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Tungsten (W), as the most promising candidate for plasma-facing materials, will experience significant irradiation hardening in nuclear fusion environment, which is originated from the formation of displacement damages, such as voids and dislocation loops. Hydrogen (H) can further exacerbate the hardening effect, but the underlying physical mechanisms remain unclear. Using molecular dynamics simulations, we investigate the impact of H aggregation within voids and ½ dislocation loops on obstructing the glide of ½ edge dislocations. On the one hand, the pinning effect of H-void complexes is closely related to the ratio of H to vacancy (H:Vac). When the H:Vac ratio is high, H atoms will overflow from the H-void complexes along the dislocation, enhancing the attractive interaction of complexes with dislocation and thereby causing a significant increase in the critical resolved shear stress (CRSS). On the other hand, the accumulation of H around dislocation loops can increase the CRSS by an order of magnitude. This is mainly because the binding of H to the dislocation loop hinders its movement along with the edge dislocation. Our findings advocate that the presence of interstitial impurities can dramatically modify the mechanical properties of materials underirradiation, and provide an important reference for the prediction of W performance and the development of advanced nuclear materials.

A non-destructive, fast and accurate extended defect counting method on large diameter SiC wafers is presented. Photoluminescence (PL) signals from extended defects on 4H-SiC substrates were correlated to the specific etch features of Basal Plane Dislocations (BPDs), Threading Screw Dislocations (TSDs), and Threading Edge Dislocations (TED). For our non-destructive technique (NDT), automated defect detection was developed using modern deep convolutional neural networks (DCNN). To train a robust network, we used our large volume data set from our selective etch method of 4H-SiC substrates, already established based on definitive correlations to Synchrotron X-Ray Topography (SXRT) [1]. The defect locations, classifications and counts determined by our DCNN correlate with the subsequently etch-delineated features and counts. Once our network is sufficiently trained we will no longer need destructive methods to characterize extended defects in 4H-SiC substrates.

Dislocations in third-generation semiconductor gallium nitride (GaN) have always been a subject of intense study. Here, we investigate the core structures and electronic properties of prismatic edge dislocations in wurtzite GaN using a combination of the discrete Peierls theory and first-principles calculations. We identify four primary analytical core configurations, some of which exhibit reconstruction. Stable glide dislocations are found to be dangling-bond-free, whereas shuffle dislocations typically possess dangling bonds yet exhibit limited electronic activity. Different shuffle-type cores show similar electronic properties, consistent with their structural similarities. The intermediate states during glide dislocation motion may significantly influence GaN's electronic behavior. This work validates the accuracy of our combined theoretical and computational approach for atomic-scale dislocation characterization and establishes a foundation for dislocation engineering in high-performance GaN devices.

Among many types of defects present in crystalline materials, dislocations are the most influential in determining the deformation process and various physical properties of the materials. However, the mathematical description of the elastic field generated around dislocations is challenging because of various theoretical difficulties, such as physically irrelevant singularities near the dislocation-core and nontrivial modulation in the spatial distribution near the material interface. As a theoretical solution to this problem, in the present study, we develop an explicit formulation for the nonsingular stress field generated by an edge dislocation near the zero-traction surface of an elastic medium. The obtained stress field is free from nonphysical divergence near the dislocation-core, as compared to classical solutions. Because of the nonsingular property, our results allow the accurate estimation of the effect of the zero-traction surface on the near-surface stress distribution, as well as its dependence on the orientation of the Burgers vector. Finally, the degree of surface-induced modulation in the stress field is evaluated using the concept of the L2-norm for function spaces and the comparison with the stress field in an infinitely large system without any surface.

The propagation expressions of elliptical Gaussian beams carrying mixed screw–edge dislocations through a uniaxial crystal orthogonal to the optical axis are derived. The effects of the source beam and crystal on the intensity and phase of such beams during propagation are discussed in detail. The obtained results show that the intensity profiles of elliptical and circular Gaussian beams carrying mixed screw–edge dislocations in uniaxial crystals are controlled by the beam parameter ratio of the waist width, edge dislocations, off-axis distance and ratio of the refractive indices of uniaxial crystals.

4H-SiC homo-epitaxial film was grown by adding HCl gas with a high Cl/Si ratio in CVD process, and defect formation and origin of the defect were investigated by confocal differential interference contrast (CDIC) microscope, PL imaging and normal differential interference contrast (DIC) microscope. It was found that a large number of large bumps are formed on the film grown at a high Cl/Si ratio of 30, and a large number of PL defects on bare substrate before the film growth are also observed. Coordinates where the bumps on the film are observed were good agreement with those where the PL defects on the bare substrate are observed. An etch pit sample on reproduced substrate from which epitaxial film was removed was fabricated by etching process using molten KOH+Na2O2, and some types of etch pits which might be originated from threading edge dislocations (TEDs), threading screw dislocations (TSDs) and basal plane dislocations (BPDs) in the substrate were observed. The coordinates where the etch pits on the reproduced substrate are observed were also good agreement with those where the bumps on the epitaxial film are observed. Therefore, it was clarified that a large number of the bumps abnormally grown on the epitaxial film are originated from the dislocations in the substrate.

Nickel-based alloys are the primary structural materials in steam generators of high-temperature gas reactors. To understand the irradiation effect of nickel-based alloys, it is necessary to examine dislocation movement and its interaction with irradiation defects at the microscale. Hardening due to voids and Ni 3 Al precipitates may significantly impact irradiation damage in nickel-based alloys. This paper employs the molecular dynamics method to analyze the interaction between edge dislocations and irradiation defects (void and Ni 3 Al precipitates) in face-centered cubic nickel. The effects of temperature and defect size on the interaction are also explored. The results show that the interaction process of the edge dislocation and irradiation defects can be divided into four stages: dislocation free slip, dislocation attracted, dislocation pinned, and dislocation unpinned. Interaction modes include the formation of stair-rod dislocations and the climbing of extended dislocation bundles for voids, as well as the generation of stair-rod dislocation and dislocation shear for precipitates. Besides, the interactions of edge dislocations with voids and Ni 3 Al precipitates are strongly influenced by temperature and defect size.

A “hard” LLL interferometer made of dislocation-free silicon single crystal has been investigated; it differs significantly from previously known types of X-ray interferometers. Such an interferometer is highly sensitive to both initially present and introduced defects in the crystal. Several dislocations were generated in the modified part of the interferometer’s mirror block, as confirmed by X-ray topograms. Interferometric images of dislocations generated in the mirror block were obtained. The numerical simulation of single edge dislocation imaging is carried out according to the considered scheme.

A moving edge dislocation in an infinite elastic medium is considered, simulating a stationary shear rupture in the Earth’s crust at a depth of seismic activity, which increases as quickly as transverse waves travel. Based on the expansion of the vector displacement field into the sum of the potential and solenoidal fields, an exact singular solution to the problem in a plane formulation is constructed in the form of convergent series. An approximate solution in the form of series segments is analyzed in the Matlab computer system using numerical differentiation and integration procedures. It is shown that the invariant -integral, whose value is equal to the driving force of the dislocation (the energy spent on the movement of the dislocation by a unit distance), is independent on its velocity.

Graphene is an ideal reinforcement material for metal-matrix composites owing to its exceptional mechanical properties. However, as a 2D layered material, graphene shows highly anisotropic behavior, which greatly affects the mechanical properties of graphene-based composites. In this study, the interaction between an edge dislocation (b = 1/2 (111)) and a pair of graphene nanosheets (GNSs) in GNS reinforced iron matrix composite (GNS/Fe) was investigated using molecular dynamic simulations under simple shearing conditions. We studied the cases wherein the GNS pair was parallel to the (1 1 ¯ 0), (11 2 ¯ ), and (111) planes, respectively. The results showed that the GNS reinforcement can effectively hinder dislocation motion, which improves the yield strength. The interaction between the edge dislocation and the GNS pair parallel to the (11 2 ¯ ) plane showed the strongest effect of blocking dislocations among the three cases, resulting in increases in the shear modulus and yield stress of 107% and 1400%, respectively. This remarkable enhancement was attributed to the Orowan “by-passing” strengthening mechanism, whereas cross-slip of dislocation segments was observed during looping around GNSs. Our results might contribute to the development of high-strength iron matrix composites.