Search

Досліджено особливості поведінки магнітно-абразивного інструменту (МАІ) і характер зміни сил переважно фрикційного походження, що виникають під час магнітно-абразивної обробки (МАО) циліндричних зразків діаметром 16 мм, виготовлених з феро-, пара- і діамагнітних матеріалів, що виникають у робочих зазорах кільцевого типу шириною 35 мм залежно від швидкості обертання навколо осі кільцевої ванни в діапазоні 100–300 об/хв, частоти обертання навколо власної осі від 0 до 80 рад/с, при магнітній індукції в зонах обробки 0,18 і 0,25 Тл, магнітно-абразивних порошкових матеріалів різного типу та розміру. Показано, що величина ефективного моменту тертя змінюється в діапазоні від 0 до 1,4 Нм. Ідентифіковано три області технологічних умов МАО: 1) область формування квазістійкого магнітно-абразивного інструменту; 2) область стабільно сформованого МАІ; 3) область з аномальним зростанням / падінням сил тертя. Аналіз отриманих закономірностей дозволив ідентифікувати процеси, пов’язані з особливостями поведінки частинок МАІ в процесі МАО при безпосередньому контакті з робочою поверхнею, а також умови утворення зон заклинювання, що виникають між полюсними наконечниками і поверхнею деталей. Показано, що використання порошків з округлою формою частинок при МАО в зазначених вище умовах обробки забезпечує переважне пластичне деформування поверхневого шару зразків з пара- і діамагнітних матеріалів. Найбільше на зміну сил фрикційного походження впливає зростання розміру частинок магнітно-абразивних порошків. Вплив зміни сил магнітного поля в досліджуваному діапазоні несуттєвий.

Nanoscale α-Al(FeMn)Si dispersoids in Al alloys play a vital role in improving the recrystallization resistance and mechanical properties of alloys at elevated temperatures. This study investigates the influence of Cu on the precipitation behavior of α-dispersoids in Al–Mg–Si alloys during heat treatment at 500 °C. α-dispersoids in an alloy without Cu addition had rod- or plate-like morphologies. The addition of Cu effectively inhibits the precipitation of α-dispersoids through the formation of fine spherical dispersoids, resulting enhanced mechanical properties of the alloy at elevated temperatures. Evidence from high-resolution transmission electron microscopy demonstrated that the rod- or plate-like structures have simple cubic structures, whereas the spherical α-dispersoids are coherent with the Al matrix along the [101] zone axis of Al, resulting in finer dispersoids, higher thermal stability, and lower coarsening rates. However, its crystal structure requires further investigation.

The UnitCell Tools package was developed to determine unit-cell parameters of a crystal from a single electron diffraction pattern with high-order Laue zone reflections acquired in the conventional transmission electron microscope., Electron diffraction techniques in transmission electron microscopy (TEM) have been successfully employed for determining the unit-cell parameters of crystal phases, albeit they exhibit a limited accuracy compared with X-ray or neutron diffraction, and they often involve a tedious measurement procedure. Here, a new package for determining unit-cell parameters from a single electron diffraction pattern has been developed. The essence of the package is to reconstruct a 3D reciprocal primitive cell from a single electron diffraction pattern containing both zero-order Laue zone and high-order Laue zone reflections. Subsequently, the primitive cell can be reduced to the Niggli cell which, in turn, can be converted into the unit cell. Using both simulated and experimental patterns, we detail the working procedure and address some effects of experimental conditions (diffraction distortions, misorientation of the zone axis and the use of high-index zone axis) on the robustness and accuracy of the software developed. The feasibility of unit-cell determination of the TiO2 nanorod using this package is also demonstrated. Should the parallel-beam, nano-beam and convergent-beam modes of the TEM be used flexibly, the software can determine unit-cell parameters of unknown-structure crystallites (typically >50 nm).

Molybdenum ditelluride (MoTe2) has attracted ever-growing attention in recent years due to its novel characteristics in spintronics and phase-engineering, and an efficient and convenient method to achieve large-area high-quality film is an essential step toward electronic applications. However, the growth of large-area monolayer MoTe2 is challenging. Here, for the first time, we achieve the growth of a centimeter-sized monoclinic MoTe2 monolayer and manifest the mechanism of immobilized precursor particle driven growth. Microscopic characterizations reveal an obvious trend of immobilized precursor particles being consumed by the monolayer and continuing to provide a source for the growth of the monolayer. Time-of-flight secondary ion mass spectrometry verifies the attachment of hydroxide ions on the surface of the MoTe2 monolayer, thereby realizing the inhibition of crystal growth along the [001] zone axis and the continuous growth of the MoTe2 monolayer. The first-principles DFT calculations prove the mechanism of immobilized precursor particles and the absorption of hydroxide ions on the MoTe2 monolayer. The as-grown MoTe2 monolayer exhibits a surface roughness of 0.19 nm and average conductivity of 1.5 × 10-5 S/m, which prove the smoothness and uniformity of the MoTe2 monolayer. Temperature-dependent electrical measurements together with the transfer characteristic curves further demonstrate the typical semimetallic properties of monoclinic MoTe2. Our research elaborates the microscopic process of immobilized precursor particles to grow large-area MoTe2 monolayer and provides a new thinking about the growth of many other two-dimensional materials.

Complex concentrated solutions of multiple principal elements are being widely investigated as high- or medium-entropy alloys (HEAs or MEAs)1–11, often assuming that these materials have the high configurational entropy of an ideal solution. However, enthalpic interactions among constituent elements are also expected at normal temperatures, resulting in various degrees of local chemical order12–22. Of the local chemical orders that can develop, chemical short-range order (CSRO) is arguably the most difficult to decipher and firm evidence of CSRO in these materials has been missing thus far16,22. Here we discover that, using an appropriate zone axis, micro/nanobeam diffraction, together with atomic-resolution imaging and chemical mapping via transmission electron microscopy, can explicitly reveal CSRO in a face-centred-cubic VCoNi concentrated solution. Our complementary suite of tools provides concrete information about the degree/extent of CSRO, atomic packing configuration and preferential occupancy of neighbouring lattice planes/sites by chemical species. Modelling of the CSRO order parameters and pair correlations over the nearest atomic shells indicates that the CSRO originates from the nearest-neighbour preference towards unlike (V−Co and V−Ni) pairs and avoidance of V−V pairs. Our findings offer a way of identifying CSRO in concentrated solution alloys. We also use atomic strain mapping to demonstrate the dislocation interactions enhanced by the CSROs, clarifying the effects of these CSROs on plasticity mechanisms and mechanical properties upon deformation. Direct experimental evidence of chemical short-range atomic-scale ordering (CSRO) in a VCoNi medium-entropy alloy is provided via diffraction and electron microscopy, analysed from specific crystallographic directions.

An epitaxial SmNiO3 thin-film grown on an LaAlO3 (001) substrate using pulsed laser deposition is investigated with spherical-aberration corrected scanning transmission electron microscopy techniques, including high-angle annular dark field, X-ray energy dispersive, and electron energy-loss spectroscopy. High-density Ruddlesden–Popper (RP)-type faults, which generate two types of image contrast due to overlaps along the electron beam direction, are identified with the translational vector of 1/2a⟨111⟩c, corresponding to 1/2a⟨101⟩c displacement of Sm atoms when observed along the [010]c zone axis. These defects originate from Sm-rich non-stoichiometry within the SmNiO3, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. The effects of high-density RP faults on the lattice strain, domain size, and strong electronic-lattice correlations indicate that RP faults can provide extra freedom to tailor the physical properties of SmNiO3 thin films for potential electronic device applications. High-density Ruddlesden–Popper-type faults are revealed in an epitaxial SmNiO3 thin film grown on LaAlO3 (001) by pulsed laser deposition, originating from Sm-rich non-stoichiometry, and their directions depend on the local stress states. Lattice distortion induced by the RP faults reduces the metal-to-insulator transition temperature to around 340 K. RP faults provide extra freedom to tailor intriguing properties of SmNiO3 for potential electronic device applications.

Various orientations and diffraction patterns from nanoscale Al precipitates in eutectic Si were investigated by high-resolution transmission electron microscopy combined with transition matrix and stereographic projection. It was found that the Al precipitates had 12 variants, all orientation relationships can be expressed as: (001)Al//{111}Si, [110]Al// 1 ¯ 10 >Si. Further, a new diffraction pattern model from Al precipitates was established under [111]Si zone axis, which was in good agreement with the experiment data. The microstructure, adhesion strength and electronic structure of the interface between Al precipitate and Si matrix were studied by first-principles calculation and experimental observation. The results show that the covalent bonds are formed between interfacial Al and Si atoms, which play a key role in interfacial bind strength. Based on the Griffith fracture theory, the cracks tend to form and expand in the interior of Al precipitates firstly, and the interfaces can act as a protective layer to prevent crack propagation. Therefore, the nanoscale Al precipitates will improve the toughness of eutectic Si particles by releasing part of stress through lattice distortion. In addition, the stretched nanoscale Al precipitates can act as effective heterogeneous nucleation sites for high density deformation nanotwins in eutectic Si during deformation, which significantly improved the deformability of eutectic Si.

Bismuth titanate based materials have wide potential applications in the fields of dielectrics, piezoelectrics, ferroelectrics, catalysis and energy storage. In this study, a two dimensional (2-D) layered H1.07Ti1.73O4·nH2O (HTO) crystal was used as a precursor to prepare 2-D bismuth titanate oriented polycrystal nanocomposites using two kinds of Bi3+ sources. The chemical reaction mechanisms for the formation of bismuth titanates are proposed, and the crystal structures and their conversions are also identified. The formation mechanism of the discontinuous-zone-axis is revealed. The obtained bismuth titanates are oriented polycrystals constructed from the orientation nanocrystals. In the process of forming the oriented polycrystal, the zone axis of the bismuth titanates obtained under different reaction conditions can vary even if the same reactants are used in the reaction. The certain topological correspondences among the oriented polycrystal, the precursor, and the intermediate, as well as the formation of bismuth titanates with a discontinuous-zone-axis based on a topochemical mesocrystal conversion reaction, were proposed. The special arrangement structure of the TiO6 octahedral layers accommodating in the HTO crystal is the main reason for the constant change of the zone axis of the bismuth titanate nanocomposite. However, based on the crystallographic investigation of the reaction mechanism involved in the formation process of construction of the bismuth titanate oriented polycrystal nanocomposite from the HTO crystal, it is found that the topochemical mesocrystal conversion reaction with a discontinuous-zone-axis is different from the conventional topochemical reactions. This may be attributed to the combination of the HTO matrix and Bi3+. It is vital to study the controllable preparation of bismuth titanate based nanocomposites and further understand the topochemical reaction.

The twin–twin interaction phenomenon in Ti is studied by incorporating experimental observation and theoretical analysis. Secondary $$ \{ {10\bar{1}2} \} $$ twins are stimulated in primary $$ \{ {11\bar{2}2} \} $$ and $$ \{ {11\bar{2}4} \} $$ via twinning dislocation dissociation. Primary twin variants are found either share the same $$ \langle {10\bar{1}0} \rangle $$ zone axis or with different zone axes. Schmid law, dislocation theory and crystallographic analysis are used to investigate the formation processes and physical mechanisms of the twin–twin interaction phenomenon. Results show that non-Schmid secondary twins are stimulated under the effect of primary twinning interactions. Besides to secondary twinning dislocations, glissile and sessile dislocations generate as a result of primary dislocation dissociation. Glissile dislocation glide on the easy slip prismatic plane, while sessile dislocation accumulates and leads to the increase of local strain.

Conventional SEM-based micro-texture technique has attracted broad interests in recent years. There is also an important need to develop TEM based micro-texture methods, since it was expected to back up some of the shortages of conventional micro-texture technique. In the present work, a new methodology was proposed for measuring the micro-texture in TEM manually without the assistance of any external commercial attachment. The orientation matrix, which maps uniquely to the Euler angles, was considered the transformation matrix between crystal coordinates and the sample coordinate. By tilting the TEM specimen to a low-index zone axis with a double-tilt sample holder, the crystal coordinates could be drawn based on the acquired diffraction pattern. The transformation matrix between each defined coordinates could be deduced; and the Euler angles were identified accordingly. The micro-texture of a twin lamella in a rolled magnesium sheet was analyzed as an example.

Deformation twin is one of the most important strain accommodation mechanisms and ultimately influences the mechanical properties for magnesium and its alloys. Especially, { 10 1 ¯ 1 } twin is usually thought to be closely related to the fracture or fatigue process of magnesium alloys. In the present work, the characteristics of microstructure near fracture region of deformed magnesium alloy have been investigated by a combination of electron back-scatter diffraction (EBSD) and transmission electron microscope (TEM). It has found that a large of deformation twins occur near fraction region, including { 10 1 ¯ 2 } and { 10 1 ¯ 1 } primary twins, { 10 1 ¯ 1 } - { 10 1 ¯ 2 } double twin and { 10 1 ¯ 1 } - { 10 1 ¯ 2 } - { 10 1 ¯ 1 } - { 10 1 ¯ 2 } quadruple twin. The actual boundaries of { 10 1 ¯ 1 } twins at atomic scale consist of { 10 1 ¯ 1 } coherent twinning boundaries (TBs) and parallel basal-pyramidal (BPy/PyB) planes. The tip of { 10 1 ¯ 1 } twin can even end up with BPy/PyB interfaces only. The experimental observations also reveal that when two { 10 1 ¯ 1 } twin variants sharing a common [ 11 2 ¯ 0 ] zone axis approach each other, the growth of one twin is usually hindered by the boundaries of the other twin. In addition, an apparent “crossing” phenomenon is also discovered when interaction of two { 10 1 ¯ 1 } twins takes place. According to these experimental observations, the possible underlying mechanisms behind such phenomena are proposed and discussed. These finding are expected to provide an insight into understanding the twinning behavior and the relationship between twin and fracture in magnesium and other materials with hexagonal structure.

In response to Wierzchos et al. (1) regarding the mechanism of water extraction from gypsum rock by desert colonizing microorganisms (2), we provide details that refute their incorrect assessments. We carefully selected areas without microorganism colonies that only contained gypsum, as confirmed by X-ray diffraction (XRD), for our culture experiments. Raman is useful for localized analysis of phase on surfaces, but here, it is complementary to XRD, which provides sample-wide detection (3, 4). Furthermore, selected area electron diffraction (SAED) confirms anhydrite, exhibiting arcs at 0.347 ± 0.003 nm and 0.278 ± 0.002 nm [(200) and (211) planes, respectively] with a [01−1] zone axis (Fig. 1 A and B ). The closest reflection for gypsum, the (130) plane, was not observed. SAED and fast Fourier transform (FFT) show twofold symmetry of the arcs, while the gypsum (130) plane exhibits fourfold symmetry, which was not observed. Finally, the crystal morphology of gypsum (monoclinic) was observably different from anhydrite (orthorhombic) (Fig. 1 C − F ). Thus, XRD, high-resolution … [↵][1]1To whom correspondence may be addressed. Email: david.k{at}uci.edu. [1]: #xref-corresp-1-1

Ferroelectric materials, and more specifically ferroelectric domain walls (DWs) have become an area of intense research in recent years. Novel physical phenomena have been discovered at these nanoscale topological polarization discontinuities by mapping out the polarization in each atomic unit cell around the DW in a scanning transmission electron microscope (STEM). However, identifying these features requires an understanding of the polarization in the overall domain structure of the TEM sample, which is often a time-consuming process. Here, a fast method of polarization mapping in the TEM is presented, which can be applied to a range of ferroelectric materials. Due to the coupling of polarization to spontaneous strain, we can isolate different strain states and demonstrate the fast mapping of the domain structure in ferroelectric lead titanate (PTO). The method only requires a high-resolution TEM or STEM image and is less sensitive to zone axis or local strain effects, which may affect other techniques. Thus, it is easily applicable to in-situ experiments. The complimentary benefits of Fourier masking with more advanced mapping strategies and its application to other materials are discussed. These results imply that Fourier masked polarization mapping will be a useful tool for electron microscopists in streamlining their analysis of ferroelectric TEM samples. LAY DESCRIPTION: This paper addresses a problem that often occurs when looking at a ferroelectric material in the Transmission Electron Microscope (TEM). Ferroelectric samples are interesting because they form tiny areas inside themselves with arrow of charge in each one. The thinner the sample, the smaller these regions, called "domains" become. These arrows of charge point in different directions in each domain of the sample. The boundary where these domains meet have interesting properties to study in a TEM but it's important to figure out which way the arrows point in the domains around the boundary. What causes the arrows in the different domains is tiny shifts of different atoms in unit cell away from their neutral position, usually because they're being squeezed by pressure from the domains nearby. The problem is that these tiny atoms moving are difficult to measure and see where the charged arrow is pointing, often it's hard to know how many different domains are even in the sample and where they begin. This paper discusses a method called "Fourier masking" to quickly see what's going on in the overall TEM sample, where the domains are and roughly where the arrows point. It does this by looking at the spacings of the atoms from a magnification where you can just about see the lines of atoms. In lead titanate the unit cell is a rectangle and the arrow always points in line with the long side of the rectangle. The Fourier masking lets you see which direction the long side of the rectangular unit cell is pointing in different parts of your TEM image. The big advantage is that it takes about two minutes to do and uses software that almost every TEM already has. That lets the TEM user quickly know where the domains are in their TEM samples and roughly which way the arrows of charge are pointing. Then they can choose the most interesting features focus on for higher resolution analysis.

Ferrihydrite is ubiquitous in natural environments, and its transformation significantly influences the fate of heavy metals. Although Pb(II) adsorption on iron oxides has been extensively studied, there is still a knowledge gap on the fate of Pb during the dynamic processes of iron oxide transformation. In this study, a set of wet chemistry experiments, spherical aberration corrected scanning transmission electron microscopy (Cs-STEM) integrated with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS) were used to unravel Pb interactions with iron oxides during ferrihydrite transformation processes under abiotic conditions. Wet chemistry experiments, STEM-EDS elemental mapping and line scans, and quantitative analysis suggested that Pb penetrated into hematite nanoparticles during the transformation processes. STEM analysis at sub-nanoscales, XRD fine scans, and XAS analysis provided evidence of Pb incorporation into the crystal structures of hematite nanoparticles, in which Pb distributed along the zone axis and enlarged the lattice distance of hematite. These results advanced our understanding of the dynamic interactions of Pb with iron oxides by offering new perspectives about the critical roles of chemical speciation, nano-scale spatial distribution, and atomic coordination environments in controlling the geochemical dynamics of heavy metals.

The direct observation of the doping sites of deep-level impurities in hyperdoped silicon is essential to determine the impurity diffusion, distribution, and precipitation via different hyperdoping processes or thermal annealing conditions. This is crucial to clarify the functioning of a mechanism, which can improve the impurity electroactivity. However, this observation, which is usually performed by using high-resolution transmission electron microscopy (HRTEM), is limited by some restrictions in the microscopic imaging conditions, such as the microscope resolution, the defocus of the objective lens, the specimen thickness, and the projected orientation of the specimen (i.e. the zone axis). Therefore, to eliminate these restrictions, conventional field-emission-gun HRTEM images in combination with image processing (deconvolution) were investigated in order to obtain structure images with atomic resolution. Both the substitutional and the interstitial doping sites of oxygen, chalcogen (sulfur and selenium), and transition metal (titanium and cobalt) impurities in silicon were determined by image contrast analysis. Finally, the favorable conditions for the direct observation of doping sites were defined.

This paper reports on the real-time observation of mechanical stress-induced micro and nano domain evolution in a single crystal relaxor ferroelectric [011] poled 24PIN-PMN-PT “3-2 mode” nano-sized lamella. Mechanical loading in the [100] direction was applied to lamella in situ within a transmission electron microscope, with a [ 0 1 ¯ 1 ] viewing direction selected for the recording of real-time videos of the domain evolution within the lamella. The observed dominant behaviour under loading is a reversible response composed of the movement of microdomains and the disappearance of nanodomains. Changes in the selected area diffraction pattern down the [ 0 1 ¯ 1 ] zone axis are reported, and provide evidence of a significant increase in crystal symmetry under compression. A qualitative insight into the behaviour of the lamella's mechanical response is obtained via predictions of the non-uniform stress distribution within the lamella found using simple finite element analysis. The correlation between the observed morphology changes, diffraction pattern changes, and the known mechanical stress induced polydomain-rhombohedral to monodomain-orthorhombic phase transition of bulk [011] poled 24PIN-PMN-PT “3-2 mode” single crystal is discussed.

The crystal structure of naturally occurring zaccariniite from Loma Peguera (Republica Dominicana) has been studied in Transmission Electron Microscopy (TEM) with variable angle Precession Electron Diffraction (PED) techniques: 0.7° Precession Electron Diffraction Tomography (Precession EDT) for unit cell and Laue class sorting, 0.5° Scanning Precession Diffraction (SPED) for crystal orientation mapping and grain alignment, and high symmetry zone axis 1.2° to 2.2° Zone Axis High Angle Precession Electron Diffraction (ZA high angle PED) for Space Group assessment and supercell information gathering. The natural sample has been prepared into an electron thin lamella by means of Focused Ion Beam (FIB). The analysis of the data has yielded tetragonal cell parameters of 3.86, 3.86, 6.77 A and space group of P4/nmm for the basic structure, and its constituent atom positions for Ni, As and Rh were determined as well by ab-initio structure resolution method in accordance to the elemental composition of the natural zaccariniite obtained with Energy Dispersive X-ray (EDX) and High Magnification Electron Microscopy (HMEM) analysis. A modulation of the crystal basic structure of 3 by 1 in the basal plane has been reported for the first time on natural occurring zaccariniite.

Due to the limited availability of slip systems, deformation twins have to play an additional role to accommodate strain in developing plastic deformation and undoubtedly influence the mechanical properties of materials with hexagonal structure. Therefore, understanding the interfacial characteristic of deformation twin and interaction behavior between different twin variants during plastic deformation is crucial to microstructural design, processing and application of hexagonal close-packed (hcp) materials. In the present study, { 11 2 ¯ 2 } twinning behavior in deformed titanium, with an emphasis on the misorientation across { 11 2 ¯ 2 } twinning boundary and the interaction between two { 11 2 ¯ 2 } twin variants sharing the same [ 10 1 ¯ 0] zone axis, is investigated by a combination of electron back-scatter diffraction (EBSD) and transmission electron microscopy (TEM) techniques. The results reveal that the actual value of misorientation across { 11 2 ¯ 2 } twinning boundary is not always equal to the theoretical one. Also, a distinctive phenomenon of one twin penetrating into the interior of the other twin, which is not observed when two { 10 1 ¯ 2 } twins encounter to each other, is discovered when the interaction between two { 11 2 ¯ 2 } twins takes place. Accordingly, the possible mechanisms behind such phenomena are proposed and discussed. These findings are expected to provide an insight into understanding the twinning behavior in hcp metals.

Nd2Fe14B and Nd2 − xDyxFe14B (x = 0.25,0.50) particles were prepared by the modified co-precipitation followed by reduction-diffusion process. Bright field scanning transmission electron microscope (BF-STEM) image revealed the formation of Nd-Fe-B trigonal prisms in [-101] viewing zone axis, confirming the formation of Nd2Fe14B/Nd2 − xDyxFe14B. Accurate site for the Dy substitution in Nd2Fe14B crystal structure was determined as “f” site by using high-angle annular dark field scanning transmission electron microscope (HAADF-STEM). It was found that all the “g” sites are occupied by the Nd, where’s and Dy occupied only the “f” site. Anti-ferromagnetic coupling at “f” site decreased the magnetic moment values for Nd1.75Dy0.25Fe14B (23.48 µB) and Nd1.5Dy0.5Fe14B (21.03 µB) as compared to Nd2Fe14B (25.50 µB). Reduction of magnetic moment increased the squareness ratio, coercivity and energy product. Analysis of magnetic anisotropy at constant magnetic field confirmed that “f” site substitution did not change the patterns of the anisotropy. Furthermore, magnetic moment of Nd2Fe14B, Nd2 − xDyxFe14B, Nd (“f” site), Nd (“g” site) and Dy (“f” site) was recorded for all angles between 0-180o.

High (or medium)-entropy alloys (H/MEAs) are complex concentrated solid solutions that may develop chemical short-range order (CSRO). In this regard, CrCoNi, the prototypical face-centered-cubic MEA, has recently kindled a debate in the H/MEA community, as it is uncertain if CSRO can possibly form in such a multi-principal-element solution, where no equilibrium or metastable intermetallic compounds have ever been seen or predicted. To answer this challenging question, here we present firm experimental evidence for the CSRO from electron diffraction as well as atomic-resolution chemical mapping, particularly under an appropriate zone axis. We also develop a methodology to reliably determine the locations of atomic columns from the line scan profiles in the chemical maps, as well as a quantitative covariance-based correlation analysis of the column chemical compositions to reveal the spatial correlations between various atomic pairs. The detailed chemical information affirms the tendency for like-pair avoidance and unlike-pair preference, specifies the preferred atomic packing and plane stacking by the three constituent species, and suggests a proposed atomic configuration that constitutes the CSRO motif. The fraction of CSRO regions is moderately lowered after either plastic deformation or high-temperature heating. A comparison is also discussed with previous endeavor identifying CSRO in H/MEAs.

Perovskite quantum dots (PeQDs) have been developed rapidly as photoactive materials in hybrid phototransistors because of their strong light absorption, broad bandgap customizability, and defect-tolerance in charge-transport properties. The solvent treatment has been well recognized as a practical approach for improving the charge transport of PeQDs and the photoresponsivity of PeQD phototransistors. However, there is a lack of fundamental understanding of the origin of its impacts on the material’s ambient stability as well as phototransistor’s operational lifetime. Especially, the relationship between surface ligands dissociation and their microstructural reconstruction has not been fully elucidated so far. Herein, we report that a simultaneous enhancement of photoresponsivity and ambient tolerance for PeQD-based hybrid phototransistors can be realized via medium-polarity-solvent treatment on solid-state PeQDs. Our comprehensive optoelectronic characterization and electron microscopic study reveals that the crystal morphology, instead of surface ligands, is the dominating factor that results in the PeQD’s stability enhancement associated with the preservation of optical property and quantum confinement. Besides, we unveil a marginal reconstruction process occurred during solvent treatment, which opens up a new route for facets-oriented attachment of PeQDs along the zone axis to suppress the damage from water molecules penetration. Our study yields a new understanding of the solvent impact on PeQD microstructures reconstruction and suggests new routes for perovskite materials and corresponding device operational stability enhancement.

International audience; Dioctahedral micas are composed of two tetrahedral sheets and one octahedral sheet to form TOT or 2:1 layers. These minerals are widespread and occur with structures differing by (i) the layer stacking mode (polytypes), (ii) the location of vacancies among non-equivalent octahedral sites (polymorphs), and (iii) the charge-compensating interlayer cation and isomorphic substitutions. The potential of parallel-illumination electron diffraction (ED) is assessed here to determine the polytype/polymorph of individual crystals of finely divided dioctahedral micas and to image their morphology. ED patterns are calculated along several zone axes close to the c *-and c-axes using the kinematical approximation for trans-and cis-vacant varieties of the four common mica polytypes (1 M , 2 M 1 , 2 M 2 , and 3 T). When properly oriented, all ED patterns have similar geometry, but differ by their intensity distribution over hk reflections of the zero-order Laue zone. Differences are enhanced for ED patterns calculated along the [001] zone-axis. Identification criteria are proposed for polytype/polymorph identification, based on the qualitative distribution of bright and weak reflections. A database of ED patterns calculated along other zone-axes is provided in case the optimum [001] orientation cannot be found. Different polytype/polymorphs may exhibit similar ED patterns depending on the zone axis considered.

Multiple electron scattering and the nonintuitive nature of image formation with coherent radiation complicate the interpretation of conventional transmission electron microscopy images. Precession of the illuminating beam in transmission electron microscopy (TEM) can lead to more robust and interpretable images with some penalty to image contrast, a technique known as dynamic hollow-cone illumination TEM. We demonstrate direct and robust imaging of light and heavy atoms in a crystalline environment with this technique. This method is similar to the annular bright-field technique in scanning transmission electron microscopy, via the principle of reciprocity. Dynamic hollow-cone illumination TEM is challenging in practice due to sensitivity to the misalignment of the precession axis, microscope objective aperture, and crystal zone axis.

This study represents a detailed investigation of the influence of post-deposition annealing on structural, morphological and optical properties of 1, 4, 5, 8-naphthalene tetracarboxylic dianhydride, NTCDA, thin films. NTCDA thin films were prepared at room temperature by the thermal evaporation technique. The prepared films were annealed at 373 K and 473 K for 2 h in a vacuum. The results of TGA proved that NTCDA is thermally stable up to 519 K. The X-ray diffraction technique (XRD) was used to investigate the crystal structure of NTCDA powder and thin films. Polycrystalline films were obtained with a preferred orientation in the [100] direction along (h00) zone axis. The negation of the decomposition of NTCDA molecular structure during preparation and/or annealing required employing Fourier transformation infrared (FTIR) technique. The topological properties characterization of as-deposited and annealed NTCDA thin films surfaces concluded that the annealing process induced an enhancement in the film smoothness. The annealing process resulted in significant variations in the optical constants of the NTCDA films. The indirect energy gap values decreased from 3.52 eV to 3.48 eV as a result of annealing up to 473 K. The nonlinear optical effects represented by the nonlinear refractive index, n2 and third-order nonlinear optical susceptibility χ (3) were determined. The nonlinear properties of NTCDA showed a magnificent switching behavior, which suggested the ability to use NTCDA in optical switching devices.

How matrix dislocations, i.e. basal, prismatic and pyramidal, interact with { 10 1 ¯ 2 } 10 1 ¯ 1 ¯ twin boundaries in hexagonal close-packed metals has been discussed extensively in the literature. However, so far no systematic investigation has been reported. In this work, we performed atomistic simulations to study interaction between matrix dislocations in pure Mg with a { 10 1 ¯ 2 } twin boundary. Our results show that for the basal and the prismatic slip, when the Burgers vector is parallel to the zone axis of the twins, a matrix basal dislocation can be transmuted to a twin prismatic dislocation and vice versa. However, when the Burgers vector of the matrix dislocation is non-parallel to the zone axis, no transmutation occurs and the dislocation is absorbed by the twin boundary which acts as a dislocation sink. For a matrix pyramidal dislocation, the dislocation is absorbed by the twin boundary and no transmutation occurs either. It appears that if the product dislocation is a real slip system, transmutation may occur during twin-slip interaction. Otherwise the matrix dislocation will be shredded by atomic shuffling and then absorbed by the twin boundary. If the core structure of the product dislocation is complex, transmutation may not occur as well and dislocation absorption will occur. Lattice correspondence in deformation twinning was applied in explaining the interaction mechanisms. Our results can be well correlated to macroscopic experimental observations which show twin-slip interaction only contributes negligibly to work hardening in deformation of hcp metals.

Vibrational effect on heterogeneous systems is one of the mechanisms for controlling the processes occurred in these systems. For hydrodynamical systems, vibrations can greatly affect the type of flows and the shape of the interfaces, leading to the behavior that is significantly different from that in static fields. In this paper, the flows and interface deformations are studied numerically for a cylindrical liquid zone surrounded by a coaxial layer of gas. In vertical direction the system is bounded by the parallel rigid plates subjected to the axial vibrations of finite frequency and amplitude. The aim of the work is to study and explain the nature of new vibrational phenomena observed experimentally. The study is performed in the framework of a full non-average approach using the fluid volume method. The data are obtained on the instantaneous and average velocity fields and the instantaneous and average shape of the interface at various frequencies and amplitudes of vibrations. It is shown that the axial vibrations of the rigid plates induce the waves at the interface which propagate from the plates to the zone center. These waves generate an average flow with the direction near interface from the oscillating plates to the zone center. Additionally, vibrations generate an average flow near rigid plates in the form of toroidal vortices with the direction near rigid plates from interface to the zone axis.