Pipe diffusion along the segment of faulted dislocation loops in aluminum

1978 ◽  
Vol 36 (1) ◽  
pp. 322-323
Author(s):  
H. Yamaguchi ◽  
H. Kawamoto ◽  
S. Yoshida
Keyword(s):  
Activation Energy ◽  
Electron Microscope ◽  
Dislocation Segment ◽  
Dislocation Loops ◽  
Coordinate Systems ◽  
Pipe Diffusion ◽  
Perfect Dislocation ◽  
Set Up ◽  
The One ◽  
Loop 2

The motion of a perfect dislocation loop during annealing was examined by several workers. They proposed a mechanism of pipe diffusion and analyzed this motion. However, these studies on pipe diffusion may have some errors caused by the prismatic glide. In this paper we studied on the motion of faulted dislocation loops under the mutual interaction and estimated the activation energy for pipe diffusion along the dislocation segment of faulted loops.Figure 1 shows schematically a pair of regular hexagonal faulted dislocation loops lying on the (111) plane in quenched aluminum as well as their images observed with an electron microscope, where (a) is the one taken from [001] direction before annealing, (b) and (c) are those taken from [001] and [011] directions after annealing at 95°C for 2 hours, respectively. In order to determine the vector S which connects the center of loop 1 and that of loop 2 in Fig. 1, three different coordinate systems (X1, Y1, Z1), (X2, Y2, Z2), (X3, Y3, Z3) are set up on a specimen, an electron microscope and a micrograph, respectively,(Fig. 2).

Loop and Void Formation in Copper During High Voltage Electron Microscope Irradiation

1973 ◽  
Vol 31 ◽  
pp. 22-23
Author(s):  
E. A. Kenik ◽  
T. E. Mitchell
Keyword(s):  
Electron Microscope ◽  
High Voltage ◽  
Void Nucleation ◽  
Cold Work ◽  
Void Formation ◽  
Dislocation Loops ◽  
Voltage Electron ◽  
High Voltage Electron Microscope ◽  
High Voltage Electron ◽  
Set Up

The formation of dislocation loops and voids under neutron, ion, and electron irradiation is well documented. Since irradiation produces Frenkel pairs, the presence of biased interstitial sinks is required for void formation to procede. It is generally accepted that dislocations, generated either by cold-work or irradiation, act as the preferential sinks.During irradiation in the high voltage electron microscope, both interstitials and vacancies are lost to foil surfaces and corresponding denuded zones are set up. As a result of image forces, dislocation loops formed upon irradiation tend to unfault and glide out of the foil. Thus, below a given thickness, the foil is unable to maintain a sufficiently high dislocation density to support void nucleation and growth.

Dislocations in Homoepitaxial Layers on "Dislocation Free" LEC-GaP Substrates

1982 ◽  
Vol 37 (7) ◽  
pp. 633-637
Author(s):  
M. Umeno ◽  
H. Kawabe ◽  
T. Kokonoi
Keyword(s):  
Lattice Distortion ◽  
Dislocation Segment ◽  
Dislocation Loops ◽  
High Voltage Electron Microscopy ◽  
Screw Dislocations ◽  
The Third ◽  
Voltage Electron ◽  
Dipole Interactions ◽  
Perfect Dislocation ◽  
Homoepitaxial Layers

Abstract Dislocation structures in S-and N-doped homoepitaxial layers on GaP wafers are studied by high voltage electron microscopy. Many dislocations are introduced in the epilayer, even if the substrate is nearly dislocation free. The origins of the dislocations in this case are the microdefects, especially the perfect dislocation loops in the substrate. Dislocation dipoles are induced by dis-location half loops appearing at the epi-substrate interface and are classified into three types, two of which are concerned with the interactions of two dipoles in the epilayer, each interaction yielding a screw dislocation segment. The third type of dipole does not extend into the epilayer so far, but terminates and forms an elongated dislocation loop. The interactions and the terminations of dipoles decrease the density of the induced dislocations in proportion to the distances from the interface. The screw dislocations generated by the dipole interactions relax the torsional lattice distortion of the epilayer caused by dopant materials.

Process of the One-Dimensional Motion of Small Interstitial-Type Dislocation Loops in Iron

2006 ◽  
Vol 512 ◽  
pp. 103-106 ◽  
Author(s):  
K. Arakawa ◽  
Hirotaro Mori
Keyword(s):  
Habit Plane ◽  
Dislocation Loops ◽  
Long Distance ◽  
One Dimensional ◽  
Large Loop ◽  
Transmission Electron ◽  
Perfect Dislocation ◽  
Motion Process ◽  
Type Dislocation ◽  
The One

Extensive simulations based on classical molecular dynamics have shown that small interstitial-type perfect dislocation loops in various metals and alloys have the structure of bundles of crowdions and a loop can easily makes the one-dimensional glide motion due to almost independent motion of crowdions in the loop. However, the experimental knowledge on the motion of loops is not enough. The present study dynamically examined the motion process of loops in pure iron under 1000 keV electron irradiation and thermal annealing by using transmission electron microscopy under which loops could move. Two types of loops were formed by irradiation. Loops of one type possessed the Burgers vector of 1/2<111> and the habit plane of {011}, and loops of the other type were <001> {001}. Loops of the former type made back-andforth glide motion and expansion towards the direction along their Burgers vectors when they were smaller than about a few-ten nanometers in diameter. This strongly suggests that these small 1/2<111> loops have the structure of the bundle of crowdions. Loops of the latter type only rarely moved less frequently when they were smaller than about the same size. When loops of two types grew larger than about 50 nm, the characteristics of the motion of loops changed drastically. Dislocation segments of each large loop made long-distance glide independently of their opposite segments, and the habit plane deviated from the original ones. This kind of motion means that selfinterstitial atoms at the central region of such large loops are no longer the crowdions.

Note on Selection of Coordinate Systems for Geodynamics

1975 ◽  
Vol 26 ◽  
pp. 395-407
Author(s):  
S. Henriksen
Keyword(s):  
Sea Level ◽  
The Other ◽  
Coordinate Systems ◽  
Mean Sea Level ◽  
The Earth ◽  
The One ◽  
Static Systems ◽  
Selection Of

The first question to be answered, in seeking coordinate systems for geodynamics, is: what is geodynamics? The answer is, of course, that geodynamics is that part of geophysics which is concerned with movements of the Earth, as opposed to geostatics which is the physics of the stationary Earth. But as far as we know, there is no stationary Earth – epur sic monere. So geodynamics is actually coextensive with geophysics, and coordinate systems suitable for the one should be suitable for the other. At the present time, there are not many coordinate systems, if any, that can be identified with a static Earth. Certainly the only coordinate of aeronomic (atmospheric) interest is the height, and this is usually either as geodynamic height or as pressure. In oceanology, the most important coordinate is depth, and this, like heights in the atmosphere, is expressed as metric depth from mean sea level, as geodynamic depth, or as pressure. Only for the earth do we find “static” systems in use, ana even here there is real question as to whether the systems are dynamic or static. So it would seem that our answer to the question, of what kind, of coordinate systems are we seeking, must be that we are looking for the same systems as are used in geophysics, and these systems are dynamic in nature already – that is, their definition involvestime.

Defects in ion implanted silicon

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.

Crystallographic Characterization of Dislocation Loops in Irradiated Tungsten

1968 ◽  
Vol 26 ◽  
pp. 290-291
Author(s):  
Robert C. Rau
Keyword(s):  
Electron Microscope ◽  
Ambient Temperature ◽  
Dislocation Loops ◽  
Polycrystalline Specimen ◽  
Post Irradiation ◽  
Neutron Fluences

Previous work has shown that post-irradiation annealing, at temperatures near 1100°C, produces resolvable dislocation loops in tungsten irradiated to fast (E > 1 MeV) neutron fluences of about 4 x 1019 n/cm2 or greater. To crystallographically characterize these loops, tilting experiments were carried out in the electron microscope on a polycrystalline specimen which had been irradiated to 1.5 × 1021 n/cm2 at reactor ambient temperature (∼ 70°C), and subseouently annealed for 315 hours at 1100°C. This treatment produced large loops averaging 1000 Å in diameter, as shown in the micrographs of Fig. 1. The orientation of this grain was near (001), and tilting was carried out about axes near [100], [10] and [110].

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.

scholarly journals The Swiss National Park

Oryx ◽  
1955 ◽  
Vol 3 (2) ◽  
pp. 64-70
Author(s):  
G. N. Zimmerli
Keyword(s):  
National Park ◽  
Swiss Society ◽  
Large Area ◽  
Nature Protection ◽  
Swiss National Park ◽  
Plant Life ◽  
Eastern Border ◽  
Set Up ◽  
The One ◽  
Protection Commission

The idea of a Swiss national park originated with the Swiss Society for Nature Research and this Society played the leading part in its realization. In 1906 the Society set up as part of its own organization a Swiss Nature Protection Commission and charged it to search for an area in Switzerland suitable for establishment as a reserve, in which all the animal and plant life could be protected against interference by man and so could be left entirely to the play of natural forces. It was not easy to find in Switzerland a suitably large area which still retained its original characteristics, was virtually free from human settlement, and contained some wealth of fauna and flora. After a careful survey of the whole country it became clear that the most suitable region was the Lower Engadine, with its isolated valleys on the eastern border of the country. The district in which, at the beginning of the century, bears had still lived was the one in which primitive nature could be found in its truest state.

scholarly journals An enhanced set of displacement parameter restraints in CRYSTALS

2018 ◽  
Vol 51 (4) ◽  
pp. 1059-1068 ◽  
Author(s):  
Pascal Parois ◽  
James Arnold ◽  
Richard Cooper
Keyword(s):  
Structural Model ◽  
Rigid Bodies ◽  
Model Parameters ◽  
Coordinate Systems ◽  
Principal Axes ◽  
Anisotropic Displacement Parameters ◽  
Set Up ◽  
Meaningful Relationships ◽  
Parameter Values ◽  
Total Model

Crystallographic restraints are widely used during refinement of small-molecule and macromolecular crystal structures. They can be especially useful for introducing additional observations and information into structure refinements against low-quality or low-resolution data (e.g. data obtained at high pressure) or to retain physically meaningful parameter values in disordered or unstable refinements. However, despite the fact that the anisotropic displacement parameters (ADPs) often constitute more than half of the total model parameters determined in a structure analysis, there are relatively few useful restraints for them, examples being Hirshfeld rigid-bond restraints, direct equivalence of parameters and SHELXL RIGU-type restraints. Conversely, geometric parameters can be subject to a multitude of restraints (e.g. absolute or relative distance, angle, planarity, chiral volume, and geometric similarity). This article presents a series of new ADP restraints implemented in CRYSTALS [Parois, Cooper & Thompson (2015), Chem. Cent. J. 9, 30] to give more control over ADPs by restraining, in a variety of ways, the directions and magnitudes of the principal axes of the ellipsoids in locally defined coordinate systems. The use of these new ADPs results in more realistic models, as well as a better user experience, through restraints that are more efficient and faster to set up. The use of these restraints is recommended to preserve physically meaningful relationships between displacement parameters in a structural model for rigid bodies, rotationally disordered groups and low-completeness data.

scholarly journals Mineral fertilizers as a governing factor of the regulation of the number of fungi in soil

2009 ◽  
pp. 201-207 ◽  
Author(s):  
Marijana Pesakovic ◽  
Dragutin Djukic ◽  
Leka Mandic ◽  
Milan Rakicevic ◽  
Rade Miletic
Keyword(s):  
Soil Fungi ◽  
Mineral Fertilizer ◽  
Mineral Fertilizers ◽  
Nitrogen Rate ◽  
Nutritive Medium ◽  
Governing Factor ◽  
Npk Fertilizer ◽  
Set Up ◽  
The One ◽  
Fertilizer Rates

Over 2003-2005 period, a study was performed on the effect of different rates of NPK fertilizer of formulation 8:16:24 + 3% MgO (N1 - 400 kg ha-1; N2 - 600 kg ha-1; N3 - 800 kg ha-1; N4 - 1000 kg ha-1) on development of the soil fungi. The trial was set up in the experimental plum orchard established by Fruit Research Institute Cacak, and the laboratory of Department of Microbiology, Faculty of Agronomy Cacak. Unfertilized soil was used as the control soil. Each of the stated variants was carried out in three replications. The size of the basic plot was 68 m2. The effect of the studied mineral fertilizer rates was determined three times over the growing season, the number of fungi being checked by the indirect rarefaction method on Chapek nutritive medium. The results of the study inferred that the application of mineral fertilizers brought about the decrease in the number of fungi. Of all studied variants, the one with the highest nitrogen rate (variant N4) exhibited the strongest effect. The influence of the fertilizer was highest at the third sampling. Furthermore, the effect was highest in season 2003.

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