Dislocation core reconstruction and its effect on dislocation mobility in silicon

1999 ◽  
Vol 86 (8) ◽  
pp. 4249-4257 ◽  
Author(s):  
João F. Justo ◽  
Vasily V. Bulatov ◽  
Sidney Yip
Keyword(s):  
Dislocation Core ◽  
Dislocation Mobility

scholarly journals The Core Structure and the Mobility of Dislocations in Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 341-359 ◽  
Author(s):  
R. W. Whitworth
Keyword(s):  
Alternative Model ◽  
Dislocation Core ◽  
Dislocation Mobility ◽  
Atomic Processes ◽  
The Core ◽  
A Value ◽  
Normal Lattice ◽  
Crystalline Core ◽  
Dislocation Movement ◽  
Proton Disorder

AbstractThe evidence concerning the velocity of glide of dislocations on the (0001) plane of ice Ih is reviewed and related to atomic processes occurring within or near the dislocation core. The velocity is directly proportional to stress at low stress, with a value of the order of 500 Burgers vectors per second at — 18°C and a stress of 105 N m-2. The usual idea of a dislocation core is that it is “crystalline” in the sense that the linkages between molecules are as far as possible the same as those in the normal lattice. For such a model the disorder of protons presents an obstacle to dislocation movement, and recent theories predict that dislocations should not be able to glide as fast as they are observed to do. Various ways of avoiding this difficulty within the context of a crystalline core are discussed, but none seems likely to be successful. An alternative model is that the core is “non-crystalline”, with a disordered arrangement of mobile molecules within it. The movement of such dislocations should not be seriously impeded by proton disorder. Dislocation mobility would then be limited at least in part by anelastic loss due to the stress-induced order of protons in the surrounding lattice.

Dynamics of Dissociated Dislocations in SI: A Micro-Meso Simulation Methodology

1998 ◽  
Vol 538 ◽  
Author(s):  
W. Cai ◽  
V.V. Bulatov ◽  
J.F. Justo ◽  
S. Yip ◽  
A.S. Argon
Keyword(s):  
Atomistic Simulation ◽  
Kinetic Monte Carlo ◽  
Dislocation Core ◽  
Dislocation Motion ◽  
Peierls Stress ◽  
Dislocation Mobility ◽  
Simulation Methodology ◽  
Structure And Dynamics ◽  
Dislocation Behavior ◽  
Stress Dependent

AbstractThe theory of dislocation motion in materials with high Peierls stress relates dislocation mobility to the underlying kink mechanisms. While one has been able to describe certain qualitative features of dislocation behavior, important details of the atomic core mechanisms are lacking. We present a hybrid micro-meso approach to modeling the mobility of a single dislocation in Si in which the energetics of defect cores and kink mechanisms are treated by atomistic simulation, while dislocation motion under applied stress and at finite temperature is described through kinetic Monte Carlo. Three important aspects pertaining to treating the details of local structure and dynamics of kinks are incorporated in our approach: (1) Realistic complexity of (multiple) kink mechanisms in the dislocation core. (2) Full Peach-Koehler formalism for treatment of curved dislocation. (3) Detailed investigation of interaction between partials. This simulation methodology is used to calculate micron-scale dislocation mobility, with no adjustable parameters; specifically we obtain temperature and stress dependent velocity results that can be compared with experimental measurements.

Electronic structure of planar faults in TiAl

1992 ◽  
Vol 7 (7) ◽  
pp. 1735-1750 ◽  
Author(s):  
C. Woodward ◽  
J.M. MacLaren ◽  
S. Rao
Keyword(s):  
Electronic Structure ◽  
Nearest Neighbor ◽  
Flow Behavior ◽  
Dislocation Core ◽  
Intermetallic Alloys ◽  
Dislocation Mobility ◽  
Defect Energies ◽  
Three Body ◽  
Anti Phase Boundary ◽  
Directional Bonding

The mechanical behavior of intermetallic alloys is related to the mobility of the dislocations found in these compounds. Currently the effect of bonding on dislocation core structure and its influence on deformation behavior is not well understood. However, the unusual properties of these materials, such as the anomalous temperature dependence of flow stress observed in TiAl, are derived in part from the aspects of bonding that determine dislocation mobility. Several recent studies have suggested a particular relationship between directional bonding in TiAl and dislocation mobility. To understand better the flow behavior of high temperature intermetallics, and as a step toward bridging the gap between electronic structure and flow behavior, we have calculated the electronic structure of various planar faults in TiAl. The self consistent electronic structure has been determined using a layered Korringa Kohn Rostoker (LKKR) method which embeds the fault region between two semi-infinite perfect crystals. Calculated defect energies in stoichiometric TiAl agree reasonably well with other theoretical estimates, though overestimating the experimental (111) anti-phase boundary (APB) energy, found for Ti46Al54. We approximate the energy of the (111) APB for the Al-rich stoichiometry by calculating the energy of Al antisites near that defect plane. The calculated (111)APB energy decreases by 6% in going from stoichiometric TiAl to Ti46Al54. The overall hierarchy of fault energies is found to be associated with the number of crystal bond states that are disrupted by the introduction of the fault plane. However, the hierarchy of fault energies is inconsistent with the traditionally accepted ordering. Changes in bonding taking place in the vicinity of the planar defects are illustrated through the density of states and charge density plots. A three body atomistic model is introduced to parameterize the bonding observed in TiAl. The L10 lattice (c/a = 1.00), within a second nearest neighbor three body model, yields a (111)APB energy which is the sum of the complex and superlattice-intrinsic stacking fault energies.

scholarly journals The Core Structure and the Mobility of Dislocations in Ice

1978 ◽  
Vol 21 (85) ◽  
pp. 341-359 ◽  
Author(s):  
R. W. Whitworth
Keyword(s):  
Alternative Model ◽  
Dislocation Core ◽  
Dislocation Mobility ◽  
Atomic Processes ◽  
The Core ◽  
A Value ◽  
Normal Lattice ◽  
Crystalline Core ◽  
Dislocation Movement ◽  
Proton Disorder

Abstract The evidence concerning the velocity of glide of dislocations on the (0001) plane of ice Ih is reviewed and related to atomic processes occurring within or near the dislocation core. The velocity is directly proportional to stress at low stress, with a value of the order of 500 Burgers vectors per second at — 18°C and a stress of 105 N m-2. The usual idea of a dislocation core is that it is “crystalline” in the sense that the linkages between molecules are as far as possible the same as those in the normal lattice. For such a model the disorder of protons presents an obstacle to dislocation movement, and recent theories predict that dislocations should not be able to glide as fast as they are observed to do. Various ways of avoiding this difficulty within the context of a crystalline core are discussed, but none seems likely to be successful. An alternative model is that the core is “non-crystalline”, with a disordered arrangement of mobile molecules within it. The movement of such dislocations should not be seriously impeded by proton disorder. Dislocation mobility would then be limited at least in part by anelastic loss due to the stress-induced order of protons in the surrounding lattice.

Direct structure images of 30° partial dislocation cores in silicon

1987 ◽  
Vol 45 ◽  
pp. 242-243
Author(s):  
J. C. Barry ◽  
H. Alexander
Keyword(s):  
Dislocation Core ◽  
Preparation Technique ◽  
Burgers Vector ◽  
Vector Type ◽  
Sample Preparation Technique ◽  
Lattice Images ◽  
Dislocation Core Structure ◽  
Type Lattice ◽  
Direct Inspection

Dislocations in silicon produced by plastic deformation are generally dissociated into partials. 60° dislocations (Burgers vector type 1/2[101]) are dissociated into 30°(Burgers vector type 1/6[211]) and 90°(Burgers vector type 1/6[112]) dislocations. The 30° partials may be either of “glide” or “shuffle” type. Lattice images of the 30° dislocation have been obtained with a JEM 100B, and with a JEM 200Cx. In the aforementioned experiments a reasonable but imperfect match was obtained with calculated images for the “glide” model. In the present experiment direct structure images of 30° dislocation cores have been obtained with a JEOL 4000EX. It is possible to deduce the 30° dislocation core structure by direct inspection of the images. Dislocations were produced by compression of single crystal Si (sample preparation technique described in Alexander et al.).

Structural analysis of a Σ5 grain boundary in YBa2Cu3O7δ

1993 ◽  
Vol 51 ◽  
pp. 942-943
Author(s):  
J.-Y. Wang ◽  
Y. Zhu ◽  
A.H. King ◽  
M. Suenaga
Keyword(s):  
Grain Boundary ◽  
Lattice Mismatch ◽  
Weak Link ◽  
Coincidence Site Lattice ◽  
Large Angle ◽  
Dislocation Core ◽  
Superconducting Order Parameter ◽  
Outstanding Problem ◽  
Transmission Electron

One outstanding problem in YBa2Cu3O7−δ superconductors is the weak link behavior of grain boundaries, especially boundaries with a large-angle misorientation. Increasing evidence shows that lattice mismatch at the boundaries contributes to variations in oxygen and cation concentrations at the boundaries, while the strain field surrounding a dislocation core at the boundary suppresses the superconducting order parameter. Thus, understanding the structure of the grain boundary and the grain boundary dislocations (which describe the topology of the boundary) is essential in elucidating the superconducting characteristics of boundaries. Here, we discuss our study of the structure of a Σ5 grain boundary by transmission electron microscopy. The characterization of the structure of the boundary was based on the coincidence site lattice (CSL) model.Fig.l shows two-beam images of the grain boundary near the projection. An array of grain boundary dislocations, with spacings of about 30nm, is clearly visible in Fig. 1(a), but invisible in Fig. 1(b).

Electron microscope studies of the plastic deformation of ternary alloys based on GaAs

1990 ◽  
Vol 48 (4) ◽  
pp. 1120-1120
Author(s):  
R. Haswell ◽  
U. Bangert ◽  
P. Charsley
Keyword(s):  
Plastic Deformation ◽  
Electron Microscope ◽  
Room Temperature ◽  
Stacking Faults ◽  
The Other ◽  
Ternary Alloys ◽  
Dislocation Mobility ◽  
Semiconducting Materials ◽  
Micro Indentation

A knowledge of the behaviour of dislocations in semiconducting materials is essential to the understanding of devices which use them . This work is concerned with dislocations in alloys related to the semiconductor GaAs . Previous work on GaAs has shown that microtwinning occurs on one of the <110> rosette arms after indentation in preference to the other . We have shown that the effect of replacing some of the Ga atoms by Al results in microtwinning in both of the rosette arms.In the work to be reported dislocations in specimens of different compositions of Gax Al(1-x) As and Gax In(1-x) As have been studied by using micro indentation on a (001) face at room temperature . A range of electron microscope techniques have been used to investigate the type of dislocations and stacking faults/microtwins in the rosette arms , which are parallel to the [110] and [10] , as a function of composition for both alloys . Under certain conditions microtwinning occurs in both directions . This will be discussed in terms of the dislocation mobility.

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