The determination of the sign of the burgers vector of frank dislocation loops

During recent years, defect structures resulting from radiation damage have been successfully studied by a large number of investigators. Early studies were based primarily on the analysis of the characteristic black-white lobe contrast from small dislocation loops. Contrast calculations indicated that the sense of the black-white contrast, relative to the diffracting vector at a given depth in the foil, could be used to determine the nature (vacancy or interstitial) of the loop. These calculations have also been used to formulate rules for the determination of the loop Burgers vector and habit plane normal [1]. For pure edge loops this simple procedure is quite satisfactory, but for loops with a shear component of the Burgers vector it becomes very involved and, in certain geometries, may lead to erroneous conclusions. Carpenter has demonstrated that “unsafe” orientations exist which do not permit the unambiguous determination of the Burgers vector relative to the loop plane [2].

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Direction of Black-White Contrast from Small Dislocation Loops

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100077906 ◽

1977 ◽

Vol 35 ◽

pp. 56-57

Author(s):

W. D. Cooper ◽

C. S. Hartley ◽

J. J. Hren

Keyword(s):

Electron Microscope ◽

Transmission Electron Microscope ◽

Image Plane ◽

Dislocation Loops ◽

Burgers Vector ◽

Simple Concept ◽

Transmission Electron ◽

Vector Projection ◽

Shear Component

Dislocation loops observed in the transmission electron microscope exhibit a characteristic black-white strain contrast under two-beam dynamical diffracting conditions. A simple concept of the nature of this contrast indicates that the black-white direction should lie parallel to the projection of the Burgers vector onto the image plane. Using the results of several contrast calculations for small loops, Wilkens and Riihle (1972) recognized that the black-white direction did not always lie parallel to the Burgers vector projection. For loops with an appreciable shear component, they concluded that a determination of the black-white direction would not be sufficient for analysis of the loop crystallography. However, for pure edge loops they predicted that the black-white direction would correspond (within a few degrees) to the projection of the Burgers vector. Numerous investigators have used this erroneous assumption to analyze the crystallography of loops.

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Weak Beam Imaging and Diffraction Studies of Stacking Faults in Silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092918 ◽

1976 ◽

Vol 34 ◽

pp. 590-591

Author(s):

T. Y. Tan ◽

W. K. Tice

Keyword(s):

Fast Neutron ◽

Rapid Determination ◽

Stacking Faults ◽

Imaging Method ◽

Large Reduction ◽

Dislocation Loops ◽

Fringe Spacing ◽

Weak Beam ◽

Kinematical Theory

In studying ion implanted semiconductors and fast neutron irradiated metals, the need for characterizing small dislocation loops having diameters of a few hundred angstrom units usually arises. The weak beam imaging method is a powerful technique for analyzing these loops. Because of the large reduction in stacking fault (SF) fringe spacing at large sg, this method allows for a rapid determination of whether the loop is faulted, and, hence, whether it is a perfect or a Frank partial loop. This method was first used by Bicknell to image small faulted loops in boron implanted silicon. He explained the fringe spacing by kinematical theory, i.e., ≃l/(Sg) in the fault fringe in depth oscillation. The fault image contrast formation mechanism is, however, really more complicated.

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Defects in ion implanted silicon

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100109070 ◽

1978 ◽

Vol 36 (1) ◽

pp. 386-387

Author(s):

J.A. Lambert ◽

P.S. Dobson

Keyword(s):

Defect Structure ◽

Dislocation Loops ◽

Frank Loop ◽

Burgers Vector ◽

Temperature Range ◽

Perfect Dislocation ◽

Contrast Analysis ◽

Image Position ◽

Ion Implanted

The defect structure of ion-implanted silicon, which has been annealed in the temperature range 800°C-1100°C, consists of extrinsic Frank faulted loops and perfect dislocation loops, together with‘rod like’ defects elongated along <110> directions. Various structures have been suggested for the elongated defects and it was argued that an extrinsically faulted Frank loop could undergo partial shear to yield an intrinsically faulted defect having a Burgers vector of 1/6 <411>.This defect has been observed in boron implanted silicon (1015 B+ cm-2 40KeV) and a detailed contrast analysis has confirmed the proposed structure.

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Determination of the Burgers vector of a dislocation in a Fe-Mn alloy by weak-beam image in HVEM

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108799 ◽

1978 ◽

Vol 36 (1) ◽

pp. 330-331

Author(s):

Y. Ishida ◽

H. Ishida ◽

K. Kohra ◽

H. Ichinose

Keyword(s):

High Order ◽

Simulation Technique ◽

The Other ◽

Image Simulation ◽

Diffraction Vector ◽

Burgers Vector ◽

Weak Beam ◽

Beam Image ◽

Edge Component

IntroductionA simple and accurate technique to determine the Burgers vector of a dislocation has become feasible with the advent of HVEM. The conventional image vanishing technique(1) using Bragg conditions with the diffraction vector perpendicular to the Burgers vector suffers from various drawbacks; The dislocation image appears even when the g.b = 0 criterion is satisfied, if the edge component of the dislocation is large. On the other hand, the image disappears for certain high order diffractions even when g.b ≠ 0. Furthermore, the determination of the magnitude of the Burgers vector is not easy with the criterion. Recent image simulation technique is free from the ambiguities but require too many parameters for the computation. The weak-beam “fringe counting” technique investigated in the present study is immune from the problems. Even the magnitude of the Burgers vector is determined from the number of the terminating thickness fringes at the exit of the dislocation in wedge shaped foil surfaces.

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Black-white contrast of dislocation loops

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100108787 ◽

1978 ◽

Vol 36 (1) ◽

pp. 328-329

Author(s):

J. J. Hren ◽

W. D. Cooper ◽

L. J. Sykes

Keyword(s):

Electron Microscopy ◽

Transmission Electron Microscopy ◽

Dislocation Loops ◽

Major Premise ◽

Burgers Vector ◽

Transmission Electron ◽

Primary Means ◽

Contrast Analysis ◽

Dot Product ◽

Imaging Conditions

Small dislocation loops observed by transmission electron microscopy exhibit a characteristic black-white strain contrast when observed under dynamical imaging conditions. In many cases, the topography and orientation of the image may be used to determine the nature of the loop crystallography. Two distinct but somewhat overlapping procedures have been developed for the contrast analysis and identification of small dislocation loops. One group of investigators has emphasized the use of the topography of the image as the principle tool for analysis. The major premise of this method is that the characteristic details of the image topography are dependent only on the magnitude of the dot product between the loop Burgers vector and the diffracting vector. This technique is commonly referred to as the (g•b) analysis. A second group of investigators has emphasized the use of the orientation of the direction of black-white contrast as the primary means of analysis.

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Anisotropy of Nanoindentation – a tool for the determination of nanocrystal orientation ?

MRS Proceedings ◽

10.1557/proc-779-w5.14 ◽

2003 ◽

Vol 779 ◽

Author(s):

David Christopher ◽

Steven Kenny ◽

Roger Smith ◽

Asta Richter ◽

Bodo Wolf ◽

...

Keyword(s):

Crystal Surface ◽

Scanning Force Microscopy ◽

Depth Range ◽

Dislocation Loops ◽

Force Microscopy ◽

Pile Up ◽

Out Of Plane ◽

Scanning Force ◽

Dynamics Simulations

AbstractThe pile up patterns arising in nanoindentation are shown to be indicative of the sample crystal symmetry. To explain and interpret these patterns, complementary molecular dynamics simulations and experiments have been performed to determine the atomistic mechanisms of the nanoindentation process in single crystal Fe{110}. The simulations show that dislocation loops start from the tip and end on the crystal surface propagating outwards along the four in-plane <111> directions. These loops carry material away from the indenter and form bumps on the surface along these directions separated from the piled-up material around the indenter hole. Atoms also move in the two out-of-plane <111> directions causing propagation of subsurface defects and pile-up around the hole. This finding is confirmed by scanning force microscopy mapping of the imprint, the piling-up pattern proving a suitable indicator of the surface crystallography. Experimental force-depth curves over the depth range of a few nanometers do not appear smooth and show distinct pop-ins. On the sub-nanometer scale these pop-ins are also visible in the simulation curves and occur as a result of the initiation of the dislocation loops from the tip.

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