Calculation of displacement fields and simulation of HRTEM images of dislocations in sphalerite type A(III)B(V) compound semiconductors

The displacement fields of different kinds of both perfect and dissociated dislocations have been calculated for an isotropic continuum, and by means of linear elasticity. Additionally, the corresponding HRTEM images have been simulated by the well-established EMS program package in order to predetermine the structural aspects of dislocations, and then to compare it with experimental HRTEM micrographs. The latter ones resulted from plastically deformed GaP single crystals and InAs/(001)GaAs single epitaxial layers. It could be established that using the simple approach of linear elasticity and isotropy results can be obtained which correspond well to the experimental images. So, the structure of various Shockley partial dislocations bounding a stacking fault can be detected unambiguously. The splitting behaviour of perfect 30° dislocations (separation into a 0° and 60° partial) and 90° dislocations (separation into two 60° partials) both with line direction along 〈112〉, 60° dislocations (separation into 30°/90° and 90°/30° configuration) and screw dislocations (separation into two 30° partials) along 〈110〉 are discussed in the more detail. Moreover, the undissociated sessile Lomer dislocation, glissile 60° dislocation and edge dislocation have been considered too.     

Microplasticity of CsI crystals

The study of the mechanisms of plastic deformation of CsI crystals has found the participation of not only the main {110} 〈100〉 slip system but also of the secondary one {110} 〈110〉. Besides that, production and motion of point defects (or small prismatic loops) take place. The gliding on secondary slip system and the deformation accounted for by the generation and motion of point defects is facilitated at low temperatures and high deformation rates. The character of the motion and multiplication of dislocations in the main slip system is investigated. From the temperature and stress dependence of the mobility of isolated dislocations quantitative data on the thermally activated motion of edge dislocations on the main slip system have been obtained. It is shown that, as in the case of other alkali halides, the thermally activated motion of edge dislocations in CsI crystals on {110} 〈100〉 system is limited by their interaction with local obstacles.     

Efficiency of dislocations as sinks of radiation defects in fcc copper crystal

The sink efficiency of perfect dislocations for self-point defects (interstitials and vacancies) in fcc copper crystal has been calculated by the kinetic Monte Carlo method in a temperature range of 293–1000 K and a range of dislocation densities from 1.3 × 10¹² to 3.0 × 10¹⁴ m^?2. Screw, mixed, and edge dislocations with a Burgers vector 1/2<110> in different slip systems are analyzed. The interaction energies of self-point defects with dislocations are calculated using the anisotropic theory of elasticity. Analytical expressions are proposed for the dependences of the calculated values of dislocation sink efficiency on temperature and dislocation density.     

Dislocation mobility in LiF at low temperatures

The mobility of dislocations in LiF has been measured at 4.2 and 10 K by means of an etch pit technique. The average velocity of screw dislocations is 2–5 times as large as edge dislocations. The results of the stress and temperature dependence of the velocities correlate well with the data of the critical shear stress in the same temperature region, and are well described by the theory of Peierls mechanism with thd Peierls stress of about 20 MPa for edge dislocations on {110} slip plane.     

Partial dislocations and stacking faults in cubic SiC

Numerous stacking faults and dislocations (formed by intersection of stacking faults and dislocations limiting nonintersecting stacking faults) in the 3C-SiC films grown by molecular beam epitaxy on a silicon substrate were studied by electron microscopy with the use of weak beams. A procedure for determining any of possible Burgers vectors of the (1/6)〈116〉-type glide dislocations and the (1/6) 〈110〉-and (1/3)〈001〉-type sessile partial dislocations (in face-centered cubic lattices) is developed based on the criterion of the contrast value. The sessile dislocations formed by intersections of stacking faults were shown to have the (1/6)〈110〉-and (1/3)〈001〈-type Burgers vectors. The width of nonintersecting stacking faults corresponds to the stacking-fault energy ranging within 0.1–2 mJ/m².     

Microstructures on {111} faces of stannic iodide single crystals

Single crystals of stannic iodide (SnI₄) havebeen grown using the controlled reaction between SnCl₂ and KI by diffusion process in silica gel medium. Orange to reddish octahedral stannic iodide crystals up to 3–4 mm in size have been grown at room temperature. Optical studies have been made on the various surface structures of {111} faces of the asgrown crystals. On octahedral faces of these crystals, triangular-shaped hillocks with growth layers in the 〈110〉 directions have been observed. Occasionally, growth spirals on octahedral faces have also been reported. Close loops of growth fronts have been investigated and have been interpreted. It has been suggested that two-diemensional nucleation, spreading and pilling up of triangular growth layers is mainly responsible for the growth and occasionally the growth is due to screw dislocations. The implications are discussed.     

Microstructure and strain relaxation of orthorhombic TmMnO3 epitaxial thin films

Orthorhombic TmMnO₃ (o-TMO) thin films have been epitaxially stabilized on (110) SrTiO₃ substrates by pulsed laser deposition (PLD) technique. The microstructure and strain relaxation mechanism of o-TMO thin films are analyzed using transmission electron microscopy. It is shown that major defects in the films are misfit dislocations with Burgers vectors of type a_p〈010〉 and a_p〈110〉, whereas a_p〈110〉 dislocations tend to dissociate into partial dislocations with Burgers vectors of type 1/2a_p〈110〉. Strain in o-TMO films is relaxed by misfit dislocations as well as surface fluctuations, which is different from most of the previous studies of the perovskite thin films.     

Dislocation behaviour in annealed and aged LiF crystals

Parallel investigation of the magnitude of the critical strear stress τ₀ and dynamic characteristics of individual screw dislocations at temperatures 4.2, 77, and 300 K has been carried out in LiF crystals after annealing and after long aging at room temperature. It has been established that in impure LiF crystals, even at such low temperatures as room temperature (0.25T_melt), diffusion processes take place which lead to quantitative and qualitative changes of the structure of obstacles determining macroscopic and microscopic mechanical properties.     

Study of the Nature and Distribution of Elementary Steps on the (100) Cleavage Faces of MgO Single Crystals by Atomic Force Microscopy

Some observations made on the nature and distribution of monolayer (elementary) steps on the (100) cleavage faces of MgO single crystals by atomic force microscopy are presented and discussed. The following types of patterns of monolayer steps are described: (1) trains of steps, (2) steps terminating on the cleaved surface at the emergence points of screw dislocations, and (3) localized pinning of advancing steps at random sites (probably at the emergence points of edge dislocations). It is shown that: (1) the origins of emergence points of monolayer steps are devoid of hollow cores due to a small Burgers vector of dislocations and (2) the minimum distance between two emerging steps due to screw dislocations and between two pinning centres due to edge dislocations depends on their sign, and is determined by the mutual interaction between neighbouring dislocations.     

Crowdions in elasticity theory

A crowdion, which is a defect in a crystal structure, is described within the mechanics of continuous linear elastic medium. In the continual approximation, the crowdion is defined, analogously with dislocations, as a singular “carrier” of the plastic deformation of the medium and as a source of elastic deformation. The geometric and force parameters of this singularity are associated with the characteristics of the lattice crowdion. The structure of the strain and stress fields of a crowdion in an anisotropic elastic continuum is described in the general form, and explicit expressions for these fields in an isotropic medium are derived.     

Struktur und Energie der Phasengrenzen in gerichtet erstarrten NiAl-Cr-Eutektikum

Morphology, crystallography and interface structure of the rod-like directionally solidified NiAl–Cr eutectic were examined by transmission electron microscopy. Regular arrays of misfit dislocations of pure edge type on the cylindrical interface between the chromium rods and the NiAl matrix has been observed. The spatial arrangement and the Burgersvectors of the dislocation networks were analysed. Measurements of the distances between the misfit dislocations yielded a mean value of 1480 Å and a mean misfit of 0.195% in 〈100〉 directions. The experimental results were used to calculate the misfit-dependent part of the interfacial energy in different ways and to prove the applicability of the interfacial theory proceeding from the work of van der Merwe to the case of directionally solidified eutectics.     

The role of structural defects in diffusion of elements of group VI in semi-insulating gallium arsenide crystals

The combined effect of the changes in the number and type of vacancies and dislocation density on selenium and sulfur diffusion in single crystals of undoped semi-insulating gallium arsenide has been studied. The differences in the diffusion mechanisms in the subsurface region of samples with an initial deficiency in gallium or arsenic are established as well as the dependence of the effective radius of arsenic trapping by dislocations on the ratio of the concentrations of gallium and arsenic vacancies.     

The features of X-ray topographic contrast formation in silicon with dislocation clusters

The features of formation of diffraction images of edge dislocation sets forming clusters (of two, three and more dislocations) as well as small-angle dislocation boundaries (walls) have been studied. A variety of diffraction effects of wave fields created in strongly distorted crystals regions along dislocation lines have been observed. Various intensity interference effects of rescattering and internal reflection of the newly formed and already existing wave fields on thickness distributions of intensity for the case of presence in the same glide plane of edge dislocations with parallel and anti-parallel Burgers vectors were discovered.     

Structural Defects in Type I Diamonds

Natural gem diamonds of Type I single crystals were observed with an ultra high voltage transmission electron microscope in order to characterize structural defects such as dislocation, dislocation loops, and platelets. The results of analyses indicated that edge dislocations with Burgers vector 1/2 [011 1] and 60° dislocations which were inclined at an angle of 60° to 〈011〉 directions were present in the diamonds. Dislocation loops were concluded to be in interstitical character. It was speculated that an impurity associated with the platelets was silicon and dislocation loops were formed by dislocation motion.     

Effects of the dislocation collective behaviour in plasticity of single crystals

An analysis has been carried out of the motion of a pair of sign-similar edge dislocations under a constant shear stress in a simplest nonuniform field of internal stresses τ_i with a constant gradient. The influence is shown of the dislocation interaction and τ_i on the activation „volume”︁ of the average velocity of a dislocation pair, which is measured by the flow stress relaxation. The experimentally revealed anomalies of the activation „volume”︁ measured by the flow stress relaxation are regarded as corroborating the analysis and as manifestations of the collective effects of the elastic interaction of sign-similar mobile dislocations.     

Evaporation Model of NaCl Cleavage Faces around Edge Dislocations in Vacuum

It is shown in the present paper that the evaporation of edge dislocations in the form of circular steps takes place in NaCl crystals by the evaporation of these steps in a high vacuum and in a temperature region of 350–500°C. The distances of steps are regular. This regularity is explained by means of a suggested model. This model explains also the change in the evaporation rate depending upon the density of dislocations. This explanation is based on the existence of an effective charge at the emergence point of the edge dislocations a/2 〈110〉. {110} with the surface planes {100}. This charge interacts with another one formed on the faults of steps. As a result of this interaction a modulation is observed of the formation of a new step in the emergence point. This means that the same is observed in the case of step distances too.     

Interaction of intrinsic point defects with dislocation stress fields in hcp zirconium crystal

The crystallographic, energetic, and kinetic characteristics of intrinsic point defects (vacancy-self-interstitial atom) in stable, metastable, and saddle configurations in hcp zirconium crystal have been calculated by the molecular-statics method. The spatial dependences of the interaction energies of intrinsic point defects and stress fields of rectilinear dislocations with Burgers vectors of 1/3[11$ \bar 2 $ \bar 2 0], 1/3 [11$ \bar 2 $ \bar 2 3], and [0001] have been found within the anisotropic linear theory of elasticity. The most likely trajectories of intrinsic point defects in dislocation stress fields (trajectories with minimum energy barriers for motion) have been constructed. Such trajectories result in dislocation only for the interaction of self-interstitial atoms with an edge dislocation that has a Burgers vector of 1/3 [11$ \bar 2 $ \bar 2 3].     

Röntgentopographische Untersuchungen plastisch verformter Si-Einkristalle

The Lang-technique has been employed for large-area characterization of the dislocation structure of weakly deformed Si-monocrystals. This method enables an analysis of the activated glide systems and some conclusions concerning the distribution of specific dislocation types. Beside 〈110〉 and 〈112〉 as line directions for dislocations higher indexed preferred orientations are observed. The observations are discussed using TEM-micrographs additionally.     

Burgers Vectors of Dislocations in Creep-deformed Fe3Si Single Crystals

In creep-deformed Fe₃Si single crystals the Burgers vectors of the dislocations were examined by transmission electron microscopy. The Burgers vector in a sample deformed under conditions of 60 MPa and 575–600 °C was of the type 1/2 〈110〉, whereas 〈111〉 superlattice dislocations were not found. 1/2 〈110〉 is the shortest translation distance in the D0₃ superlattice structure of Fe₃Si.     

Possible dynamical mechanism of dislocation drag in metals in the easy slip stage

The slip of an edge dislocation through a system of parallel immobile dislocation dipoles oriented parallel to it has been investigated. A new mechanism of dislocation drag (irreversible transformation of the kinetic energy of a moving dislocation into the energy of natural vibrations of a pair of edge dislocations (forming a dipole), excited by the elastic field of the moving dislocation) is proposed and analyzed. The dynamic drag force of moving dislocation caused by this mechanism is calculated. It is shown that this force is inversely proportional to the slip velocity of mobile dislocations.