scholarly journals Defect-driven selective metal oxidation at atomic scale

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Qi Zhu ◽  
Zhiliang Pan ◽  
Zhiyu Zhao ◽  
Guang Cao ◽  
Langli Luo ◽  
...  
Keyword(s):  
Reaction Dynamics ◽  
Binding Energies ◽  
Crystal Defects ◽  
Oxidation Catalysis ◽  
Atomic Scale ◽  
Layer By Layer ◽  
Oxygen Binding ◽  
Planar Defects ◽  
Transmission Electron ◽  
Site Selective

AbstractNanoscale materials modified by crystal defects exhibit significantly different behaviours upon chemical reactions such as oxidation, catalysis, lithiation and epitaxial growth. However, unveiling the exact defect-controlled reaction dynamics (e.g. oxidation) at atomic scale remains a challenge for applications. Here, using in situ high-resolution transmission electron microscopy and first-principles calculations, we reveal the dynamics of a general site-selective oxidation behaviour in nanotwinned silver and palladium driven by individual stacking-faults and twin boundaries. The coherent planar defects crossing the surface exhibit the highest oxygen binding energies, leading to preferential nucleation of oxides at these intersections. Planar-fault mediated diffusion of oxygen atoms is shown to catalyse subsequent layer-by-layer inward oxide growth via atomic steps migrating on the oxide-metal interface. These findings provide an atomistic visualization of the complex reaction dynamics controlled by planar defects in metallic nanostructures, which could enable the modification of physiochemical performances in nanomaterials through defect engineering.

scholarly journals Defect-driven Selective Metal Oxidation at Atomic Scale

2020 ◽  
Author(s):  
Qi Zhu ◽  
Zhiliang Pan ◽  
Zhiyu Zhao ◽  
Langli Luo ◽  
Chaolun Ni ◽  
...  
Keyword(s):  
Reaction Dynamics ◽  
Binding Energies ◽  
Crystal Defects ◽  
Oxidation Catalysis ◽  
Atomic Scale ◽  
Fast Diffusion ◽  
Layer By Layer ◽  
Oxygen Binding ◽  
Planar Defects ◽  
Site Selective

Abstract Nanoscale materials modified by crystal defects exhibit significantly different behaviours upon chemical reactions such as oxidation, catalysis, lithiation and epitaxial growth. However, unveiling the exact defect-controlled reaction dynamics (e.g. oxidation) at atomic scale remains a challenge for applications. Here, using in situ high-resolution transmission electron microscopy and first-principles calculations, we reveal the dynamics of a general site-selective oxidation behaviour in nanotwinned Ag and Pd driven by isolated stacking-faults and twin-boundaries. The coherent planar defects crossing the surface exhibit the highest oxygen binding energies, leading to preferential nucleation of oxides at these intersections. Fast diffusion of oxygen atoms along the planar-fault highways is shown to catalyse subsequent layer-by-layer inward oxide growth via atomic steps migrating on the oxide-metal interface. These findings provide an atomistic visualization of the complex reaction dynamics controlled by coherent planar defects in metallic nanostructures, which could enable the modification of physiochemical performance of nanomaterials through defect engineering.

Relationship Between Crystal Defects, Ge Outdiffusion and V/III Ratio in MOVPE Grown (001) GaAs/Ge

1993 ◽  
Vol 319 ◽  
Author(s):  
C. Frigeri ◽  
G. Atrolini ◽  
C. Pelosi ◽  
F. Longo
Keyword(s):  
Stacking Faults ◽  
Layer Growth ◽  
Crystal Defects ◽  
Misfit Dislocations ◽  
Layer By Layer ◽  
Island Growth ◽  
Planar Defects ◽  
Fault Density ◽  
Unintentional Doping ◽  
Enhanced Mobility

AbstractTwo regimes of defect generation have been found in MOVPE GaAs/Ge layers upon changing the V/III ratio between 1.3 and 11.8. For low V/III ratio the layers contained misfit dislocations along with stacking faults that had been generated by dissociation of the misfit dislocations. The stacking fault density increased with decreasing V/III ratio. This might be explained by an enhanced mobility of the dissociated partials due the reduced unintentional doping of the layer caused by reduced Ge outdiffusion from the substrate when V/III is small. The secon regime corresponds to high V/III ratios and is characterized by the absence of misfit dislocations and the presence of a high density of planar defects. This means that breakdown of the 2D layer-by-layer growth occurred and 3D island growth prevailed.

Many-Beam Lattice Images from Thicker Crystals

1978 ◽  
Vol 36 (3) ◽  
pp. 130-139
Author(s):  
S. Iijima
Keyword(s):  
Electron Microscopy ◽  
Materials Science ◽  
Complex Oxides ◽  
Crystal Defects ◽  
Planar Defects ◽  
Transmission Electron ◽  
Lattice Images ◽  
The Many ◽  
Atom Configuration ◽  
Beam Lattice

Nearly a decade ago, the usefulness of lattice images for studying crystal defects was reported by Allpress et al. (1969). They analyzed abnormally spaced lattice fringes of crystals of the complex oxides and derived successfully the nature of planar defects occurring on a unit cell scale. Since then the method for studying atom configuration in crystals using high resolution transmission electron microscopy (HRTEM) has been investigated extensively. The studies have involved theoretical calculation of the many-beam lattice images of perfect crystals and applications of the method to solve problems in materials science.

scholarly journals STEM-EELS Investigation of Planar Defects in Olivine in the Allende Meteorite

Minerals ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 35
Author(s):  
Maya Marinova ◽  
Hugues Leroux ◽  
Priscille Cuvillier ◽  
Alexandre Gloter ◽  
Damien Jacob
Keyword(s):  
Structural Features ◽  
Dark Field ◽  
Parent Body ◽  
Atomic Scale ◽  
Crystalline Lattice ◽  
Planar Defects ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Annular Dark Field ◽  
Small Distortion

The present study focuses on a detailed structural investigation at atomic scale of the planar defects that appear in the olivine grains in the Allende meteorite, and it aims to clarify their nature and the related formation mechanism. The investigation was performed using advanced spectro-microscopy techniques such as atomically resolved high-angle annular dark field (HAADF) images coupled with electron energy loss spectroscopy in the scanning transmission electron microscopy mode (STEM-EELS). Two prominent structural features appear in the investigated olivine grains: (i) Exsolution platelets with a thickness between 2 and 10 nm with the spinel structure and chemical composition expressed as a solid solution between magnetite, chromite, and MgAl2O4. (ii) Thinner planar defects appeared with thickness between 2 to 4 atomic planes, which were rich in Fe and had a strong Fe3+ contribution. The structure of these defects was described by the crystalline lattice of the olivine grains with small distortion of the measured cationic distances, which can be related to Fe3+-Si substitution in the tetrahedral sites. Those metastable defects should have preceded the formation of the thicker spinel exsolutions and could have formed during an oxidizing event in the Allende parent body.

Quantitative HREM analysis of planar defects in high-pressure synthesized infinite-layer superconductor

1994 ◽  
Vol 52 ◽  
pp. 720-721
Author(s):  
Hong Zhang ◽  
L. D. Marks ◽  
Y. Y. Wang ◽  
H. Zhang ◽  
V. P. Dravid ◽  
...  
Keyword(s):  
High Pressure ◽  
Atomic Scale ◽  
Structure Model ◽  
Hrem Image ◽  
Ion Milling ◽  
Planar Defects ◽  
Infinite Layer ◽  
Transmission Electron ◽  
Best Fit ◽  
Image Simulations

Planar defects in the infinite-layer (Sr1-xCax)1-yCuO2 structure (planar CuO2 sheets separated by single Sr and Ca cations) have been suggested to be responsible for superconductivity with Tc up to about 110K. It is therefore important to understand the details of these defects at the atomic scale. In this work, we have used high resolution transmission electron microscopy to identify these defects and χ2 minimizations to best fit the experimental images; an optimized structure model from these studies is proposed.Thin samples of the infinite layer superconductor with the nominal chemical formula (Sr1-xCax)1-y CuO2 (x=0 and 0.3; y=0.9, 1.0 and 1.1) synthesized by high pressure treatment were prepared using a combination of mechanical polishing, dimpling and ion milling techniques. Through focal (10 nm steps) [100] HREM images of the defects (Fig. 1) were obtained on a 300kV Hitachi H-9000 microscope. HREM image simulations were carried out using NUMIS software and these were quantitatively compared against the experimental images using conventional χ2 minimizations with SEMPER software.

Atomic Scale Analysis of Planar Defects in Polycrystalline Diamond

2006 ◽  
Vol 12 (6) ◽  
pp. 492-497 ◽  
Author(s):  
Rolf Erni ◽  
Bert Freitag ◽  
Peter Hartel ◽  
Heiko Müller ◽  
Peter Tiemeijer ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Polycrystalline Diamond ◽  
Atomic Scale ◽  
Twin Boundaries ◽  
Axis Orientation ◽  
Planar Defects ◽  
Transmission Electron ◽  
Local Distortions

Planar defects in a polycrystalline diamond film were studied by high-resolution transmission electron microscopy (HRTEM) and high-resolution scanning transmission electron microscopy (STEM). In both modes, sub-Ångström resolution was achieved by making use of two aberration-corrected systems; a TEM and a STEM CS-corrected microscope, each operated at 300 kV. For the first time, diamond in 〈110〉 zone-axis orientation was imaged in STEM mode at a resolution that allows for resolving the atomic dumbbells of carbon at a projected interatomic distance of 89 pm. Twin boundaries that show approximately the Σ3 CSL structure reveal at sub-Ångström resolution imperfections; that is, local distortions, which break the symmetry of the ideal Σ3 type twin boundary, are likely present. In addition to these imperfect twin boundaries, voids on the atomic level were observed. It is proposed that both local distortions and small voids enhance the mechanical toughness of the film by locally increasing the critical stress intensity factor.

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.

Images and Applications of Ion Explosion Spike Pits

1990 ◽  
Vol 48 (1) ◽  
pp. 584-585
Author(s):  
P. Fraundorf ◽  
J. Tentschert
Keyword(s):  
Electron Microscope ◽  
Transmission Electron Microscope ◽  
Bulk Material ◽  
Coulomb Repulsion ◽  
The Body ◽  
Atomic Scale ◽  
Early Solar System ◽  
Transmission Electron ◽  
Nuclear Particle ◽  
Particle Tracks

Since the discovery of their etchability in the early 1960‘s, nuclear particle tracks in insulators have had a diverse and exciting history of application to problems ranging from the selective filtration of cancer cells from blood to the detection of 244Pu in the early solar system. Their usefulness stems from the fact that they are comprised of a very thin (e.g. 20-40Å) damage core which etches more rapidly than does the bulk material. In fact, because in many insulators tracks are subject to radiolysis damage (beam annealing) in the transmission electron microscope, the body of knowledge concerning etched tracks far outweighs that associated with latent (unetched) tracks in the transmission electron microscope.With the development of scanned probe microscopies with lateral resolutions on the near atomic scale, a closer look at the structure of unetched nuclear particle tracks, particularly at their point of interface with solid surfaces, is now warranted and we think possible. The ion explosion spike model of track formation, described loosely, suggests that a burst of ionization along the path of a charged particle in an insulator creates an electrostatically unstable array of adjacent ions which eject one another by Coulomb repulsion from substitutional into interstitial sites. Regardless of the mechanism, the ejection process which acts to displace atoms along the track core seems likely to operate at track entry and exit surfaces, with the added feature of mass loss at those surfaces as well. In other words, we predict pits whose size is comparable to the track core width.

Transmission Electron Microscopy characterization of epitaxial III-V semiconductor thin films grown on Si(100) by ion-assisted deposition

1990 ◽  
Vol 48 (4) ◽  
pp. 686-687
Author(s):  
L. Hultman ◽  
C.-H. Choi ◽  
R. Kaspi ◽  
R. Ai ◽  
S.A. Barnett
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Ion Irradiation ◽  
High Energy ◽  
Nucleation Mechanism ◽  
Layer By Layer ◽  
Extended Defect ◽  
Island Formation ◽  
Si Substrates ◽  
Transmission Electron

III-V semiconductor films nucleate by the Stranski-Krastanov (SK) mechanism on Si substrates. Many of the extended defects present in the films are believed to result from the island formation and coalescence stage of SK growth. We have recently shown that low (-30 eV) energy, high flux (4 ions per deposited atom), Ar ion irradiation during nucleation of III-V semiconductors on Si substrates prolongs the 1ayer-by-layer stage of SK nucleation, leading to a decrease in extended defect densities. Furthermore, the epitaxial temperature was reduced by >100°C due to ion irradiation. The effect of ion bombardment on the nucleation mechanism was explained as being due to ion-induced dissociation of three-dimensional islands and ion-enhanced surface diffusion.For the case of InAs grown at 380°C on Si(100) (11% lattice mismatch), where island formation is expected after ≤ 1 monolayer (ML) during molecular beam epitaxy (MBE), in-situ reflection high-energy electron diffraction (RHEED) showed that 28 eV Ar ion irradiation prolonged the layer-by-layer stage of SK nucleation up to 10 ML. Otherion energies maintained layer-by-layer growth to lesser thicknesses. The ion-induced change in nucleation mechanism resulted in smoother surfaces and improved the crystalline perfection of thicker films as shown by transmission electron microscopy and X-ray rocking curve studies.

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