Imaging single platinum atoms on zeolites in the STEM

1990 ◽  
Vol 48 (4) ◽  
pp. 240-241
Author(s):  
Stephen B. Rice ◽  
Michael M. J. Treacy ◽  
Mark M. Disko
Keyword(s):  
Atomic Number ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Supported Metal Catalysts ◽  
Bright Field ◽  
Fourier Filtering ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Contrast Technique ◽  
Z Contrast

High angle annular dark-field (HAAD) imaging in the scanning transmission electron microscope has been shown in recent years to be a very effective tool in characterizing materials in which there are large differences in atomic number. Supported metal catalysts, in particular, have been explored extremely successfully using this Z-contrast technique. HAAD has very good sensitivity to high atomic number clusters on low atomic number supports, due to the approximately Z2 relationship. Furthermore, since the image contrast is due primarily to amplitude contrast, the resulting images are maps of mass thickness. Owing to the linear proportionality between intensity and the number of atoms probed, the intensity values integrated over metal clusters can be used as a measure of the cluster size.High resolution bright-field imaging is better suited for resolving structure in periodic specimens, and can be used to obtain structure images of zeolites. However, even with contrast enhancements such as Fourier filtering available from image processing, bright-field images are ineffective for detecting clusters containing fewer than about 20 Pt atoms in supports thicker than about 100Å. In comparison, we have demonstrated that the HAAD technique can be used successfully to detect single atoms of platinum on a 200Å thick zeolite support.

Prospects For Imaging of Single Dopant Atoms in Silicon by ADF Stem

1998 ◽  
Vol 4 (S2) ◽  
pp. 646-647
Author(s):  
Richard R. Vanfleet ◽  
John Silcox
Keyword(s):  
Atomic Number ◽  
Misfit Strain ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Technology Roadmap ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dopant Atoms ◽  
Z Contrast

The demands of the National Technology Roadmap for Semiconductors will necessitate measurement of dopant concentrations with greater spatial resolution than now possible. Current experimental and simulation experience indicate that Annular Dark Field (ADF) imaging in a Scanning Transmission Electron Microscope (STEM) should be able to determine dopant distributions with near atomic resolution. The ADF signal is derived from electrons diffusely scattered to high angles, resulting in contrast due to atomic number (Z-contrast) and defects in the crystal lattice. Thus, heavy atoms can be imaged by their Z-contrast and small atoms by the misfit strain induced in the silicon lattice. Atomic number scattering is proportional to Zn where n is between 1.5 and 1.9 depending upon the inner detector angle of the ADF detector.

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.

Calculations of Z-Contrast for organic and biological specimens

1983 ◽  
Vol 41 ◽  
pp. 284-285
Author(s):  
R.F. Egerton ◽  
M. Misra
Keyword(s):  
Atomic Number ◽  
Cross Sections ◽  
Phase Contrast ◽  
Detection System ◽  
Dark Field ◽  
Single Atom ◽  
Bright Field ◽  
Annular Dark Field ◽  
Z Contrast ◽  
Increasing Function

So-called "atomic-number contrast" is obtained in STEM by displaying a ratio signal formed by dividing the annular-dark-field signal Iad by the inelastic component Ii of the bright-field intensity (isolated by means of an electron spectrometer; see Fig. 1). Originally used for single-atom imaging, the technique has more recently been applied to polymer samples and biological tissue.We report here estimates of the ratio signal from organic specimens, based on the following assumptions:(1) That the specimen is amorphous and that phase contrast may be neglected for the electron-optical conditions and specimen features being considered; (2) That atomic cross sections may be used to estimate the amount of elastic and inelastic scattering. Modern calculations differ from simple Lenz theory in predicting that the cross section is not a smoothly-increasing function of atomic number (see Fig. 2), particularly for the 1ighter elements. (3) We assume a slightly idealized detection system in which all elastically scattered electrons contribute to Iad, while all electrons which have been inelastically (but not elastically) scattered contribute to Ii.

Theory of Lattice Resolution in High-angle Annular Dark-field Images

1997 ◽  
Vol 3 (1) ◽  
pp. 28-46 ◽  
Author(s):  
Adam Amali ◽  
Peter Rez
Keyword(s):  
Atomic Number ◽  
Large Angle ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Incoherent Scattering ◽  
Theoretical Interpretation ◽  
High Angle ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Lattice Resolution

Abstract: The theoretical interpretation of lattice resolution in high-angle annular dark-field images produced in a scanning transmission electron microscope (STEM) has been a subject of controversy. A first-order perturbation theoretical analysis is presented here, which shows that the contrast in the image arises from large-angle multiphonon, incoherent scattering, which is atomic number dependent. The lattice resolution is a consequence of coherently filling the objective aperture, and dynamical elastic diffraction preceding the large-angle multiphonon scattering is not a necessary requirement. Elastic scattering to the higher order Laue zone (HOLZ) is also shown to be negligible, compared with the incoherent scattering. Calculations from application of the theory are also presented. They show that lattice images formed using the high-angle annular dark-field detector are sensitive to atomic number and are relatively insensitive to defocus. Although high-angle annular dark-field lattice imaging appears to be simple, scattering into the high-angle detector can only be approximately described by an incoherent imaging model.

Observations of Pt-Ir on Al2O3 Catalysts Using a Fast Digital System Controlled STEM

1981 ◽  
Vol 39 ◽  
pp. 136-137 ◽  
Author(s):  
J. H. Butler
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Heavy Atoms ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
On Line ◽  
Imaging Mode ◽  
Z Contrast ◽  
Thermal Vibrations

The familiar Scanning Transmission Electron Microscope (STEM) technique of Z-contrast, used to image heavy atoms on amorphous supports, can be applied to the study of metal catalysts with only partial success. The contrast is reduced when crystalline systems are studied since a Bragg contribution is introduced in the standard annular dark-field collector. At large angles, the Bragg reflections diminish due to thermal vibrations; and the scattering cross section is approximately proportional to Z2. Thus scattering in this region is predominately Rutherford-like. The atomic number dependence of this high angle detectoro (HAD) signal makes it particularly suited for identifying small (20-50Å diameter) catalyst particles suspended in polycrystal line alumina.The experimental configuration for this imaging mode suggests concurrent acquisition of the HAD signal and the corresponding bright field signal , as on-line arithmetic of the two is necessary to optimize image contrast. In the conventional STEM it is impossible to detect the HAD signal because it is cut off by the specimen cartridge. Treacy, et al. have developed a sophisticated method for obtaining these signals.

Electron Microscopy Studies and Image Simulation of the YBa2Cu3O7−x/ BaF2 Interface

1994 ◽  
Vol 357 ◽  
Author(s):  
J. L. Lee ◽  
J. Silcox
Keyword(s):  
Significant Contribution ◽  
Wide Band ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Interface Plane ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Contrast Mechanism ◽  
Annular Dark Field ◽  
Z Contrast

AbstractImages of the YBa2Cu3OT7−x (YBCO) / BaF2 interface obtained with a scanning transmission electron microscope (STEM) show a relatively wide (∼40 Å) band of contrast at the interface, despite attempts to orient the interface plane parallel to the beam. Simulation of STEM annular dark field (ADF) images of several different interface geometries suggests that strain is the dominant cause of this wide band of contrast at the interface. In particular, it is the dislocations which run normal to the beam direction which make a significant contribution to the width of the contrast band in the case of this YBCO / BaF2 interface. A line scan taken across the interface using energy dispersive X-ray spectrometry (EDX) suggests that there is no significant Ba concentration at the interface, indicating that Z-contrast is not the primary contrast mechanism in these ADF images of the YBCO / BaF2 interface.

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.

Atomic resolution Z-contrast imaging of bulk crystal surfaces in Scanning Reflection Electron Microscopy

1990 ◽  
Vol 48 (4) ◽  
pp. 414-415
Author(s):  
Z. L. Wang ◽  
J. Bentley
Keyword(s):  
Electron Microscopy ◽  
Elastic Scattering ◽  
Dark Field ◽  
Contrast Imaging ◽  
Crystal Lattices ◽  
Small Probe ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Image Position ◽  
Z Contrast

The success of obtaining atomic-number-sensitive (Z-contrast) images in scanning transmission electron microscopy (STEM) has shown the feasibility of imaging composition changes at the atomic level. This type of image is formed by collecting the electrons scattered through large angles when a small probe scans across the specimen. The image contrast is determined by two scattering processes. One is the high angle elastic scattering from the nuclear sites,where ϕNe is the electron probe function centered at bp = (Xp, yp) after penetrating through the crystal; F denotes a Fourier transform operation; D is the detection function of the annular-dark-field (ADF) detector in reciprocal space u. The other process is thermal diffuse scattering (TDS), which is more important than the elastic contribution for specimens thicker than about 10 nm, and thus dominates the Z-contrast image. The TDS is an average “elastic” scattering of the electrons from crystal lattices of different thermal vibrational configurations,

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.

Sign in / Sign up

Export Citation Format

Share Document