Contrast From Point Defects in The Infinitesimal Approximation

1980 ◽  
Vol 38 ◽  
pp. 350-351
Author(s):  
L. J. Sykes ◽  
J. J. Hren
Keyword(s):  
Electron Microscope ◽  
Point Defects ◽  
Broad Class ◽  
Stacking Fault ◽  
Crystalline Solids ◽  
Dislocation Loops ◽  
Analytical Expression ◽  
Stacking Fault Tetrahedra

In electron microscope studies of crystalline solids there is a broad class of very small objects which are imaged primarily by strain contrast. Typical examples include: dislocation loops, precipitates, stacking fault tetrahedra and voids. Such objects are very difficult to identify and measure because of the sensitivity of their image to a host of variables and a similarity in their images. A number of attempts have been made to publish contrast rules to help the microscopist sort out certain subclasses of such defects. For example, Ashby and Brown (1963) described semi-quantitative rules to understand small precipitates. Eyre et al. (1979) published a catalog of images for BCC dislocation loops. Katerbau (1976) described an analytical expression to help understand contrast from small defects. There are other publications as well.

Electron microscope image contrast of small dislocation loops and stacking-fault tetrahedra

1979 ◽  
Vol 292 (1397) ◽  
pp. 523-537 ◽  
Keyword(s):  
Electron Microscope ◽  
Numerical Solutions ◽  
Preceding Paper ◽  
Stacking Fault ◽  
Image Contrast ◽  
Dislocation Loops ◽  
Displacement Fields ◽  
Microscope Image ◽  
Stacking Fault Tetrahedra ◽  
Electron Microscope Image

With the use of the method described in the preceding paper (to be referred to subsequently as I) for constructing the displacement fields, the electron microscope image contrast of small dislocation loops and of stacking-fault tetrahedra has been computed from numerical solutions of the Howie-Whelan (1961) equations. The computer-simulated images, displayed in the form of half-tone pictures, have been used to identify the nature and geometry of such defects in ion-irradiated foils. A systematic study of the contrast of small Frank loops in Cu + ion irradiated copper under a wide variety of diffraction conditions is reported. In particular the variations of the contrast of loops edge-on and inclined to the electron beam with the operating Bragg reflexion, the thickness and inclination of the foil, depth of the defect in the foil and deviation from the Bragg-reflecting condition have been studied. Methods of obtaining useful information, such as the diameters of the loops, are suggested. The contrast of stacking-fault tetrahedra, and of non-edge perfect dislocation loops in ion-irradiated molybdenum is also investigated.

Periodic {001} Walls of Defects in Proton-Irradiated Cu and Ni

1986 ◽  
Vol 82 ◽  
Author(s):  
P. Ehrhart ◽  
W. Jäger ◽  
W. Schilling ◽  
F. Dworschak ◽  
Afaf A. Gadalla ◽  
...  
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Defect Structure ◽  
Average Concentration ◽  
Stacking Fault ◽  
Dislocation Loops ◽  
Transmission Electron ◽  
Stacking Fault Tetrahedra

ABSTRACTThe evolution of the defect structure in 3 MeV-proton irradiated Cu and Ni has been investigated by transmission electron microscopy and by differential dilatometry. The proton irradiations were performed at T≦100°C up to irradiation doses of 2 dpa. An efficient loss of selfinterstitial atoms at dislocations and a consequently high average concentration of vacancies in clusters is observed starting from rather low fluences. In addition an ordering of the defects in the form of periodic {001} walls with a typical periodicity length of ≈ 60 nm is observed for all equivalent {001} planes. The walls consist of high local concentrations of dislocations, dislocation loops and stacking-fault tetrahedra. The observed formation of periodic arraysof defect walls is considered as an example for a possibly general microstructural phenomenon in metals under irradiation.

The climb of dislocation loops in zinc

1966 ◽  
Vol 293 (1434) ◽  
pp. 423-431 ◽  
Keyword(s):  
Zinc Oxide ◽  
Electron Microscope ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Surface Oxide Layer ◽  
Chemical Stress ◽  
Dislocation Loops ◽  
Foil Surface ◽  
A Value ◽  
Normal Manner

The annealing behaviour of faulted dislocation loops in quenched zinc has been studied with the aid of the electron microscope. On annealing, it is observed that some of the loops grow rather than shrink, and this has been attributed to the growth of zinc oxide on the foil surface, which results in the formation of vacancies. Loops which shrink on annealing are considered to lie beneath breaks in the surface oxide layer such that these regions are able to act in the normal manner as vacancy sinks. An estimation of the vacancy supersaturation near such shrinking loops shows that the chemical stress is low, and the climb rate of loops shrinking in the presence of a negligible chemical stress has been analysed to give a value for the stacking fault energy, y. An analysis of the climb rate of a faulted loop based on the emission of vacancies as the controlling process gives a value of 290 erg/cm 2 . A more reliable value of y, which is thought to be independent of the rate-controlling process, is obtained by comparing the climb rate of a faulted loop with that of a prismatic loop. A stacking fault energy value for zinc of 220 erg/cm 2 is deduced.

scholarly journals The Determination of Stacking Fault Energy by the Tetrahedron Method

1968 ◽  
Vol 21 (6) ◽  
pp. 941 ◽  
Author(s):  
P Humble ◽  
CT Forwood
Keyword(s):  
Electron Microscope ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
The Other ◽  
Dislocation Loops ◽  
The Third ◽  
Wide Range ◽  
Length Measurements ◽  
Incomplete Theory

At present there are three methods for obtaining values of the stacking fault energy y of face-centred cubic (f.c.c.) materials by direct observation of dislocationstacking fault configurations in the electron microscope. These are based on measurements of extended three-fold dislocation nodes (e.g. Whelan 1958; Brown and ThOlen 1964), faulted dipole configurations (e.g. Haussermann and Wilkens 1966; Steeds 1967), and triangular Frank dislocation loops and stacking fault tetrahedral (e.g. Silcox and Hirsch 1959; Loretto, Clarebrough, and Segall 1965). The main advantages of the third method over the other two are that it is applicable to materials of a very wide range of stacking fault energy and involves only simple length measurements of defects that are easily recognized. However, it has suffered from the disadvantage that the values of y deduced from these measurements relied on an incomplete theory. The present authors have reconsidered this problem and, subject to the limitations of isotropic linear elasticity, have taken into account the major variables that may affect the values of y. It is the purpose of this note to present the results of this theory in a form in which values of y may easily be obtained from measurements of Frank dislocation loops and stacking fault tetrahedral without the resources of a large digital computer.

Stacking-fault tetrahedra in ion-implanted III-V compounds

1987 ◽  
Vol 45 ◽  
pp. 316-317
Author(s):  
B.C. De Cooman ◽  
S. McKeman ◽  
C.B. Carter
Keyword(s):  
Surface Layer ◽  
Solid Phase ◽  
High Resolution Electron Microscopy ◽  
Stacking Fault ◽  
Dislocation Loops ◽  
Present Contribution ◽  
Stacking Fault Tetrahedra ◽  
Type Layer ◽  
Resolution Electron ◽  
Before And After

The implantation of heavy ions into GaAs for the purpose of obtaining a shallow n-type layer has been studied in detail, The results obtained by Rutherford Backscattering and high-resolution electron microscopy show that the surface layer is amorphized during implantation and that the solid-phase epitactic regrowth gives rise to a surface layer containing a large density of microtwins and stacking faults. No other defects have been reported other than interstitial-type dislocation loops in the implanted material, despite the fact that P-implants in Si had shown that a high density of stacking-fault tetrahedra (SFT) were formed after annealing. The present contribution reviews the major findings obtained during the first observation of SFT in Ga1-xAlxAs/GaAs (x=0.3) superlattices and Ga1-xAlxAs (x=0.3) epilayers grown on (001) GaAs. The material was grown by molecular-beam epitaxy (MBE). The ion energy used was 175kV, the dose was 1015 cm-2 and the Se ions were implanted at room-temperature The specimens were examined before and after a 4 hour anneal at 660°C.

FAULTED DEFECTS AND STACKING-FAULT ENERGY

1967 ◽  
Vol 45 (2) ◽  
pp. 1135-1146 ◽  
Author(s):  
L. M. Clarebrough ◽  
P. Humble ◽  
M. H. Loretto
Keyword(s):  
Direct Methods ◽  
Stacking Fault ◽  
Stacking Fault Energy ◽  
Face Centered Cubic ◽  
Dislocation Loops ◽  
Cubic Metals ◽  
The Third ◽  
Stacking Fault Tetrahedra ◽  
Dislocation Energy ◽  
Face Centered

Four direct methods of obtaining values of stacking-fault energy from observation of faulted defects in pure face-centered cubic metals are discussed. It is shown that there is essential agreement between the method based on the observation of threefold nodes and that based on the observation of triangular Frank dislocation loops and stacking-fault tetrahedra in deformed f.c.c. metals, in the range where both methods are applicable. On the other hand, it is shown that the third method, based on the collapse size of stacking-fault tetrahedra in quenched metals, cannot yield even an upper limit. New experimental results show that the fourth method, based on the annealing rate of faulted loops, is applicable only to metals of high stacking-fault energy and then only if jog nucleation and propagation are not rate controlling; for low stacking-fault energy metals, these factors, together with the dislocation energy, must be considered, and cannot be completely taken into account.

Electron microscope weak-beam imaging of stacking fault tetrahedra: observations and simulations

2006 ◽  
Vol 41 (14) ◽  
pp. 4445-4453 ◽  
Author(s):  
M. L. Jenkins ◽  
Z. Zhou ◽  
S. L. Dudarev ◽  
A. P. Sutton ◽  
M. A. Kirk
Keyword(s):  
Electron Microscope ◽  
Stacking Fault ◽  
Weak Beam ◽  
Stacking Fault Tetrahedra
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