Z-Contrast Transmission Electron Microscopy: Direct Atomic Imaging of Materials

Pennycook, S.J.

doi:10.1146/annurev.ms.22.080192.001131

Cited by 122 publications

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“…It is not only capable of directly visualizing the atomic configurations but can also elucidate chemical information at a sub-angstrom spatial resolution using electron energy loss spectroscopy (EELS) and energy-dispersive X-ray spectroscopy (EDS) (Pennycook, 1992;Muller et al, 2008;Chi et al, 2011;Yabuuchi et al, 2011;Wu et al, 2015). However, STEM investigations of solid electrolytes pose numerous challenges as the high Li mobility and poor electronic conductivity make these materials highly vulnerable to electron irradiation damage (Egerton et al, 2004).…”

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confidence: 99%

Novel Solid Electrolytes for Li-Ion Batteries: A Perspective from Electron Microscopy Studies

Chi

2016

Front. Energy Res.

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Solid electrolytes can simultaneously overcome two of the most formidable challenges of Li-ion batteries: the severe safety issues and insufficient energy densities. However, before they can be implemented in actual batteries, the ionic conductivity needs to be improved and the interface with electrodes must be optimized. The prerequisite for addressing these issues is a thorough understanding of the material's behavior at the microscopic and/or the atomic level. (Scanning) transmission electron microscopy is a powerful tool for this purpose, as it can reach an ultrahigh spatial resolution. Here, we review recent electron microscopy investigations on the ion transport behavior in solid electrolytes and their interfaces. Specifically, three aspects will be highlighted: the influence of grain interior atomic configuration on ionic conductivity, the contribution of grain boundaries, and the behavior of solid electrolyte/electrode interfaces. Based on this, the perspectives for future research will be discussed.

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confidence: 99%

Novel Solid Electrolytes for Li-Ion Batteries: A Perspective from Electron Microscopy Studies

Chi

2016

Front. Energy Res.

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“…Scanning transmission electron microscopes (STEMs) employ a highly focused electron beam, which produces direct images of crystalline films with atomic resolution. The primary imaging mode of the STEM is Z-contrast imaging, which relies on high-angle Rutherford scattering by atomic nuclei [3]. The intensity of scattered electrons is proportional to approximately the square of the atomic number Z.…”

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confidence: 99%

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

et al. 2015

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Photon-based spectroscopies have played a central role in exploring the electronic properties of crystalline solids and thin films. Though they remain a powerful tool for probing the electronic properties of nanostructures, they are limited by lack of spatial resolution. On the other hand, electron-based spectroscopies, e.g., electron-energy-loss spectroscopy (EELS) are now capable of sub-Angstrom spatial resolution. Core-loss EELS, a spatially-resolved analog of X-ray absorption, has been used extensively in the study of inhomogeneous complex systems. In this paper, we demonstrate that low-loss EELS in an aberration-corrected scanning transmission electron microscope, which probes low-energy excitations, combined with a theoretical framework for simulating and analyzing the spectra, is a powerful tool to probe low-energy electron excitations with atomic-scale resolution. The theoretical component of the method combines densityfunctional-theory (DFT) based calculations of the excitations with dynamical scattering theory for the electron beam. We apply the method to monolayer graphene in order to demonstrate that atomic-scale contrast is inherent in low-loss EELS even in a perfectly periodic structure. The method is a complement to optical spectroscopy as it probes transitions entailing momentum transfer. The theoretical analysis identifies the spatial and orbital origins of excitations, holding the promise of ultimately becoming a powerful probe of the structure and electronic properties of individual point and extended defects in both crystals and inhomogeneous complex nanostructures. The method can be extended to probe magnetic and vibrational properties with atomic resolution. I. INTRODUCTIONOptical spectroscopies along with energy-band theory were the cornerstones upon which modern solid-state physics was founded. Ultraviolet and X-ray photoemission spectroscopies (UPS and XPS) were subsequently instrumental in the field of surface science. X-ray emission and absorption spectra (XAE and XAS) and their many variants, e.g., resonant x-ray scattering, have also played significant roles in probing the electronic properties of solids. Infrared absorption has been a powerful probe of phonons and lowenergy electronic excitations. The spatial resolution of these spectroscopies, however, is quite limited by the respective photon wavelengths and other factors.[1,2] Nevertheless, they continue to make major contributions in the study of nanostructures.Electron-based spectroscopies have the advantage of ultrasmall de Broglie wave lengths, which enable high spatial resolution. Scanning transmission electron microscopes (STEMs) employ a highly focused electron beam, which produces direct images of crystalline films with atomic resolution. The primary imaging mode of the STEM is Z-contrast imaging, which relies on high-angle Rutherford scattering by atomic nuclei [3]. The intensity of scattered electrons is proportional to approximately the square of the atomic number Z. In addition, inelastic scattering of the foc...

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“…[ 8,9 ] This is one of the main reasons why electron tomography in materials science is mostly based on high angle annular dark fi eld scanning transmission electron microscopy (HAADF-STEM). [ 1,10 ] For each composition, the intensity of the HAADF-STEM images changes monotonically with specimen thickness thus fulfi lling the projection requirement. To obtain 3D reconstructions from HAADF-STEM tilt series, reconstruction algorithms such as the simultaneously iterative reconstruction technique (SIRT), [ 11 ] total variation minimization, [ 12,13 ] and the discrete algebraic reconstruction technique [ 14 ] are currently used.…”

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confidence: 71%

Combination of HAADF‐STEM and ADF‐STEM Tomography for Core–Shell Hybrid Materials

Sentosun

Sanz-Ortiz

Batenburg

et al. 2015

Part & Part Syst Charact

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1wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Characterization of core-shell type nanoparticles in 3D by transmission electron microscopy (TEM) can be very challenging. Especially when both heavy and light elements coexist within the same nanostructure, artifacts in the 3D reconstruction are often present. A representative example would be a particle comprising an anisotropic metallic (Au) nanoparticle coated with a (mesoporous) silica shell. To obtain a reliable 3D characterization of such an object, a dose-effi cient strategy is proposed to simultaneously acquire high-angle annular dark-fi eld scanning TEM and annular dark-fi eld tilt series for tomography. The 3D reconstruction is further improved by applying an advanced masking and interpolation approach to the acquired data. This new methodology enables us to obtain high-quality reconstructions from which also quantitative information can be extracted. This approach is broadly applicable to investigate hybrid core-shell materials.of an object from its 2D projections, a monotonic relationship between image intensity and mass thickness is required. [ 1 ] When applying electron tomography to crystalline solids, diffraction contrast must therefore be avoided. [ 7 ] Indeed, diffraction contrast depends on the orientation of the object with respect to the electron beam and therefore the projection requirement for electron tomography is not fulfi lled. [ 1 ] As a consequence, artifacts will occur in the fi nal 3D reconstruction. [ 8,9 ] This is one of the main reasons why electron tomography in materials science is mostly based on high angle annular dark fi eld scanning transmission electron microscopy (HAADF-STEM). [ 1,10 ] For each composition, the intensity of the HAADF-STEM images changes monotonically with specimen thickness thus fulfi lling the projection requirement. To obtain 3D reconstructions from HAADF-STEM tilt series, reconstruction algorithms such as the simultaneously iterative reconstruction technique (SIRT), [ 11 ] total variation minimization, [ 12,13 ] and the discrete algebraic reconstruction technique [ 14 ] are currently used. Also for samples that consist of more than one type of element, HAADF-STEM tomography is very valuable since not only morphological but also chemical information can be extracted. [ 10 ] However, for samples in which elements with a high and low atomic number ( Z ) are simultaneously present, data acquisition becomes even more challenging. Since the intensity is strongly dependent on the atomic number, [ 10 ] a high difference in Z in the material leads to a large difference in the collected signal that is not always possible to cover with detector's dynamic range. Therefore, some areas of the image can be either overor undersaturated. This situation is often encountered when investigating core-shell hybrid materials such as nanoparticles encapsulated by a lighter matrix. In this paper, we propose an improved approach to obtain reliable 3D reconstructions for these systems, which requires optim...

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Z-Contrast Transmission Electron Microscopy: Direct Atomic Imaging of Materials

Cited by 122 publications

References 0 publications

Novel Solid Electrolytes for Li-Ion Batteries: A Perspective from Electron Microscopy Studies

Novel Solid Electrolytes for Li-Ion Batteries: A Perspective from Electron Microscopy Studies

Low-loss electron energy loss spectroscopy: An atomic-resolution complement to optical spectroscopies and application to graphene

Combination of HAADF‐STEM and ADF‐STEM Tomography for Core–Shell Hybrid Materials

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