Nanoscale characterization of nautilus shell structure: An example of natural self-assembly

2006 ◽  
Vol 21 (6) ◽  
pp. 1484-1489 ◽  
Author(s):  
R. Velázquez-Castillo ◽  
J. Reyes-Gasga ◽  
D.I. García-Gutierrez ◽  
M. Jose-Yacaman
Keyword(s):  
Self Assembly ◽  
Organic Matrix ◽  
Dark Field ◽  
Orthorhombic Unit Cell ◽  
Transmission Electron ◽  
Nanoscale Characterization ◽  
Annular Dark Field ◽  
First Time ◽  
Inorganic Components

Structural characterization at the nanometric scale of the Nautilus sp shell was carried out by high-resolution transmission electron microscopy and high-angle annular dark field to understand how the organic and inorganic components are related. The inorganic phase that built the shell is made of calcium carbonate (CaCO3), with the orthorhombic unit cell of the aragonite, in a texturized arrangement in such a way that the c-axis is always perpendicular to the shell surface. The organic material forms films through the plates. We observed for a very first time some aragonite nanocrystals embedded in the organic matrix. This observation supports the hypothesis that the proteins and other organic compounds guide the crystal growth because the organic matrixes are the places where the nanocrystals grow.

HREM and HAADF Studies of Precipitates in the Mg-Y-Nd Alloy System

2007 ◽  
Vol 561-565 ◽  
pp. 275-278
Author(s):  
Wei Sun ◽  
Li Sun ◽  
Lin Lin Liu ◽  
Ze Zhang
Keyword(s):  
Structural Model ◽  
Imaging Technique ◽  
Dark Field Image ◽  
Alloy System ◽  
Dark Field ◽  
Orthorhombic Unit Cell ◽  
Characteristic Distribution ◽  
Transmission Electron ◽  
Annular Dark Field ◽  
Image Technique

By means of high resolution transmission electron microscopy (HREM) and high-angle annular dark-field image technique (HAADF), morphological, structural and compositional characteristics of the precipitates in the Mg-4Y-3Nd alloy aged at 200°C for different periods of time have been studied. On the basis of HREM observations, an atomic structural model for the β’-precipitate with an orthorhombic unit cell has been proposed. The characteristic distribution of the precipitates which are rich in rare-earth elements (Y, Nd) has been clearly revealed by the HAADF imaging technique.

Matrix-Mediated Biomineralization in Marine Mollusks: A Combined Transmission Electron Microscopy and Focused Ion Beam Approach

2011 ◽  
Vol 17 (2) ◽  
pp. 220-225 ◽  
Author(s):  
Martin Saunders ◽  
Charlie Kong ◽  
Jeremy A. Shaw ◽  
Peta L. Clode
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Focused Ion Beam ◽  
Ion Beam ◽  
High Strength ◽  
Organic Matrix ◽  
Dark Field ◽  
Transmission Electron ◽  
Annular Dark Field ◽  
The Relationship

AbstractThe teeth of the marine mollusk Acanthopleura hirtosa are an excellent example of a complex, organic, matrix-mediated biomineral, with the fully mineralized teeth comprising layers of iron oxide and iron oxyhydroxide minerals around a calcium apatite core. To investigate the relationship between the various mineral layers and the organic matrix fibers on which they grew, sections have been prepared from specific features in the teeth at controlled orientations using focused ion beam processing. Compositional and microstructural details of heterophase interfaces, and the fate of the organic matrix fibers within the mineral layers, can then be analyzed by a range of transmission electron microscopy (TEM) techniques. Energy-filtered TEM highlights the interlocking nature of the various mineral phases, while high-angle annular dark-field scanning TEM imaging demonstrates that the organic matrix continues to exist in the fully mineralized teeth. These new insights into the structure of this complex biomaterial are an important step in understanding the relationship between its structural and physical properties and may help explain its high strength and crack-resistance behavior.

Imaging dislocations with an annular dark-field detector

1992 ◽  
Vol 50 (2) ◽  
pp. 1224-1225 ◽  
Author(s):  
J. Liu ◽  
J. M. Cowley
Keyword(s):  
Supported Catalysts ◽  
Dark Field ◽  
Contrast Effects ◽  
Thermal Diffuse Scattering ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Active Research ◽  
Thermal Diffuse

High-angle annular dark-field (HAADF) scanning transmission electron microscopy (STEM) has been recently the subject of active research because of its successful applications to the characterization of supported catalysts, interface problems in MBE grown semiconductors, superconductors and X-ray multilayers. The characteristics of HAADF images are different from those of the TEM images. For perfect single crystals the HAADF signal is mainly generated from thermal diffuse scattering. HAADF technique has also been used to study dopant contrast effects in semiconductors and dislocations have also been observed with an ADF detector. In this paper we report a study of dislocation contrasts and their dependence on the inner collection angle of the ADF detector.The STEM instrument used for the observations was the HB5 from VG Microscopes, Ld., modified by the addition of an ultra-high resolution pole piece (Cs = 0.8 mm) and a two-dimensional detector system. Post specimen lenses and various beam stops were used to change the inner (α) and outer (β) collection angles of the ADF detector.

Origin of the superstructure elucidated by atomic resolution HAADF-STEM and HREM in the Ce10W22O81lanthanide tungstate phase

2018 ◽  
Vol 51 (2) ◽  
pp. 344-350 ◽  
Author(s):  
Loïc Patout ◽  
Abdelali Hallaoui ◽  
Thomas Neisius ◽  
Andrea P. C. Campos ◽  
Christian Dominici ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
High Resolution Electron Microscopy ◽  
Dark Field ◽  
Atomic Resolution ◽  
Orthorhombic Unit Cell ◽  
Transmission Electron ◽  
New Information ◽  
Resolution Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

The present paper provides new information on the attribution of the cationic sites of the orthorhombic Ce10W22O81crystal phase prepared in the CeO2–Ce2O3–WO3ternary system. Atomic resolution HAADF-STEM (high-angle annular dark-field scanning transmission electron microscopy) and HREM (high-resolution electron microscopy) investigations have highlighted the presence of two mixed columns of Ce and W cations along theaaxis that were previously assigned to pure W cations in the asymmetric unit. This discovery explains the presence of a commensurate superstructure doubling the orthorhombic unit-cell lengthao.

Incoherent Stem Imaging at 1.5 Å Resolution With A 200 Kv FEGTEM

1999 ◽  
Vol 5 (S2) ◽  
pp. 610-611
Author(s):  
E.M. James ◽  
N.D. Browning
Keyword(s):  
Spatial Resolution ◽  
Image Interpretation ◽  
Dark Field ◽  
Contrast Imaging ◽  
Contrast Method ◽  
Transmission Electron ◽  
Annular Dark Field ◽  
Z Contrast ◽  
First Time ◽  
Electron Energy Loss

Here we demonstrate sub- 1.5 Å resolution in compositionally sensitive high-angle annular dark-field (HAADF) (“Z-contrast”) imaging. For the first time this has been achieved on a 200 kV field-emission transmission electron microscope (FEGTEM), the JEOL JEM-2010F. With a Gatan imaging filter, this type of instrument is then capable of both analytical imaging and electron energy-loss spectroscopy at similar spatial resolution as in the 300 kV dedicated STEM.The Z-contrast imaging technique has a spatial resolution given by the size of the electron probe. When used to image periodic specimens and their defects, the effective incoherent nature of the Z-contrast method leads to higher resolution for given lens Cs, higher sensitivity to atomic number and easier qualitative image interpretation than in HRTEM.In practice, the ability to form a small (atomic resolution) probe depends on the brightness of the electron source, and achieving low enough levels of mechanical and electrical instabilities that otherwise incoherently broaden the probe.

A Novel TEM Technique for Characterizing As-Grown CVD Diamond Films

1991 ◽  
Vol 49 ◽  
pp. 956-957 ◽  
Author(s):  
Z.L. Wang ◽  
J. Bentley ◽  
R.E. Clausing ◽  
L. Heatherly ◽  
L.L. Horton
Keyword(s):  
Diamond Films ◽  
Chemical Vapor ◽  
Growth Direction ◽  
Dark Field ◽  
Growth Surface ◽  
Specimen Preparation ◽  
Transmission Electron ◽  
Diffraction Patterns ◽  
First Time ◽  
Microstructural Studies

Microstructural studies by transmission electron microscopy (TEM) of diamond films grown by chemical vapor deposition (CVD) usually involve tedious specimen preparation. This process has been avoided with a technique that is described in this paper. For the first time, thick as-grown diamond films have been examined directly in a conventional TEM without thinning. With this technique, the important microstructures near the growth surface have been characterized. An as-grown diamond film was fractured on a plane containing the growth direction. It took about 5 min to prepare a sample. For TEM examination, the film was tilted about 30-45° (see Fig. 1). Microstructures of the diamond grains on the top edge of the growth face can be characterized directly by transmitted electron bright-field (BF) and dark-field (DF) images and diffraction patterns.

Design of a new objective lens for an HB-501A STEM

1991 ◽  
Vol 49 ◽  
pp. 416-417
Author(s):  
Earl J. Kirkland ◽  
Robert J. Keyse
Keyword(s):  
High Resolution ◽  
Spherical Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Objective Lens ◽  
Specimen Holder ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
High Resolution Microscopy

An ultra-high resolution pole piece with a coefficient of spherical aberration Cs=0.7mm. was previously designed for a Vacuum Generators HB-501A Scanning Transmission Electron Microscope (STEM). This lens was used to produce bright field (BF) and annular dark field (ADF) images of (111) silicon with a lattice spacing of 1.92 Å. In this microscope the specimen must be loaded into the lens through the top bore (or exit bore, electrons traveling from the bottom to the top). Thus the top bore must be rather large to accommodate the specimen holder. Unfortunately, a large bore is not ideal for producing low aberrations. The old lens was thus highly asymmetrical, with an upper bore of 8.0mm. Even with this large upper bore it has not been possible to produce a tilting stage, which hampers high resolution microscopy.

Intergrowth of niobium tungsten oxides of the tetragonal tungsten bronze type

2020 ◽  
Vol 75 (11) ◽  
pp. 913-919
Author(s):  
Frank Krumeich
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Tungsten Bronze ◽  
Structural Complexity ◽  
Dark Field ◽  
Tetragonal Tungsten Bronze ◽  
Tungsten Oxides ◽  
Transmission Electron ◽  
Scanning Transmission

AbstractSince the 1970s, high-resolution transmission electron microscopy (HRTEM) is well established as the most appropriate method to explore the structural complexity of niobium tungsten oxides. Today, scanning transmission electron microscopy (STEM) represents an important alternative for performing the structural characterization of such oxides. STEM images recorded with a high-angle annular dark field (HAADF) detector provide not only information about the cation positions but also about the distribution of niobium and tungsten as the intensity is directly correlated to the local scattering potential. The applicability of this method is demonstrated here for the characterization of the real structure of Nb7W10O47.5. This sample contains well-ordered domains of Nb8W9O47 and Nb4W7O31 besides little ordered areas according to HRTEM results. Structural models for Nb4W7O31 and twinning occurring in this phase have been derived from the interpretation of HAADF-STEM images. A remarkable grain boundary between well-ordered domains of Nb4W7O31 and Nb8W9O47 has been found that contains one-dimensionally periodic features. Furthermore, short-range order observed in less ordered areas could be attributed to an intimate intergrowth of small sections of different tetragonal tungsten bronze (TTB) based structures.

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