Combination of EELS modes and electron spectroscopic imaging and diffraction in an energy-filtering electron microscope

Reimer, Ludwig; Fromm, I.; Hirsch, P. B.; Plate, Ulrich; Rennekamp, R.

doi:10.1016/0304-3991(92)90023-d

Cited by 55 publications

(22 citation statements)

References 37 publications

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“…However, ultimate visualization of ultrastructures of fine polysaccharidic fibrils without producing artefact is usually difficult to achieve, mainly because of non-specific precipitation of stains when the aqueous matrix of the sample is complex [277 . On the other hand, it has been observed that contrast enhancement of EF-TEM is improved with stained specimens when visualized in CT-TEM mode below the carbon Kionisation edge [23]. Figure 1 is a spectacular example of the increase in contrast which is obtained by CT-TEM under optimal conditions for a synthetic network of slightly stained polysaccharides.…”

Section: Resultsmentioning

confidence: 98%

“…The EF-TEM discriminates elastically and inelastically forwardscattered electrons that have lost discrete amounts of energy (AEIo~) during their interaction with the specimen; a series of characteristic AEIos~ edges arises for each element present in the analysed specimen [21][22][23]. In previous studies [18,24] we have shown with aquatic suspensions (mineral particles and organic matter) that EF-TEM can be applied to (i) elemental analysis (spectrum mode; electron energy loss spectrometry, EELS-TEM), (ii) elemental mapping (imaging mode; electron spectroscopic Imaging, ESI-TEM), and (iii) the visualization of organic matter (structure-sensitive mode; contrast tuning, CT-TEM).…”

Section: Analytical Electron Microscopymentioning

confidence: 99%

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Enhanced visualization of polysaccharides from aqueous suspensions

1997

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Abstract. Aqueous suspensions of polysaccharides such as those prepared for domestic and industrial applications or present in natural waters, although difficult to visualize by conventional transmission electron microscopy (TEM) because of their poor electron density, can be characterized at the ultrastructural level by using mild en bloc staining and contrast enhancement by energy-filtered TEM (EF-TEM). The advantages and drawbacks of the proposed method are discussed in relation to the different parameters controlling the quality of final images. It is shown, with synthetic polysaccharides, purified algal fibrils and lacustrine exocellular polymers as key examples, that optimizing specimen preparation and visualization parameters allows unbiased identification of organic substructures never revealed or strongly degraded by classical microscopic procedures.Key words: fibrillar polysaccharides, contrast enhancement, energyfiltered transmission electron microscopy (EF-TEM), densitometry, stain, uranyl acetate.Carbohydrates in nature show high diversity and complexity in their composition, structure and function [1,2]. They are produced as neutral or acidic compounds by all living species, from micro-organisms to higher animal cells, and it is not surprising to detect them in our environment (soils, waters), as a consequence of exocellular release (extracellular polysaccharides, EPS) or degradation process in the natural reservoirs [3].Because of their thickening properties, native or derivatized polysaccharide biopolymers from botanical and microbial sources have found widespread * To whom correspondence should be addressed applications for industrial, domestic and environmental uses where rheology, gelling or pseudoplasticity is of concern [4,5].The behaviour of polysaccharides in synthetic formulations and natural suspensions will primarily depend on their macromolecular structure, varying from totally linear (cellulose) to strongly branched (spherocolloids like amylopectin or gum arabic) compounds; due to minimal steric hindrances, the former have a strong tendency to pack into water-insoluble thick fibres, while the latter are usually highly hydrated (hydrocolloids) and form gels which can contain up to 99.5% water [6].Polysaccharides have a high complexing capacity for di-and trivalent ions [7,8]. Furthermore, the hydroxyl groups of polysaccharides tend to interact with the hydrated surfaces of dispersed mineral particles (oxyhydroxides) and with hydrophilic organic material by hydrogen binding, and to form biofilms on submerged surfaces [9,10]. These properties are demonstrated in soils, where fungal polysaccharides act as binding/aggregating agents between clay particles and as water stabilizers [11][12][13]. Polysaccharides are used in water treatment plant for the removal of undesirable substances by cross-linking, micro-gel formation and flocculation. However, the role of EPS on the stability of suspended mineral particles and on the transport processes of micropollutants in freshwaters and marine envi...

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Section: Resultsmentioning

confidence: 98%

Section: Analytical Electron Microscopymentioning

confidence: 99%

Enhanced visualization of polysaccharides from aqueous suspensions

1997

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“…The complete procedure leading to energy filtered images and energy-loss spectra has been discussed in details elsewhere [13,16] ; it will be briefly described here.…”

Section: Ef-tem Analysismentioning

confidence: 99%

“…As the specimen is prepared by direct deposition of material on TEM grids, the EELS analysis will be dependent on the thickness of each individual particle, which might be limiting for microparticles in the > 150 nm range [14]. In a previous study [15], we have demonstrated that a combination of zero-loss imaging, Contrast Tuning (CT) [16], Electron Spectroscopic Imaging (ESI) and Electron Energy Loss Spectrometry (EELS) could ascertain the existence of strong interactions between hematite microparticles and xanthan polysaccharides forming large networks. These results were in agreement with observations in natural aquatic samples, and could be explained by the theory of bridging developed to explain the stability of particles in the presence of macromolecules [17,18].…”

Section: Introductionmentioning

confidence: 99%

EELS-ESI Identification of Heterogeneous Suspensions of Aquatic Microparticles

Perret

Lienemann

Mavrocordatos

1995

Microsc. Microanal. Microstruct.

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Abstract. 2014 Submicron mineral particles in freshwaters represent an important proportion of the total particle number. These microparticles are frequently associated to macromolecular organic matter and have a high specific surface area; they might thus be strong heavy metal and nutrient scavengers in aquatic systems. Their non-artefacted characterization at the level of individual particles represents a promising challenge, while preservation of the undisturbed state of natural fragile specimens is a prerequisite. We have used a TEM-EELS-ESI procedure which allows the identification of mineral microparticles in individual model suspensions of iron oxides, aluminum oxides and clays in the presence of polysaccharides, at concentrations typical of natural levels. As expected, core-loss ionization edge intensities measured by this method are limited by the thickness of particles. Heterogeneous mixtures of the former microparticles/macromolecules were prepared in order to mimic natural specimens. Under optimum analytical conditions, it was possible to extract the very nature of these entities, to reveal low electron-density polysaccharides and even to identify microparticles masked within complex aggregates.

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“…This information can be acquired in a general-purpose transmission electron microscope ͑TEM͒ fitted with a Gatan imaging filter ͑GIF͒ using a technique known as energy-loss spectroscopic profiling ͑ELSP͒, 6,7 without the need for focusing the electron probe to subnanometer sizes. While the spatial sampling of the electronic structure information obtained in this manner is below that of a dedicated scanning TEM, it has significantly better spatial resolution than if the same TEM were used to form a small electron probe, whose diameter is not smaller than 1.5 nm in our case.…”

mentioning

confidence: 99%

Dielectric properties of WS2-coated multiwalled carbon nanotubes studied by energy-loss spectroscopic profiling

Stolojan

Silva

Goringe

et al. 2005

Applied Physics Letters

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We investigate experimentally the electronic properties of the coating for multiwalled carbon nanotubes covered in tungsten disulfide ͑WS 2 ͒ of various thicknesses. Coatings of thicknesses between 2 and 8 monolayers ͑ML͒ are analyzed using energy-loss spectroscopic profiling ͑ELSP͒, by studying the variations in the plasmon excitations across the coated nanotube, as a function of the coating thickness. We find a change in the ELSP for coatings above 5 ML thickness, which we interpret in terms of a change in its dielectric properties. © 2005 American Institute of Physics. ͓DOI: 10.1063/1.1861985͔The discovery of carbon nanotubes 1 and fullerenes 2 has started a significant research effort into developing carbon electronics as a possible alternative to the end-of-the-road for silicon-based electronics, which is predicted to be reached in the next 10-15 years. Recent advances in controlling the growth of nanotubes 3 and the manipulation and welding of individual nanotubes 4 have brought the goal of producing working carbon devices within reach. Carbon nanotubes coated with functional layers are excellent candidates as starting blocks for these devices. The heterojunctions formed at multiwalled carbon nanotubes ͑MWCNTs͒ coated with WS 2 , a known bulk semiconductor, 5 could have applications in high-efficiency large-area photovoltaics and light-emitting structures. Their use, however, requires knowledge of the dielectric properties of the coating, as a function of its thickness, which we investigate here.This information can be acquired in a general-purpose transmission electron microscope ͑TEM͒ fitted with a Gatan imaging filter ͑GIF͒ using a technique known as energy-loss spectroscopic profiling ͑ELSP͒, 6,7 without the need for focusing the electron probe to subnanometer sizes. While the spatial sampling of the electronic structure information obtained in this manner is below that of a dedicated scanning TEM, it has significantly better spatial resolution than if the same TEM were used to form a small electron probe, whose diameter is not smaller than 1.5 nm in our case. 8MWCNTs coated with a varying number of ordered WS 2 layers were produced by pyrolysis; the production method and the characteristics of the nanotube and the coating are described elsewhere. 5 The tungsten disulfide coating appears to cover the nanotubes along their whole length. Small coating thickness variations ͓1-2 monolayers ͑ML͔͒ can occur along the length of the nanotube, so we only analyzed regions where the coating thickness was constant over lengths 5-10 times the nanotube's diameter. There was no detectable oxygen ͓using electron energy loss spectroscopy ͑EELS͔͒ in the coating. The samples were analyzed using a Philips CM200TEM with a LaB 6 filament, fitted with a GIF2000 spectrometer.When orienting a linear feature along the axis integrated by the quadrupoles of the GIF, the CCD records a twodimensional image where one coordinate is the energy loss and other is, to within a scaling factor, the spatial coordinate normal to the linear f...

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Combination of EELS modes and electron spectroscopic imaging and diffraction in an energy-filtering electron microscope

Cited by 55 publications

References 37 publications

Enhanced visualization of polysaccharides from aqueous suspensions

Enhanced visualization of polysaccharides from aqueous suspensions

EELS-ESI Identification of Heterogeneous Suspensions of Aquatic Microparticles

Dielectric properties of WS2-coated multiwalled carbon nanotubes studied by energy-loss spectroscopic profiling

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