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.

Rapid and Semi-automated Method for Analysis of the Number of Atoms of Ultra-small Platinum Clusters on Carbon

2000 ◽  
Vol 6 (4) ◽  
pp. 353-357
Author(s):  
J.C. Yang ◽  
S. Bradley ◽  
J.M. Gibson
Keyword(s):  
Three Dimensional ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Automated Method ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dimensional Shape ◽  
Three Dimensional Shape

Abstract Very high angle (~100 mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the number of atoms in a cluster on a support material. We have developed a computer program which will automatically find the location of the particles and then integrate the intensity to find the number of atoms per cluster. We have examined ultra-small Pt clusters on a C substrate by this novel mass-spectroscopic technique. We discovered that the Pt clusters maintain their three-dimensional shape, and are probably spherical.

An Automated and Rapid Process for Determining Number of Atoms in Supported Ultra-Small Metal Clusters

1999 ◽  
Vol 5 (S2) ◽  
pp. 696-697
Author(s):  
J.C. Yang ◽  
S. Bradley ◽  
J.M. Gibson
Keyword(s):  
Amorphous Carbon ◽  
Cross Sections ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Measured Intensity ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Scattering Cross Sections

Since heterogeneous catalysis depends on surface chemistry, insights into the structure of supported catalytic materials is vital for understanding catalysis. We have developed a mass spectroscopic technique using very high angle annular dark field images in a scanning transmission electron microscope (STEM), that gives the number of atoms per cluster. We have also developed a robust interactive computer program to analyze these images rapidly. In this proceeding, we will present our method and results on analyzing ultra-small and dispersed Pt clusters on amorphous carbon, as well as our preliminary results of Pt on γ-A12 O3.The ultra-small Pt clusters on the amorphous carbon Cu grid were made by a proprietary technique. Imaging for the STEM-based mass-spectroscopic technique was performed on a Field Emission Gun (FEG) VG HB601 STEM operated at l00kV. The absolute measured intensity from the clusters were converted to scattering cross-sections, which can then be converted to number of atoms: More details of this method can be found in Singhal, Yang and Gibson.

A Novel Stem-Based Mass Spectroscopic Technique: Applications to Catalytic Materials

1996 ◽  
Vol 466 ◽  
Author(s):  
J. C. Yang ◽  
A. Singhal ◽  
S. Bradley ◽  
J. M. Gibson
Keyword(s):  
Elastic Scattering ◽  
Cross Sections ◽  
Absolute Intensity ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Scattering Cross ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Scattering Cross Sections

ABSTRACTVery high angle (∼ 100mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the mass of a cluster on a support material. With knowledge of the annular dark field (ADF) detector efficiency, the absolute intensity of very HAADF images can be converted to elastic scattering cross-sections. By comparing the theoretical and experimental elastic scattering cross-sections, the number of atoms can be determined. Statistical measurement of absolute cross-sections from Re-6 clusters show good agreement with theoretical cross-sections. The experimental error corresponded to ±2 Re atoms. Our experiments demonstrate the exceptional stability of the Re-6 organometallic compound relative to Re-8 clusters. This technique is presently being applied to Pt clusters.

Three Dimensional Ultra-Small Pt Clusters on Carbon As Studied by A Novel Stem Technique

1998 ◽  
Vol 549 ◽  
Author(s):  
J. C. Yang ◽  
S. Bradley ◽  
J. M. Gibson
Keyword(s):  
Three Dimensional ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dimensional Shape ◽  
Three Dimensional Shape ◽  
Very High

AbstractVery 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 in a cluster on a support material. We have developed a computer program which will automatically find the location of the particles and then integrate the intensity to find the number of atoms per cluster. We have examined ultra-small Pt clusters on a C substrate by this novel mass-spectroscopic technique. We discovered that the Pt clusters maintain their three-dimensional shape, and are probably spherical in shape.

Rapid and Semi-automated Method for Analysis of the Number of Atoms of Ultra-small Platinum Clusters on Carbon

2000 ◽  
Vol 6 (4) ◽  
pp. 353-357 ◽  
Author(s):  
J.C. Yang ◽  
S. Bradley ◽  
J.M. Gibson
Keyword(s):  
Three Dimensional ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Automated Method ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dimensional Shape ◽  
Three Dimensional Shape

AbstractVery high angle (~100 mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the number of atoms in a cluster on a support material. We have developed a computer program which will automatically find the location of the particles and then integrate the intensity to find the number of atoms per cluster. We have examined ultra-small Pt clusters on a C substrate by this novel mass-spectroscopic technique. We discovered that the Pt clusters maintain their three-dimensional shape, and are probably spherical.

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.

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