Z-Contrast in a Conventional TEM

1997 ◽  
Vol 3 (S2) ◽  
pp. 1147-1148 ◽  
Author(s):  
E.J. Kirkland
Keyword(s):  
Dark Field ◽  
Small Probe ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Commercial Supplier ◽  
Annular Detector ◽  
Z Contrast ◽  
Contrast Image ◽  
Transmission Microscope

Z-contrast produces an image that varies strongly with atomic number and offers limited chemical sensitivity. The annular dark field scanning transmission microscope (ADF-STEM) has recently been used to produce Z-contrast images at high resolution. In a STEM the electron beam is focused into a small probe at the specimen plane and scanned across the specimen. The electrons scattered at high angle are collected by an annular detector to produce a signal that approximately varies as Z11.5 to Z2. The only commercial supplier of dedicated STEM'S (VG-Microscopes, now Thermo) has recently discontinued production, so it is worth considering how to produce an equivalent Z-contrast image in a conventional transmission electron microscope (CTEM).The reciprocity theorem states that the STEM and CTEM are equivalent if the source and detector are interchanged (reciprocity hold for all orders of elastic scattering so it is not necessary to restrict this discussion to weakly scattering specimens).

Observing dislocations with ADF-STEM

1991 ◽  
Vol 49 ◽  
pp. 668-669
Author(s):  
Y. Huang ◽  
J. M. Cowley
Keyword(s):  
Material Science ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
High Angle ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Contrast Mechanism ◽  
Annular Dark Field ◽  
Annular Detector ◽  
Z Contrast

Scanning transmission electron microscopy (STEM) with a high angle annular detector has become a useful technique in material science. The atomic number sensitive contrast (Z-contrast) of the Annular Dark-Field (ADF) image is good for looking at the distribution of heavy elements in a relatively light substrate. In many cases the impurity distributions are substantially affected by the defects in the materials and their interaction with the impurities. Therefore it is also desirable to observe defects with ADF images. This is possible and has some advantages over normal STEM. We have studied the ADF imaging of dislocations, its contrast mechanism and visibility in the ADF image.

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,

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.

scholarly journals Z-Contrast STEM Imaging of Long-Range Ordered Structures in Epitaxially Grown CoPt Nanoparticles

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Kazuhisa Sato ◽  
Keigo Yanajima ◽  
Toyohiko J. Konno
Keyword(s):  
Intermediate Stage ◽  
Dark Field ◽  
Structural Domains ◽  
Ordered Structures ◽  
Axis Orientation ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Z Contrast ◽  
Variant Structure

We report on atomic structure imaging of epitaxial L10CoPt nanoparticles using chemically sensitive high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). Highly ordered nanoparticles formed by annealing at 973 K show single-variant structure with perpendicularc-axis orientation, while multivariant ordered domains are frequently observed for specimens annealed at 873 K. It was found that the (001) facets of the multivariant particles are terminated by Co atoms rather than by Pt, presumably due to the intermediate stage of atomic ordering. Coexistence of single-variant particles and multivariant particles in the same specimen film suggests that the interfacial energy between variant domains be small enough to form such structural domains in a nanoparticle as small as 4 nm in diameter.

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.

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.

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.

Resolution limits in annular dark-field STEM

1991 ◽  
Vol 49 ◽  
pp. 484-485
Author(s):  
Russell F. Loane ◽  
Peirong Xu ◽  
John Silcox
Keyword(s):  
Dark Field ◽  
Clear Understanding ◽  
Atomic Structures ◽  
Imaging Model ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Incoherent Imaging ◽  
Z Contrast ◽  
Better Than

Annular dark field scanning transmission electron microscopy (ADF STEM) is capable of resolving atomic structures with Z contrast. Better than 2 Å resolution at 100 kV has been demonstrated with a Cs of 1.3 mm and 0.7 mm. The images are apparently simple to interpret and change little with thickness or defocus. However, much of the reported work is qualitative, or semi-quantitative at best, so that the customarily adopted incoherent imaging model is not well established and a clear understanding of the limits (e.g., detectable AZ at a given ratio of spacing to resolution) is lacking. We present an exploration of such limits for the simple specimen, (100) InP, using quantitative ADF STEM and image simulation.

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.

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