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The elastic problem of a spherical core-shell particle with a truncated core is solved within the isotropic classical theory of elasticity. A transition to a Janus particle consisting of two unequal spherical segments with lattice mismatch is demonstrated. Elastic fields in the Janus particle are found and described in detail. The strain energy of the Janus particle in dependence on the interface coordinate is discussed.

This paper presents the study of oxide film heterojunction made of CuAlCrO2and ZnO:Al (AZO) deposited on fused quartz by sol-gel spin coating. Transmission electronmicroscopy (TEM) analysis has showed that the solvent, which was used to prepare the AZO sol, affects the thickness and planarity of the applied layers and the grain size of the polycrystalline film. The formation of a fine-grained structure of AZO films (grain size is up to 12 nm) leads to the formation of a smoother p-CuAlCrO2/ n-AZO heterojunction. X-ray diffraction (XRD) analysis and TEM have revealed that the heterojunction was formed by AZO polycrystals, which orient axes [101] and [100] against the [101] and [006] directions in CuAlCrO2polycrystals. The optical transmission of the heterojunction in the visible range reached 70 %. The current -voltage (I-V) characteristics of p-CuAlCrO2/ n-AZO corresponds to a diode one in the range from 4 up to 4 V. For the large values of the reverse bias, an increase in the leakage current is observed, which is associated with tunneling breakdown of heterojunction. The ideality factor of fabricated p-CuAlCrO2/ n-AZO heterojunction is more than 2, which indicates the mechanisms of conductivity by defect-levels. In additional, it has been observed the response of the current-voltage characteristics to the green illumination (532 nm) of the diode that is associated with indirect band-gap absorption in CuAlCrO2. The impact of the white LED illumination had no effect on the current-voltage characteristics of the diode.

Graphene crystals, containing arrays of disclination defects, are modeled and their energies are calculated using molecular dynamics (MD) simulation technique. Two cases are analyzed in details: (i) pseudo-graphenes, which contain the alternating sign disclination ensembles and (ii) graphene with periodic distribution of disclination quadrupoles. Electronic band structures of disclinated graphene crystals are calculated in the framework of density functional theory (DFT) approach. The evolution of the Dirac cone and magnitude of band gap in the band structure reveal a dependence on the density of disclination quadrupoles and alternating sign disclinations. The electronic properties of graphene with disclination ensembles are discussed.

Results of the studies of the properties of single-crystalline bulk β-Ga2O3grown from the melt are presented. High chemical purity and phase uniformity of the grown material are demonstrated. Raman spectroscopy studies confirmed low energies of optical phonons in β-Ga2O3, which makes it a promising material for laser optics applications.

The paper presents the investigation of lithium-potassium-alumoborate glasses (0- 25 mol.% Li2O) doped by copper ions. The effect of glass annealing on the Raman scattering patterns is discussed. It is shown that such an annealing results in drastic changes in the Raman scattering patterns for the glass with 10 mol.%of Li2O: the band at 481 cm-1conventionally attributed to boron-oxygen bonds in metaborate rings disappears, while a set of narrow bands at 1236, 1500, and 1783 cm-1is observed. We consider one of these bands, 1783 cm-1, as being the identifier of the formed Li(Al7B4O17) nanophase, XRD analysis supported the above suggestion. The effect of newly formed nanophase on the luminescence spectra is discussed.

A screw dislocation perpendicular to free surfaces and an interface in a two-phase plate, and a screw dislocation piercing a two-phase hollow sphere are considered. The analytical solutions of the boundary-value problems have been found for the first time with the help of the virtual defects technique. Elastic fields of the screw dislocation in the plate are presented in the form of integrals with Bessel functions. Elastic fields of the screw dislocation in the hollow sphere have the form of series with Legendre polynomials. Stress distributions in both of the considered geometries are plotted. The influence of the geometric parameters of the considered solids and the ratio of the shear moduli on the stresses is analyzed. The interaction of a screw dislocation with a parallel edge dislocation is discussed.

The formation of copper pentagonal micropyramids (PMPs) with high (multiatomic) spiral growth steps, which are grown by electrocrystallization with mechanical activation of the cathode, is studied experimentally. A new spiral-layer growth mechanism for the formation of such PMP is proposed. It is shown that PMPs grow on flat pentagonal microcrystals (PMCs) formed initially and containing fivefold twins with one of the twin boundaries being inclined by the angle of 35°16’ to the {110}-type substrate crystallographic plane. Such crystal geometry causes an inclined growth step on the PMC surface. The preferential deposition of metal atoms on this step leads to the spiral-layer PMC growth and the formation of PMPs with a structure inherited from the PMCs.

GaN epitaxial layers were successfully grown by hydride vapour phase epitaxy (HVPE) on β-Ga2O3 substrates produced by cleaving. The initial stages of GaN epitaxial growth on β-Ga2O3 were studied by scanning electron microscopy (SEM) and x-ray diffraction analysis (XRD). The nucleation and the transition from the nucleation layer to a continuous GaN film were studied. It was found that the growth starts with formation of small crystallites on the substrate surface. As the growth continues, crystallites transform into pyramidal islands which increase in size and merge together. It was found that the structural quality of the GaN layers rapidly improves with increasing thickness. The full width at half maximum of x-ray ω rocking curves for (0002) peak decreased from 1370 to 540 arcsec as the deposition time was increased from 30 to 120 sec. This corresponds to the variation of the nominal layer thickness from 250 nm to 1000 nm.

We investigate electron spin resonance (ESR), absorption, and photoluminescence spectra of potassium-boron copper-containing glasses. In previous works it was found, that the considered glasses demonstrate a red shift of photoluminescence. In present work, we provide an evidence on the formation in glasses specific copper-containing structures that can be responsible for the red shift of photoluminescence “copper” band.

The possibility of forming the misfit-strain-induced out-of-interface prismatic dislocation loops (PDLs) in axially inhomogeneous hybrid two-phase nanowires with a transverse interface is theoretically studied. It is shown that, due to the misfit stresses caused by the contact of two crystalline materials with different lattice parameters, the PDLs of certain radii can generate at certain distances from the interface when the nanowire radius is larger than a critical value, which depends on the lattice misfit. The critical parameters of the relaxation process are calculated and discussed in detail.

Gradient nanomechanics is a generalized continuum mechanics framework accounting for “bulk-surface” interactions in the form of gradient terms that enter in the evolution equations of the relevant constitutive variables and/or in the governing field equations. This approach is discussed in the paper by developing appropriate differential equations for the plastic strain and/or the structural defects that bring this about. The effectiveness of the approach is illustrated by considering size-dependent stress-strain curves for nanopolycrystals with varying grain size.

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A short overview of recent achievements in disclination approach application to severe plastically deformed materials is given. Necessary definitions and designations: Volterra rotational and translational dislocations, disclination Frank (rotation) vector, wedge and twist disclinations, are introduced and explained. The properties of screened disclination configurations (loops, dipoles, defects in small particles etc.) with relatively small energies are considered. Disclination models for the processes in the structure of plastically deformed materials are reviewed. The bands with misorientated crystal lattice in metals and other materials are described as a result of partial wedge disclination dipole motion. The disclination approach is applied to the description of workhardening at large strains and to the analysis of grain boundaries and their junctions in conventional polycrystals and nanocrystals.

A short overview of recent achievements in disclination approach application to severe plastically deformed materials is given. Necessary definitions and designations: Volterra rotational and translational dislocations, disclination Frank (rotation) vector, wedge and twist disclinations, are introduced and explained. The properties of screened disclination configurations (loops, dipoles, defects in small particles etc.) with relatively small energies are considered. Disclination models for the processes in the structure of plastically deformed materials are reviewed. The bands with misorientated crystal lattice in metals and other materials are described as a result of partial wedge disclination dipole motion. The disclination approach is applied to the description of workhardening at large strains and to the analysis of grain boundaries and their junctions in conventional polycrystals and nanocrystals.

The generation and propagation of misorientation bands in polycrystalline metals under large deformation are theoretically investigated and discussed. Disclination models are proposed to describe the generation of misorientation bands at grain boundary kinks and junctions. The models consider edge disclination dipole and quadrupole configurations and predict the value for the critical external shear stress τg, above which nucleation of misorientation bands takes place. The numerical estimates for τg give values of G/1000 – G/400 (G being the shear modulus), which correspond to the level of the deforming stress observed in the materials with fine grain structure. The critical stress τg is shown to be strongly dependent on the geometry and strengths of initial disclinations at grain boundary faults. The further development of the disclination structure at an isolated grain boundary fault demonstrates two main regimes of misorientation band development: stable and unstable propagation. The transition between the two regimes is controlled by another critical value for external stress τp which is several times higher than τg. To better understand the cooperative behavior of dislocations and disclinations in metals at late stages of plastic deformation, computer simulation of dislocation–disclination interaction has also been performed, using a 2D dislocation–disclination dynamics code. Some preliminary results of these calculations are reported and discussed.

The generation and propagation of misorientation bands in polycrystalline metals under large deformation are theoretically investigated and discussed. Disclination models are proposed to describe the generation of misorientation bands at grain boundary kinks and junctions. The models consider edge disclination dipole and quadrupole configurations and predict the value for the critical external shear stress τg, above which nucleation of misorientation bands takes place. The numerical estimates for τg give values of G/1000 – G/400 (G being the shear modulus), which correspond to the level of the deforming stress observed in the materials with fine grain structure. The critical stress τg is shown to be strongly dependent on the geometry and strengths of initial disclinations at grain boundary faults. The further development of the disclination structure at an isolated grain boundary fault demonstrates two main regimes of misorientation band development: stable and unstable propagation. The transition between the two regimes is controlled by another critical value for external stress τp which is several times higher than τg. To better understand the cooperative behavior of dislocations and disclinations in metals at late stages of plastic deformation, computer simulation of dislocation–disclination interaction has also been performed, using a 2D dislocation–disclination dynamics code. Some preliminary results of these calculations are reported and discussed.

Transmission electron microscopy (TEM) images of disclination defects are modeled in the framework of Howie–Whelan two-beam approach and by taking into account elastic distortions associated with the defects. Disclinations are generated in crystalline materials in the course of plastic deformation and can be observed in the junctions of several grain or cell boundaries. The lines of disclinations are assumed to be parallel or perpendicular to the free surfaces of a thin foil. For such a geometry disclination elastic fields (e.g. displacements and stresses) in the foil interior are constructed by applying the technique of ”virtual“ surface defects. The obtained results demonstrate the possibility to extract the disclination parameters from the data of TEM observations.

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In this work, a model is developed to treat threading dislocation (TD) reduction in (0001) wurtzite epitaxial GaN thin films. The model is based on an approach originally proposed for (001) f.c.c. thin film growth and uses the concepts of mutual TD motion and reactions. We show that the experimentally observed slow TD reduction in GaN can be explained by low TD reaction probabilities due to TD line directions practically normal to the film surface. The behavior of screw dislocations in III-nitride films is considered and is found to strongly impact TD reduction. Dislocation reduction data in hydride vapor phase epitaxy (HVPE) grown GaN is well-described by this model. The model provides an explanation for the non-saturating TD density in thick GaN films.

The possible domain patterns are developed for (111) oriented epitaxial tetragonal ferroelectric (FT) films. The domain patterns in the film form as the result of phase transition from the paraelectric to ferroelectric state to minimize the elastic energy of the system at the expense of creating of domain boundaries and developing non-uniform elastic fields near the film/substrate interface. Six possible domain variants may form, half of which are related by the inversion of the polarization vector. The possible domain walls arising between pairs of variants can be derived from the conditions of the mechanical and charge compatibility. These walls are {101} boundaries (pseudocubic indexing) and can either be inclined or normal to film/substrate interface. The domain patterns with inclined boundaries have a flat free film surface and possess non-zero net polarization in the direction normal to the film surface, i.e., they correspond to the poled film state. The domain patterns with normal boundaries lead to ‘puckering’ of the film surface, simultaneously they are related to the unpoled state of ferroelectric films.The coherency defect technique is developed for domain pattern energetics for (111) oriented FT films. The coherency defects include (i) a cross-grid of edge dislocations with unbalanced densities (which lead to in-plane biaxial strain field), (ii) Somigliana screw dislocations (which produce alternating sense of shear in neighboring domains), and (iii) wedge disclinations (which are related to out-of-plane rotations in neighboring domains). Analytical calculations of the pattern energy are performed for single embedded domain and multidomain patterns. These calculations are based on the use of screened configurations for representative coherency elements: disclination and Somigliana screw dislocation dipoles and quadrupoles. It is predicted that there is no critical thickness for domain pattern formation in (111) oriented epitaxial tetragonal ferroelectric films. Tiling of different domain patterns in complex mesoscopic structures is also discussed and supported by experimental observations.

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The emergence of non-uniform distributions of misfit dislocations (MDs) in thin films is discussed. A three-element reaction–diffusion model for the kinetics of gliding, climbing and misfit dislocations as proposed by Romanov and Aifantis (R-A model) is used to describe the corresponding pattern. The non-local integral expression for the effective stress field at the film surface, which is the main driving force for MD patterning, is approximated by a gradient expression in the MD density. The corresponding gradient coefficients have an explicit dependence on the film thickness which, thus, defines a characteristic length for the pattern. Analytical solutions of the model are obtained which describe transient spatially uniform dislocation distributions, as well as steady-state spatially periodic dislocation distributions. Linear stability analysis around a uniform steady-state solution demonstrates the formation of MD patches as a result of a dynamical spatial instability. This instability is governed by the competition of the spatial coupling provided by the MD stress field and a diffusion-like term entering the dynamics of the gliding dislocations. A stochastic argument for the corresponding diffusion coefficient, which depends on the average spacing between MDs (thus providing a second characteristic length scale), yields an explanation for not observing MD patterns for film thicknesses below 1 μm.

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The “effective kinetics” of threading dislocations (TDs) in growing epitaxial films is developed on the basis of the crystallographic and geometrical considerations from Part I of the paper. A system of coupled first-order nonlinear differential equations for twenty-four families of TDs is derived and solved for several initial conditions for TD densities. Numerical solutions demonstrated two general types of asymptotic behavior with increasing film thickness: linear decrease or saturation of total TD density. This behavior agrees with experimental data on TD reduction in mismatched homogeneous buffer layers.

Vacancy diffusion and the possibility of pore formation during oxide growth by cation diffusion are investigated. For a parabolic time dependence of the oxide thickness growth, the evolution of the vacancy concentration in the metal is analysed by taking into account the annihilation of vacancies at sinks located at the oxide–metal interface and within the metal. By omitting vacancy absorption at growing vacancy agglomerates, upper estimates of the vacancy supersaturation are calculated, from which the nucleation and growth rates of pores are derived. The nucleation rate strongly decreases with increasing oxidation time and temperature whereas the growth rate increases with increasing temperature. The analysis suggests that the appearance of pores is crucially controlled by the strength of vacancy sinks at the oxide–metal interface and by the presence of impurities lowering the surface energy by impurity segregation to the metal surface of vacancy clusters. Possible flaws of the approach which are related to the assumption of parabolic oxide growth are discussed.

AbstractIn this talk we treat domain patterns that develop in epitaxial ferroelectric (FE) films. The models are applicable to ferroelectric films grown epitaxially in their paraelectric cubic state (PE) on single crystal substrates. We explicitly treat misfit strain relaxation by both misfit dislocations and by domain pattern formation. We have developed temperature dependent stability maps that predict the energetically favorable domain structure that will form at the PE → FE transition. The stability maps incorporate the role of: (i) the substrate lattice parameter; (ii) differential thermal expansion; (iii) cooling rate; (iv) depolarizing fields and electrode geometry; and (v) applied electric fields. We treat the formal defect description both the … a1/a2/a1/a2… and the …a1/c/a1/c… domain patterns and show rigorous mechanics solutions for the elastic energy of both configurations. As a result of the PE → FE transition, the crystal axes of individual domain are rotated in the far-field. The concepts of the domain stability map, the relative coherency strain, and far field rotation of crystals axes in the domain are verified by three independent measurements (integrated x-ray peak intensity, partitioning of crystals tilts, and domain volume fraction by TEM) for MOCVD PbTiO3films grown on MgO(001), SrTiO3(001), LaAlO3(001) and SrRuO3/SrTiO3(001).