A STEM/EELS method for mapping iron valence ratios in oxide minerals

Cavé, Lisa; Al, Tom A.; Loomer, Diana B.; Cogswell, Steven; Weaver, Louise

doi:10.1016/j.micron.2005.10.006

Cited by 75 publications

(63 citation statements)

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“…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.…”

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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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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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“…5A. This method has also been used to acquire 2D analytical images of the Fe valence across the magnetite/ilmenite interface (Cavé et al 2006) (Andersen et al 1991). Intermediate Fe 3+ 3+ /ΣFe values were found for 5 points along the interface region between the two minerals in the line scan (Fig.…”

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confidence: 99%

“…Advances in X-ray microbeam and synchrotron methods have allowed Fe 3+ 3+ /ΣFe measurements to be made on individual mineral grains using techniques such as X-ray Photoelectron Spectroscopy (XPS) (Raeburn et al 1997), X-ray absorption spectroscopy (Cressey et al 1993;Dyar et al 2002) and Synchrotron Mössbauer Spectroscopy (SMS) (Jackson et al 2005). However, the best spatial resolution to date for measuring Fe 3+ 3+ /ΣFe ratios has been obtained from EELS in the TEM (Garvie and Buseck 1998;van Aken et al 1998;van Aken and Liebscher 2002;Cavé et al 2006).…”

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Geoscience at the nanometre scale: review of analytical transmission electron microscopy applications

Petrunic

Cavé

et al. 2006

atgeol

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This paper describes applications of analytical Transmission Electron Microscopy (TEM) in the geosciences. The topics include: 1) sulphide-mineral oxidation; 2) trace-metal attenuation by secondary Mn oxides; 3) silicate weathering; 4) transition-metal valence in minerals; and 5) secondary Hg minerals in stream sediments. The main advantage of the analytical TEM is the ability to obtain images, chemical information, and electron diffraction patterns at the nanometre scale. With such high spatial resolution, it is possible to observe physical and chemical features in samples that cannot be resolved with most other techniques. This information can lead to signifi cant improvement in our understanding of the system under investigation. Sample preparation techniques that are used in each study are also described in this paper. The preparation of samples for TEM analysis can be challenging because of the heterogeneity commonly encountered in geological materials, the fragility of some geological samples (e.g., low-temperature minerals), and the need to maintain spatial relationships present in the samples. The sample preparation techniques presented are specifi c to the needs of the study and the appropriateness of these methods is demonstrated by the high quality analytical TEM data that are obtained. RÉSUMÉCet exposé décrit des applications de la microscopie électronique à transmission analytique dans les sciences de la terre. Les aspects étudiés comprennent : 1) l'oxydation des minéraux sulfurés; 2) l'atténuation des métaux-traces par des oxydes de Mn secondaires; 3) la silicatisation météorique; 4) la valence des métaux de transition dans les minéraux; et 5) les minéraux de Hg secondaires dans les sédiments fl uviatiles. Le principal avantage qu'offre la MET analytique est la possibilité d'obtenir des images, des données chimiques et des fi gures de diffraction des électrons à l'échelle nanométrique. Une résolution spatiale aussi élevée permet l'observation dans les échantillons de propriétés physiques et chimiques impossibles à éclaircir au moyen de la majorité des autres techniques. De tels renseignements peuvent mener à une amélioration marquée de notre compréhension du système à l'étude. Cet exposé décrit en plus les techniques de préparation des échantillons utilisées lors de chaque étude. La préparation des échantillons à une analyse MET peut s'avérer compliquée en raison de l'hétérogénéité que présentent communément les matières géologiques, de la fragilité de certains échantillons géologiques (p. ex. minéraux à basse température) et de la néces-sité de maintenir les liens spatiaux présents dans les échantillons. Les techniques de préparation des échantillons présentées sont propres aux besoins de l'étude; les données de haute qualité obtenues des analyses MET témoignent de la pertinence de ces méthodes.

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“…Recently, EELS has been combined with electron tomography to study the 3D distribution of elements in biological samples [13], particularly iron in degenerating neurons in mice with abnormal regulation of iron metabolism [14]. ATEM, with high energy resolution EELS spectra, allows the characterization of iron compounds by EXAFS and ELNES techniques (equivalent to XAFS and XANES derived synchrotron techniques) [15][16][17][18][19][20].…”

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Comment to “Mapping and Characterization of Iron Compounds in Alzheimer's Tissue”

Quintana

2007

JAD

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The recent article of Collingwood and Dobson [1] is an important article that emphasizes the importance of the characterization and mapping of iron compounds in the iron-rich brain regions with the aim contributing to our understanding of the role of pathological accumulations of iron in the regions of the brain affected by neurodegenerative disease. Nonetheless, below, I discuss ion and electron microprobe techniques for detecting and quantifying iron, not specifically cited by the authors, that allow the mapping of total iron (SIMS and XEDS) at the cellular and sub cellular level and the characterization and mapping of iron compounds (EELS) at ultra structural level.SIMS (Secondary Ion Mass Spectroscopy) imaging technique, allows direct identification of chemical elements with high sensitivity and specificity and, as a consequence, elemental distribution can be visualized (chemical mapping) by SIMS imaging. The physical basis of the method is the following: under the bombardment of the samples by primary ions, the monoatomic or polyatomic species that composed the analyzing object are sputtered. One part of these emitted species is ionized and the SIMS instrument, with the help of a mass spectrometer, sort and maps the ejected ions by their m/e ratio. The latest generation of SIMS instruments, the NanoSIMS-50 TM instrument, operating in scanning mode, is equipped with a parallel detection system that allows the simultaneous acquisition of five elements which insures a perfect colocalization between simultaneously recorded images. This instrument is particularly useful to identify elements at a sub cellular level, because it is possible to attain resolutions of 50-100 nm with the Cs + source and 150-200 nm with the O − source [2]. NanoSIMS microscopy has been already used with success for the visualization of the morphological and chemical alterations taking place in well-characterized regions in pathological brain, in particular in the study of iron distribution in Alzheimer disease tissue [3,4]. Multielemental analysis (nitrogen, phosphorus, sulphur and iron) were performed on semi-thin or ultra-thin sections of Transmission Electron Microscopy (TEM) preparations brain tissue. The possibility of using light microscopy, TEM, and SIMS on the same semi-thin and ultra-thin sections allows correlation between structural and analytical observations at sub-cellular and ultrastructural level. It has been shown that the iron-rich region mapped by nanoSIMS in the hippocampus of AD patients are ferritin and/or hemosiderin rich regions.XEDS (X-Ray Energy dispersive Spectroscopy) and EELS (Electron Energy Loss Spectroscopy) are electron probe nanoanalysis techniques that, associated with transmission electron microscopes (ConventionalTEM, ScanningTEM or ConventionalTEM working in scanning mode, so-called AnalyticalTEM, ATEM), provide compositional maps of ultra-thin sections with nanometric resolution (1-10 nm): XEDS by detecting the element specific X-ray emission under excitation of incident electrons: EELS by detectin...

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A STEM/EELS method for mapping iron valence ratios in oxide minerals

Cited by 75 publications

References 14 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

Geoscience at the nanometre scale: review of analytical transmission electron microscopy applications

Comment to “Mapping and Characterization of Iron Compounds in Alzheimer's Tissue”

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