygen cage distortions in ABF images, appear pronounced compared with the structural projections inCm(Cs3). Columnar chemical inhomogeneity has been commonly observed in bothB-site and Pb columns in PZTmpb. Weak 〈110〉 diffuse streaking along the [001], [110] and [111] zone axes has been imaged, suggestive of correlation with the systematic ion disorder along 〈110〉.

Atomic-Scale Structure of Intercalated/De-Intercalated Electrode Materials in Lithium/Sodium Ion Batteries Via Aberration-Corrected Annular-Bright-Field Electron Microscopy

To satisfy ever-demanding inquires upon energy storage for applications in portable electronics, electric vehicles and smart grid etc., lithium ion batteries have been proved to be one of the ideal candidates in terms of energy density and power density. However, limited understanding for the structural evolution of electrode materials at atomic scale amid electrochemical process substantially hinders their further performance optimization. The recent success of annular-bright-field (ABF) imaging method erected on aberration-corrected scanning transmission electron microscopy (STEM) has been demonstrated to be a powerful technique to directly visualize individual light atoms, in particular the lithium ions, probing the nearly-equilibrated local structure of lithiated/delithiated electrodes under electrochemical cycling at atomic resolution. Compared to the high-angle annular-dark-field (HAADF) image, it is clearly demonstrated that not only heavy elements are revealed in ABF image, but also the atomic columns of O and Li. The ABF contrast tends to minimize the variance of the atomic number (Z) by following a Z1/3 dependency. With the unique ABF method, we have further studied possible electrochemical reaction mechanisms and detailed microstructure for (partially) lithiated/delithiated 1D-LiFePO4, 2D-LiCoO2, Li2MnO3 and 3D-Li4Ti5O12 and other lithium-based active materials with atomic resolution, which are essential for basic understanding and further performance optimization. These achievements provide new insight into the lithium/sodium storage mechanism in important cathode materials for lithium/sodium ion batteries.

Heteroepitaxial ZnO films on diamond: Optoelectronic properties and the role of interface polarity

We demonstrate the growth of heteroepitaxial ZnO films on (110) diamond substrates by molecular beam epitaxy and report on a major advance in structural quality, as confirmed by XRD and high-resolution TEM measurements. The growth direction is found to be along the polar c-axis with Zn-polarity, deduced from annular bright-field scanning transmission electron microscopy imaging. This is important information, as simulations of the electronic band structure reveal the ZnO polarity to dominate the electronic structure of the interface: the formation of a two-dimensional electron gas on the ZnO side or a two-dimensional hole gas on the diamond side are predicted for Zn- and O-polarity, respectively. In addition, photoluminescence and absorption studies exhibit good optical properties and reveal stimulated emission for optical excitation above a threshold of 30 kW/cm2.

Optoelectronic Properties of Single-Crystalline Zn2GeO4 Nanowires

In this work, Zn2GeO4 nanowires (NWs) were successfully synthesized on Si(100) substrates through carbon thermal reduction and a vapor–liquid–solid method. The NWs were of around 100 nm diameter and high aspect ratio (AR > 150). High-resolution transmission electron microscopy studies indicate that the NWs are single-crystalline with [110] growth direction. Moreover, the atomic resolution high-angle annular dark-field and bright-field images of scanning transmission electron microscopy have distinguished the different elements. They also further identified the structure of Zn2GeO4 and located the positions of the elements. Additionally, we have fabricated devices and measured the electrical properties of a single NW. It is remarkable that individual Zn2GeO4 NW devices exhibited excellent optoelectronic properties with fast switching speed under 254 nm UV illuminations. Furthermore, with short wavelength UV illumination, as we soaked Zn2GeO4 NWs in methyl orange solution, the methyl orange was degraded. Therefore, Zn2GeO4 NWs have potential applications in UV photodetectors and degradation of organic pollutants.

Atomic configuration of irradiation-induced planar defects in 3C-SiC

The atomic configuration of irradiation-induced planar defects in single crystal 3C-SiC at high irradiation temperatures was shown in this research. A spherical aberration corrected scanning transmission electron microscope provided images of individual silicon and carbon atoms by the annular bright-field (ABF) method. Two types of irradiation-induced planar defects were observed in the ABF images including the extrinsic stacking fault loop with two offset Si-C bilayers and the intrinsic stacking fault loop with one offset Si-C bilayer. The results are in good agreement with images simulated under identical conditions.

Chemical Analysis at Atomic Resolution of Isolated Extended Defects in an Oxygen‐Deficient, Complex Manganese Perovskite

A general approach to the structural and analytical characterization of complex bulk oxides that exploits the advantage of the atomic spatial resolution and the analytical capability of aberration-corrected microscopy is described. The combined use of imaging and spectroscopic techniques becomes necessary to the complete characterization of the oxygen-deficient colossal magnetoresistant La(0.56)Sr(0.44)MnO(2.5)-related perovskite. In this compound, the formation of isolated (La/Sr)O and MnO rock-salt-type planar defects are identified from atomically resolved High Angle Annular Dark Field (HAADF) images. The location of the oxygen atomic columns from Annular Bright Field (ABF) images indicates edge-sharing MnO6 octahedra in the MnO planes and the study performed by Electron Energy Loss Spectroscopy (EELS) reveals different Mn oxidation states derived from the corner- or edge-sharing MnO6 octahedra environment.