scholarly journals New insights into microstructure of irradiated beryllium based on experiments and computer simulations

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
M. Klimenkov ◽  
P. Vladimirov ◽  
U. Jäntsch ◽  
V. Kuksenko ◽  
R. Rolli ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Gas Bubbles ◽  
Atomic Scale ◽  
Average Height ◽  
Secondary Phases ◽  
Atomistic Modelling ◽  
Transmission Electron ◽  
Intermetallic Precipitates ◽  
Diffusion Mechanisms ◽  
Small Bubbles

Abstract The microstructural response of beryllium after neutron irradiation at various temperatures (643–923 K) was systematically studied using analytical transmission electron microscope that together with outcomes from advanced atomistic modelling provides new insights in the mechanisms of microstructural changes in this material. The most prominent feature of microstructural modification is the formation of gas bubbles, which is revealed at all studied irradiation temperatures. Except for the lowest irradiation temperature, gas bubbles have the shape of thin hexagonal prisms with average height and diameter increasing with temperature. A high number density of small bubbles is observed within grains, while significantly larger bubbles are formed along high-angle grain boundaries (GB). Denuded zones (DZ) nearly free from bubbles are found along both high- and low-angle grain boundaries. Precipitations of secondary phases (mainly intermetallic Al-Fe-Be) were observed inside grains, along dislocation lines and at GBs. EDX analysis has revealed homogeneous segregation of chromium and iron along GBs. The observed features are discussed with respect to the available atomistic modelling results. In particular, we present a plausible reasoning for the abundant formation of gas bubbles on intermetallic precipitates, observation of various thickness of zones denuded in gas bubbles and precipitates, and their relation to the atomic scale diffusion mechanisms of solute-vacancy clusters.

Electron microscopy of ceramic superconductors

1993 ◽  
Vol 51 ◽  
pp. 934-935
Author(s):  
M. Grant Norton ◽  
C. Barry Carter
Keyword(s):  
Electron Microscopy ◽  
Grain Boundaries ◽  
Analytical Techniques ◽  
Atomic Scale ◽  
Weak Links ◽  
Chemical Information ◽  
High Angle ◽  
Ceramic Superconductors ◽  
Transmission Electron ◽  
Current Densities

The microstructure of ceramic superconductors plays a crucial role in the transport properties of these materials. For example, it has been shown that high-angle grain boundaries can act as weak links and atomic scale defects can act as pinning centers. The nature and spatial distribution of such defects is related to the way in which the material is processed. Transmission electron microscopy (TEM) is an essential technique for understanding the relationship between microstructure, processing, and properties and for defect characterization. The advantage of TEM is that it is possible to combine various imaging modes with electron diffraction and other analytical techniques such as x-ray energy dispersive spectroscopy in order to obtain both structural and chemical information.Early measurements of critical current densities (Jc) across individual tilt grain boundaries in YBa2Cu3O7-δ (YBCO) thin films demonstrated that Jc decreased with increasing misorientation angle. More recently, however, it has been observed that this phenomenon may not be the case for all high-angle grain boundaries.

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.

Atomic-Scale Segregation and Fluctuations in Chemical Ordering FePt Thin Films

2007 ◽  
Vol 1032 ◽  
Author(s):  
Karen L Torres ◽  
Chandan Srivastava ◽  
Richard L Martens ◽  
Gregory B Thompson
Keyword(s):  
Thin Films ◽  
Grain Boundaries ◽  
Atom Probe ◽  
Density Fluctuations ◽  
Atomic Scale ◽  
Chemical Ordering ◽  
Transmission Electron ◽  
Deposited Film ◽  
Deposited Films ◽  
Fept Thin Films

AbstractA series of atom probe and transmission electron microscopy (TEM) studies have been performed to quantify minute compositional fluctuations in Fe55Pt45 thin films during the A1 to L10 phase transformation. The atom probe specimens were analyzed in an Imago Local Electrode Atom Probe (LEAP®) at a target evaporation of 0.5%, a pulse fraction of 20% and a temperature of 120K. We noted a propensity of fracture failures in the LEAP with this material at lower temperatures. The atom probe reconstruction showed small levels of Pt segregation at grain boundaries in the as-deposited films. Fresnel-contrast TEM imaging confirmed high density fluctuations in these boundaries. Upon annealing at 600°C for 10 minutes, the film transformed from A1 to L10 and the grain boundaries become Fe enriched as compared to the as-deposited film.

Atomic Scale Mapping of Phase Segregation at CMR Grain Boundaries in the Scanning Transmission Electron Microscope

2004 ◽  
Vol 10 (S02) ◽  
pp. 330-331
Author(s):  
Maria Varela ◽  
Vanessa Peña ◽  
Zouhair Sefrioui ◽  
Andrew R. Lupini ◽  
Jacobo Santamaria ◽  
...  
Keyword(s):  
Electron Microscope ◽  
Grain Boundaries ◽  
Transmission Electron Microscope ◽  
Phase Segregation ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Scanning Transmission Electron ◽  
Transmission Electron ◽  
Scanning Transmission

Extended abstract of a paper presented at Microscopy and Microanalysis 2004 in Savannah, Georgia, USA, August 1–5, 2004.

scholarly journals Near–atomic-scale observation of grain boundaries in a layer-stacked two-dimensional polymer

2020 ◽  
Vol 6 (33) ◽  
pp. eabb5976 ◽  
Author(s):  
Haoyuan Qi ◽  
Hafeesudeen Sahabudeen ◽  
Baokun Liang ◽  
Miroslav Položij ◽  
Matthew A. Addicoat ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Atomic Scale ◽  
Great Promise ◽  
Formation Mechanisms ◽  
Two Dimensional ◽  
Transmission Electron ◽  
2D Polymers ◽  
Tilt Boundaries ◽  
2D Polymer ◽  
Grain Coalescence

Two-dimensional (2D) polymers hold great promise in the rational materials design tailored for next-generation applications. However, little is known about the grain boundaries in 2D polymers, not to mention their formation mechanisms and potential influences on the material’s functionalities. Using aberration-corrected high-resolution transmission electron microscopy, we present a direct observation of the grain boundaries in a layer-stacked 2D polyimine with a resolution of 2.3 Å, shedding light on their formation mechanisms. We found that the polyimine growth followed a “birth-and-spread” mechanism. Antiphase boundaries implemented a self-correction to the missing-linker and missing-node defects, and tilt boundaries were formed via grain coalescence. Notably, we identified grain boundary reconstructions featuring closed rings at tilt boundaries. Quantum mechanical calculations revealed that boundary reconstruction is energetically allowed and can be generalized into different 2D polymer systems. We envisage that these results may open up the opportunity for future investigations on defect-property correlations in 2D polymers.

A Field Ion Observation of a Grain Boundary Node

1981 ◽  
Vol 39 ◽  
pp. 10-11
Author(s):  
H. C. Eaton
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Regular Structure ◽  
Atomic Scale ◽  
Polycrystalline Materials ◽  
Conventional Imaging ◽  
Boundary Node ◽  
Computer Reconstruction ◽  
Transmission Electron ◽  
Field Ion Microscope

In recent years there has been considerable interest in relating the structure of high angle grain boundaries to the properties of polycrystalline materials. It has been firmly established that these interfaces exhibit a highly complex, and often regular structure on the near atomic scale which can control the chemical or mechanical macro-behavior of the aggregate. However, unlike external surfaces, which can be probed by conventional surface spectroscopic and diffraction techniques, the internal structure of the grain boundary is usually only accessible with the transmission electron microscope. Interpretation of such images is at best complex and oftentimes the fine-scale structure is not observed due to resolution limitation of conventional imaging modes. The field ion microscope (FIM), on the other hand, offers both high resolution and a more direct imaging process. The FIM has been used in numerous grain boundary observations and more recently the results have been improved by computer reconstruction techniques providing detailed topographies of the interface. Presented in the present work is a computer reconstruction of the point of junction between three grains and two of the associated grain boundaries (see Figure 1).

Atomic Scale Analysis of Oxygen Vacancy Segregation At Grain Boundaries in Ceramic Oxides

2001 ◽  
Vol 7 (S2) ◽  
pp. 308-309
Author(s):  
N. D. Browning ◽  
J. P. Buban ◽  
Y. Ito ◽  
R. F. Klie ◽  
Y. Lei
Keyword(s):  
Grain Boundaries ◽  
Elevated Temperatures ◽  
Scanning Transmission Electron Microscope ◽  
Atomic Scale ◽  
Contrast Imaging ◽  
Ceramic Oxides ◽  
Transmission Electron ◽  
Scanning Transmission ◽  
Resolution Analysis ◽  
Z Contrast

The properties of ceramic oxides being developed for such varied applications as fuel cells, ionic transporting membranes, high-Tc superconductors, ferroelectrics and varistors are dominated by the presence of grain boundaries. Key to controlling the electronic properties of the grain boundaries in these materials is a fundamental understanding of the complex relationship between structure, composition and local electronic structure. The ability to characterize and directly correlate these parameters on the atomic scale is afforded by the combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM). Furthermore, the recent development of in-situ heating capabilities in the JEOL 201 OF STEM/TEM permits atomic resolution analysis to be performed at elevated temperatures and the interactions of grain boundaries with the oxygen vacancies determined.Figure 1 shows an example of the type of experiment that can be performed using these methods.

Interfacial Microstructure of Titanium Nitride – Titanium Diboride Composite Synthesized by Hot Shock Compaction

2007 ◽  
Vol 561-565 ◽  
pp. 2481-2484
Author(s):  
Seiichiro Ii ◽  
Teruko Nishitani ◽  
Ryuichi Tomoshige
Keyword(s):  
Electron Microscopy ◽  
Grain Boundaries ◽  
High Resolution Electron Microscopy ◽  
Interfacial Microstructure ◽  
Secondary Phases ◽  
Shock Compaction ◽  
High Temperature Synthesis ◽  
Transmission Electron ◽  
Resolution Electron ◽  
Average Grain Size

Interfacial microstructure of TiN-TiB2 composite, which was synthesized by hot shock compaction combined explosively shock condolidation and self-propagating high-temperature synthesis, was investigated by transmission electron microscopy (TEM). In the TiN-TiB2 composite included 60mol% TiN, an experimentally measured average grain size of the both TiN and TiB2 was approximately 500nm, and it decreased rather than those of the raw powders. By the conventional TEM observations, we clarified that there was a specific orientation relationship between cubic TiN and hexagonal TiB2. The high resolution electron microscopy (HREM) observations revealed that the TiN/TiB2 interphase boudnaries were atomically flat. We also observed grain boundaries of the composite and found that no secondary phases such as amorphous phase and precipitates were observed at the grain boundaries in the composite.

Electron Energy Analysis of Germanium and Silica Layers on Silicon Substrates

1975 ◽  
Vol 33 ◽  
pp. 96-97
Author(s):  
R. W. Ditchfield ◽  
A. G. Cullis
Keyword(s):  
Epitaxial Growth ◽  
Electron Energy ◽  
Silicon Substrates ◽  
Secondary Phases ◽  
Si Substrates ◽  
Transmission Electron ◽  
Layer Structures ◽  
Si Films ◽  
Electron Energy Loss ◽  
Growth Centres

An energy analyzing transmission electron microscope of the Möllenstedt type was used to measure the electron energy loss spectra given by various layer structures to a spatial resolution of 100Å. The technique is an important, method of microanalysis and has been used to identify secondary phases in alloys and impurity particles incorporated into epitaxial Si films.Layers Formed by the Epitaxial Growth of Ge on Si Substrates Following studies of the epitaxial growth of Ge on (111) Si substrates by vacuum evaporation, it was important to investigate the possible mixing of these two elements in the grown layers. These layers consisted of separate growth centres which were often triangular and oriented in the same sense, as shown in Fig. 1.

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.

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