High-angle annular dark-field stem imaging: more than just z-contrast!

1992 ◽  
Vol 50 (2) ◽  
pp. 1336-1337
Author(s):  
D.D. Perovic
Keyword(s):  
Experimental Studies ◽  
Dark Field ◽  
High Angle ◽  
Contrast Imaging ◽  
Atomic Displacements ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Stem Image ◽  
Incoherent Imaging ◽  
Z Contrast

Following the development of dedicated scanning-transmission electron microscopy (STEM), significant advances have been made in atomic number (Z)-contrast imaging using a high-angle annular detector (HAAD). With the exclusion of coherent (ie. Bragg) scattering, the HAAD allows for truly incoherent imaging with high compositional sensitivity approaching the simple Z2-dependence of unscreened Rutherford scattering. However, recent experimental studies have indicated that HAADF-STEM imaging is not always straightforward. For example, Fig. 1 shows a digitally acquired HAADF-STEM image of a (B,As)-doped Si multilayer. The B-doped (˜ 0.7 at.%B) layers appear significantly brighter than the adjacent Si matrix in contradiction with a simple Z-contrast argument. It was found that an increase in incoherent scattering from the B-doped regions results due to the presence of atomic displacements of the surrounding Si atoms which effectively behave as “frozen-in” static phonons. Accordingly, the B-doped layers quasi-elastically scatter electrons to relatively high angles giving rise to enhanced contrast in HAADF.

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.

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.

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.

Quantification of Compositional Modulations in Self-Assembled Multisheet (Cd, Zn, Mn)Se Quantum Dot Structures

2001 ◽  
Vol 7 (S2) ◽  
pp. 202-203
Author(s):  
T. Topuria ◽  
P. Möck ◽  
N.D. Browning ◽  
L.V. Titova ◽  
M. Dobrowolska ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Imaging Technique ◽  
Optoelectronic Device ◽  
Scanning Transmission Electron Microscope ◽  
Contrast Imaging ◽  
Cdse Qds ◽  
Scanning Transmission ◽  
Device Applications ◽  
Incoherent Imaging ◽  
Z Contrast

CdSe/ZnSe based semiconductor quantum dot (Q D) structures are a promising candidate for optoelectronic device applications. However, key to the luminescence properties is the cation distribution and ordering on the atomic level within the CdSe QDs/agglomerates. Here the Z contrast imaging technique in the scanning transmission electron microscope (STEM) is employed to study multisheet (Cd,Zn,Mn)Se QD structures. Since Z-contrast is an incoherent imaging technique, problems associated with strain contrast in conventional TEM are avoided an accurate size and composition determinations can be made.For this work we used a JEOL JEM 201 OF field emission STEM/TEM. The sample was grown by molecular beam epitaxy in order to achieve vertical self-ordering of Cd rich quasi-2D platelet This sample comprises 8 sequences of 10 ML (2.83 nm)Zn0.9Mn0.1Se cladding layer and 0.3 ML (0.09 nm) CdSe sheet, a further 10 ML of Zn0.9Mn0.1Se, and a 50 nm ZnSe capping layer.

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