The Burgers Vector and the Flow of Screw and Edge Dislocations

2012 ◽  
pp. 588-592
Author(s):  
Morton E. Gurtin ◽  
Eliot Fried ◽  
Lallit Anand
Keyword(s):  
Burgers Vector ◽  
Edge Dislocations

scholarly journals Influence of the Rake Angle on Nanocutting of Fe Single Crystals: A Molecular-Dynamics Study

Crystals ◽  
2020 ◽  
Vol 10 (6) ◽  
pp. 516 ◽  
Author(s):  
Iyad Alabd Alhafez ◽  
Herbert M. Urbassek
Keyword(s):  
Molecular Dynamics ◽  
Chip Thickness ◽  
Mass Conservation ◽  
Friction Angle ◽  
Rake Angle ◽  
Shear Angle ◽  
Dynamics Simulation ◽  
Burgers Vector ◽  
Edge Dislocations ◽  
Cutting Direction

Using molecular dynamics simulation, we study the cutting of an Fe single crystal using tools with various rake angles α . We focus on the (110)[001] cut system, since here, the crystal plasticity is governed by a simple mechanism for not too strongly negative rake angles. In this case, the evolution of the chip is driven by the generation of edge dislocations with the Burgers vector b = 1 2 [ 111 ] , such that a fixed shear angle of ϕ = 54.7 ∘ is established. It is independent of the rake angle of the tool. The chip form is rectangular, and the chip thickness agrees with the theoretical result calculated for this shear angle from the law of mass conservation. We find that the force angle χ between the direction of the force and the cutting direction is independent of the rake angle; however, it does not obey the predictions of macroscopic cutting theories, nor the correlations observed in experiments of (polycrystalline) cutting of mild steel. Only for (strongly) negative rake angles, the mechanism of plasticity changes, leading to a complex chip shape or even suppressing the formation of a chip. In these cases, the force angle strongly increases while the friction angle tends to zero.

Characterization of Basal Plane Dislocations in 4H-SiC Substrates by Topography Analysis of Threading Edge Dislocations in Epilayers

2010 ◽  
Vol 645-648 ◽  
pp. 303-306 ◽  
Author(s):  
Isaho Kamata ◽  
Masahiro Nagano ◽  
Hidekazu Tsuchida
Keyword(s):  
High Resolution ◽  
Epitaxial Layer ◽  
Basal Plane ◽  
Grazing Incidence ◽  
Size Difference ◽  
Etch Pits ◽  
Burgers Vector ◽  
Vector Direction ◽  
Edge Dislocations

Burgers vector directions of threading edge dislocations (TEDs) in 4H-SiC epitaxial layer are distinguished by grazing incidence high resolution topography. Based on comparison between appearance of KOH etch pits and direction of TED Burgers vector, the size difference of the TED etch pits is found to be dependent on their Burgers vector directions. Examining TEDs in the epilayer by topography, the Burgers vector direction of basal plane dislocations (BPDs) in the substrate is identified. Correspondence between the topography contrast and the sense of a BPD is also investigated.

Variation of dislocation morphology with strain in GexSi1−x epilayers on (100)Si

1990 ◽  
Vol 5 (9) ◽  
pp. 1900-1907 ◽  
Author(s):  
E. P. Kvam ◽  
D. M. Maher ◽  
C. J. Humphreys
Keyword(s):  
Orthogonal Array ◽  
Small Range ◽  
Internal Source ◽  
Threading Dislocations ◽  
Misfit Dislocations ◽  
Burgers Vector ◽  
Vector Length ◽  
Surface Nucleation ◽  
And Behavior ◽  
Edge Dislocations

A change in microstructure, including dislocation Burgers vector, length, and behavior, has been observed to occur when the epilayer mismatch is varied in GexSi1−x layers grown on (100) Si. At low mismatches (<1.5%), there is an orthogonal array of very long 60° misfit dislocations. At higher mismatches (>2.3%) there is an orthogonal array of short edge dislocations. At intermediate mismatches (1.5 to 2.3%) there is a mixture of 60° and edge dislocations. The nature of the microstructure has a pronounced effect on the density of threading dislocations in the epilayer, which increase by a factor of ∼60× through a relatively small range of mismatch (1.7 to 2.1%, corresponding to x ranging from 0.4 to 0.5). These morphologies are discussed in the light of recent work on the sources of misfit dislocations. While mechanisms for the introduction and propagation of dislocations at low mismatch have recently been observed and explained, the high misfit case is clearly very different; i.e., surface nucleation seems to be likely in the latter case as opposed to operation of an internal source in the former. A mechanism for edge dislocation formation is proposed.

Interactions between Edge Dislocations and Interstitial Clusters in Iron and Copper

2000 ◽  
Vol 653 ◽  
Author(s):  
Yu.N. Osetsky ◽  
D.J. Bacon ◽  
A. Serra ◽  
B.N. Singh
Keyword(s):  
Elasticity Theory ◽  
Atomistic Simulation ◽  
Dislocation Line ◽  
Dislocation Loops ◽  
Burgers Vector ◽  
Isotropic Elasticity ◽  
Deformation Processes ◽  
Small Clusters ◽  
Edge Dislocations ◽  
Isotropic Theory

AbstractDislocations decorated by both clusters of self-interstitial atoms (SIAs) and small dislocation loops, are one of the microstructure features which can play an important role in post-irradiated deformation processes. The interactions between dislocations and clusters are important and are usually treated within the framework of isotropic elasticity theory. However, it is still not clear whether or not these interactions, especially for small clusters at short distances, can be treated accurately by elasticity theory. Comparative studies by atomistic simulation and elasticity theory can clarify this. Here we present a simple example of such a study where interactions between a glissile SIA cluster and an edge dislocation are studied in bcc-Fe and fcc-Cu using both techniques. In Fe we have studied the interaction of a dislocation with Burgers vector b= 1/2<111> lying along <112> direction with a SIA cluster with the same b situated at different distances below the extra half-plane. In Cu, the dislocation and cluster had b = 1/2<110> and the dislocation line was along the <112> direction. Interactions with clusters of diameter about 1nm were simulated. Elastic calculations were made within the isotropic theory with parameters estimated from atomistic simulation. The results obtained by both techniques are discussed and some preliminary conclusions for different cases are drawn.

Edge dislocations in fibrous grunerite

1981 ◽  
Vol 44 (335) ◽  
pp. 287-291
Author(s):  
E. J. W. Whittaker ◽  
B. A. Cressey ◽  
J. L. Hutchison
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
High Resolution ◽  
Cross Sections ◽  
The Other ◽  
Two Dimensional ◽  
Equal Frequency ◽  
Burgers Vector ◽  
Transmission Electron ◽  
Edge Dislocations

AbstractSections perpendicular to [001] of ion-thinned specimens of fibrous grunerite (amosite) have been examined by high-resolution transmission electron microscopy. In this orientation, two kinds of dislocation have been observed with about equal frequency. One lies on [001] and has a Burgers vector a. The other is on [001] and has a Burgers vector ½a+½b Interpretation of features associated with these dislocations has been assisted by the use of two-dimensional models of I-beam cross-sections which can be interlocked to simulate the possible modes of stacking.

Edge dislocations with large burgers vector in sphalerite crystals

2002 ◽  
Vol 28 (9) ◽  
pp. 762-764 ◽  
Author(s):  
A. N. Builov ◽  
L. N. Danil’chuk
Keyword(s):  
Burgers Vector ◽  
Edge Dislocations

Effects of Different Defect Types on the Performance of Devices Fabricated on a 4H-SiC Homoepitaxial Layer

2006 ◽  
Vol 911 ◽  
Author(s):  
Hui Chen ◽  
Balaji Raghothamachar ◽  
William Vetter ◽  
Michael Dudley ◽  
Y. Wang ◽  
...  
Keyword(s):  
Grain Boundaries ◽  
Basal Plane ◽  
Schottky Contacts ◽  
Device Performance ◽  
Hollow Core ◽  
Screw Dislocations ◽  
Burgers Vector ◽  
Edge Dislocations ◽  
Sic Wafer ◽  
Koh Etching

AbstractAn 8° off-axis 4H-SiC wafer with circular Schottky contacts fabricated on a CVD grown 4H-SiC homoepitaxial layer was studied to investigate the influence of various defects, including small (closed-core) screw dislocations (Burgers vector of 1c or 2c), hollow-core (micropipes; Burgers vector larger than 2c), threading edge dislocations (from conversion of basal plane dislocations from the substrate into the epilayer), grain boundaries and triangular defects, on the device performance in the form of breakdown voltages. The defects were examined using synchrotron white beam x-ray topography (SWBXT) based techniques and molten KOH etching. The devices commonly contained basal plane dislocations, small screw dislocations and threading edge dislocations, the latter two of which could give rise to low breakdown voltages for the devices. In addition, less commonly observed defects such as micropipes, grain boundaries and triangular defects are much more destructive to device performance than closed-core screw dislocations and threading edge dislocations.

Simulation of Grazing-Incidence Synchrotron X-ray Topographic Images of Threading c+a Dislocations in 4H-SiC

2012 ◽  
Vol 1433 ◽  
Author(s):  
Fangzhen Wu ◽  
Shayan Byrappa ◽  
Huanhuan Wang ◽  
Yi Chen ◽  
Balaji Raghothamachar ◽  
...  
Keyword(s):  
Ray Tracing ◽  
Potassium Hydroxide ◽  
Grazing Incidence ◽  
Burgers Vector ◽  
X Ray ◽  
Edge Dislocations ◽  
Ray Tracing Simulation ◽  
Simulated Images ◽  
Non Destructive ◽  
Vector Magnitude

ABSTRACTSynchrotron X-ray topography (SXRT) of various geometries has been successfully utilized to image c+a dislocations in 4H-SiC crystals. Although molten potassium hydroxide(KOH) can be used to reveal the location of such dislocations, it is not possible to determine their senses or their Burgers vector magnitude. A simple, non-destructive method has been proposed to determine the Burgers vector of these c+a dislocations called the ray tracing simulation, which has been successfully implemented previously in revealing the dislocation sense and magnitude of micropipes, closed-core threading screw dislocations (TSDs) and threading edge dislocations (TEDs) in 4H-SiC. In this paper, grazing incidence topography is performed using the monochromatic beam for the horizontally cut wafers to record pyramidal reflections of 11-28 type. Ray tracing simulation has been successfully implemented to correlate the simulated images with experimental images which are discussed in the paper.

High-Resolution Topography Analysis on Threading Edge Dislocations in 4H-SiC Epilayers

2008 ◽  
Vol 600-603 ◽  
pp. 305-308 ◽  
Author(s):  
Isaho Kamata ◽  
Masahiro Nagano ◽  
Hidekazu Tsuchida ◽  
Yi Chen ◽  
Michael Dudley
Keyword(s):  
Spatial Distribution ◽  
High Resolution ◽  
Epitaxial Layer ◽  
Mapping Method ◽  
Burgers Vector ◽  
Topography Analysis ◽  
Edge Dislocations ◽  
Simulated Images ◽  
Crystal Boundaries

Threading edge dislocations (TEDs) in a 4H-SiC epitaxial layer are investigated using high-resolution synchrotron topography. Six types of TED image are confirmed to correspond to the Burgers vector directions by a comparison of computer simulated images and observed topography images in crystal boundaries. Using a mapping method, a wide spatial distribution of the six types of TED is examined in a quarter section of a 2-inch wafer.

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