The principles and interpretation of annular dark-field Z-contrast imaging

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,

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Incoherent High-Resolution Z-Contrast Imaging of Silicon and Gallium Arsenide Using HAADF-STEM

MRS Proceedings ◽

10.1557/proc-589-185 ◽

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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Z-Contrast Imaging of Heavy Metal Particles Supported in A Zeolitic Matrix Via High-Resolution Stem

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100125920 ◽

1987 ◽

Vol 45 ◽

pp. 204-205

Author(s):

J. H. Butler ◽

G. M. Brown

Keyword(s):

High Resolution ◽

Incident Beam ◽

Dark Field ◽

Irradiation Damage ◽

Contrast Imaging ◽

Vacuum Oven ◽

Annular Dark Field ◽

Resolution Imaging ◽

Beam Currents ◽

Z Contrast

High resolution Imaging of zeolites is difficult because these materials are very susceptible to Irradiation damage. It is now well known that dehydrated samples are more stable under the electron beam. Thus the most successful high resolution studies of zeolites to date have been on samples which were freeze-fractured and subsequently dehydrated via heating in a vacuum oven. Electron microscopy was then performed using a combination of low Incident beam currents and sensitive detectors. One problem with this method is that zeolites fracture along cleavage planes and therefore are deposited on microscope grids In a particular orientation. This limits the range of viewing angles. Here we describe a method of sample preparation via ultramlctrotomy as well as the establishment of suitable FEG/STEM Imaging conditions which permit the observation of small (7-14 A diameter) Pt particles within Individual zeolite channels using the method of Z-contrast as applied with a high-angle annular dark field detector. This method allows observation over all crystalline orientations for relatively long exposures to the beam.

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High-Resolution Bright-Field and Dark-Field Hollow Cone Illumination

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100178938 ◽

1990 ◽

Vol 48 (1) ◽

pp. 36-37

Author(s):

R.A. Herring ◽

M.E. Twigg

Keyword(s):

Large Angle ◽

Dark Field ◽

Hollow Cone ◽

Contrast Imaging ◽

Lattice Image ◽

Dark Field Imaging ◽

Annular Dark Field ◽

Lattice Images ◽

Z Contrast ◽

Field Imaging

Hollow cone illumination using a large C2 blocked-aperture (bl apt) in the conventional TEM (CTEM) can remove the beams within the zero-order Laue zone (ZOLZ) thereby making lattice images more simply interpretable. Dark-field (DF) hollow cone illumination has the added advantage of enhancing the Z-contrast within the lattice image, since the electrons contributing to the image must be scattered over a large angle (approximately 10 mrad). Both of these imaging methods have been explored, using a 600 um C2 bl apt and objective aperture sizes of 70, 20 and 10 um, and are reported in this paper.Much interest has been generated by the report of Pennycook [1] on STEM Z-contrast imaging using annular dark-field. In earlier work ,it was noted that CTEM hollow cone imaging and STEM annular dark-field imaging are related via reciprocity [2] (Fig. 1). In addition, Zernike has shown the advantages of hollow cone illumination in optical phase-contrast microscopy [3]. The electron-optical analogues to these optical techniques are now possible because of the low Cs values achieved in modern TEMs.

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Structural Insights of Supported Nanoparticles By Z-Contrast and High Resolution Electron Microscopy

Microscopy and Microanalysis ◽

10.1017/s1431927600031585 ◽

2001 ◽

Vol 7 (S2) ◽

pp. 1102-1103

Author(s):

Judith C. Yang ◽

Erin Devlin ◽

William Rhodes ◽

Steven Bradley

Keyword(s):

Electron Microscopy ◽

Three Dimensional ◽

High Resolution Electron Microscopy ◽

Dark Field ◽

Contrast Imaging ◽

Essential Information ◽

Support Materials ◽

Annular Dark Field ◽

Z Contrast ◽

Structural Insights

A vital component to nanoparticle science will be the three dimensional (3-D) characterization of both structure and chemistry of these nanoparticles on their supports at the nanometer scale and below. to achieve this goal, quantitative Z-contrast and atomic resolution will provide essential information about their structure. Z-contrast imaging is ideal for imaging these large Z nanoparticles on low Z supports. in this proceedings, we present a quantitative Z-contrast method to determine number of atoms and a few examples of a combination of electron microscopy methods to gain structural insights into supported nanoparticle, such as Pt on different support materials, PtRu5 on C and Pt-Sn on SiO2.A relatively new and powerful method is to determine the number of atoms in a nanoparticle, by very high angle annular dark-field (HAADF) imaging or Z-contrast technique [1, 2]. We have shown that quantification of the absolute image intensity from very HAADF microscopy will provide the number of atoms in very small particles of high atomic number to ±2 atoms for Re6 nanoparticles supported on carbon [3].

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

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100131310 ◽

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.

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Incoherent Stem Imaging at 1.5 Å Resolution With A 200 Kv FEGTEM

Microscopy and Microanalysis ◽

10.1017/s1431927600016378 ◽

1999 ◽

Vol 5 (S2) ◽

pp. 610-611

Author(s):

E.M. James ◽

N.D. Browning

Keyword(s):

Spatial Resolution ◽

Image Interpretation ◽

Dark Field ◽

Contrast Imaging ◽

Contrast Method ◽

Transmission Electron ◽

Annular Dark Field ◽

Z Contrast ◽

First Time ◽

Electron Energy Loss

Here we demonstrate sub- 1.5 Å resolution in compositionally sensitive high-angle annular dark-field (HAADF) (“Z-contrast”) imaging. For the first time this has been achieved on a 200 kV field-emission transmission electron microscope (FEGTEM), the JEOL JEM-2010F. With a Gatan imaging filter, this type of instrument is then capable of both analytical imaging and electron energy-loss spectroscopy at similar spatial resolution as in the 300 kV dedicated STEM.The Z-contrast imaging technique has a spatial resolution given by the size of the electron probe. When used to image periodic specimens and their defects, the effective incoherent nature of the Z-contrast method leads to higher resolution for given lens Cs, higher sensitivity to atomic number and easier qualitative image interpretation than in HRTEM.In practice, the ability to form a small (atomic resolution) probe depends on the brightness of the electron source, and achieving low enough levels of mechanical and electrical instabilities that otherwise incoherently broaden the probe.

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Z-Contrast Imaging: Quantitative Aspects of the Dynamical Object Function.

Microscopy and Microanalysis ◽

10.1017/s1431927600033183 ◽

2000 ◽

Vol 6 (S2) ◽

pp. 138-139

Author(s):

B Rafferty ◽

S J Pennycook ◽

P D Nellist

Keyword(s):

Dark Field ◽

Bloch Wave ◽

Zone Axis ◽

Contrast Imaging ◽

Oriented Crystal ◽

Atomic Column ◽

Dynamical Object ◽

Annular Dark Field ◽

Structural Configurations ◽

Z Contrast

In this paper, we use a Bloch wave approach to show that the elastically scattered electrons from neighbouring atomic columns in a zone-axis oriented crystal contribute incoherently to a Z-contrast image regardless of the fact that we have coherent dynamical scattering from a stationary lattice with no absorption. This incoherent nature of the elastic scattering means that through the filtering of the ls-type Bloch states by the detector geometry we approach the Rutherford Z2 dependence of the column intensity for sufficiently large inner detector angle. Thus, annular dark-field (ADF) imaging provides us with a direct incoherent structure image of the atomic-column positions in a zone-axis oriented crystal.Bloch wave simulations were carried out at 300 kV for the 〈110〉 orientation of InAs (a = 6.06Å) with full, half and empty columns of In atoms. Calculations including 411-beams were carried out for each of the above structural configurations for a single incident partial plane wave vector parallel to the optic axis.

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The Effect of Substrates / Ligands on Metal Nanocatalysts Investigated By Quantitative Z-Contrast Imaging and High Resolution Electron Microscopy

MRS Proceedings ◽

10.1557/proc-876-r9.4/p6.4 ◽

2005 ◽

Vol 876 ◽

Cited By ~ 1

Author(s):

Huiping Xu ◽

Laurent Menard ◽

Anatoly Frenkel ◽

Ralph Nuzzo ◽

Duane Johnson ◽

...

Keyword(s):

Electron Microscopy ◽

High Resolution ◽

Three Dimensional ◽

High Resolution Electron Microscopy ◽

Dark Field ◽

Contrast Imaging ◽

Mixed Ligands ◽

Resolution Electron ◽

Annular Dark Field ◽

Z Contrast

AbstractOur direct density function-based simulations of Ru-, Pt- and mixed Ru-Pt clusters on carbon-based supports reveal that substrates can mediate the PtRu5 particles [1]. Oblate structure of PtRu5 on C has been found [2]. Nevertheless, the cluster-substrate interface interactions are still unknown. In this work, we present the applications of combinations of quantitative z-contrast imaging and high resolution electron microscopy in investigating the effect of different substrates and ligand shells on metal particles. Specifically, we developed a relatively new and powerful method to determine numbers of atoms in a nanoparticle as well as three-dimensional structures of particles including size and shape of particles on the substrates by very high angle (~96mrad) annular dark-field (HAADF) imaging [2-4] techniques. Recently, we successfully synthesize icosahedra Au13 clusters with mixed ligands and cuboctahedral Au13 cores with thiol ligands, which have been shown by TEM to be of sub-nanometer size (0.84nm) and highly monodisperse narrow distribution. X-ray absorption and UV-visible spectra indicate many differences between icosahedra and cuboctahedral Au13 cores. Particles with different ligands show different emissions and higher quantum efficiency has been found in Au11 (PPH3) SC12)2C12. We plan to deposit those ligands-protected gold clusters onto different substrates, such as, TiO2 and graphite, etc. Aforementioned analysis procedure will be performed for those particles on the substrates and results will be correlated with that of our simulations and activity properties. This approach will lead to an understanding of the cluster-substrates relationship for consideration in real applications.

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

Journal of Nanomaterials ◽

10.1155/2013/679638 ◽

2013 ◽

Vol 2013 ◽

pp. 1-6 ◽

Cited By ~ 1

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.

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