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.

TEM Z-contrast imaging with wide-angle hollow-cone illumination

1990 ◽  
Vol 48 (4) ◽  
pp. 400-401
Author(s):  
J. Bentley ◽  
K. B. Alexander ◽  
Z. L. Wang
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Dark Field ◽  
Wide Angle ◽  
Hollow Cone ◽  
Contrast Imaging ◽  
Field Mode ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Z Contrast

High resolution scanning transmission electron microscopy (STEM) images with contrast sensitive to atomic number (Z-contrast) have been obtained with the use of a high-angle annular detector. The equivalent conventional transmission electron microscopy (TEM) dark-field mode reciprocally related to Z-contrast STEM is wide-angle hollow-cone illumination with an on-axis objective aperture. There are two ways to obtain hollow cone illumination; with an annular condenser aperture or by conically scanning the beam tilt coils. As in the case of STEM Z-contrast imaging, resolution with hollow-cone illumination should theoretically be higher than for phase contrast imaging in the same instrument.Philips CM30/STEM, CM12/STEM, and EM400T/FEG/STEM instruments have been used to investigate this imaging technique. The conical illumination dark-field mode is standard on the CM series and was implemented with a hybrid diffraction unit on the EM400. Commercial (SPI Supplies #1780) copper annular apertures with inner and outer diameters of 600 and 900 μm, respectively, spot welded to suitable supports for use as condenser apertures, resulted in cone angles too small to give good Z-contrast in the microprobe mode, because there is still a large diffraction contrast contribution.

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).

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

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].

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.

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

2005 ◽  
Vol 876 ◽  
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.

Atomic-scale structural and compositional analyses of Ruddlesden-Popper planar faults in AO-excess SrTiO3 (A = Sr2+, Ca2+, Ba2+) ceramics

2009 ◽  
Vol 24 (8) ◽  
pp. 2596-2604 ◽  
Author(s):  
Sašo Šturm ◽  
Makoto Shiojiri ◽  
Miran Čeh
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Dark Field ◽  
Atomic Scale ◽  
Transmission Electron ◽  
Initial Stage ◽  
Final Microstructure ◽  
Scanning Transmission ◽  
The Matrix ◽  
Annular Dark Field

The microstructure in AO-excess SrTiO3 (A = Sr2+, Ca2+, Ba2+) ceramics is strongly affected by the formation of Ruddlesden-Popper fault–rich (RP fault) lamellae, which are coherently intergrown with the matrix of the perovskite grains. We studied the structure and chemistry of RP faults by applying quantitative high-resolution transmission electron microscopy and high-angle annular dark-field scanning transmission electron microscopy analyses. We showed that the Sr2+ and Ca2+ dopant ions form RP faults during the initial stage of sintering. The final microstructure showed preferentially grown RP fault lamellae embedded in the central part of the anisotropic perovskite grains. In contrast, the dopant Ba2+ ions preferably substituted for Sr2+ in the SrTiO3 matrix by forming a BaxSr1−xTiO3 solid solution. The surplus of Sr2+ ions was compensated structurally in the later stages of sintering by the formation of SrO-rich RP faults. The resulting microstructure showed RP fault lamellae located at the surface of equiaxed BaxSr1-xTiO3 perovskite grains.

scholarly journals Ru Catalyst Encapsulated into the Pores of MIL-101 MOF: Direct Visualization by TEM

Materials ◽  
2021 ◽  
Vol 14 (16) ◽  
pp. 4531
Author(s):  
Maria Meledina ◽  
Geert Watson ◽  
Alexander Meledin ◽  
Pascal Van Der Voort ◽  
Joachim Mayer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Dark Field ◽  
Catalyst Nanoparticles ◽  
Ru Catalyst ◽  
Ru Nanoparticles ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

Ru catalyst nanoparticles were encapsulated into the pores of a Cr-based metal-organic framework (MOF)—MIL-101. The obtained material, as well as the non-loaded MIL-101, were investigated down to the atomic scale by annular dark-field scanning transmission electron microscopy using low dose conditions and fast image acquisition. The results directly show that the used wet chemistry loading approach is well-fitted for the accurate embedding of the individual catalyst nanoparticles into the cages of the MIL-101. The MIL-101 host material remains crystalline after the loading procedure, and the encapsulated Ru nanoparticles have a metallic nature. Annular dark field scanning transmission electron microscopy, combined with EDX mapping, is a perfect tool to directly characterize both the embedded nanoparticles and the loaded nanoscale MOFs. The resulting nanostructure of the material is promising because the Ru nanoparticles hosted in the MIL-101 pores are prevented from agglomeration—the stability and lifetime of the catalyst could be improved.

scholarly journals Synthesis of nickel/gallium nanoalloys using a dual-source approach in 1-alkyl-3-methylimidazole ionic liquids

2019 ◽  
Vol 10 ◽  
pp. 1754-1767
Author(s):  
Ilka Simon ◽  
Julius Hornung ◽  
Juri Barthel ◽  
Jörg Thomas ◽  
Maik Finze ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Photoelectron Spectroscopy ◽  
Dark Field ◽  
X Ray ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Dual Source ◽  
Induced Decomposition

NiGa is a catalyst for the semihydrogenation of alkynes. Here we show the influence of different dispersion times before microwave-induced decomposition of the precursors on the phase purity, as well as the influence of the time of microwave-induced decomposition on the crystallinity of the NiGa nanoparticles. Microwave-induced co-decomposition of all-hydrocarbon precursors [Ni(COD)2] (COD = 1,5-cyclooctadiene) and GaCp* (Cp* = pentamethylcyclopentadienyl) in the ionic liquid [BMIm][NTf2] selectively yields small intermetallic Ni/Ga nanocrystals of 5 ± 1 nm as derived from transmission electron microscopy (TEM) and high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) and supported by energy-dispersive X-ray spectrometry (EDX), selected-area energy diffraction (SAED) and X-ray photoelectron spectroscopy (XPS). NiGa@[BMIm][NTf2] catalyze the semihydrogenation of 4-octyne to 4-octene with 100% selectivity towards (E)-4-octene over five runs, but with poor conversion values. IL-free, precipitated NiGa nanoparticles achieve conversion values of over 90% and selectivity of 100% towards alkene over three runs.

Sign in / Sign up

Export Citation Format

Share Document