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We demonstrate the dynamical x-ray diffraction analysis of metamorphic triple-junction solar cells grown on Ge (001) substrates. The solar cells investigated involve an In_0.67Ga_0.33P top cell, an In_0.17Ga_0.83As middle cell, and a Ge bottom cell. A graded buffer layer is inserted between the bottom and middle cells for the purpose of accommodating the lattice mismatch. Linearly-graded, step-graded, and S-graded compositional profiles were considered for this buffer layer. The x-ray rocking curve analysis for a number of hkl reflections including 004, 113, 116, 044, 026, and 117 was conducted for the case of Cu Kα₁ radiation. We show that the use of non-destructive x-ray analysis allows determination of the threading dislocation densities in the top two cells. In the cases of S-graded or step-graded buffer layers, the buffer threading dislocation density could also be estimated.

In this paper we apply a mosaic crystal model for dynamical x-ray diffraction to step-graded metamorphic semiconductor device structures containing dislocations. This model represents an extension of the previously-reported phase-invariant model, which is broadly applicable and serves as the basis for the x-ray characterization of metamorphic structures, allowing determination of the depth profiles of strain, composition, and dislocation density. The new model has more general applicability and is more appropriate for step-graded metamorphic device structures, which are of particular interest for high electron mobility transistors and light emitting diodes. Here we present the computational details of the mosaic crystal model and demonstrate its application to step-graded In_xGa_1-xAs/GaAs (001) and In_xAl_1-xAs/GaAs (001) metamorphic buffers and device structures.

We applied the mosaic crystal model to calculate the dynamical x-ray rocking curves for a coherently-strained GaAs/In_0.3Ga_0.7As/GaAs single quantum well grown epitaxially on a GaAs (001) substrate for a number of reflection profiles, including 004, 113, 224, 044 and 444 reflections. We show that it is possible to estimate the threading dislocation density in the quantum well, and therefore detect the pseudomorphic-metamorphic transition, using the widths or normalized intensities of the primary quantum well Bragg peak, or using the widths of the Pendellösung fringes associated with the quantum well structure.

Halide perovskite materials such as FAPbI3 are of great interest for photovoltaic applications and could replace silicon cells if problems of chemical instability, strain and crystal defects are solved. In this paper we present a preliminary modeling study of lattice relaxation in epitaxial FAPbI₃ on MAPbCl_xBr_3-x (001).

A quantum mechanical treatment of the effects of dislocations on planar channeling of positrons is presented. The effects of anharmonic terms on the positron planar potential are considered in these calculations. The wavefunction of channeled positron in the perfect channel and the two regions of dislocation affected channel are found and compared with harmonic case. The corresponding effects on bound states and the transitions among these states are calculated. The transition probabilities and the resulting dechanneling probabilities are found for initially channelled particles in states |0〉 and |1〉. The calculations are carried out with varying channel distance from the dislocation core. Applications of anharmonic interactions on channeling radiation are also investigated.

In this work, we investigate the quantum motions of nonrelativistic particles interacting with a potential in the presence of the Aharonov–Bohm (AB) flux field within a topological defect geometry, for example space–time with a distortion of a vertical line into a vertical spiral. We begin by deriving the radial Schrödinger wave equation, incorporating an anharmonic oscillator potential, which is a superposition of a harmonic oscillator and an inverse square potential, along with a constant term. The eigenvalue solution is obtained through the confluent Heun equation focusing on the ground state energy level and the radial wave function for the radial mode $n=1$ as an example and analyze the results. Subsequently, we use these results to molecular potential models, considering pseudoharmonic and shifted pseudoharmonic potentials. The derived eigenvalue solutions provide insights into the behavior of particles within these potentials. Expanding our exploration, we study the quantum system featuring only an inverse square potential in the presence of the quantum flux field in the same geometry background. Employing the same procedure, we determine the ground state energy level and the radial wave function. Notably, our findings reveal that the eigenvalue solutions are significantly influenced by the topological defect characterized by the parameter $\beta$, and the quantum flux field ${\mathrm{\Phi }}_{\mathrm{\text{AB}}}$. This influence manifests as a shift in the energy spectrum, drawing parallels to the gravitational analog of the AB effect.

The microplastic deformation behavior of 20 vol.% SiCp/Al composites with various SiC particle sizes were investigated. The SiC particles are in four nominal sizes of 1, 5, 20 and 56 µm. The experimental results showed that the micro-yield strength is very sensitive to composite microstructure features. As the particle size increases, the micro-yield strength of composites decrease firstly, and then increase. The observed results were attributed to thermal residual stress and dislocation density due to the large difference in coefficient of thermal expansion between the matrix and reinforcement.

The hardness properties of materials are tracked from early history until the present time. Emphasis is placed on the hardness test being a useful probe for determining the local elastic, plastic and cracking properties of single crystal, polycrystalline, polyphase or amorphous materials. Beginning from connection made between individual hardness pressure measurements and the conventional stress–strain properties of polycrystalline materials, the newer consideration is described of directly specifying a hardness-type stress–strain relationship based on a continuous loading curve, particularly, as obtained with a spherical indenter. Such effort has received impetus from order-of-magnitude improvements in load and displacement measuring capabilities that are demonstrated for nanoindentation testing. Details of metrology assessments involved in various types of hardness tests are reviewed. A compilation of measurements is presented for the separate aspects of Hertzian elastic, dislocation-mechanics-based plasticity and indentation-fracture-mechanics-based cracking behaviors of materials, including elastic and plastic deformation rate effects. A number of test applications are reviewed, most notably involving the hardness of thin film materials and coatings.

Theoretical as well as experimental studies in the literature suggest that defect sites associated with the threading dislocation lines within $n$-type gallium nitride (GaN) act to trap free electrons from the bulk of this semiconductor material. As a result, the core of the threading dislocation lines become negatively charged. The charge accumulated along the core of a threading dislocation line should be screened by a charge of opposite polarity and equal in absolute value per unit length along the dislocation line. In the present work, we model this screened charge buildup along the threading dislocation lines by two concentric space-charge cylinders. Quantum mechanical theory of scattering in cylindrical coordinates is then employed in order to numerically compute the electron mobility limited by scattering from the charged threading dislocation lines. The dependence of the computed electron mobility on the dislocation line density and on the amount of charge accumulated per unit length along the core of the dislocation lines is also investigated in this work. Our computed electron mobility results are compared with results from existing calculations of the GaN dislocation scattering limited electron mobility in the literature.

The activation enthalpy for migration of dislocations of plastically deformed 8006 Al-alloy was investigated by positron annihilation lifetime technique. Plastic deformation using a hydraulic press produces mainly dislocations and may produce point defects. The type of defect was studied by isochronal annealing which determines the temperature range of recovery of each type. Only one type of defect (dislocations) was observed for the investigated sample and was found to be recovered within the range 455–700 K. Isothermal annealing by slow cooling was performed through this range and used in determination of the activation enthalpy of migration of dislocations which was found to be 0.26 ± 0.01 eV.

The present work studies and analyses the effect of compression on LiF crystal. The compression is of the order that it deforms the LiF crystal plastically. The sequence of closed packed structure of plastically deformed crystal is disturbed and we expect stacking faults i.e., faults in the crystal along a plane. Plastically deformed crystal contains high density of dislocations. The depression of phonon conductivity in plastically deformed crystal is associated with interaction of the phonon with high density of dislocations. Phonon or the quantised lattice wave scatters with these stacking faults and dislocation cores, as a result, there is depression of lattice thermal conductivity near the peak. The number of stacking faults/cm N${}_S$ has been calculated which is of the order of 10¹/cm, and dislocation core size which is of the order of burger vector if dislocation density is of the order of 10⁸/cm². Separate contributions of relaxation rates for various phonon scattering processes have been calculated for both longitudinal and transverse phonons. Present work strongly supports that phonons are mainly scattered by stacking faults and dislocation cores in plastically deformed LiF crystal.

Cold work (compression) is an important method that produces dislocations mainly used to improve the mechanical properties of Al-alloys. The effect of deformation on 5754 Al-alloy was investigated by Positron Annihilation Lifetime Spectroscopy (PALS), Vickers micro-hardness (HV) and X-ray diffraction (XRD) techniques. The observation of results obtained by these techniques as a function of degree of deformation showed approximately the same behavior. Mean lifetime and Vickers micro-hardness values changed from 168.0 ± 7.0 ps and 32.0 ± 1.5 Hv, respectively, for the annealed (undeformed) sample to be 214.0 ± 7.0 ps and 43.0 ± 1.5 Hv, respectively, for saturated dislocation samples. Both PALS and HV results seems to be approximately constant above 8.0% degree of deformation which is the start of the saturated dislocation region. 10% degree of deformation is considered to be a threshold point or preferred orientation point obtained from XRD measurements after which saturation of dislocation is also obtained. Due to the variation in the interatomic spacing caused by plastic deformation, a significant increase in the peak broadening and line intensities of the XRD reflections is obtained.

An overview of recent work on the interaction of elastic waves with dislocations is given. The perspective is provided by the wish to develop nonintrusive tools to probe plastic behavior in materials. For simplicity, ideas and methods are first worked out in two dimensions, and the results in three dimensions are then described. These results explain a number of recent, hitherto unexplained, experimental findings. The latter include the frequency dependence of ultrasound attenuation in copper, the visualization of the scattering of surface elastic waves by isolated dislocations in LiNbO₃, and the ratio of longitudinal to transverse wave attenuation in a number of materials.

Specific results reviewed include the scattering amplitude for the scattering of an elastic wave by a screw, as well as an edge, dislocation in two dimensions, the scattering amplitudes for an elastic wave by a pinned dislocation segment in an infinite elastic medium, and the wave scattering by a sub-surface dislocation in a semi-infinite medium. Also, using a multiple scattering formalism, expressions are given for the attenuation coefficient and the effective speed for coherent wave propagation in the cases of anti-plane waves propagating in a medium filled with many, randomly placed screw dislocations; in-plane waves in a medium similarly filled with randomly placed edge dislocations with randomly oriented Burgers vectors; elastic waves in a three-dimensional medium filled with randomly placed and oriented dislocation line segments, also with randomly oriented Burgers vectors; and elastic waves in a model three-dimensional polycrystal, with only low angle grain boundaries modeled as arrays of dislocation line segments.

We develop a rigorous framework for modeling the geometry equilibration of crystalline defects. We formulate the equilibration of crystal defects as a variational problem on a discrete energy space and establish qualitatively sharp far-field decay estimates for the equilibrium configuration. This work extends [V. Ehrlacher, C. Ortner and A. Shapeev, Analysis of boundary conditions for crystal defect atomistic simulations, Arch. Ration. Mech. Anal.222 (2016) 1217–1268] by admitting infinite-range interaction which in particular includes some quantum chemistry based interatomic interactions.

This paper focuses on the connections between four stochastic and deterministic models for the motion of straight screw dislocations. Starting from a description of screw dislocation motion as interacting random walks on a lattice, we prove explicit estimates of the distance between solutions of this model, an SDE system for the dislocation positions, and two deterministic mean-field models describing the dislocation density. The proof of these estimates uses a collection of various techniques in analysis and probability theory, including a novel approach to establish propagation-of-chaos on a spatially discrete model. The estimates are non-asymptotic and explicit in terms of four parameters: the lattice spacing, the number of dislocations, the dislocation core size, and the temperature. This work is a first step in exploring this parameter space with the ultimate aim to connect and quantify the relationships between the many different dislocation models present in the literature.

This work introduces a model for large-strain, geometrically nonlinear elasto-plastic dynamics in single crystals. The key feature of our model is that the plastic dynamics are entirely driven by the movement of dislocations, that is, 1-dimensional topological defects in the crystal lattice. It is well known that glide motion of dislocations is the dominant microscopic mechanism for plastic deformation in many crystalline materials, most notably in metals. We propose a novel geometric language, built on the concepts of space-time “slip trajectories” and the “crystal scaffold” to describe the movement of (discrete) dislocations and to couple this movement to plastic flow. The energetics and dissipation relationships in our model are derived from first principles drawing on the theories of crystal modeling, elasticity, and thermodynamics. The resulting force balances involve a new configurational stress tensor describing the forces acting against slip. In order to place our model into context, we further show that it recovers several laws that were known in special cases before, most notably the equation for the Peach–Koehler force (linearized configurational force) and the fact that the combination of all dislocations yields the curl of the plastic distortion field. Finally, we also include a brief discussion on how a number of other effects, such as hardening, softening, dislocation climb, and coarse-graining, could be incorporated into our model.

Positron annihilation was performed to study the isochronal annealing of wrought (2024, 7075) and casting (AlSi_11.35Mg_0.23, AlSi_10.9Mg_0.17Sr_0.06) aluminum alloys in the temperature range from room temperature to 773 K after they had been deformed at room temperature with 25% deformation. Two annealing stages of microstructures were distinguished which were attributed to recovery in 2024, and AlSi_11.35Mg_0.23, AlSi_10.9Mg_0.17Sr_0.06 due to point and dislocations respectively, and only one due to dislocations in 7075.

The migration enthalpy for point defects and dislocations is estimated by using positron lifetime technique; point defects and dislocations are produced as a result of plastic deformation at room temperature (RT) for the decomposition sequence, namely 5005, 5052 and 5083, of commercial Al–Mg systems. The results show that for the three systems increases as the Mg content is increased to u₁=0.34±0.09 eV, u₂=0.39±0.12 eV, and u₃=0.42±0.08 eV for the point defect state, and u₁=1.12±0.08 eV and u₂=1.37±0.13 eV for the dislocation state to 5005 and 5052, respectively. All the data are analyzed in terms of the two state trapping model.

We report a case of rotatory subluxation of the metacarpophalangeal joint (MCPJ) of the finger. A 40-year-old man sustained an open injury to his index finger following an explosive injury. Radiographs showed rotatory subluxation of the index finger MCPJ. The index finger extensor digitorium was found interposed in the MCPJ, with a complete tear of the radial collateral ligament. Treatment was by open reduction and repair of the collateral ligament and the extensor tendon. A high level of clinical suspicion is needed to diagnose this entity.

Background: Perilunate dislocations are severe uncommon carpal injuries. They are sometimes missed with a reported incidence of up to 25%. Neglect for a period of time allows for soft tissue contractures, as well as bony changes that make reduction extremely difficult. For neglected cases, procedures such as staged open reduction, proximal row carpectomy, and wrist arthrodesis have been offered. The objective of this study was to examine whether scaphoid excision and four-corner fusion could be used to treat neglected perilunate dislocations.

Methods: Ten patients with neglected perilunate dislocations were managed by scaphoid excision and four-corner fusion. The dominant hand was involved in eight cases. Graft material for the fusion was obtained from the excised scaphoid. Results: Six patients had complete relief of pain both at rest and during stressful activities. Two patients had no pain at rest and mild pain on stressful activities. The remaining two patients had mild pain at rest and moderate pain on stressful activities. The arc of extension/flexion of the wrist and grip strength both improved as compared to their preoperative levels. The average postoperative Quick DASH score was 12.5.

Conclusions: Scaphoid excision with four corner fusion could be used to treat neglected perilunate dislocations with good pain relief and good hand function.