scholarly journals Subunit cell–level measurement of polarization in an individual polar vortex

2019 ◽  
Vol 5 (11) ◽  
pp. eaav4355 ◽  
Author(s):  
Yuanwei Sun ◽  
Adeel Y. Abid ◽  
Congbing Tan ◽  
Chuanlai Ren ◽  
Mingqiang Li ◽  
...  
Keyword(s):  
Dipole Moments ◽  
Polar Vortex ◽  
Scanning Transmission Electron Microscope ◽  
Contrast Imaging ◽  
Cell Level ◽  
Polarization Distribution ◽  
Scanning Transmission ◽  
Out Of Plane ◽  
Sound Foundation ◽  
Ferroelectric Vortex

Recently, several captivating topological structures of electric dipole moments (e.g., vortex, flux closure) have been reported in ferroelectrics with reduced size/dimensions. However, accurate polarization distribution of these topological ferroelectric structures has never been experimentally obtained. We precisely measure the polarization distribution of an individual ferroelectric vortex in PbTiO3/SrTiO3 superlattices at the subunit cell level by using the atomically resolved integrated differential phase contrast imaging in an aberration-corrected scanning transmission electron microscope. We find, in vortices, that out-of-plane polarization is larger than in-plane polarization, and that downward polarization is larger than upward polarization. The polarization magnitude is closely related to tetragonality. Moreover, the contribution of the Pb─O bond to total polarization is highly inhomogeneous in vortices. Our precise measurement at the subunit cell scale provides a sound foundation for mechanistic understanding of the structure and properties of a ferroelectric vortex and lattice-charge coupling phenomena in these topological ferroelectric structures.

Secondary electron imaging of YBa2Cu3O7-x high-Tc superconductors in Scanning Transmission Electron Microscope

1989 ◽  
Vol 47 ◽  
pp. 684-685
Author(s):  
D. R. Liu ◽  
D. B. Williams
Keyword(s):  
Electron Microscope ◽  
Secondary Electron ◽  
Scanning Transmission Electron Microscope ◽  
Superconducting Phase ◽  
Contrast Imaging ◽  
High Tc ◽  
Bright Contrast ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Electron Imaging

The secondary electron imaging technique in a scanning electron microscope (SEM) has been used first by Millman et al. in 1987 to distinguish between the superconducting phase and the non-superconducting phase of the YBa2Cu3O7-x superconductors. They observed that, if the sample was cooled down below the transition temperature Tc and imaged with secondary electrons, some regions in the image would show dark contrast whereas others show bright contrast. In general, the contrast variation of a SEM image is the variation of the secondary electron yield over a specimen, which in turn results from the change of topography and conductivity over the specimen. Nevertheless, Millman et al. were able to demonstrate with their experimental results that the dominant contrast mechanism should be the conductivity variation and that the regions of dark contrast were the superconducting phase whereas the regions of bright contrast were the non-superconducting phase, because the latter was a poor conductor and consequently, the charge building-up resulted in high secondary electron emission. This observation has since aroused much interest amoung the people in electron microscopy and high Tc superconductivity. The present paper is the preliminary report of our attempt to carry out the secondary electron imaging of this material in a scanning transmission electron microscope (STEM) rather than in a SEM. The advantage of performing secondary electron imaging in a TEM is obvious that, in a TEM, the spatial resolution is higher and many more complementary techniques, e.g, diffraction contrast imaging, phase contrast imaging, electron diffraction and various microanalysis techniques, are available.

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.

Analysis of the Atomic Scale Defect Chemistry in Oxygen Deficient Materials by STEM

1999 ◽  
Vol 589 ◽  
Author(s):  
Y. Ito ◽  
S. Stemmer ◽  
R. F. Klie ◽  
N. D. Browning ◽  
A. Sane ◽  
...  
Keyword(s):  
Preliminary Investigation ◽  
High Mobility ◽  
Scanning Transmission Electron Microscope ◽  
Defect Chemistry ◽  
Atomic Scale ◽  
Contrast Imaging ◽  
Separation Membranes ◽  
Oxidation Reduction ◽  
Scanning Transmission ◽  
Z Contrast

AbstractThe high mobility of anion vacancies in oxygen deficient perovskite type materials makes these ceramics potential candidates for oxygen separation membranes. As a preliminary investigation of the defect chemistry in these oxides, we show here the analysis of SrCoO3−σ using atomic resolution Z-contrast imaging and electron energy loss spectroscopy in the scanning transmission electron microscope. In particular, after being subjected to oxidation/reduction cycles at high temperatures we find the formation of ordered microdomains with the brownmillerite structure.

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.

Progress in Aberration-Corrected STEM

2000 ◽  
Vol 6 (S2) ◽  
pp. 100-101
Author(s):  
N. Dellby ◽  
O.L. Krivanek ◽  
A.R. Lupini
Keyword(s):  
Second Generation ◽  
Spherical Aberration ◽  
Chromatic Aberration ◽  
Scanning Transmission Electron Microscope ◽  
Aberration Correction ◽  
Resolution Limit ◽  
Contrast Imaging ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Fixed Beam

Electron probe formation in a scanning transmission electron microscope (STEM) has two properties that maximize the benefits of spherical aberration correction: the smallest and brightest probes are formed when all the geometric aberrations are set to zero, and the size of the probe is not greatly affected by the presence of chromatic aberration. This contrasts with the case of conventional, fixed-beam TEM (CTEM), in which optimized phase-contrast imaging demands a non-zero spherical aberration coefficient (Cs), and chromatic aberration constitutes a major resolution limit. As a result, a consensus is presently emerging that the benefits of aberration correction will be felt most strongly in STEM.Our efforts in Cs-corrected STEM have progressed from a proof-of-principle Cs corrector [1] to an optimized second-generation design [2]. The corrector in both cases is of the quadrupole-octupole type. The second-generation corrector uses separate quadrupoles and octupoles, and concentrates on maximizing the octupole strength.

Atomic-Resolution Z-Contrast Imaging and its Application to Compositional Ordering and Segregation

1999 ◽  
Vol 583 ◽  
Author(s):  
S. J. Pennycook ◽  
Y. Yan ◽  
A. Norman ◽  
Y. Zhang ◽  
M. Al-Jassim ◽  
...  
Keyword(s):  
High Resolution Electron Microscopy ◽  
Scanning Transmission Electron Microscope ◽  
Ferroelectric Materials ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
High Angle ◽  
Contrast Imaging ◽  
Resolution Electron ◽  
Scanning Transmission ◽  
Z Contrast

AbstractIn the last ten years, the scanning transmission electron microscope (STEM) has become capable of forming electron probes of atomic dimensions making possible a new approach to high-resolution electron microscopy, Z-contrast imaging. Formed by mapping the intensity of high-angle scattered electrons as the probe is scanned across the specimen, the Z-contrast image represents a direct map of the specimen scattering power at atomic resolution. It is an incoherent image, and can be directly interpreted in terms of atomic columns. High angle scattering comes predominantly from the atomic nuclei, so the scattering cross section depends on atomic number (Z) squared. Z-contrast microscopy can therefore be used to study compositional ordering and segregation at the atomic scale. Here we present three examples of ordering: first, ferroelectric materials, second, III-V semiconductor alloys, and finally, cooperative segregation at a semiconductor grain boundary, where a combination of Z-contrast imaging with first principles theory provides a complete atomic-scale view of the sites and configurations of the segregant atoms.

Atomic resolution determination of the structure and chemistry of ceramic grain boundaries

1995 ◽  
Vol 53 ◽  
pp. 320-321
Author(s):  
N. D. Browning ◽  
M. M. McGibbon ◽  
M. F. Chisholm ◽  
S. J. Pennycook
Keyword(s):  
Grain Boundaries ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Secondary Phases ◽  
Contrast Imaging ◽  
Scanning Transmission ◽  
Recent Developments ◽  
Contrast Technique ◽  
Z Contrast

Characterization of grain boundaries in ceramics is complicated by the multicomponent nature of the materials, the presence of secondary phases, and the tendency for the grain boundary plane to “wander” on the length scale of a few nanometers. However, recent developments in the scanning transmission electron microscope (STEM) have now made it possible to correlate directly the structure, composition and bonding at grain boundaries on the atomic scale. This direct experimental characterization of grain boundaries is achieved through the combination of Z-contrast imaging (structure) and electron energy loss spectroscopy (EELS) (composition and bonding). For crystalline materials in zone-axis orientations, where the atomic spacing is larger than the probe size, the Z-contrast technique provides a direct image of the metal (high Z) columns. This image, being formed from only the high-angle scattering, can be used to position the electron probe with atomic precision for simultaneous EELS. Under certain collection conditions, the spectrum can have the same atomic spatial resolution as the image, thus permitting the spectra to be correlated with a known atomic location.

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.

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