Electron energy-loss spectrum-imaging

Hunt, John; Williams, David B.

doi:10.1016/0304-3991(91)90108-i

Cited by 303 publications

(125 citation statements)

References 16 publications

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“…This technique is commonly referred to as spectrum imaging [34]. To improve the energy resolution of the spectra, all imaging and spectroscopy was performed with a monochromator, providing an energy resolution of 0.4 eV.…”

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confidence: 99%

2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

et al. 2011

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Using a combination of high-angle annular dark-field scanning transmission electron microscopy and atomically resolved electron energy-loss spectroscopy in an aberration-corrected transmission electron microscope we demonstrate the possibility of 2D atom by atom valence mapping in the mixed valence compound Mn 3 O 4 . The Mn L 2;3 energy-loss near-edge structures from Mn 2þ and Mn 3þ cation sites are similar to those of MnO and Mn 2 O 3 references. Comparison with simulations shows that even though a local interpretation is valid here, intermixing of the inelastic signal plays a significant role. This type of experiment should be applicable to challenging topics in materials science, such as the investigation of charge ordering or single atom column oxidation states in, e.g., dislocations. DOI: 10.1103/PhysRevLett.107.107602 PACS numbers: 79.20.Uv, 68.37.Ma, 75.25.Dk In transition metal oxides, the oxidation state of the transition metal cations is of fundamental importance as the physical properties of many oxides are determined by the occupancy of the cation d bands. Multiferroicity, for example, can be driven by charge ordering of these cations, as in Fe 3 O 4 and Pr 1Àx Ca x MnO 3 [1-3]. However, the exact mechanism of multiferroic behavior is not fully understood to date. A method allowing for direct mapping of cation valence states in these materials at atomic resolution should therefore provide further insight into the origin of multiferroicity.Recently, atomic resolution elemental mapping has become feasible by means of spatially resolved electron energy-loss spectroscopy and energy dispersive x-ray spectroscopy in a scanning transmission electron microscope (STEM-EELS and STEM-EDX) [4][5][6][7][8][9]. At the same time, tremendous effort is being invested into the identification of the oxidation states of cations using electron energy-loss spectroscopy (EELS). The shape of the L 2;3 edge [10], the chemical shift [11,12] and the L 3 =L 2 ratio [13] have all been used as a fingerprint for the transition metal valence. In fact, the correlation between the energy-loss near-edge structure (ELNES) and valence in different transition metal oxides was confirmed by several experiments in literature [10,[14][15][16][17][18][19][20][21]. The higher the energy resolution, the more convincing this link between valence and ELNES features becomes. Combining the atomic resolution capabilities of a STEM with bonding and valence information from EELS is a highly attractive prospect. While bonding information has been obtained at atomic resolution [7,17,22], 2D oxidation state mapping at the atomic level in, e.g., metaloxide materials has remained challenging due to poor EELS signal-to-noise ratio and the need for simultaneous high spatial and energy resolution of the instrument [10,17,23].Mn 3 O 4 is known to be a mixed valence compound, containing both Mn 2þ and Mn 3þ ions at room temperature [24]. It has a spinel structure with lattice parameters a ¼ 5:762 A and c ¼ 9:4696 A and space group I41=amd. Many interesting...

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2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

et al. 2011

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“…This will increase the electron dose by an order of magnitude beyond the PEELS dose, but it will make it possible to acquire quantitative chemical maps as large as 1024 x 1024 pixel in a few tens of second. The required software will incorporate elements of the spectrum-image approach originally developed for PEELS mapping [20,21], and is now being written in our laboratory. Figure 4 shows an energy-loss spectrum of a thorium pyromellitate particle recorded with the imaging filter operating in the spectrum mode.…”

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Design and first applications of a post-column imaging filter

Krivanek¹,

Gubbens²,

Dellby³

et al. 1992

Microsc. Microanal. Microstruct.

145

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Abstract. 2014 We have designed and built an imaging filter which can be attached to most standard TEMs, and is capable of operating at primary energies of up to 400 keV. The filter uses a 90°m agnetic sector prism, a piezoelectrically controlled energy-selecting slit, and 6 quadrupole and 5 sextupole lenses. It fully corrects second-order aberrations and distortions in images formed with electrons of selected energies, and it also produces second-order aberration-corrected spectra of variable dispersion. We show the first applications of the filter at 200 keV primary energy, which indicate that the filter will excel in chemical mapping and spectroscopy, in improving contrast of electron images and diffraction patterns, and in making high resolution electron microscopy and diffraction more quantitative. We conclude the paper with a discussion about atomic resolution image formation using inelastically scattered electrons, and the relationship between energy-filtered diffraction patterns and images formed with electrons of the same energy.

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“…Despite the lower collection efficiency of energy filtered TEM (EFTEM) relative to spectrum-imaging in the scanning TEM (STEM) due to the EFTEM's sequential acquisition of the EELS information one energy band at a time, much higher total currents (~100 nA) are available with wide-beam illumination [2][3][4][5]. This means that in EFTEM large numbers of pixels (~10 6 ) can be read out in a few seconds [6][7][8][9].…”

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Compositional Imaging of Cells and Bionanoparticles by EFTEM

Aronova

Leapman

2014

Microsc Microanal

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Elemental mapping based on electron energy loss spectroscopy (EELS) provides cell biologists with information that complements the ultrastructure obtained by conventional transmission electron microscopy (TEM) [1]. Despite the lower collection efficiency of energy filtered TEM (EFTEM) relative to spectrum-imaging in the scanning TEM (STEM) due to the EFTEM's sequential acquisition of the EELS information one energy band at a time, much higher total currents (~100 nA) are available with wide-beam illumination [2][3][4][5]. This means that in EFTEM large numbers of pixels (~10 6 ) can be read out in a few seconds [6][7][8][9]. In particular, EFTEM mapping when combined with electron tomography facilitates quantitative electron spectroscopic tomography (QuEST), which provides three-dimensional elemental distributions from a tilt series of two-dimensional projections [10][11][12]. It is then possible to interrogate specific voxels in the 3D elemental maps to determine numbers of atoms in structures of interest.In the first example, we have used a correlative microscopy approach based on light microscopy, EFTEM imaging, and STEM to localize specific protein complexes. We have explored the ultrastructure of the well-studied Drosophila melanogaster gypsy chromatin insulator body by immunolabeling a key insulator protein CP190 using a fluoronanogold conjugated antibody probe. We have used fluorescent imaging to identify nuclei that contain the insulator bodies, which are rare structures within the thin sections. A comparison of low-magnification electron micrograph of a whole cell with the corresponding fluorescent image reveals the approximate location of the structure of interest. The fluorescence signal observed by light microscope guarantees the presence of the conjugated nanogold, which can be visualized using STEM, and used to locate precisely the labeled CP190 proteins. The EFTEM and QuEST techniques are then performed to image the nitrogen and phosphorus and thus to map distributions of protein and nucleic acid within the cell nucleus. From our quantitative analysis of these two elemental distributions, it is evident that the insulator body contains an abundance of protein but a small quantity of nucleic acid. Even though dense chromatin surrounds the insulator body, it is difficult to determine whether the low levels of phosphorus within the insulator body structures correspond to DNA or RNA; this requires further investigation.In the second example we use EFTEM imaging together with electron tomography to characterize different types of nanoparticles, which have potential use in diagnostic medical imaging. For some types of nanoparticles it was more efficient to generate 2D EFTEM maps for one projection only, and then combine those with structural information from conventional TEM tomography. For other nanoparticles it was necessary first to perform EFTEM spectrum-imaging and then STEM tomography. These hybrid nanoparticles are composed of a core, which can include the therapeutic drug, and outer layer that ca...

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Electron energy-loss spectrum-imaging

Cited by 303 publications

References 16 publications

2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

2D Atomic Mapping of Oxidation States in Transition Metal Oxides by Scanning Transmission Electron Microscopy and Electron Energy-Loss Spectroscopy

Design and first applications of a post-column imaging filter

Compositional Imaging of Cells and Bionanoparticles by EFTEM

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