A novel 3D absorption correction method for quantitative EDX-STEM tomography

Burdet, Pierre; Saghi, Zineb; Filippin, A. Nicolas; Borrás, Anaisabel; Midgley, Paul A.

doi:10.1016/j.ultramic.2015.09.012

Cited by 36 publications

(33 citation statements)

References 32 publications

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“…Postprocessing of EDX data was performed with the open source Hyperspy software, hyperspy.org, as described elsewhere. 45 Xray absorption spectra at the Fe K edge in fluorescence mode were recorded at the SAMBA beamline of the SOLEIL Synchrotron. The objectives of these measurements were (a) to determine the atomic distances on the local environments of the Fe ions in both the FePc and the FePcCl nanowires and crystalline reference samples and (b) to quantify the vertical Fe−Fe separation on the nanowire stacking.…”

Section: Chemistry Of Materialsmentioning

confidence: 99%

Self-Assembly of the Nonplanar Fe(III) Phthalocyanine Small-Molecule: Unraveling the Impact on the Magnetic Properties of Organic Nanowires

et al. 2018

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In this article we show for the first time the formation of magnetic supported organic nanowires (ONWs) driven by self-assembly of a nonplanar Fe(III) phthalocyanine chloride (FePcCl) molecule. The ONWs grow by a crystallization mechanism on roughness-tailored substrates. The growth methodology consists of a vapor deposition under low vacuum and mild temperature conditions. The structure, microstructure, and chemical composition of the FePcCl NWs are thoroughly elucidated and compared with those of Fe(II) phthalocyanine NWs by a consistent and complementary combination of advanced electron microscopies and X-ray spectroscopies. In a further step, we vertically align the NWs by conformal deposition of a SiO 2 shell. Such orientation is critical to analyze the magnetic properties of the FePcCl and FePc supported NWs. A ferromagnetic behavior below 30 K with an easy axis perpendicular to the phthalocyanine plane was observed in the two cases with the FePcCl nanowires presenting a wider hysteresis. These results open the path to the fabrication of nanostructured one-dimensional small-molecule spintronic devices. T ailoring material structure at the nanoscale has prompted research on new and exciting properties over the last two decades. This is particularly true for one-dimensional (1D) nanostructures (nanotubes, nanowires, nanorods, or nanobelts) with longitudinal sizes orders of magnitude larger than the cross-sectional sizes.1 Among them, organic nanowires (ONWs) form a family of nanostructures with remarkable optic, electronic, sensing, and wetting properties.2−12 In addition, the development of ONW devices offers potential for low cost and flexible devices and versatility through the molecular design of their building blocks. The methods for the synthesis of these 1D systems generally rely on three approaches including template procedures, solution-phase deposition, and vapor transport. [2][3][4]6,10,13 Condensation from the vapor phase at low pressure (or simply physical vapor deposition, PVD) counts within the last group and presents interesting features such as (i) direct formation of single crystal nanowires with controlled morphology on different substrates; (ii) high adaptability to a large amount of different π-conjugated small molecules; (iii) high growth rate and controlled density of nanowires with appropriated homogeneity; (iv) solventless and one-step synthesis; and (v) straightforward compatibility with other vacuum deposition and processing methods. 2,14−18 The method consists of the low-pressure sublimation of purely organic or metalorganic small-molecules from the bulk crystals counterpart and their condensation on the surface of diverse supports. These molecules self-assemble into supported single-crystal nanowires tens of nanometers in width and several micrometers in length.14,15,18 Such a heterogeneous crystallization process can be enhanced by including nucleation centers at the substrate to trigger the preferential condensation of molecules on those spots.14,15 Formation of ONWs...

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Section: Chemistry Of Materialsmentioning

confidence: 99%

Self-Assembly of the Nonplanar Fe(III) Phthalocyanine Small-Molecule: Unraveling the Impact on the Magnetic Properties of Organic Nanowires

et al. 2018

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“…The error bars were determined through error propagation as described in the literature . In cases where absorption effects cannot be ignored, it is still possible to obtain a quantitative XEDS reconstruction, but it is necessary to integrate our method with the iterative technique proposed by Burdet et al…”

Section: Resultsmentioning

confidence: 99%

“…These maps can be used directly as an input for a tomographic algorithm such that a different reconstruction for each element is obtained . Next, these reconstructions can be quantified by analyzing the voxel intensities using the Cliff–Lorimer or ζ ‐factor method . The outcome of this approach is predominantly determined by the quality of the tomogram and therefore by the number of available projections.…”

Section: Methodsmentioning

confidence: 99%

“…Such maps are not affected by shadowing effects since the XEDS counts for both types of elements are acquired at the same tilt angle and are influenced by shadowing in the same manner. This assumption is valid for “hard” X‐rays with energies >3 keV, else an absorption correction method should be applied.…”

Section: Methodsmentioning

confidence: 99%

“…Different methodologies have been proposed to overcome this challenge. For example, signals from individual detectors can be combined, the acquisition time can be adjusted as a function of the tilt angle or the total signal for every map can be normalized to the same value . However, in order to maximize the signal‐to‐noise ratio, it is of great importance to collect as many counts as possible.…”

Section: Introductionmentioning

confidence: 99%

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A New Method for Quantitative XEDS Tomography of Complex Heteronanostructures

Zanaga

Altantzis

Polavarapu

et al. 2016

Part & Part Syst Charact

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396 wileyonlinelibrary.com www.particle-journal.com www.MaterialsViews.com Reliable quantifi cation of 3D results obtained by X-ray energy-dispersive spectroscopy (XEDS) tomography is currently hampered by the presence of shadowing effects and poor spatial resolution. Here, a method is presented which overcomes these problems by synergistically combining quantifi ed XEDS data and high angle annular dark fi eld-scanning transmission electron microscopy tomography. As a proof of principle, the approach is applied to characterize a complex Au/Ag nanorattle obtained through a galvanic replacement reaction. However, the technique that is proposed here is widely applicable to a broad range of nanostructures.very challenging to use HAADF-STEM tomography for samples in which mixing of elements is expected. Also for samples that contain unknown elements or elements with atomic number Z close to each other, HAADF-STEM tomography may no longer be informative. However, it is well known that the properties and applications of nanostructures are strongly dependent on their morphology as well as their chemical composition. [ 4 ] Traditional electron microscopy techniques do not provide quantitative information on the composition of single nanoparticles. In an increasing number of recent studies, X-ray energy-dispersive spectroscopy (XEDS) is combined with tomography to understand complex nanostructure morphology and composition in 3D. These studies rely on newly developed XEDS detectors, [ 5,6 ] such as the Super-X detection system, which consists of four individual detectors, symmetrically arranged around the Transmission Electron Microscope (TEM) sample. Although qualitative results obtained by XEDS tomography have been reported, [7][8][9][10] it remains challenging to obtain quantitative information by 3D XEDS and therefore further progress is required. By using the Super-X detector, one is able to overcome problems that were previously related to extreme shadowing of the XEDS signal caused by the sampledetector confi guration. Although this problem can be largely overcome, some shadowing effects remain, [ 11,12 ] as illustrated in Figure 1 . Since such shadowing effects vary for different tilt angles, the XEDS signal integrated over the four detectors will also depend on the tilt angle [11][12][13] and the projection principle for electron tomography is no longer fulfi lled. [ 12 ] Different methodologies have been proposed to overcome this challenge. For example, signals from individual detectors can be combined, [ 11,14 ] the acquisition time can be adjusted as a function of the tilt angle [ 12 ] or the total signal for every map can be normalized to the same value. [ 13,15 ] However, in order to maximize the signal-to-noise ratio, it is of great importance to collect as many counts as possible. Selectively switching off detectors is therefore disadvantageous, while changing the acquisition time improves the quality of the tilt series, but a calibration of the holder is required and the fi nal result is still hampered by ...

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3D structure and chemical composition reconstructed simultaneously from HAADF ‐ STEM images and EDS ‐ STEM maps

Zhong

Goris

Schoenmakers³

et al. 2016

European Microscopy Congress 2016: Proceedings

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Electron tomography (ET) is nowadays commonly used in materials science to obtain a three dimensional (3D) structural characterization of nanomaterials. Typically it is based on tomographic reconstruction from high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) images yielding Z‐contrast in final reconstructions. However, when investigating heteronanostructures with small differences in Z, spectroscopic techniques such as Electron Energy Loss Spectroscopy (EELS) and Energy Dispersive X‐ray Spectroscopy (EDS) should be used. Here, we focus on EDS‐STEM spectroscopic imaging. Recently, EDS in combination with electron tomography was demonstrated [1,2], but the quality of these reconstructions is limited because of the small signal‐to‐noise ratio (SNR) in the acquired elemental maps compared to HAADF‐STEM projection images. In this study, we propose to combine HAADF‐STEM tomography with EDS‐STEM tomography instead of processing both signals independently. This combination has not yet been completely explored except for using HAADF‐STEM images for aligning EDS‐STEM maps [3] and for estimating density to correct X‐ray absorption [4]. Here, we introduce the concept of multi‐modal tomography to ET by proposing a novel HAADF‐EDS bimodal tomographic reconstruction technique. The technique is based on the physical model that both types of projection images are linearly related to the projections of chemical compositions. Based on this assumption, HAADF‐STEM images can be approximated as a linear combination of EDS‐STEM maps. By estimating the linear relation, we can scale EDS‐STEM maps to the same physical unit as HAADF‐STEM images. The two types of images are related and used together as the input data for one single reconstruction process. As a result, we are able to reconstruct 3D elemental distributions with reduced noise levels compared to conventional EDS‐STEM tomography. To evaluate the technique, it has been applied to two Au‐Ag nanoparticles. The samples were imaged by an electron microscope (Tecnai Osiris, FEI) equipped with four silicon drift detectors (SuperX system, FEI). The first sample was tilted from −75° to 75° (from −70° to 70° for the second sample) with a step of 5°. At each tilt, a Z‐contrast image was recorded by HAADF‐STEM and two elemental maps for Au and Ag were generated from X‐rays spectrum images acquired by EDS‐STEM. Both the HAADF‐STEM and the elemental maps were aligned using cross correlation algorithms. The first sample that is investigated consists of a Ag nanoparticle with an embedded Au octahedral core. As indicated in Figure 1, Au and Ag are well separated in this sample. Consequently, a segmention based on the Z‐contrast of a HAADF‐STEM reconstruction can be considered as ground truth for the distributions of the chemical elements (Figure 1 (a)). As illustrated in Figure 1 (c), we are able to determine the 3D elemental distributions using our novel HAADF‐EDS bimodal reconstruction technique. This figure indicates a significant improvement in comparison to conventional EDX tomography (Figure 1 (b)) where the raw elemental maps are used as input for a tomographic reconstruction. The second sample that is investigated is an alloy of Au and Ag. Since no clear boundaries exist between the two compositions, we are not able to segment their 3D distributions based on the HAADF‐STEM tomographic reconstructions. Although 3D compositional distributions can be reconstructed from EDS‐STEM maps, the 3D image is very noisy and difficult to interpret (Figure 2 (b)). In comparison, the 3D compositional distributions reconstructed by HAADF‐EDS bimodal tomography (Figure 2 (c)) provides more information on the concentration of the different elements while the outer shape of the nanoparticle agrees well with the 3D shape reconstructed from HAADF‐STEM images (Figure 2 (a)).

show abstract

A novel 3D absorption correction method for quantitative EDX-STEM tomography

Cited by 36 publications

References 32 publications

Self-Assembly of the Nonplanar Fe(III) Phthalocyanine Small-Molecule: Unraveling the Impact on the Magnetic Properties of Organic Nanowires

Self-Assembly of the Nonplanar Fe(III) Phthalocyanine Small-Molecule: Unraveling the Impact on the Magnetic Properties of Organic Nanowires

A New Method for Quantitative XEDS Tomography of Complex Heteronanostructures

3D structure and chemical composition reconstructed simultaneously from HAADF ‐ STEM images and EDS ‐ STEM maps

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