Interpreting atomic-resolution spectroscopic images

Oxley, Mark P.; Varela, M.; Pennycook, Timothy J.; Benthem, Klaus van; Findlay, Scott; D’Alfonso, Adrian J.; Allen, LJ; Pennycook, S. J.

doi:10.1103/physrevb.76.064303

Cited by 68 publications

(55 citation statements)

References 24 publications

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“…While minima similar to those seen in the resonance images have been observed in the past [7,29,[31][32][33][34][35][36][37], those observations could be attributable to coherent effects arising from the use of a collection angle comparable or smaller than the probe convergence angle. In the present work, we use a large collection angle (80 mrad), where the incoherent nature of scattering and detection means that such minima are unexpected.…”

Section: Resultsmentioning

confidence: 76%

Fano resonance in atomic-resolution spectroscopic imaging of solids

2012

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We report direct evidence of Fano resonances in atomic-resolution imaging of a crystalline material using a focused electron beam. Spectroscopic images of DyScO3 that are derived from the Fano resonance in the Dy-N4,5 spectrum can exhibit unexpected atomic-scale contrast, markedly different to non-resonant images. These effects are explained by our theoretical calculations of the inelastic and elastic scattering, and show excellent agreement with the experimental data. The results have significant implications for spectroscopic imaging of rare-earth elements at the atomic scale.

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Section: Resultsmentioning

confidence: 76%

Fano resonance in atomic-resolution spectroscopic imaging of solids

2012

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“…However, it has also been revealed that extra caution is required to properly interpret the contrast of maps acquired at the atomic scale. 2,[12][13][14][18][19][20] In particular, a substantial component of undesirable "elastic contrast" can be preserved due to probe electrons being elastically scattered beyond the EELS collection angle. Such large-angle elastic scattering occurs especially in the presence of heavy-atom columns, and it is the basic mechanism to form an incoherent bright-field (IBF) image.…”

mentioning

confidence: 99%

“…If the scattering angles associated with relevant core-level excitations are small compared to the collection angle, as they are here, the contrast in the EELS elemental maps can be interpreted as a multiplication of chemical and elastic (IBF) contrast (an approximation that becomes more accurate for lower core losses). When elastic contrast dominates, which can occur especially for heavy-atom columns, lower energy losses, or small collection angles, artifacts such as volcano-like structures 12,13,18,21 and contrast reversals on atomic columns 2,20,22 have been reported. On the other hand, these effects are significantly reduced in characteristic x-ray maps because such maps are impervious to any scattering that follows the core-level excitations.…”

mentioning

confidence: 99%

“…While the benefits of using EELS over characteristic x-rays include superior detection efficiency, access to bonding information, and the ability to map light elements, atomic-resolution elemental maps acquired using EELS are, in fact, prone to artifacts associated with elastic scattering of the electron probe within the sample. [12][13][14] Such artifacts, which occur especially in the presence of heavy elements, can confound data interpretation to the extent that simulations must be invoked to gain a reliable understanding. X-ray elemental maps, on the other hand, are less prone to this effect because any probe scattering following a core-level excitation cannot influence the x-ray yield.…”

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confidence: 99%

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Towards artifact-free atomic-resolution elemental mapping with electron energy-loss spectroscopy

Zhu

Soukiassian

Schlom

et al. 2013

Applied Physics Letters

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Atomic-resolution elemental maps of materials obtained using energy-loss spectroscopy in the scanning transmission electron microscope (STEM) can contain artifacts associated with strong elastic scattering of the STEM probe. We demonstrate how recent advances in instrumentation enable a simple and robust approach to reduce such artifacts and produce atomic-resolution elemental maps amenable to direct visual interpretation. The concept is demonstrated experimentally for a (BaTiO3)8/(SrTiO3)4 heterostructure, and simulations are used for quantitative analysis. We also demonstrate that the approach can be used to eliminate the atomic-resolution elastic contrast in maps obtained from lower-energy excitations, such as plasmon excitations.

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“…A complex array of physical processes, including beam broadening and channeling effects (Oxley et al, 2007), can lead to serious misinterpretations of chemical maps. Channeling is particularly problematic, since it tends to occur when imaging along low-order zone axes commonly used for atomic-scale imaging; in this case, the strong Coulombic interaction between the electron probe and the atoms in the crystal focuses the probe intensity along columns, complicating the analysis of ionization signals (Lugg et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

Measurement Error in Atomic-Scale Scanning Transmission Electron Microscopy—Energy-Dispersive X-Ray Spectroscopy (STEM-EDS) Mapping of a Model Oxide Interface

Spurgeon

Chambers

2017

Microsc Microanal

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With the development of affordable aberration-correctors, analytical scanning transmission electron microscopy (STEM) studies of complex interfaces can now be conducted at high spatial resolution at laboratories worldwide. Energy-dispersive X-ray spectroscopy (STEM-EDS) in particular has grown in popularity, since it enables elemental mapping over a wide range of ionization energies. However, the interpretation of atomically-resolved data is greatly complicated by beam-sample interactions that are often overlooked by novice users. Here we describe the practical factors-namely, sample thickness and the choice of ionization edge-that affect the quantification of a model perovskite oxide interface. Our measurements of the same sample in regions of different thickness indicate that interface profiles can vary by as much as 2-5 unit cells, depending on the spectral feature. This finding is supported by multislice simulations, which reveal that on-axis maps of even perfectly abrupt interfaces exhibit significant delocalization. Quantification of thicker samples is further complicated by channeling to heavier sites across the interface, as well as an increased signal background. We show that extreme care must be taken to prepare samples to minimize channeling effects and argue that it may not be possible to extract atomically-resolved information from many chemical maps.

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Interpreting atomic-resolution spectroscopic images

Cited by 68 publications

References 24 publications

Fano resonance in atomic-resolution spectroscopic imaging of solids

Fano resonance in atomic-resolution spectroscopic imaging of solids

Towards artifact-free atomic-resolution elemental mapping with electron energy-loss spectroscopy

Measurement Error in Atomic-Scale Scanning Transmission Electron Microscopy—Energy-Dispersive X-Ray Spectroscopy (STEM-EDS) Mapping of a Model Oxide Interface

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