A. L. Kolesnikova

Misfit dislocation loops and critical parameters of quantum dots and wires

Quantum dots and wires, having a mismatch of crystal lattice parameters with respect to the surrounding matrix, are modelled by spherical and cylindrical inclusions, respectively. By considering the energy of a circular prismatic dislocation loop nucleation in the inclusions, the critical radius and critical dilatation for a dot and a wire are calculated. The results are compared with similar critical parameters for a mismatched film on a substrate.

Disclinations and rotational deformation in fine-grained materials

A theoretical model is presented which describes a new mechanism of plastic deformation in fine-grained materials. In the framework of the model, rotational deformation occurs via motion of dipoles of grain-boundary disclinations and is associated with the emission of lattice dislocations from grain boundaries into adjacent grain interiors. Ranges of defect system parameters are identified in which the disclination motion is energetically favourable. It is shown that the mechanism can contribute to plastic flow in fine-grained materials prepared by highly non-equilibrium methods such as ball milling, severe deformation and high-pressure compaction.

Misfit dislocations and other defects in thin films

Abstract The methods and the results of calculations of the elastic properties of misfit and lattice dislocations and disclinations in thin films are considered. For one-phase films the following problems are solved: a straight edge dislocation perpendicular to the film surfaces; wedge disclinations parallel or perpendicular to the surfaces. In the case of a film on a substrate, the critical thickness for the appearance of misfit dislocations is determined in the continuum model. For multilayer films (superlattices) the effect of a reduction in the grown-in dislocation density is analysed. The behaviour of dislocations in two-phase films is also briefly reviewed.

Dislocation and disclination loops in the virtual-defect method

A method of virtual circular defect loops is developed for determining the elastic fields produced by defects in a bounded medium in the case of an axially symmetric geometry. In this method, continuously distributed virtual circular Volterra and Somigliana dislocation loops are adjusted in such a way as to satisfy the boundary conditions imposed at free surfaces and interfaces. Original calculations of the elastic fields of circular defect loops of different types are carried out. The elastic fields are found for the case of straight dislocations and disclinations in a plate that are perpendicular to the plate plane and for the case of circular disclination loops parallel to the plate plane or to an interface.

Misfit Dislocation Loops in Composite Core-Shell Nanoparticles

The critical conditions have been calculated for the generation of circular prismatic loops of misfit dislocations at the interfaces in spherically symmetric composite core-shell nanoparticles. It has been shown that the formation of these loops becomes energetically favorable if the misfit parameter exceeds a critical value, which is determined by the geometry of the system. The most preferred position of the dislocation loop is in the equatorial plane of the nanoparticle. For a given radius of the nanoparticle, there is a minimum value of the critical misfit parameter below which the generation of a misfit dislocation is energetically unfavorable for any ratio of the core and shell radii. For a misfit parameter exceeding the minimum critical value, there are two critical values of the reduced radius of the particle core in the interval between which the generation of a dislocation loop is energetically favorable. This interval increases with increasing misfit parameter for a fixed particle size and decreases with decreasing particle size for a fixed misfit parameter.

Elastic-energy relaxation in heterostructures with strained nanoinclusions

Elastic-energy relaxation in systems with nanoinclusions is considered. The relaxation is related to the formation of the following dislocation loops: a single misfit dislocation loop or a group of such loops on the matrix-nanoinclusion interface and/or a satellite dislocation loop near the inclusion. The critical inclusion sizes beginning from which misfit dislocation loops and satellite dislocation loops can nucleate are determined for various models of relaxation processes. The dependences of the satellite-dislocation-loop diameter on the inclusion size are calculated and compared with experimental data.

Rotational Deformation Mechanism in Fine-Grained Materials Prepared by Severe Plastic Deformation

j k h l f m n l o L : G = > A = : ; F H C D > M = C ; 9 9 < J J = 9 : = M p G ; F G M = 9 F A ; B = 9 : G = A > : H : ; > 8 H C M = ? > A D H : ; > 8 D = F G H 8 ; 9 D ; 8 q 8 = \ J A H ; 8 = M D H : = A ; H C 9 ` A = ` H A = M B N 9 = X = A = ` C H 9 : ; F M = ? > A D H : ; > 8 V 7 8 : G = ? A H D = \ p > A ^ > ? : G = D > M = C T : G = A > : H : ; > 8 H C M = ? > A D H : ; > 8 > F F < A 9 X ; H : G = D > : ; > 8 > ? J A H ; 8 B > < 8 M H A N M ; 9 F C ; 8 H : ; > 8 M ; ` > C = 9 T H 9 9 > F ; H : = M p ; : G = D ; 9 9 ; > 8 > ? M ; 9 C > F H : ; > 8 ` H ; A 9 ? A > D J A H ; 8 B > < 8 M H A ; = 9 ; 8 : > : G = H M Q H F = 8 : J A H ; 8 ; 8 : = A ; > A 9 V I 8 = A J = : ; F F G H A H F : = A ; 9 : ; F 9 > ? : G = M ; 9 F C ; 8 H : ; > 8 M ; ` > C = D > \ : ; > 8 H A = F H C F < C H : = M V K H 8 J = 9 > ? ` H A H D = : = A 9 > ? : G = M = ? = F : 9 N 9 : = D H A = A = X = H C = M H : p G ; F G : G = M ; 9 F C ; 8 H : ; > 8 D > : ; > 8 ; 9 = 8 = A J = : ; F H C C N ? H X > < A H B C = V 7 : ; 9 9 G > p 8 : G H : : G = A > : H : ; > 8 H C M = ? > A D H : ; > 8 D = F G H 8 ; 9 D H 9 9 > F ; H : = M p ; : G : G = = D ; 9 9 ; > 8 > ? M ; 9 C > F H : ; > 8 ` H ; A 9 ; 9 F H ` H B C = > ? = 9 9 = 8 : ; H C C N F > 8 \ : A ; B < : ; 8 J : > ` C H 9 : ; F r > p ; 8 q 8 = \ J A H ; 8 = M D H : = A ; H C 9 ` A = ` H A = M B N 9 = X = A = ` C H 9 : ; F M = ? > A D H : ; > 8 V

Elastic behavior of a spherical inclusion with a given uniaxial dilatation

The elastic behavior of a spherical inclusion with a uniaxial dilatation is considered. As an example, the experimental data on stressed nanoclusters in doped semiconductors (As-Sb clusters in GaAs) are presented. The fields of displacements, elastic strains, and stresses are determined for spherical inclusions with uniaxial dilatation, and the specific features of these fields are revealed. The elastic energy of a uniaxial spheroid is calculated and compared with that for a triaxial spheroid. The relaxation mechanisms for the elastic field of the inclusion associated with the formation of prismatic dislocation loops are considered.

Transmission Electron Microscopy Image Contrast of Disclination Defects in Crystals (Computer Simulation)

(a) Institute for Problems of Mechanical Engineering, Russian Academy of Sciences,Bolshoj 61, Vas. Ostrov, 199178 St. Petersburg, Russia(b) Institute of Physical Metallurgy, Freiberg University of Mining and Technology,Gustav-Zuener-Str. 5, 09596 Freiberg, Germany(c) Ioffe Physico-Technical Institute, Russian Academy of Sciences, Polytechnicheskaya 26,194021 St. Petersburg, Russia(Received August 27, 2001; in revised form March 1, 2002; accepted March 4, 2002)Subject classification: 61.72.Lk; 68.37.LpTransmission electron microscopy (TEM) images of disclination defects are modeled in the fra-mework of Howie–Whelan two-beam approach and by taking into account elastic distortionsassociated with the defects. Disclinations are generated in crystalline materials in the course ofplastic deformation and can be observed in the junctions of several grain or cell boundaries. Thelines of disclinations are assumed to be parallel or perpendicular to the free surfaces of a thinfoil. For such a geometry disclination elastic fields (e.g. displacements and stresses) in the foilinterior are constructed by applying the technique of “virtual” surface defects. The obtainedresults demonstrate the possibility to extract the disclination parameters from the data of TEMobservations.

A disclination-based approach to describing the structure of fullerenes

The possibility of using a disclination approach to describe the structure and properties of fullerenes is discussed. It is shown that the conversion of a planar carbon monolayer into a spherical macromolecule can be viewed as the result of introducing 12 disclinations with power π/3 into the original layer.