Theoretical Study of Weak-Beam Images of Stacking Faults Decorated with Impurities

1990 ◽  
Vol 48 (1) ◽  
pp. 586-587
Author(s):  
G. R. Anstis
Keyword(s):  
Repeat Unit ◽  
Experimental Studies ◽  
Stacking Faults ◽  
Dark Field ◽  
Smooth Transition ◽  
Crystal Potential ◽  
Impurity Atoms ◽  
Weak Beam ◽  
Kinematical Theory ◽  
Rigid Ion Model

Weak—beam dark—field images of stacking faults in silicon vary in an interesting way as the angle of inclination of a fault to the beam changes. It is observed that the contrast of images formed with beam +g varies with angle of inclination at a rate different from that associated with beam −g. For the case of an extrinsic fault it was found that this variation can be calculated using the kinematical theory of scattering and by modelling the fault as two discontinuous changes to the crystal potential across neighbouring (111) plane. Thus the weak—beam imaging technique is sensitive to some of the details of atomic arrangements near the fault. To explain the contrast variation of intrinsic faults it is necessary to model the smooth transition of the crystal potential from one side of the fault to the other. While such a model gives a qualitatative description of experimental studies it is not able to account for the large differences in contrast between +g images and −g images that have been observed experimentally. In this paper it is postulated that the presence of impurity atoms near the plane of the fault accounts for some of the features of experimental observations.The theory is based on the kinematical theory of scattering and the rigid ion model of the crystal potential. A crystal containing a stacking fault consists of a unit which repeats indefinitely in directions parallel to the plane of the fault. Along a line perpendicular to the fault the repeat unit is displaced by a vector R across the plane of the fault. The impurity atoms are assumed to be distributed periodically on planes parallel to the fault.

Weak Beam Imaging and Diffraction Studies of Stacking Faults in Silicon

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.

Spacings and Intensities of Weak-Beam Dark Field Thickness Fringes

1981 ◽  
Vol 39 ◽  
pp. 222-223
Author(s):  
M. Avalos-Borja ◽  
K. Heinemann
Keyword(s):  
Selection Criterion ◽  
Dark Field ◽  
Dynamical Theory ◽  
Bragg Condition ◽  
Weak Beam ◽  
Kinematical Theory ◽  
Equal Thickness

Weak-beam dark field (WBDF) TEM produces narrowly spaced equal-thickness fringes in wedge-shaped crystals. Using non-systematic diffraction conditions, we have shown elsewhere that simple 2-beam kinematical theory (KT) calculations yield average fringe spacings that are for most practical purposes as satisfactorily accurate as the average spacings obtained from optimized multibeam dynamical theory (DT) calculations, As Fig. 1 shows, this result holds for deviations from the Bragg condition as low as 2x10-1 nm-1, and the differences between the results from the two calculational methods become increasingly insignificant for larger excitation errors. (Unless otherwise noted, all results reported here are for gold crystals, using the 200 beam at 100 KV; the DT calculations were made for 74 beams, using the selection criterion D as discussed in ref. [3]).

A Weak-Beam Dark-Field Study of Stacking Faults in a Co-Cr-Mo-C Alloy

1976 ◽  
Vol 34 ◽  
pp. 378-379
Author(s):  
Ernest L. Hall
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Field Study ◽  
Previous Investigation ◽  
Stacking Faults ◽  
Aging Treatment ◽  
Dark Field ◽  
Bright Field ◽  
Weak Beam ◽  
Transmission Electron

In a previous investigation (1) of the mechanisms of strengthening in a Co-28 wt% Cr-6 wt% Mo-0.29 wt% C alloy (H.S. 21), it was observed that the fee regions of this alloy were generally heavily faulted, and the density of stacking faults was seen to be dependent upon the time and temperature of the aging treatment after solutionizing. In the present study, weak-beam darkfield transmission electron microscopy was used to examine the interaction of stacking faults on intersecting {111} planes. The alloy was solutionized at 1230°C for 4 hours, quenched in water, and aged at 650°C for 8 hours in order to produce a suitable density of faults. Figure 1 shows a bright-field (BF), weak-beam dark-field (WB DF) pair of micrographs illustrating both the successful and unsuccessful intersection of faults which exist in different ﹛111﹜ planes.

Observations of unusual stacking fault configurations using complimentary strong and weak beam images

1995 ◽  
Vol 53 ◽  
pp. 696-697
Author(s):  
H. S. Kim ◽  
S. S. Sheinin
Keyword(s):  
Displacement Vector ◽  
Stacking Faults ◽  
Dark Field Image ◽  
Dark Field ◽  
Stacking Fault ◽  
The Other ◽  
Weak Beam ◽  
Conventional Analysis ◽  
Fcc Materials ◽  
Beam Diffraction

In this paper, the authors present both strong and weak beam images of stacking faults in FCC cobalt which indicate the presence of an unusual stacking fault configuration. Experimental images have been obtained at 100 kV from a specimen in a orientation with (1-1-1) stacking fault planes. Fig. 1 shows the (-1-11) strong beam dark field image. It can be seen that the contrast in faults A, B and D are very similar, while the fault at C is different. Using conventional techniques for identifying the nature of stacking faults in FCC materials A, B and D have been identified as single or intrinsic faults with a displacement vector R=l/3[-111]. On the other hand, the fault at C can be identified as a double or extrinsic fault. At this point, the interpretation of the faults in the image in Fig. 1 appears to be completely straightforward and in keeping with results obtained from a conventional analysis. The next image of interest is shown in Fig. 2 which shows the same four faults as in Fig. 1 obtained under weak beam diffraction conditions.

Dissociation of Misfit Dislocations in GeSi/{111}Si Interfaces

1993 ◽  
Vol 319 ◽  
Author(s):  
Frank Ernst
Keyword(s):  
Lattice Mismatch ◽  
Stacking Faults ◽  
Chemical Vapor ◽  
Interfacial Area ◽  
Dark Field ◽  
Dislocation Network ◽  
Misfit Dislocations ◽  
Si Substrates ◽  
Weak Beam ◽  
Transmission Electron

AbstractThe accommodation of lattice mismatch is studied in Ge0.15Si0.85 layers grown epitaxially on {111}-oriented Si substrates by chemical vapor deposition (CVD) at 1100°C. Weak beam dark field microscopy reveals a regular misfit dislocation network, which resembles the honeycomb network of edge-type dislocations anticipated by the O-lattice theory. In contrast to the latter, however, the real network exhibits extended nodes where the misfit dislocations dissociate into misfit partial dislocations. Between the partials, high resolution transmission electron microscopy (HRTEM) reveals intrinsic and extrinsic stacking faults. Owing to the presence of these stacking faults, three different atomistic structures of the GeSi/Si interface coexist and compete for the interfacial area according to their energy. The observed configuration is shown to minimize the total energy of the interface.

Two Investigations into Grain Boundary Structure

1977 ◽  
Vol 35 ◽  
pp. 688-691
Author(s):  
P. Humble
Keyword(s):  
Grain Boundary ◽  
Dark Field ◽  
Boundary Structure ◽  
Boundary Dislocation ◽  
Bright Field ◽  
Intrinsic Structure ◽  
Weak Beam ◽  
Grain Boundary Structure ◽  
Independent Information ◽  
Diffraction Patterns

There has been sustained interest over the last few years into both the intrinsic (primary and secondary) structure of grain boundaries and the extrinsic structure e.g. the interaction of matrix dislocations with the boundary. Most of the investigations carried out by electron microscopy have involved only the use of information contained in the transmitted image (bright field, dark field, weak beam etc.). Whilst these imaging modes are appropriate to the cases of relatively coarse intrinsic or extrinsic grain boundary dislocation structures, it is apparent that in principle (and indeed in practice, e.g. (1)-(3)) the diffraction patterns from the boundary can give extra independent information about the fine scale periodic intrinsic structure of the boundary.In this paper I shall describe one investigation into each type of structure using the appropriate method of obtaining the necessary information which has been carried out recently at Tribophysics.

A Many-Beam Technique for Enhanced Resolution of Partial Dislocations

1972 ◽  
Vol 30 ◽  
pp. 646-647
Author(s):  
J. M. Oblak ◽  
B. H. Kear
Keyword(s):  
Phase Shift ◽  
Field Method ◽  
Dark Field ◽  
Bright Field ◽  
Field Technique ◽  
Weak Beam ◽  
Partial Dislocations ◽  
Enhanced Resolution ◽  
Nickel Base ◽  
Beam Technique

The “weak-beam” and systematic many-beam techniques are the currently available methods for resolution of closely spaced dislocations or other inhomogeneities imaged through strain contrast. The former is a dark field technique and image intensities are usually very weak. The latter is a bright field technique, but generally use of a high voltage instrument is required. In what follows a bright field method for obtaining enhanced resolution of partial dislocations at 100 KV accelerating potential will be described.A brief discussion of an application will first be given. A study of intermediate temperature creep processes in commercial nickel-base alloys strengthened by the Ll2 Ni3 Al γ precipitate has suggested that partial dislocations such as those labelled 1 and 2 in Fig. 1(a) are in reality composed of two closely spaced a/6 <112> Shockley partials. Stacking fault contrast, when present, tends to obscure resolution of the partials; thus, conditions for resolution must be chosen such that the phase shift at the fault is 0 or a multiple of 2π.

TEM evaluation of graded SixGe1-x heterolayers

1991 ◽  
Vol 49 ◽  
pp. 894-895
Author(s):  
N. David Theodore ◽  
Mamoru Tomozane ◽  
Ming Liaw
Keyword(s):  
Heterojunction Bipolar Transistors ◽  
Gas Flow ◽  
Field Effect Transistors ◽  
Chemical Vapor ◽  
Dark Field ◽  
Bipolar Transistors ◽  
Structural Quality ◽  
Weak Beam ◽  
Transmission Electron ◽  
And Behavior

There is extensive interest in SiGe for use in heterojunction bipolar transistors. SiGe/Si superlattices are also of interest because of their potential for use in infrared detectors and field-effect transistors. The processing required for these materials is quite compatible with existing silicon technology. However, before SiGe can be used extensively for devices, there is a need to understand and then control the origin and behavior of defects in the materials. The present study was aimed at investigating the structural quality of, and the behavior of defects in, graded SiGe layers grown by chemical vapor deposition (CVD).The structures investigated in this study consisted of Si1-xGex[x=0.16]/Si1-xGex[x= 0.14, 0.13, 0.12, 0.10, 0.09, 0.07, 0.05, 0.04, 0.005, 0]/epi-Si/substrate heterolayers grown by CVD. The Si1-xGex layers were isochronally grown [t = 0.4 minutes per layer], with gas-flow rates being adjusted to control composition. Cross-section TEM specimens were prepared in the 110 geometry. These were then analyzed using two-beam bright-field, dark-field and weak-beam images. A JEOL JEM 200CX transmission electron microscope was used, operating at 200 kV.

Growth of hematite on (0001) and {1102} sapphire substrates

1990 ◽  
Vol 48 (4) ◽  
pp. 376-377
Author(s):  
Lisa A. Tietz ◽  
Scott R. Summerfelt ◽  
C. Barry Carter
Keyword(s):  
Imaging Techniques ◽  
Chemical Vapor ◽  
Interface Energy ◽  
Dark Field ◽  
Cation Sublattice ◽  
Sapphire Substrates ◽  
Dark Field Imaging ◽  
Weak Beam ◽  
Pressure Chemical ◽  
Interface Structures

Defects in thin films are often introduced at the substrate-film interface during the early stages of growth. The interface structures of semiconductor heterojunctions have been extensively studied because of the electrical activity of defects in these materials. Much less attention has been paid to the structure of oxide-oxide heterojunctions. In this study, the structures of the interfaces formed between hematite (α-Fe2O3) and two orientations of sapphire (α-Al2O3) are examined in relationship to the defects introduced into the hematite film. In such heterojunctions, the oxygen sublattice is expected to have a strong influence on the epitaxy; however, defects which involve only the cation sublattice may be introduced at the interface with little increase in interface energy.Oxide heterojunctions were produced by depositing small quantities of hematite directly onto electrontransparent sapphire substrates using low-pressure chemical vapor deposition. Prior to deposition, the ionthinned substrates were chemically cleaned and annealed at 1400°C to give “clean”, crystalline surfaces. Hematite was formed by the reaction of FeCl3 vapor with water vapor at 1150°C and 1-2 Torr. The growth of the hematite and the interface structures formed on (0001) and {102} substrates have been studied by bright-field, strong- and weak-beam dark-field imaging techniques.

Radiation-Induced Precipitation in Ti-6A1-4V

1980 ◽  
Vol 38 ◽  
pp. 154-155
Author(s):  
J. E. O'Neal ◽  
S. M. L. Sastry ◽  
J. W. Davis
Keyword(s):  
Dark Field ◽  
Dislocation Loops ◽  
Beta Titanium Alloy ◽  
Defect Clusters ◽  
Weak Beam ◽  
Beta Titanium ◽  
Small Defect ◽  
Radiation Induced ◽  
Vector Orientation ◽  
Defect Microstructures

The radiation-induced defect structure and nonequilibrium phase precipitation were studied in T1-6A1-4V (an alpha-beta titanium alloy), irradiated at 450 ± 30°C in row VII of the EBR-II to a fluence of 3.0 × 1021 neutrons/cm2 (En > 0.1 MeV). The Irradiation-induced defect microstructures were examined using bright-field, conventional dark-field, and weak-beam dark-field techniques. The nature of dislocations and dislocation loops was determined by standard-contrast experiments under two-beam conditions, and the small defect clusters were identified using the line-of-contrast criterion and black-white vector orientation criterion.

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