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.

Atomic Structure and Property Correlation in Pulsed Laser Deposited High -Tc Films

1998 ◽  
Vol 526 ◽  
Author(s):  
R. Kalyanaraman ◽  
S. Oktyabrsky ◽  
K. Jagannadham ◽  
J. Narayan
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Grain Boundaries ◽  
Atomic Structure ◽  
Substrate Surface ◽  
Pulsed Laser ◽  
Structure And Property ◽  
Transmission Electron ◽  
Tilt Boundaries ◽  
Z Contrast

AbstractThe atomic structure of grain boundaries in pulsed laser deposited YBCO/MgO thin films have been studied using transmission electron microscopy. The films have perfect texturing with YBCO(001)//MgO(001), giving rise to low-angle [001] tilt boundaries from the grains with the c-axis normal to substrate surface. Low angle grain boundaries have been found to be aligned preferentially along (100) and (110) interface planes. The energy of (110) boundary planes described by an alternating array of [100] and [010] dislocation is found to be comparable to the energy of a (100) boundary. The existence of these split dislocations is shown to further reduce the theoretical current densities of these boundaries indicating that (110) boundaries carry less current as compared to (100) boundaries of the same misorientation angle. Further, Z-contrast transmission electron microscopy of a 42° asymmetric high-angle grain boundary of YBCO shows evidence for the existence of boundary fragments and a reduced atomic density along the boundary plane

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.

Grain boundary faceting in YBa2Cu3O7–x bicrystal thin films on SrTiO3 substrates

2002 ◽  
Vol 17 (2) ◽  
pp. 323-335 ◽  
Author(s):  
Qiang Jin ◽  
Siu-Wai Chan
Keyword(s):  
Thin Films ◽  
Boundary Plane ◽  
Atomic Scale ◽  
Transmission Electron ◽  
Film Boundary ◽  
Lattice Images ◽  
Tilt Boundaries ◽  
The Difference ◽  
Straight Segments ◽  
Misorientation Angles

The structure of [001] tilt boundaries in YBa2Cu3O7–x (YBCO) thin films deposited on [001] tilt SrTiO3 (STO) bicrystal substrates has been characterized by transmission electron microscopy (TEM). These boundaries are (100)/(210), (310)/(510), (410)/(310), (510)/(210), (210)/(410), and (210)/(310), with corresponding misorientation angles of 26°, 29°, 32°, 37°, 40°, and 44°. It was found that the YBCO film boundaries were meandering along the relatively straight substrate boundaries. High-resolution lattice images indicated that the microscopic meandering of the film boundary essentially consisted of many straight segments of facets at the atomic scale. On the basis of the observed facets, three competing factors controlling the formation of facets are discussed. First, the boundary plane is defined by Miller indices (hk0) in both crystals with sufficiently small h, k (i.e., h, k ≤ 5) and sufficiently large effective interplanar spacing (i.e., deff > 0.06 nm). Second, the closure failure defined by the difference between the local misorientation from the design misorientation is small, i.e., less than 2°. Third, the deviation of a local facet plane is observed to be less than 30° from the design boundary plane. Higher values of deffs are observed to give tolerance to higher deviation angles.

scholarly journals In Situ Observation of Crystalline Silicon Growth from SiO2 at Atomic Scale

Research ◽  
2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Kaihao Yu ◽  
Tao Xu ◽  
Xing Wu ◽  
Wen Wang ◽  
Hui Zhang ◽  
...  
Keyword(s):  
Electron Beam ◽  
Crystalline Silicon ◽  
Atomic Scale ◽  
Formation Mechanisms ◽  
In Situ Observation ◽  
Transmission Electron ◽  
Si Nanoparticles ◽  
Speed Up ◽  
Silicon Growth

The growth of crystalline Si (c-Si) via direct electron beam writing shows promise for fabricating Si nanomaterials due to its ultrahigh resolution. However, to increase the writing speed is a major obstacle, due to the lack of systematic experimental explorations of the growth process and mechanisms. This paper reports a systematic experimental investigation of the beam-induced formation of c-Si nanoparticles (NPs) from amorphous SiO2 under a range of doses and temperatures by in situ transmission electron microscopy at the atomic scale. A three-orders-of-magnitude writing speed-up is identified under 80 keV irradiation at 600°C compared with 300 keV irradiation at room temperature. Detailed analysis reveals that the self-organization of c-Si NPs is driven by reduction of c-Si effective free energy under electron irradiation. This study provides new insights into the formation mechanisms of c-Si NPs during direct electron beam writing and suggests methods to improve the writing speed.

Structure of high-angle-tilt boundaries in YBa2Cu3-O7-x thin films

1991 ◽  
Vol 49 ◽  
pp. 1086-1087
Author(s):  
D. H. Shin ◽  
J. Silcox ◽  
S. E. Russek ◽  
D. K. Lathrop ◽  
B. H. Moeckly ◽  
...  
Keyword(s):  
Thin Films ◽  
Grain Boundaries ◽  
Weak Link ◽  
Boundary Region ◽  
Atomic Scale ◽  
High Resolution Imaging ◽  
High Angle ◽  
Superconducting Properties ◽  
Tilt Boundaries ◽  
Resolution Imaging

It has been known that high angle tilt grain boundaries in c-axis oriented YBa2Cu3O7-x thin films cause weak link behavior in the transport properties reducing Jc's by several orders of magnitude. These grain boundaries have been shown to be clean both structurally and chemically by high resolution imaging and microanalysis studies. Therefore the mechanism of weak link behavior in thin film YBa2Cu3O7-x is not yet understood.Recently it has been deduced from the behavior of weak link Jc under small magnetic fields that the high angle tilt boundaries are nonuniform, consisting of several regions of good contact, each about 5-10 % of the boundary length, with the rest of the boundary region being poor. This seems to suggest that the superconducting properties at the boundary may be sensitive to changes in structures of atomic scale, since typical grain boundaries are free of macroscopic (≥ 10 Å) defects all along the boundaries.

Structural analysis of faceted grain boundaries in Bi-doped Cu

1989 ◽  
Vol 47 ◽  
pp. 278-279
Author(s):  
D. E. Luzzi ◽  
B. Blum ◽  
H. Inui
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Phase Transformation ◽  
Structural Analysis ◽  
Grain Boundaries ◽  
Degrees Of Freedom ◽  
Pattern Analysis ◽  
Two Dimensional ◽  
Kikuchi Pattern ◽  
Transmission Electron

Conventional(CTEM)and high-resoIution(HREM) transmission electron microscopy have been used to investigate the structure of faceted grain boundaries in Cu doped with Bi. The solubility of Bi in Cu exhibits retrograde behavior with a maximum of 160 at. ppm. at 850 ° C and decreasing above and below this temperature (eg. to < 3 at. ppm. at 600 ° C). When aged at temperatures below this retrograde region, Blis known to segregate tothe grain boundaries. In addition to this segregation, these materials exhibit a reversible faceting-de-faceting transition at 710 ° C which has been postulated asarising from a two-dimensional phase transformation at the grain boundaries. Until the present time, little experimental work has been doneto characterize the structures of these faceted boundaries.In the present experiments, Kikuchi pattern analysis and edge-on imaging have been used to characterize the five macroscopic degrees of freedom of individual facets. Bulk Cu specimens with 50 at.ppm.

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.

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