Incoherent Imaging by Z-Contrast Stem: Towards 1Å Resolution

1994 ◽  
Vol 332 ◽  
Author(s):  
S. J. Pennycook ◽  
D. E. Jesson ◽  
A. J. Mcgibbon
Keyword(s):  
Phonon Scattering ◽  
Scanning Transmission Electron Microscope ◽  
Complex Materials ◽  
Intrinsic Resolution ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Detector Geometry ◽  
Incoherent Imaging ◽  
Z Contrast ◽  
Contrast Image

ABSTRACTBy averaging phase correlations between scattered electrons a high angle detector in the scanning transmission electron microscope (STEM) can provide an incoherent, Z-contrast image at atomic resolution. Phase coherence is effectively destroyed through a combination of detector geometry (transverse incoherence) and phonon scattering (longitudinal incoherence). Besides having a higher intrinsic resolution, incoherent imaging offers the possibility of robust reconstruction to higher resolutions, provided that some lower frequency information is present in the image. This should have value for complex materials and regions of complex atomic arrangements such as grain boundaries. Direct resolution of the GaAs sublattice with a 300kV is demonstrated.

Z-Contrast Imaging in the Scanning Transmission Electron Microscope

1995 ◽  
Vol 1 (6) ◽  
pp. 231-251 ◽  
Author(s):  
S.J. Pennycook ◽  
D.E. Jesson ◽  
M.F. Chisholm ◽  
N.D. Browning ◽  
A.J. McGibbon ◽  
...  
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Entropy Analysis ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Angle Scattering ◽  
Scanning Transmission ◽  
Recent Developments ◽  
Annular Detector ◽  
Incoherent Imaging ◽  
Z Contrast

Z-contrast STEM using an annular detector can provide an intuitively interpretable, column-by-column, compositional map of crystals. Incoherent imaging reduces dynamical effects to second order so that the map directly reflects the positions of the atomic columns and their relative high-angle scattering power. This article outlines how these characteristics arise, presents some examples of the insights available from a direct image, and discusses recent developments of atomic-resolution microanalysis, direct structure retrieval by maximum entropy analysis, and Z-contrast imaging at 1.4 Å resolution using a 300-kV STEM.

Z-contrast Imaging in an Aberration-corrected Scanning Transmission Electron Microscope

2000 ◽  
Vol 6 (4) ◽  
pp. 343-352 ◽  
Author(s):  
S.J. Pennycook ◽  
B. Rafferty ◽  
P.D. Nellist
Keyword(s):  
Spherical Aberration ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Zone Axis ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Contrast Image ◽  
Aberration Corrected

AbstractWe show that in the limit of a large objective (probe-forming) aperture, relevant to a spherical aberration corrected microscope, the Z-contrast image of a zone-axis crystal becomes an image of the 1s Bloch states. The limiting resolution is therefore the width of the Bloch states, which may be greater than that of the free probe. Nevertheless, enormous gains in image quality are expected from the improved contrast and signal-to-noise ratio. We present an analytical channeling model for the thickness dependence of the Z-contrast image in a zone-axis crystal, and show that, at large thicknesses, columnar intensities become proportional to the mean square atomic number, Z2.

Z-contrast Imaging in an Aberration-corrected Scanning Transmission Electron Microscope

2000 ◽  
Vol 6 (4) ◽  
pp. 343-352 ◽  
Author(s):  
S.J. Pennycook ◽  
B. Rafferty ◽  
P.D. Nellist
Keyword(s):  
Spherical Aberration ◽  
Signal To Noise Ratio ◽  
Scanning Transmission Electron Microscope ◽  
Zone Axis ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Contrast Image ◽  
Aberration Corrected

Abstract We show that in the limit of a large objective (probe-forming) aperture, relevant to a spherical aberration corrected microscope, the Z-contrast image of a zone-axis crystal becomes an image of the 1s Bloch states. The limiting resolution is therefore the width of the Bloch states, which may be greater than that of the free probe. Nevertheless, enormous gains in image quality are expected from the improved contrast and signal-to-noise ratio. We present an analytical channeling model for the thickness dependence of the Z-contrast image in a zone-axis crystal, and show that, at large thicknesses, columnar intensities become proportional to the mean square atomic number, Z2.

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.

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.

SiO2 Formation at the Aluminum Oxide/Si(100) Interface

2002 ◽  
Vol 747 ◽  
Author(s):  
A. Roy Chowdhuri ◽  
C. G. Takoudis ◽  
R. F. Klie ◽  
N. D. Browning
Keyword(s):  
Electron Microscope ◽  
Aluminum Oxide ◽  
Energy Loss ◽  
Electron Energy ◽  
Transmission Electron Microscope ◽  
Scanning Transmission Electron Microscope ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Electron Energy Loss

ABSTRACTThin films of aluminum oxide were deposited on clean Si(100) substrates using trimethylaluminum and oxygen at 300°C. Infrared spectroscopic and x-ray photoelectron spectroscopic analyses of these films showed no aluminum silicate or SiO2 phase formation at the film/substrate interface. The O/Al ratio in the as deposited film was found to be higher than that in stoichiometric Al2O3. On annealing the as deposited samples in Ar at higher temperatures, a peak due to the transverse optical phonon for the Si-O-Si stretching mode appeared in the infrared spectra. A combination of Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope confirmed that the annealed samples developed a layer of silicon dioxide at the aluminum oxide-Si interface. Z-contrast images and electron energy loss spectra, obtained while heating the sample inside the scanning transmission electron microscope were used to follow the interfacial SiO2 formation.

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.

Aberration-corrected scanning transmission electron microscopy: from atomic imaging and analysis to solving energy problems

2009 ◽  
Vol 367 (1903) ◽  
pp. 3709-3733 ◽  
Author(s):  
S. J. Pennycook ◽  
M. F. Chisholm ◽  
A. R. Lupini ◽  
M. Varela ◽  
A. Y. Borisevich ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Single Atom ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast ◽  
Contrast Image ◽  
Aberration Corrected

The new possibilities of aberration-corrected scanning transmission electron microscopy (STEM) extend far beyond the factor of 2 or more in lateral resolution that was the original motivation. The smaller probe also gives enhanced single atom sensitivity, both for imaging and for spectroscopy, enabling light elements to be detected in a Z-contrast image and giving much improved phase contrast imaging using the bright field detector with pixel-by-pixel correlation with the Z-contrast image. Furthermore, the increased probe-forming aperture brings significant depth sensitivity and the possibility of optical sectioning to extract information in three dimensions. This paper reviews these recent advances with reference to several applications of relevance to energy, the origin of the low-temperature catalytic activity of nanophase Au, the nucleation and growth of semiconducting nanowires, and the origin of the eight orders of magnitude increased ionic conductivity in oxide superlattices. Possible future directions of aberration-corrected STEM for solving energy problems are outlined.

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