Microdiffraction studies of small crystallites

1988 ◽  
Vol 46 ◽  
pp. 708-709
Author(s):  
S. A. Bradley ◽  
H. J. Robota
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Dark Field Image ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Angle Scattering ◽  
Dark Field Microscopy ◽  
Scanning Transmission ◽  
Annular Dark Field

Identification of nano-crystallites (<5 nm) on a high surface area support such as a catalyst is critical in the development of improved catalysts. Bright field imaging of small particles can be obscured by the phase contrast of the support. A common approach is to utilize annular dark field microscopy; however, wide angle scattering from the high surface area support can easily appear in the annular dark field image. Often one utilizes the energy dispersive detector to identify conclusively the nanosized metal crystallite, but this approach is troublesome when crystallites are very thin since counting times for imaging can become excessive. One technique for avoiding some of these difficulties is to utilize microdiffraction to identify the crystallite and then to image the crystallite by axial dark field microscopy.In the work reported here, the imaging was performed with a dedicated VG HB-5 scanning transmission electron microscope.

scholarly journals Fabrication of Maghemite Nanoparticles with High Surface Area

Nanomaterials ◽  
2019 ◽  
Vol 9 (7) ◽  
pp. 1004 ◽  
Author(s):  
Yulia Trushkina ◽  
Cheuk-Wai Tai ◽  
German Salazar-Alvarez
Keyword(s):  
Surface Area ◽  
High Surface ◽  
High Surface Area ◽  
Dark Field ◽  
Maghemite Nanoparticles ◽  
Dark Field Imaging ◽  
Transmission Electron ◽  
Powerful Approach ◽  
Scanning Transmission ◽  
Annular Dark Field

Maghemite nanoparticles with high surface area were obtained from the dehydroxylation of lepidocrocite prismatic nanoparticles. The synthesis pathway from the precursor to the porous maghemite nanoparticles is inexpensive, simple and gives high surface area values for both lepidocrocite and maghemite. The obtained maghemite nanoparticles contained intraparticle and interparticle pores with a surface area ca. 30 × 103 m2/mol, with pore volumes in the order of 70 cm3/mol. Both the surface area and pore volume depended on the heating rate and annealing temperature, with the highest value near the transformation temperature (180–250 °C). Following the transformation, in situ X-ray diffraction (XRD) allowed us to observe the temporal decoupling of the decomposition of lepidocrocite and the growth of maghemite. The combination of high-angle annular dark-field imaging using scanning transmission electron microscopy (HAADF-STEM) and surface adsorption isotherms is a powerful approach for the characterization of nanomaterials with high surface area and porosity.

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.

STEM measurement of subcellular water distributions

1993 ◽  
Vol 51 ◽  
pp. 568-569
Author(s):  
R.D. Leapman ◽  
S.Q. Sun ◽  
S-L. Shi ◽  
R.A. Buchanan ◽  
S.B. Andrews
Keyword(s):  
Water Content ◽  
Internal Standard ◽  
Dry Weight ◽  
Dry Mass ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Bulk Water ◽  
Inelastic Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

Recent advances in rapid-freezing and cryosectioning techniques coupled with use of the quantitative signals available in the scanning transmission electron microscope (STEM) can provide us with new methods for determining the water distributions of subcellular compartments. The water content is an important physiological quantity that reflects how fluid and electrolytes are regulated in the cell; it is also required to convert dry weight concentrations of ions obtained from x-ray microanalysis into the more relevant molar ionic concentrations. Here we compare the information about water concentrations from both elastic (annular dark-field) and inelastic (electron energy loss) scattering measurements.In order to utilize the elastic signal it is first necessary to increase contrast by removing the water from the cryosection. After dehydration the tissue can be digitally imaged under low-dose conditions, in the same way that STEM mass mapping of macromolecules is performed. The resulting pixel intensities are then converted into dry mass fractions by using an internal standard, e.g., the mean intensity of the whole image may be taken as representative of the bulk water content of the tissue.

Incoherent High-Resolution Z-Contrast Imaging of Silicon and Gallium Arsenide Using HAADF-STEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Y Kotaka ◽  
T. Yamazaki ◽  
Y Kikuchi ◽  
K. Watanabe
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Contrast Imaging ◽  
High Spatial Resolution Image ◽  
Transmission Electron ◽  
Eigen Value ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Convergent Beam ◽  
Z Contrast

AbstractThe high-angle annular dark-field (HAADF) technique in a dedicated scanning transmission electron microscope (STEM) provides strong compositional sensitivity dependent on atomic number (Z-contrast image). Furthermore, a high spatial resolution image is comparable to that of conventional coherent imaging (HRTEM). However, it is difficult to obtain a clear atomic structure HAADF image using a hybrid TEM/STEM. In this work, HAADF images were obtained with a JEOL JEM-2010F (with a thermal-Schottky field-emission) gun in probe-forming mode at 200 kV. We performed experiments using Si and GaAs in the [110] orientation. The electron-optical conditions were optimized. As a result, the dumbbell structure was observed in an image of [110] Si. Intensity profiles for GaAs along [001] showed differences for the two atomic sites. The experimental images were analyzed and compared with the calculated atomic positions and intensities obtained from Bethe's eigen-value method, which was modified to simulate HAADF-STEM based on Allen and Rossouw's method for convergent-beam electron diffraction (CBED). The experimental results showed a good agreement with the simulation results.

Direct observation ofB-site cation displacements in Pb-based complex perovskite relaxor oxides

2010 ◽  
Vol 44 (1) ◽  
pp. 111-121 ◽  
Author(s):  
K. Z. Baba-Kishi
Keyword(s):  
Long Range ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Unit Cells ◽  
Annular Dark Field ◽  
Pb Ions ◽  
Diffraction Patterns ◽  
Spatial Displacements

Electron diffraction patterns recorded using a scanning transmission electron microscope (STEM) from PbMg1/3Nb2/3O3(PMN) crystallites and PbZn1/3Nb2/3O3(PZN) crystals show weak and systematic continuous diffuse streaking along the 〈110〉 directions. Detailed high-angle annular dark-field (HAADF) images recordedviaan aberration-corrected STEM show that theB-site cations in PMN and PZN undergo correlated and long-range displacements towards the Pb2+ions on the (110) planes. The planarB-site displacement measured from the centres of the octahedra is about 0.3–0.5 Å in PMN and about 0.20–0.4 Å in PZN. In the HAADF images of the PMN crystallites and PZN crystals studied, there is insufficient evidence for systematic long-range planar displacements of the Pb2+ions. The observed Pb2+ion displacements in PMN and PZN appear randomly distributed, mostly displaced along 〈110〉 towards theB-site columns. There is also evidence of possible stress-related distortion in certain unit cells of PMN. In the relaxors studied, two distinct types of displacements were observed: one is the long-range planarB-site spatial displacement on the (110) planes, correlated with the Pb2+ions, possibly resulting in the observed diffuse streaking; the other is short-range Pb2+ion displacement on the (110) planes. The observed displacement status indicates a mutual attraction between the Pb ions and theB-site cations in which theBsites undergo the largest spatial displacements towards the Pb ions along 〈110〉.

Nano-Sized Catalytic Materials Investigated by a STEM-Based Mass Spectroscopic Technique

1997 ◽  
Vol 3 (S2) ◽  
pp. 443-444
Author(s):  
J. C. Yang ◽  
A. Singhal ◽  
S. Bradley ◽  
J. M. Gibson
Keyword(s):  
Bimetallic Catalyst ◽  
Structural Information ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Carbon Substrate ◽  
Support Material ◽  
Catalytic Materials ◽  
Scanning Transmission ◽  
Annular Dark Field

Knowledge of catalysts' sizes and shapes on their support material is crucial in understanding catalytic properties. With increasing interest in nanosized catalytic materials, it is vital to obtain structural information at the nanometer level in order to understand their catalytic behavior. We have recently demonstrated that very high angle (˜100mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the number of atoms of individual nano-sized clusters on a support material We are presently applying this technique to a bimetallic catalyst, PtRu5, where our data suggest that the shape of the PtRu5 particle is, surprisingly, oblate on the carbon substrate.PtRu5 is of interest for methanol oxidation for applications in batteries. PtRu5 compounds were produced by a molecular precursor method. Imaging was performed on a Field Emission Gun (FEG) Vacuum Generators HB501 STEM operated at 100kV.

High-angle annular dark-field STEM imaging of doped semiconductor layers

1991 ◽  
Vol 49 ◽  
pp. 704-705
Author(s):  
D.D. Perovic ◽  
J.H. Paterson
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
High Angle ◽  
Axis Orientation ◽  
Undoped Material ◽  
Transmission Electron ◽  
Ultrathin Layers ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
P Type

With the development of crystal growth techniques such as molecular beam epitaxy (MBE), it is now possible to fabricate modulation-doped superlattices consisting of alternating ultrathin layers of n-and/or p-type material abruptly separated by undoped material. At sufficiently high dopant concentrations these abrupt layers may be imaged in cross section by electron microscopy. Pennycook et al. and Treacy et al. have used high angle annular dark-field (HAAD) imaging in the scanning transmission electron microscope (STEM) to image low levels of dopants (∼1 at. %) in semiconductors. This work is concerned with imaging boron and arsenic doped layers in silicon at levels « 1 at.%.Fig. 1 shows a HAAD image of a B-Si superlattice at the <110> zone-axis orientation taken at 100 kV using a VG HB501UX STEM. The bright vertical layers are the B-doped regions, containing ∼4 x 1020 B/cm3. The horizontal lines are due to beam instability while the image was recorded. Fig.2 shows a line scan across the same superlattice, recorded by scanning the beam across the specimen in a direction perpendicular to the layers.

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