Atomistic Studies of Dislocation Glide in γ-TiAl

2002 ◽  
Vol 753 ◽  
Author(s):  
R. Porizek ◽  
S. Znam ◽  
D. Nguyen-Manh ◽  
V. Vitek ◽  
D. G. Pettifor
Keyword(s):  
Single Phase ◽  
Tight Binding ◽  
Orientation Dependence ◽  
Core Structure ◽  
Peierls Stress ◽  
Tight Binding Approximation ◽  
Dislocation Glide ◽  
Ordinary Dislocation ◽  
Atomic Interactions ◽  
Directional Bonding

ABSTRACTComputer simulation of the core structure and glide of ordinary 1/2<110] dislocations and <101] superdislocations in L10 TiAl has been performed using the recently constructed BondOrder Potentials. This description of atomic interactions includes explicitly, within the tight-binding approximation, the most important aspects of the directional bonding, namely d-d, p-p and d-p bonds. The ordinary dislocation in the screw orientation was found to have a non-planar core and, therefore, high Peierls stress. The superdislocation was found to possess in the screw orientation either a planar (glissile) or a non-planar (sessile) core structure. However, the glissile core transforms into the sessile one for certain orientations of the applied stress. This implies a strong asymmetry of the yield stress and the break down of the Schmid law when the plastic flow is mediated by superdislocations. At the same time, this may explain the orientation dependence of the dislocation substructure observed in the single-phase γ-TiAl by electron microscopy.

Tight-Binding Theory and Computational Materials Synthesis

MRS Bulletin ◽  
1996 ◽  
Vol 21 (2) ◽  
pp. 42-48 ◽  
Author(s):  
A.P. Sutton ◽  
P.D. Godwin ◽  
A.P. Horsfield
Keyword(s):  
Ab Initio ◽  
Density Functional ◽  
Tight Binding ◽  
Materials Synthesis ◽  
Tight Binding Approximation ◽  
Embedded Atom ◽  
Empirical Potentials ◽  
Ionic Systems ◽  
Atomic Interactions ◽  
Computational Materials

At the heart of any atomistic simulation is a description of the atomic interactions. A whole hierarchy of models of atomic interactions has been developed over the last twenty years or so, ranging from ab initio density-functional techniques, to simple empirical potentials such as the embedded-atom method and Finnis-Sinclair potentials in metals, valence force fields in covalently bonded materials, and the somewhat older shell model in ionic systems. Between the ab initio formulations and empirical potentials lies the tight-binding approximation: It involves the solution of equations that take into account the electronic structure of the system, but at a small fraction of the cost of an ab initio simulation, because those equations contain simplifying approximations and parameters that are usually fitted empirically.Tight binding may be characterized as the simplest formulation of atomic interactions that incorporates the quantum-mechanical nature of bonding. The particular features that it captures are as follows: (1) the strength of a bond being dependent not only on the interatomic separation but also on the angles it forms with respect to other bonds, which arises fundamentally from the spatially directed characters of p and d atomic orbitals, (2) the filling of bonding (and possibly antibonding) states with electrons, which controls the bond strengths, and (3) changes in the energy distribution of bonding and antibonding states as a result of atomic displacements. These features enable one to obtain considerable improvements in accuracy compared to the simple “glue models” of bonding since use is made of the physics and chemistry of bonding.

Molecular dynamics simulations of wafer bonding

2001 ◽  
Vol 681 ◽  
Author(s):  
Kurt Scheerschmidt
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Wafer Bonding ◽  
Tight Binding ◽  
Tight Binding Approximation ◽  
Elementary Processes ◽  
Empirical Potentials ◽  
Atomic Interactions ◽  
Dynamics Simulations ◽  
Interface Structures

ABSTRACTMolecular dynamics simulations using empirical potentials have been employed to describe atomic interactions at interfaces created by the macroscopic wafer bonding process. Investigating perfect or distorted surfaces of different semiconductor materials as well as of silica enables one to study the elementary processes and the resulting defects at the interfaces, and to characterize the ability of the potentials used. Twist rotation due to misalignment and bonding over steps influence strongly the bondability of larger areas. Empirical potentials developed by the bond order tight-binding approximation include ∏-bonds and yield enhanced interface structures, energies, and transferability to new materials systems.

Core energy and Peierls stress of a screw dislocation in bcc molybdenum: A periodic-cell tight-binding study

2004 ◽  
Vol 70 (10) ◽  
Author(s):  
Ju Li ◽  
Cai-Zhuang Wang ◽  
Jin-Peng Chang ◽  
Wei Cai ◽  
Vasily V. Bulatov ◽  
...  
Keyword(s):  
Screw Dislocation ◽  
Tight Binding ◽  
Binding Study ◽  
Peierls Stress ◽  
Periodic Cell ◽  
Core Energy

Electrical Transport Properties of Carbon Nanotube Metal-Semiconductor Heterojunction

2016 ◽  
Vol 15 (05n06) ◽  
pp. 1660009 ◽  
Author(s):  
Keka Talukdar ◽  
Anil Shantappa
Keyword(s):  
Electrical Transport ◽  
Nearest Neighbor ◽  
Electronic Devices ◽  
Tight Binding ◽  
Transmission Function ◽  
Topological Defects ◽  
Dynamics Simulation ◽  
Internal Stresses ◽  
Electrical Transport Properties ◽  
Tight Binding Approximation

Carbon nanotubes (CNTs) have been proved to have promising applicability in various fields of science and technology. Their fascinating mechanical, electrical, thermal, optical properties have caught the attention of today’s world. We have discussed here the great possibility of using CNTs in electronic devices. CNTs can be both metallic and semiconducting depending on their chirality. When two CNTs of different chirality are joined together via topological defects, they may acquire rectifying diode property. We have joined two tubes of different chiralities through circumferential Stone–Wales defects and calculated their density of states by nearest neighbor tight binding approximation. Transmission function is also calculated to analyze whether the junctions can be used as electronic devices. Different heterojunctions are modeled and analyzed in this study. Internal stresses in the heterojunctions are also calculated by molecular dynamics simulation.

scholarly journals Optical scatterings in layered systems

2020 ◽  
Author(s):  
Chang-Ting Liu ◽  
Chih-Wei Chiu ◽  
Chiun-Yan Lin ◽  
Ming-Fa Lin
Keyword(s):  
Tight Binding ◽  
State Transitions ◽  
Finite Width ◽  
Bulk Materials ◽  
Layered Systems ◽  
Binding Model ◽  
Reflection And Transmission ◽  
Atomic Interactions ◽  
Dynamic Charge ◽  
Electro Magnetic

Abstract Optical properties, reflectance, absorbance and transmittance spectra, are fully investigated for the layered structures through the development of theoretical framework. The transverse dielectric function, which characterizes the dynamic charge screenings, can cover all the intralayer and interlayer atomic interactions under the electro-magnetic wave perturbation. By the continuous reflection and transmission scatterings at two surfaces, their analytic formulas are established from the vertical valence-state transitions and the boundary conditions. They are also suitable for finite-width bulk materials. Most important, this study is fully combined with the generalized tight-binding model with all the intrinsic interactions and external field.

Stress Orientation Dependence of Dislocation Glide in Epitaxial Films

1990 ◽  
Vol 202 ◽  
Author(s):  
S. Dakshinamurthy ◽  
K. Rajan
Keyword(s):  
Crystal Orientation ◽  
Stereographic Projection ◽  
Epitaxial Films ◽  
Orientation Dependence ◽  
Stress Axis ◽  
Dislocation Glide ◽  
Stress Orientation ◽  
Slip Transfer

ABSTRACTThe effect of different stresses on the glide of the commonly observed dislocations in epitaxial films is systematically investigated. The possibility of planar dissociation of perfect dislocations and the conditions for their subsequent glide are explored.Slip transfer from one plane to another is affected by the crystal orientation relative to the stress axis. This process is quantitatively analyzed by calculating iso-Schmid factors on a stereographic projection. The results of this model are correlated with those found in the literature.

Luminescent Amorphous Silicon Layers

1997 ◽  
Vol 486 ◽  
Author(s):  
G. Allan ◽  
C. Delerue ◽  
M. Lannoo
Keyword(s):  
Electronic Structure ◽  
Amorphous Silicon ◽  
Radiative Recombination ◽  
Crystalline Silicon ◽  
Tight Binding ◽  
Blue Shift ◽  
Localized States ◽  
Structure Model ◽  
Radiative Recombination Rate ◽  
Tight Binding Approximation

AbstractThe electronic structure of amorphous silicon layers has been calculated within the empirical tight binding approximation using the Wooten-Winer-Weaire atomic structure model. We predict an important blue shift due to the confinement for layer thickness below 3 nm and we compare with crystalline silicon layers. The radiative recombination rate is enhanced by the disorder and the confinement but remains quite small. The comparison of our results with experimental results shows that the density of defects and localized states in the studied samples must be quite small.

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