Off-Axis STEM or TEM Holography Combined with Four-Dimensional Diffraction Imaging

2004 ◽  
Vol 10 (1) ◽  
pp. 9-15 ◽  
Author(s):  
J.M. Cowley
Keyword(s):  
Reference Beam ◽  
Transmission Function ◽  
Two Dimensional ◽  
Data Set ◽  
Ultrahigh Resolution ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Diffraction Imaging ◽  
Resolution Imaging ◽  
Dimensional Section

Ultrahigh-resolution imaging may be achieved using modifications of the off-axis holography scheme in a scanning transmission electron microscopy (STEM) instrument equipped with one or more electrostatic biprisms in the illuminating system. The resolution is governed by the diameter of a reference beam, reduced by channeling through a line of atoms in an atomic-focuser crystal. Alternatively, the off-axis holography may be combined with the Rodenburg method in which a four-dimensional data set is obtained by recording a nanodiffraction pattern from each point of the specimen as the incident beams are scanned. An ultrahigh-resolution image is derived by computer processing to give a particular two-dimensional section of this data set. The large amount of data recording and data processing involved with this method may be avoided if the two-dimensional section is derived by recording the hologram while the four beams produced by two perpendicular biprisms are scanned in opposing directions across the specimen by varying the voltages on the biprisms. An equivalent scheme for conventional TEM is also possible. In each case, the complex transmission function of the specimen may be derived and resolutions of about 0.05 nm may be expected.

Single-atom electron microscopy for energy-related nanomaterials

2020 ◽  
Vol 8 (32) ◽  
pp. 16142-16165 ◽  
Author(s):  
Mingquan Xu ◽  
Aowen Li ◽  
Meng Gao ◽  
Wu Zhou
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Scanning Transmission Electron Microscopy ◽  
Atomic Resolution ◽  
Single Atom ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Resolution Imaging ◽  
Imaging And Spectroscopy ◽  
Atom Level

The advances in aberration correction have enabled atomic-resolution imaging and spectroscopy in scanning transmission electron microscopy (STEM) under low primary voltages and pushed their detection limit down to the single-atom level.

scholarly journals Structural Evolution of Ni-Based Co-Catalysts on [Ca2Nb3O10]− Nanosheets during Heating and Their Photocatalytic Properties

Catalysts ◽  
2019 ◽  
Vol 10 (1) ◽  
pp. 13 ◽  
Author(s):  
Siyuan Zhang ◽  
Leo Diehl ◽  
Sina Wrede ◽  
Bettina V. Lotsch ◽  
Christina Scheu
Keyword(s):  
Ostwald Ripening ◽  
Structural Evolution ◽  
Scanning Transmission Electron Microscope ◽  
Ex Situ ◽  
Shell Nanoparticles ◽  
Co Catalysts ◽  
Nickel Compounds ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Resolution Imaging

Nickel compounds are among the most frequently used co-catalysts for photocatalytic water splitting. By loading Ni(II) precursors, submonolayer Ni(OH)2 was uniformly distributed onto photocatalytic [Ca2Nb3O10]− nanosheets. Further heating of the nanocomposite was studied both ex situ in various gas environments and in situ under vacuum in the scanning transmission electron microscope. During heating in non-oxidative environments including H2, argon and vacuum, Ni nanoparticles form at ≥200 °C, and they undergo Ostwald ripening at ≥500 °C. High resolution imaging and electron energy loss spectroscopy revealed a NiO shell around the Ni core. Ni loading of up to 3 wt% was demonstrated to enhance the rates of photocatalytic hydrogen evolution. After heat treatment, a further increase in the reaction rate can be achieved thanks to the Ni core/NiO shell nanoparticles and their large separation.

scholarly journals A symmetry-derived mechanism for atomic resolution imaging

2020 ◽  
Vol 117 (45) ◽  
pp. 27805-27810
Author(s):  
Matus Krajnak ◽  
Joanne Etheridge
Keyword(s):  
Electron Probe ◽  
Local Symmetry ◽  
Symmetry Operation ◽  
Specimen Thickness ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Contrast Mechanism ◽  
Electron Intensity ◽  
Resolution Imaging ◽  
Degree Of Similarity

We introduce an image-contrast mechanism for scanning transmission electron microscopy (STEM) that derives from the local symmetry within the specimen. For a given position of the electron probe on the specimen, the image intensity is determined by the degree of similarity between the exit electron-intensity distribution and a chosen symmetry operation applied to that distribution. The contrast mechanism detects both light and heavy atomic columns and is robust with respect to specimen thickness, electron-probe energy, and defocus. Atomic columns appear as sharp peaks that can be significantly narrower than for STEM images using conventional disk and annular detectors. This fundamentally different contrast mechanism complements conventional imaging modes and can be acquired simultaneously with them, expanding the power of STEM for materials characterization.

scholarly journals Two-Dimensional Frank-Kasper Z Phase with One Unit-Cell Thickness

2020 ◽  
Author(s):  
Xie Hongbo ◽  
Junyuan Bai ◽  
Haiyan Ren ◽  
Shanshan Li ◽  
Hucheng Pan ◽  
...  
Keyword(s):  
Density Functional ◽  
Three Dimensional ◽  
Volume Ratio ◽  
Dark Field ◽  
Unit Cell ◽  
Two Dimensional ◽  
Cell Height ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field

Abstract Z phase is one of the three basic units by which the Frank-Kasper phases are generally assembled. Compared to the other two basic units, i.e., A15 and C15 structures, the Z phase structure is rarely experimentally observed because of a relatively large volume ratio among the constituents to inhibit its formation. Moreover, the discovered Z structures are generally the three-dimensional (3D) ordered Gibbs bulk phases to conform to their thermodynamic stability. Herein, we confirmed the existence of a metastable two-dimensional (2D) Frank-Kasper Z phase with one unit-cell height in the crystallography in a model Mg-Sm-Zn system, by using aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with density functional theory (DFT) calculations. This finding is important for understanding the relationship between the traditional crystal structures and the quasicrystals, and it is also expected to provide a new insight to understand the clustering and stacking behavior of atoms in condensed matters.

Surface resonance channelling in scanning reflection electron microscopy

1988 ◽  
Vol 46 ◽  
pp. 692-693
Author(s):  
J.M. Cowley ◽  
P.A. Crozier
Keyword(s):  
Electron Microscopy ◽  
Crystal Surface ◽  
Scanning Transmission Electron Microscope ◽  
Diffraction Effect ◽  
Transmission Electron ◽  
Surface Resonance ◽  
Scanning Transmission ◽  
Reflection Electron Microscopy ◽  
Resolution Imaging ◽  
Electron Energy Loss

The phenomena of the channelling of electrons along planes or rows of atoms in the surface layers of crystals has been investigated recently in relation to microdiffraction and RHEED, REM, (reflection electron microscopy) and REELS (reflection electron energy loss spectroscopy) by using a conventional TEM in the reflection mode.The renewed interest in this phenomenon, known for many years, is the evidence from calculations of dynamical diffraction effect at surfaces that the electrons may be channelled along the topmost layers of atoms on a crystal surface and that the RHEED, REM and REELS signals may thus be sensitive to the structure and composition of the surface layer. These techniques may therefore provide a powerful new approach to the study of surfaces in which surface microanalysis and diffraction studies may be combined with nanometer-resolution imaging.An investigation has now been made of the analogous techniques which may be applied to the study of surfaces by use of a scanning transmission electron microscope.

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