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179
Magnetic microstructure of magnetotactic bacteria by electron holography. Science
, 1998
"... Off-axis electron holography in the transmission electron microscope was used to correlate the physical and magnetic microstructure of magnetite nanocrys-tals in magnetotactic bacteria. The magnetite crystals were all single magnetic domains, and the magnetization directions of small superparamagnet ..."
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Off-axis electron holography in the transmission electron microscope was used to correlate the physical and magnetic microstructure of magnetite nanocrys-tals in magnetotactic bacteria. The magnetite crystals were all single magnetic domains, and the magnetization directions of small superparamagnetic crystals were constrained by magnetic interactions with larger crystals in the chains. Shape anisotropy was found to dominate magnetocrystalline anisotropy in elongated crystals. A coercive Þeld between 300 and 450 oersted was deter-mined for one chain. Magnetic crystals below 100 nm in size occur in organisms in many biological phyla (1). For example, magnetotactic bacteria contain magnetosomes, which are intracellular, ferri-magnetic crystals of magnetite (Fe3O4) or greigite (Fe3S4). The magnetosomes are usu-ally arranged in one or more linear chains
The Flat-Ribbon Configuration of the Periplasmic Flagella of Borrelia burgdorferi and Its Relationship to Motility and Morphology � †
, 2008
"... Electron cryotomography was used to analyze the structure of the Lyme disease spirochete, Borrelia burgdorferi. This methodology offers a new means for studying the native architecture of bacteria by eliminating the chemical fixing, dehydration, and staining steps of conventional electron microscopy ..."
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Electron cryotomography was used to analyze the structure of the Lyme disease spirochete, Borrelia burgdorferi. This methodology offers a new means for studying the native architecture of bacteria by eliminating the chemical fixing, dehydration, and staining steps of conventional electron microscopy. Using electron cryotomography, we noted that membrane blebs formed at the ends of the cells. These blebs may be precursors to vesicles that are released from cells grown in vivo and in vitro. We found that the periplasmic space of B. burgdorferi was quite narrow (16.0 nm) compared to those of Escherichia coli and Pseudomonas aeruginosa. However, in the vicinity of the periplasmic flagella, this space was considerably wider (42.3 nm). In contrast to previous results, the periplasmic flagella did not form a bundle but rather formed a tight-fitting ribbon that wraps around the protoplasmic cell cylinder in a right-handed sense. We show how the ribbon configuration of the assembled periplasmic flagella is more advantageous than a
Electron Vortex Beams with High Quanta of
, 2011
"... This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following ..."
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This copy is for your personal, non-commercial use only. If you wish to distribute this article to others, you can order high-quality copies for your colleagues, clients, or customers by clicking here. Permission to republish or repurpose articles or portions of articles can be obtained by following the guidelines here. The following resources related to this article are available online at www.sciencemag.org (this infomation is current as of March 28, 2011): Updated information and services, including high-resolution figures, can be found in the online version of this article at:
Quantitative three-dimensional reconstruction of catalyst particles for bamboo-like
- C Nanotubes, Nano. Lett.
, 2007
"... ABSTRACT The three-dimensional (3D) structure and chemical composition of bamboo-like carbon nanotubes including the catalyst particles that are used during their growth are studied by discrete electron tomography in combination with energy-filtered transmission electron microscopy. It is found tha ..."
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Cited by 5 (2 self)
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ABSTRACT The three-dimensional (3D) structure and chemical composition of bamboo-like carbon nanotubes including the catalyst particles that are used during their growth are studied by discrete electron tomography in combination with energy-filtered transmission electron microscopy. It is found that cavities are present in the catalyst particles. Furthermore, only a small percentage of the catalyst particles consist of pure Cu, since a large volume fraction of the particles is oxidized to Cu 2 O. These volume fractions are determined quantitatively from 3D reconstructions obtained by discrete tomography.
Nanoscale chemical and structural characterization of transient metallic nanowires using aberration-corrected STEM-EELS
- Nano Lett
"... ABSTRACT: Direct chemical and structural characterization of transient iron−nickel alloy nanowires was performed at subnanometer spatial resolution using probe spherical aberration-corrected scanning transmission electron micros-copy and electron energy-loss spectroscopy. Nanowires with diameter les ..."
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ABSTRACT: Direct chemical and structural characterization of transient iron−nickel alloy nanowires was performed at subnanometer spatial resolution using probe spherical aberration-corrected scanning transmission electron micros-copy and electron energy-loss spectroscopy. Nanowires with diameter less than 2 nm retaining their nominal bulk alloy composition were observed. In some cases, the nanowires were oxidized. Before rupture, a nanojunction as thin as three atoms in width could be imaged. The time-dependent structural analyses revealed the nanowire rupture mechanisms. It is found that the atoms on the {111} planes were the easiest to be removed by electron irradiation and fluctuations between low-energy and high-energy facets were observed. The hitherto unknown rich variety of structural and chemical behavior in alloyed magnetic nanojunctions should be considered for understanding their physical properties.
Fractals and magnetic
, 1996
"... analysis of cation valence states and oxygen vacancies in ..."
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analysis of cation valence states and oxygen vacancies in
Optical Properties of Aluminum Oxide: Determined from Vacuum Ultraviolet and Electron Energy-Loss Spectroscopies
"... The optical properties of a-Al2O3 have been determined by two independent methods, vacuum ultraviolet (VUV) spec-troscopy and electron energy-loss spectroscopy (EELS) over the energy range from 6 to 142 eV. For each experi-mental method two sets of high-quality data have been measured and analyzed f ..."
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The optical properties of a-Al2O3 have been determined by two independent methods, vacuum ultraviolet (VUV) spec-troscopy and electron energy-loss spectroscopy (EELS) over the energy range from 6 to 142 eV. For each experi-mental method two sets of high-quality data have been measured and analyzed from a-Al2O3. The evolution of the differences between the data for each experimental method and its associated analytical method indicate the reliability of the results, and the comparison between the methods emphasizes the relative advantages of each. VUV spectros-copy offers a higher energy resolution, resolving sharper features in the spectra, whereas EELS significantly extends the energy range, which has been exploited here to 140 eV but can be extended even further. Good overall consistency is found, but there are pronounced differences in the va-lence region from 10 to 30 eV, where strong absorptions are present, increasing the relative variability of the analysis. This demonstrates that accuracy estimates of the optical properties are meaningful only when supplied as a function of energy, because both strong intrinsic absorptions and weak experimental signals make accurate determinations difficult. Moreover, variations in the optical properties are observed most easily in the interband transition strength, Jcv, and are less evident when the optical properties are represented as the complex index of refraction. Because the optical properties can change with specimen origin and preparation and because of the details of data acquisition and numerical analysis procedures, assessing the contribu-tions of each of these methods to our accurate knowledge of the optical constants is essential. I.
Dispersion Forces and Hamaker Constants for Intergranular Films in Silicon Nitride from Spatially Resolved–Valence Electron Energy Loss Spectrum Imaging
- Acta Materialia
, 1998
"... Abstract—The van der Waals (vdW) dispersion forces represent one of the fundamental long range inter-facial and surface forces in materials. The dispersion forces, for a set of materials in close proximity, arise from the electronic structure of the materials wherein the electrons in interatomic bon ..."
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Abstract—The van der Waals (vdW) dispersion forces represent one of the fundamental long range inter-facial and surface forces in materials. The dispersion forces, for a set of materials in close proximity, arise from the electronic structure of the materials wherein the electrons in interatomic bonds acting as oscillat-ing dipoles exhibit an attractive interaction energy. These vdW dispersion forces, represented by a propor-tionality constant, the full spectral Hamaker constant (A), can be calculated directly from optical property based electronic structure spectra such as the interband transition strength (Jcv) using the Lifshitz theory. Si3N4 exhibits equilibrium intergranular films (IGFs) whose thickness is determined by a force balance where the contribution of the van der Waals dispersion force is dictated by the IGF chemistry. Using spatially resolved-valence electron energy loss (SR-VEEL) spectroscopy in the STEM with a 0.6 nm probe permits the in situ determination of vdW forces on the IGFs in viscous sintered polycrystalline systems. In addition local variations in IGF chemistry and dispersion forces throughout the microstructure of individ-ual silicon nitride samples can be determined using these methods. From multiplexed zero loss/plasmon loss optimized SR-VEEL spectra across IGFs with subsequent single scattering deconvolution, Kramers Kronig analysis and London dispersion analysis, the index of refraction and Hamaker constants can be determined. The method proved to be accurate and reproducible with comparison to VUV measurements
Computing electron energy loss spectra with the discontinuous galerkin time-domain method
- Photonics Nanostruct
"... Abstract In this work, we demonstrate how to extract electron energy loss spectra of metallic nano-particles from time-domain computations. Specifically, we employ the Discontinuous Galerkin Time-Domain (DGTD) method in order to model the excitation of individual metallic nano-spheres and dimers of ..."
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Abstract In this work, we demonstrate how to extract electron energy loss spectra of metallic nano-particles from time-domain computations. Specifically, we employ the Discontinuous Galerkin Time-Domain (DGTD) method in order to model the excitation of individual metallic nano-spheres and dimers of spheres by a tightly focussed electron beam. The resulting electromagnetic fields that emanate from the particles act back on the electrons and the accumulated effect determines the electrons' total energy loss. We validate this approach by comparing with analytical results for single spheres. For dimers, we find that the electron beam allows for an efficient excitation of dark modes that are inaccessible for optical spectroscopy. In addition, our time-domain approach provides a basis for dealing with materials that exhibit a significant nonlinear response. #
