Probing vacancies and structural distortions at individual defects in ceramics using EELS

1996 ◽  
Vol 54 ◽  
pp. 678-679
Author(s):  
D. J. Wallis ◽  
N. D. Browning
Keyword(s):  
Structural Information ◽  
Core Loss ◽  
Nearest Neighbors ◽  
Ceramic Materials ◽  
Scanning Transmission Electron Microscope ◽  
Real Space ◽  
Atomic Scale ◽  
Structure Property ◽  
Scanning Transmission ◽  
Key Issues

In electron energy loss spectroscopy (EELS), the near-edge region of a core-loss edge contains information on high-order atomic correlations. These correlations give details of the 3-D atomic structure which can be elucidated using multiple-scattering (MS) theory. MS calculations use real space clusters making them ideal for use in low-symmetry systems such as defects and interfaces. When coupled with the atomic spatial resolution capabilities of the scanning transmission electron microscope (STEM), there therefore exists the ability to obtain 3-D structural information from individual atomic scale structures. For ceramic materials where the structure-property relationships are dominated by defects and interfaces, this methodology can provide unique information on key issues such as like-ion repulsion and the presence of vacancies, impurities and structural distortion.An example of the use of MS-theory is shown in fig 1, where an experimental oxygen K-edge from SrTiO3 is compared to full MS-calculations for successive shells (a shell consists of neighboring atoms, so that 1 shell includes only nearest neighbors, 2 shells includes first and second-nearest neighbors, and so on).

Atomic Scale Characterization of Vacancy Ordering in Oxygen Conducting Membranes

2002 ◽  
Vol 8 (6) ◽  
pp. 475-486 ◽  
Author(s):  
Robert F. Klie ◽  
Nigel D. Browning
Keyword(s):  
Defect Formation ◽  
Bulk Material ◽  
Electronic Conductivity ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Atomic Scale ◽  
Structure Property ◽  
Dark Field Imaging ◽  
Scanning Transmission ◽  
Scale Characterization

This article presents a comprehensive investigation of (La, Sr)FeO3 by correlated atomic resolution annular dark field imaging and electron energy loss spectroscopy. Here, the ability of these techniques to characterize point defect formation and phase transitions under reducing conditions in situ in the scanning transmission electron microscope is evaluated and the influence of oxygen vacancies on the structure–property relationships is discussed. In particular, the evolution of the Ruddlesden–Popper, Brownmillerite, and Aurivillius phases can be associated directly with the ionic and electronic conductivity of the bulk material under different thermodynamic conditions. These results lead naturally to an atomistic defect chemistry model to explain the high temperature ionic and electronic conductivity in this and other perovskite materials.

Atomic-resolution eels for composition and 3-D coordination determination at interfaces and defects

1996 ◽  
Vol 54 ◽  
pp. 530-531
Author(s):  
N. D. Browning ◽  
D. J. Wallis ◽  
S. Sivananthan ◽  
P. D. Nellist ◽  
S. J. Pennycook
Keyword(s):  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Atomic Resolution ◽  
Structure Property ◽  
Contrast Imaging ◽  
Angle Scattering ◽  
Structural Differences ◽  
Scanning Transmission ◽  
Composition Structure ◽  
Z Contrast

Materials properties associated with interfaces and defects are dominated by atomic scale fluctuations in composition, structure and bonding. Although electron energy loss spectroscopy (EELS) provides a powerful tool to probe these features, low signal, lens aberrations, image coherence and specimen drift preclude the use of spectrum imaging and energy filtered imaging for these high-resolution problems. However, by utilizing Z-contrast imaging in conjunction with EELS in the scanning transmission electron microscope (STEM), these limitations are largely overcome and EELS appears capable of providing fudamental 3-D characterization of defect and interface structures with atomic resolution and sensitivity.The main premise in utilizing these combined techniques is that the properties of defects and interfaces must be associated with structural differences relative to the bulk. If those structural differences can be located, then it is only necessary to perform spectroscopy in their vicinity to understand the structure property relationship. For crystalline materials in zone-axis orientations, the Z-contrast image provides this atomic resolution structural map. As this direct image is generated with only the high-angle scattering, it can be used to position the electron probe with atomic precision and does not interfere with the low-angle scattering for spectroscopy.

Electron Microscopy Studies of The Chemistry And Microstructure of BaF2 / YBa2Cu3O7-x Thin Films

1994 ◽  
Vol 52 ◽  
pp. 796-797
Author(s):  
J. L. Lee ◽  
C. A. Weiss ◽  
R. A. Buhrman ◽  
J. Silcox
Keyword(s):  
Thin Film ◽  
Electron Microscopy ◽  
Thin Films ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Island Growth ◽  
Multilayer Systems ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Mgo Substrate

BaF2 thin films are being investigated as candidates for use in YBa2Cu3O7-x (YBCO) / BaF2 thin film multilayer systems, given the favorable dielectric properties of BaF2. In this study, the microstructural and chemical compatibility of BaF2 thin films with YBCO thin films is examined using transmission electron microscopy and microanalysis. The specimen was prepared by using laser ablation to first deposit an approximately 2500 Å thick (0 0 1) YBCO thin film onto a (0 0 1) MgO substrate. An approximately 7500 Å thick (0 0 1) BaF2 thin film was subsequendy thermally evaporated onto the YBCO film.Images from a VG HB501A UHV scanning transmission electron microscope (STEM) operating at 100 kV show that the thickness of the BaF2 film is rather uniform, with the BaF2/YBCO interface being quite flat. Relatively few intrinsic defects, such as hillocks and depressions, were evident in the BaF2 film. Moreover, the hillocks and depressions appear to be faceted along {111} planes, suggesting that the surface is smooth and well-ordered on an atomic scale and that an island growth mechanism is involved in the evolution of the BaF2 film.

scholarly journals Single-atom vibrational spectroscopy in the scanning transmission electron microscope

Science ◽  
2020 ◽  
Vol 367 (6482) ◽  
pp. 1124-1127 ◽  
Author(s):  
F. S. Hage ◽  
G. Radtke ◽  
D. M. Kepaptsoglou ◽  
M. Lazzeri ◽  
Q. M. Ramasse
Keyword(s):  
Electron Microscope ◽  
Vibrational Spectroscopy ◽  
Materials Science ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Single Atom ◽  
Phonon Modes ◽  
Resonant States ◽  
Resolution Electron ◽  
Scanning Transmission

Single-atom impurities and other atomic-scale defects can notably alter the local vibrational responses of solids and, ultimately, their macroscopic properties. Using high-resolution electron energy-loss spectroscopy in the electron microscope, we show that a single substitutional silicon impurity in graphene induces a characteristic, localized modification of the vibrational response. Extensive ab initio calculations reveal that the measured spectroscopic signature arises from defect-induced pseudo-localized phonon modes—that is, resonant states resulting from the hybridization of the defect modes and the bulk continuum—with energies that can be directly matched to the experiments. This finding realizes the promise of vibrational spectroscopy in the electron microscope with single-atom sensitivity and has broad implications across the fields of physics, chemistry, and materials science.

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.

Microdiffraction from Cleaved Si-Si1-xGex Multilayers

1989 ◽  
Vol 160 ◽  
Author(s):  
W. T. Pike
Keyword(s):  
Cross Section ◽  
Structural Information ◽  
Scanning Transmission Electron Microscope ◽  
High Angle ◽  
Small Probe ◽  
Periodicity Analysis ◽  
Transmission Electron ◽  
Probe Size ◽  
Scanning Transmission ◽  
Diffraction Patterns

AbstractUsing the nanometer probe available in the dedicated scanning transmission electron microscope (STEM) local structural information can be obtained from individual layers in [100] grown Si-Si1-xGex multilayer structures. Furthermore the small probe size enables cleaved specimens with their very large wedge angles to be analyzed in cross-section. Diffraction patterns are shown from multilayers of varying periodicity. Analysis of the patterns concentrates on the higher order Laue zone (holz) reflections in the high angle excess ring . The behaviour of the excess holz reflections indicates the transition from a strained layer superiattice to a dislocated structure as the thickness of the layers increases for a given composition.

Identification of site-specific isotopic labels by vibrational spectroscopy in the electron microscope

Science ◽  
2019 ◽  
Vol 363 (6426) ◽  
pp. 525-528 ◽  
Author(s):  
Jordan A. Hachtel ◽  
Jingsong Huang ◽  
Ilja Popovs ◽  
Santa Jansone-Popova ◽  
Jong K. Keum ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Spatial Resolution ◽  
Theoretical Calculations ◽  
Scanning Transmission Electron Microscope ◽  
Real Space ◽  
Site Specific ◽  
Spatially Resolved ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Isotopic Labels

The identification of isotopic labels by conventional macroscopic techniques lacks spatial resolution and requires relatively large quantities of material for measurements. We recorded the vibrational spectra of an α amino acid, l-alanine, with damage-free “aloof” electron energy-loss spectroscopy in a scanning transmission electron microscope to directly resolve carbon-site–specific isotopic labels in real space with nanoscale spatial resolution. An isotopic red shift of 4.8 ± 0.4 milli–electron volts in C–O asymmetric stretching modes was observed for 13C-labeled l-alanine at the carboxylate carbon site, which was confirmed by macroscopic infrared spectroscopy and theoretical calculations. The accurate measurement of this shift opens the door to nondestructive, site-specific, spatially resolved identification of isotopically labeled molecules with the electron microscope.

scholarly journals Correlating the electronic structures of metallic/semiconducting MoTe2 interface to its atomic structures

2020 ◽  
Author(s):  
Bo Han ◽  
Chen Yang ◽  
Xiaolong Xu ◽  
Yuehui Li ◽  
Ruochen Shi ◽  
...  
Keyword(s):  
Phase Boundary ◽  
Electronic Structures ◽  
2D Materials ◽  
Atomic Scale ◽  
Contact Interface ◽  
Structure Property ◽  
Atomic Structures ◽  
Structure Property Relationships ◽  
Scanning Transmission ◽  
Unit Cells

Abstract Contact interface properties are important in determining the performances of devices that are based on atomically thin two-dimensional (2D) materials, especially for those with short channels. Understanding the contact interface is therefore important to design better devices. Herein, we use scanning transmission electron microscopy, electron energy loss spectroscopy, and first-principles calculations to reveal the electronic structures within the metallic (1T′)-semiconducting (2H) MoTe2 coplanar phase boundary across a wide spectral range and correlate its properties to atomic structures. We find that the 2H-MoTe2 excitonic peaks cross the phase boundary into the 1T′ phase within a range of approximately 150 nm. The 1T′-MoTe2 crystal field can penetrate the boundary and extend into the 2H phase by approximately two unit-cells. The plasmonic oscillations exhibit strong angle dependence, that is a red-shift of π+σ (approximately 0.3–1.2 eV) occurs within 4 nm at 1T′/2H-MoTe2 boundaries with large tilt angles, but there is no shift at zero-tilted boundaries. These atomic-scale measurements reveal the structure–property relationships of the 1T′/2H-MoTe2 boundary, providing useful information for phase boundary engineering and device development based on 2D materials.

Nano-Sized Catalytic Materials Investigated by a STEM-Based Mass Spectroscopic Technique

1997 ◽  
Vol 3 (S2) ◽  
pp. 443-444
Author(s):  
J. C. Yang ◽  
A. Singhal ◽  
S. Bradley ◽  
J. M. Gibson
Keyword(s):  
Bimetallic Catalyst ◽  
Structural Information ◽  
Scanning Transmission Electron Microscope ◽  
Dark Field ◽  
Spectroscopic Technique ◽  
Carbon Substrate ◽  
Support Material ◽  
Catalytic Materials ◽  
Scanning Transmission ◽  
Annular Dark Field

Knowledge of catalysts' sizes and shapes on their support material is crucial in understanding catalytic properties. With increasing interest in nanosized catalytic materials, it is vital to obtain structural information at the nanometer level in order to understand their catalytic behavior. We have recently demonstrated that very high angle (˜100mrad) annular dark-field (HAADF) images in a dedicated scanning transmission electron microscope (STEM) can be used to quantitatively measure the number of atoms of individual nano-sized clusters on a support material We are presently applying this technique to a bimetallic catalyst, PtRu5, where our data suggest that the shape of the PtRu5 particle is, surprisingly, oblate on the carbon substrate.PtRu5 is of interest for methanol oxidation for applications in batteries. PtRu5 compounds were produced by a molecular precursor method. Imaging was performed on a Field Emission Gun (FEG) Vacuum Generators HB501 STEM operated at 100kV.

Multiple scattering calculations at the oxygen K-edge for SiO2

1995 ◽  
Vol 53 ◽  
pp. 602-603
Author(s):  
DJ Wallis ◽  
R Brydson ◽  
PH Gaskell
Keyword(s):  
Multiple Scattering ◽  
Structural Information ◽  
Core Loss ◽  
Calculated Data ◽  
Real Space ◽  
Edge Structure ◽  
Exchange Correlation ◽  
Valence Electrons ◽  
Electron Energy Loss ◽  
Atom Energy

Electron Energy Loss Spectroscopy (EELS) in the STEM is potentially a very powerful technique for studying the structure of materials. The Near Edge Structure (NES) in core loss edges carries information about triplet, and higher order correlation functions and under certain conditions is sensitive to long range atomic correlations. However, since the NES contains strong contributions due to multiple elastic scattering, a simple interpretation in terms of atomic structure is not possible. It is therefore necessary to perform some form of modeling to obtain structural information. One approach to modeling NES is Multiple Scattering (MS) theory.MS calculations have been performed to model the O K-edge ELNES for the α-quartz phase of SiO2 The calculations use a real-space atomic cluster and model the atomic potentials using the Muffin Tin approximation. Effects of the core hole produced upon excitation were accounted for using the (Z+1)* approximation for the excited atom. Energy scales of the calculated data have also been compressed to correct for the energy dependence of the exchange correlation between the photoelectron and the valence electrons which is not accounted for in the calculation.

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