Simulation of the Organization of Heteroepitaxial Monolayer Islands Under Anisotropic Conditions

2004 ◽  
Vol 854 ◽  
Author(s):  
Gajendra Pandey ◽  
Robert V. Kukta
Keyword(s):  
Point Defects ◽  
Surface Stress ◽  
Lattice Mismatch ◽  
Finite Size ◽  
Source Model ◽  
Crystalline Material ◽  
Elastic Fields ◽  
High Anisotropy ◽  
Degree Of Anisotropy ◽  
Hexagonal Arrays

ABSTRACTThis paper addresses the effect of anisotropy on the organization of epitaxial islands deposited on a substrate. Focus is on in-plane anisotropies in surface stress and lattice mismatch between the film and substrate materials. Starting from a configuration where island sizes and position are random, evolution towards equilibrium through mass transport via condensation/evaporation is simulated. The effect of the degree of anisotropy is investigated. An efficient numerical method is obtained by reducing a model of square monolayer islands of finite size to point defects that interact through their elastic fields. Models for both the kinetics and energetics of the system are obtained by this reduction. It is found that the point source model is accurate for island separations larger than about 3 times the width of an island. Under isotropic conditions islands tend to form into hexagonal arrays, and as there is no preferred orientation of these arrays, defects analogous to grain boundaries in a crystalline material tend to arise. With anisotropy islands tend to align in particular directions. This is found to enhance organization in cases of modest anisotropy and cause islands to form into zigzagged lines in cases of high anisotropy.

Temporal Evolution of Bimodal Distribution of γ’ Precipitates in Ni-Al-Mo Alloys under the Influence of Coherency Strains

1995 ◽  
Vol 398 ◽  
Author(s):  
A.D. Sequeira ◽  
H.A. Calderon ◽  
G. Kostorz
Keyword(s):  
Lattice Mismatch ◽  
Bimodal Distribution ◽  
X Ray Diffraction ◽  
Double Step ◽  
Bimodal Size Distribution ◽  
Elastic Fields ◽  
Transmission Electron ◽  
The Matrix ◽  
Kinetics Of ◽  
Coherency Strains

ABSTRACTThe influence of coherency strains produced by the γ-γ’ lattice mismatch, δ, on the decomposition process of Ni-Al-Mo alloys with a bimodal size distribution is presented. Samples with δ ranging from positive to negative, were investigated in a double-step aging procedure. The evolution of the microstructure and the kinetics of coarsening were studied using transmission electron microscopy (TEM). The lattice mismatch between the matrix and the different classes of precipitates was determined by high-resolution high-temperature x-ray diffraction. It is shown that the strain fields produced by the lattice mismatch can influence dramatically the decomposition of metallic alloys. It is suggested that the reduction of the coarsening rate of the large precipitates, the fast coarsening rate of the small precipitates and the distortions detected in the matrix are all direct consequences of the elastic fields produced by the γ-γ’ lattice mismatch.

Model of Subgrain Structure Formation in HTS Cuprates and Ferropnictides

2012 ◽  
Vol 1434 ◽  
Author(s):  
Constantin G. Tretiatchenko ◽  
Vassily L. Svetchnikov ◽  
Harold Wiesmann
Keyword(s):  
Film Growth ◽  
Lattice Mismatch ◽  
Subgrain Size ◽  
Finite Size ◽  
Interface Energy ◽  
Rotational Relaxation ◽  
Subgrain Structure ◽  
Relaxation Of Stresses ◽  
Validity Range ◽  
Edge Dislocations

ABSTRACTWe have modified the model of rotational relaxation of stresses at mismatched interface by taking into account elastic strains of the growing film. This extended the model validity range to a wider class of compounds including pnictides. The model describes formation of low angle boundaries consisting of threading edge dislocations. Calculated interface energy shows that rotational relaxation occurs due to finite size of clusters and to non-equilibrium effect of the film growth. Subgrain size and expected angle of domain rotation depending on the lattice mismatch have been estimated. Unusual effect of increasing angle between the film subgrains at reduction of the deposition rate is predicted. The computed parameters of subgrains are consistent with the observed film nanostructure.

Elastic fields of interacting point defects within an ultra-thin fcc film bonded to a rigid substrate

2013 ◽  
Vol 3 (4) ◽  
Author(s):  
Hossein Shodja ◽  
Maryam Tabatabaei ◽  
Alireza Ostadhossein ◽  
Ladan Pahlevani
Keyword(s):  
Point Defects ◽  
Binary Systems ◽  
Nearest Neighbor ◽  
Atomic Scale ◽  
Surface Shape ◽  
Atomic Interaction ◽  
Interatomic Potentials ◽  
Layer By Layer ◽  
Face Centered Cubic ◽  
Elastic Fields

AbstractCertain physical and mechanical phenomena within ultra-thin face-centered cubic (fcc) films containing common types of interacting point defects are addressed. An atomic-scale lattice statics in conjunction with many-body interatomic potentials suitable for binary systems is conducted to analyze the effects of the depth on the: (1) formation energy and layer-by-layer displacements due to the presence of vacancy-octahedral self-interstitial atom (OSIA) ensemble, and (2) elastic fields as well as the free surface shape in the case of vacancy-dopant interaction. Moreover, the effects of the inter-defect spacing for various depths are also examined. To ensure reasonable accuracy and numerical convergence, the atomic interaction up to the second-nearest neighbor is considered.

The Role of Cation Point Defects and Oxygen Interstitials on Modulations in Undoped and Doped Bi-Sr-Ca-Cu-O Superconductors

1990 ◽  
Vol 209 ◽  
Author(s):  
P. L. Gai ◽  
M. A. Subramanian ◽  
A. W. Sleight
Keyword(s):  
Electron Diffraction ◽  
Point Defects ◽  
High Spatial Resolution ◽  
Lattice Mismatch ◽  
Hole Concentration ◽  
Microstructural Analysis ◽  
Partial Substitution ◽  
X Ray Diffraction ◽  
X Ray

ABSTRACTVariations in superstructure modulations and transition tempeartures (Tc) in undoped and yttrium-doped Bi2Sr2CaCu2O8 (2212) superconductors annealed in different environments have been examined by microstructural analysis. The hole concentration is changed either by annealing the samples in reducing or oxidizing environments, or by partial substitution of Y3+ cations on the Ca-sites. Systematic investigations of the 2212 samples annealed in both the reducing (nitrogen) and oxidizing (oxygen) environments show commensurate and incommensurate modulations, respectively, and a decrease of Tc in oxygen. Commensurate modulations have also been found for samples prepared entirely in nitrogen. High spatial resolution microanalysis reveals that the modulations are insensitive to cation point defects. These results indicate that modulations are intrinsic to the 2212 materials and that they are caused by the lattice mismatch between the perovskite and Bi-O layers. Such periodic variations in interplanar spacings are expected to lead to satellite spots as observed in electron diffraction. The results are consistent with single crystal X-ray diffraction studies reported in the literature. In the Y- doped samples Tc values are similar in Bi2Sr2Ca1-xYxCu2O8 for x=0.2, in both the environments, but decrease with increasing value of x.

Surface and Interface Stress in Epitaxial Growth

1996 ◽  
Vol 440 ◽  
Author(s):  
H. Ibach ◽  
A. Grossmann.
Keyword(s):  
Charge Transfer ◽  
Epitaxial Growth ◽  
Surface Stress ◽  
Critical Thickness ◽  
Lattice Mismatch ◽  
Interface Stress ◽  
Experimental Measurements ◽  
Surface And Interface ◽  
Large Factor

AbstractRecent experimental measurements on the interface stresses in two heteroepitaxial systems have shown that the interface stresses were unexpectedly large. For thin deposited layers, the interface stress can exceed the stress caused by the lattice mismatch by far. Arguments are presented which indicate that the surface stress may be caused by the charge transfer between the deposit and the substrate. The consequences for the critical thickness of pseudomorphic films are discussed and it is shown that depending on the sign of the interface stress and the mismatch the critical thickness can be either reduced or enhanced by a large factor.

Physics of Elasticity and Crystal Defects

2020 ◽  
Author(s):  
Adrian P. Sutton
Keyword(s):  
Point Defects ◽  
Unique Feature ◽  
Materials Science ◽  
Theory Of Elasticity ◽  
Crystal Defects ◽  
Atomic Diffusion ◽  
Postgraduate Students ◽  
Crystalline Materials ◽  
Elastic Fields ◽  
Fundamental Research

Mechanical properties of crystalline materials are almost always dominated by the defects within them. The ability to shape metals into pipes, girders and furniture stems from the generation, motion and interaction of these defects. Defects are also the agents of chemical changes within crystals, enabling mass transport by atomic diffusion and changes of phase. Defects distort the crystal and these distortions enable defects to interact over large distances. The theory of elasticity is used to describe these interactions. Assuming no familiarity with the theory, this book introduces the reader to linear elasticity and its application to point defects, dislocations and cracks. A unique feature of the book is the attention given to the atomic structure of defects and its influence on their properties and their elastic fields. Where it is available brief biographical information is provided about prominent contributors to the field. This textbook is written for postgraduate students in physics, engineering and materials science. It is very likely that even those students with some knowledge of elasticity and defects will find much that is new to them in this book.There are exercises to help the student check their understanding as they work through each chapter. The student is guided through more advanced problems at the end of each chapter. Worked solutions to all exercises and problems are available to course instructors from the OUP website. The last chapter describes four technologically important areas requiring fundamental research, with suggestions for possible PhD projects.

Elastic fields due to defects in transversely isotropic bimaterials

1995 ◽  
Vol 449 (1935) ◽  
pp. 1-30 ◽  
Keyword(s):  
Point Defects ◽  
Analytic Solution ◽  
Transversely Isotropic ◽  
Planar Interface ◽  
Dislocation Loops ◽  
Elastic Fields ◽  
Closed Form Solutions ◽  
Transversely Isotropic Solids ◽  
Isotropic Solids ◽  
Plane Of Isotropy

A method for obtaining the analytic solution of the elastic fields due to defects such as inclusions, dislocations, disclinations, and point defects in transversely isotropic bimaterials is presented. The bimaterial consists of two semi-infinite transversely isotropic solids either perfectly bonded together or in frictionless contact with each other at a planar interface which is parallel to the plane of isotropy of both solids. The elastic solution is expressed in terms of the hexagonal stress vectors for the double force and the double force with moment. Closed form solutions for inclusions with pure dilatational eigenstrain, straight dislocation and disclination lines, circular, dislocation loops, and point defects are presented.

scholarly journals On the Elastic Description of a Spherical Janus Particle

2018 ◽  
Vol 57 (2) ◽  
pp. 246-256 ◽  
Author(s):  
A.L. Kolesnikova ◽  
M.Yu. Gutkin ◽  
S.A. Krasnitckii ◽  
A.M. Smirnov ◽  
M.V. Dorogov ◽  
...  
Keyword(s):  
Classical Theory ◽  
Strain Energy ◽  
Lattice Mismatch ◽  
Theory Of Elasticity ◽  
Elastic Problem ◽  
Core Shell ◽  
Janus Particle ◽  
Elastic Fields ◽  
Shell Particle ◽  
Spherical Core

Abstract 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.

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