scholarly journals Hardening in AlN Induced by Point Defects

1991 ◽  
Vol 235 ◽  
Author(s):  
H. Suematsu ◽  
T. E. Mitchell ◽  
T. Iseki ◽  
T. Yano
Keyword(s):  
Point Defects ◽  
Defect Density ◽  
Single Point ◽  
Length Change ◽  
Dislocation Loops ◽  
Three Samples ◽  
Different Temperatures ◽  
Hardness Change ◽  
Isolated Point ◽  
Small Clusters

ABSTRACTPressureless-sintered AlN was neutron irradiated and the hardness change was examined by Vickers indentation. The hardness was increased by irradiation. When the samples were annealed at high temperature, the hardness gradually decreased. Length was also found to increase and to change in the same way as the hardness. A considerable density of dislocation loops still remained, even after the hardness completely recovered to the value of the unirradiated sample. Thus, it is concluded that the hardening in AlN is caused by isolated point defects and small clusters of point defects, rather than by dislocation loops.Hardness was found to increase in proportion to the length change. If the length change is assumed to be proportional to the point defect density, then the curve could be fitted qualitatively to that predicted by models of solution hardening in metals. Furthermore, the curves for three samples irradiated at different temperatures and fluences are identical. There should be different kinds of defect clusters in samples irradiated at different conditions, e.g, the fraction of single point defects is the highest in the sample irradiated at the lowest temperature. Thus, hardening is insensitive to the kind of defects remaining in the sample and is influenced only by those which contribute to length change.

Recent Advances in Huang Diffuse Scattering

1984 ◽  
Vol 41 ◽  
Author(s):  
P. Ehrhart
Keyword(s):  
Point Defects ◽  
Diffuse Scattering ◽  
Reciprocal Lattice ◽  
Theoretical Background ◽  
Dislocation Loops ◽  
Short Introduction ◽  
X Ray ◽  
Different Types ◽  
Isolated Point ◽  
Influence Of Impurities

AbstractMeasurements of the diffuse X-ray (or neutron) scattering allow the detailed investigation of point defects in crystalline solids. The method can be applied for defect sizes ranging from isolated point defects up to large dislocation loops. The diffuse scattering intensity close to the Bragg reflections, Huang Diffuse Scattering and Asymptotic Diffuse Scattering, is of special interest as the intensities from lattice distorting defects are high and the scattering theory is most straightforward for this region of the reciprocal lattice. After a short introduction to the theoretical background and to the experimental techniques the capabilities and limitations of the method will be demonstrated with examples of experimental results. i) The structure of interstitial atoms has been investigated for low temperature irradiated crystals and for metals with interstitially dissolved solute atoms. ii) The mobility and growth of interstitial agglomerates during annealing stage II of irradiated metals is discussed. The influence of impurities on the cluster growth is demonstrated for the example of Nibase alloys. iii) Defect clusters and defect distributions within cascades as observed after different types of irradiations are discussed.

scholarly journals Influence of Bath Additives on the Thermal Stability of the Nanostructure and Hardness of Ni Films Processed by Electrodeposition

Coatings ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 644 ◽  
Author(s):  
Tamás Kolonits ◽  
Zsolt Czigány ◽  
László Péter ◽  
Imre Bakonyi ◽  
Jeno Gubicza
Keyword(s):  
Thermal Stability ◽  
Driving Force ◽  
Defect Density ◽  
Trisodium Citrate ◽  
Free Sample ◽  
Three Samples ◽  
Different Temperatures ◽  
Thermodynamic Driving Force ◽  
Thermal Stability Of ◽  
Bath Additives

The effect of bath additives on the thermal stability of the microstructure and hardness of nanocrystalline Ni foils processed by electrodeposition was studied. Three samples with a thickness of 20 μ m were prepared: one without any additive and two others with saccharin or trisodium citrate additives. Then, the specimens were heat-treated at different temperatures up to 1000 K. It was found that for the additive-free sample the recovery of the microstructure and the reduction of the hardness started only at temperatures higher than 500 K. At the same time, a decrease of the defect density and hardness was observed even at 400 K for the additive-containing films. This was explained by the higher defect density, which increased the thermodynamic driving force for recovery during annealing. At the highest applied temperature (1000 K), this larger thermodynamic driving force resulted in a recrystallization in the sulfur-containing sample, leading to a very low hardness of about 1000 MPa as compared to the additive-free sample (1300 MPa). On the other hand, the sample deposited with trisodium citrate additive showed a better thermal stability at 1000 K than the additive-free sample: the hardness remained as high as 2000 MPa even at 1000 K.

scholarly journals Transmission Electron Microscopy Study In-Situ of Radiation-Induced Defects in Copper at Elevated Temperatures

1996 ◽  
Vol 439 ◽  
Author(s):  
T. L. Daulton ◽  
M. A. Kirk ◽  
L. E. Rehn
Keyword(s):  
Point Defects ◽  
Elevated Temperatures ◽  
Defect Density ◽  
Microscopy Study ◽  
High Energy ◽  
Dislocation Loops ◽  
Contrast Imaging ◽  
High Concentration ◽  
Transmission Electron

AbstractNeutrons and high-energy ions incident upon a solid can initiate a displacement collision cascade of lattice atoms resulting in localized regions within the solid containing a high concentration of interstitial and vacancy point defects. These point defects can collapse into various types of dislocation loops and stacking fault tetrahedra (SFT) large enough that their lattice strain fields are visible under diffraction-contrast imaging using a Transmission Electron Microscope (TEM). The basic mechanisms driving the collapse of point defects produced in collision cascades is investigated in situ with TEM for fcc-Cu irradiated with heavy (100 keV Kr) ions at elevated temperature. The isothermal stability of these clusters is also examined in situ.Areal defect yields were observed to decrease abruptly for temperatures greater than 300°C. This decrease in defect yield is attributed to a proportional decrease in the probability of collapse of point defects into clusters. The evolution of the defect density under isothermal conditions appears to be influenced by three different rate processes active in the decline of the total defect density. These rate constants can be attributed to differences in the stability of various types of defect clusters and to different loss mechanisms. Based upon observed stabilities, estimations for the average binding enthalpies of vacancies to SFT are calculated for copper.

Study of dislocation loops in Arsenic-Rich as-grown GaAs

1987 ◽  
Vol 45 ◽  
pp. 350-351
Author(s):  
Byung-Teak Lee
Keyword(s):  
Point Defects ◽  
Electronic Devices ◽  
Arsenic Concentration ◽  
Stoichiometric Compound ◽  
Dislocation Loops ◽  
Gaas Crystal ◽  
Ion Milling ◽  
Transmission Electron ◽  
Arsenic Source ◽  
High Arsenic

Grown-in dislocations in GaAs have been a major obstacle in utilizing this material for the potential electronic devices. Although it has been proposed in many reports that supersaturation of point defects can generate dislocation loops in growing crystals and can be a main formation mechanism of grown-in dislocations, there are very few reports on either the observation or the structural analysis of the stoichiometry-generated loops. In this work, dislocation loops in an arsenic-rich GaAs crystal have been studied by transmission electron microscopy.The single crystal with high arsenic concentration was grown using the Horizontal Bridgman method. The arsenic source temperature during the crystal growth was about 630°C whereas 617±1°C is normally believed to be optimum one to grow a stoichiometric compound. Samples with various orientations were prepared either by chemical thinning or ion milling and examined in both a JEOL JEM 200CX and a Siemens Elmiskop 102.

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.

H NMR Evidence for a Change in The Local Hydrogen Environment of Sites Associated with the Staebler-Wronski Effect in a-Si:H

2002 ◽  
Vol 715 ◽  
Author(s):  
T. Su ◽  
Robin Plachy ◽  
P. C. Taylor ◽  
S. Stone ◽  
G. Ganguly ◽  
...  
Keyword(s):  
Line Shape ◽  
Defect Density ◽  
Hydrogen Atoms ◽  
Hydrogen Environment ◽  
H Nmr ◽  
Line Shapes ◽  
Different Temperatures ◽  
Staebler Wronski Effect

AbstractWe study the H NMR line shapes of a sample of a-Si:H under several conditions: 1) as grown, 2) light-soaked for 600 hours, and 3) light-soaked followed by annealing at different temperatures. At T = 7 K, the NMR line shape of the sample after light soaking exhibits an additional doublet compared to that of the sample as-grown. This doublet is an indication of a closely separated hydrogen pair. The distance between the two hydrogen atoms is estimated to be about (2.3 ± 0.2) Å. The concentration of these hydrogen sites is estimated to be between 1017 and 1018 cm-3 consistent with ESR measurements of the defect density after light soaking. This doublet disappears after the sample is annealed at 200°C for 4 hours.

scholarly journals Kinetics and thermodynamic properties related to the drying of 'Cabacinha' pepper fruits

2016 ◽  
Vol 20 (2) ◽  
pp. 174-180 ◽  
Author(s):  
Hellismar W. da Silva ◽  
Renato S. Rodovalho ◽  
Marya F. Velasco ◽  
Camila F. Silva ◽  
Luís S. R. Vale
Keyword(s):  
Experimental Data ◽  
Activation Energy ◽  
Free Energy ◽  
Thermodynamic Properties ◽  
Gibbs Free Energy ◽  
Removal Rate ◽  
Effective Diffusion ◽  
Drying Time ◽  
Three Samples ◽  
Different Temperatures

ABSTRACT The objective of this study was to determine and model the drying kinetics of 'Cabacinha' pepper fruits at different temperatures of the drying air, as well as obtain the thermodynamic properties involved in the drying process of the product. Drying was carried out under controlled conductions of temperature (60, 70, 80, 90 and 100 °C) using three samples of 130 g of fruit, which were weighed periodically until constant mass. The experimental data were adjusted to different mathematical models often used in the representation of fruit drying. Effective diffusion coefficients, calculated from the mathematical model of liquid diffusion, were used to obtain activation energy, enthalpy, entropy and Gibbs free energy. The Midilli model showed the best fit to the experimental data of drying of 'Cabacinha' pepper fruits. The increase in drying temperature promoted an increase in water removal rate, effective diffusion coefficient and Gibbs free energy, besides a reduction in fruit drying time and in the values of entropy and enthalpy. The activation energy for the drying of pepper fruits was 36.09 kJ mol-1.

scholarly journals The effects of temperature on aberrant ascus frequencies at the Buff locus in Sordaria brevicollis

1975 ◽  
Vol 26 (2) ◽  
pp. 127-135 ◽  
Author(s):  
A. F. Ahmad
Keyword(s):  
Single Point ◽  
Different Temperatures ◽  
Effects Of Temperature

SUMMARYSingle-point crosses using five allelic spore colour mutants at the buff locus were carried out at different temperatures. The data suggest (i) that fixed or preferred opening points in the DNA, required for initiation of recombination events, are available more often at higher than at lower temperatures, (ii) opening points at or beyond both proximal and distal ends of the buff locus respond similarly to variations in temperature, and (iii) the correction pattern seems to be independent of temperature at the buff locus in S. brevicollis.

EFFECTS OF QUANTUM CONFINEMENT ON LOW FREQUENCY NOISE IN δ-DOPED GaAs STRUCTURES GROWN BY MBE

2002 ◽  
Vol 02 (01) ◽  
pp. L37-L45
Author(s):  
X. Y. CHEN ◽  
P. M. KOENRAAD
Keyword(s):  
Quantum Confinement ◽  
Low Frequency ◽  
Frequency Noise ◽  
Low Frequency Noise ◽  
Free Carriers ◽  
In Doping ◽  
Three Samples ◽  
Different Temperatures ◽  
Lower Magnitude ◽  
Different Thickness

Low frequency noise (LFN) was measured in δ-doped GaAs structures in which the free carriers are confined to a 2-dimensional plane. Three samples grown at different temperatures, resulting in doping layers of a different thickness, are used to study the effects of quantum confinement on the LFN. We observed both 1/f noise and generation-recombination noise components. We find that a stronger quantum confinement results in a bigger Hall mobility and a lower magnitude of the 1/f noise.

Impurity and Stoichiometry Control in Atomic Layer Epitaxy

1992 ◽  
Vol 262 ◽  
Author(s):  
H. Yokoyama ◽  
K. Ikuta ◽  
N. Inoue
Keyword(s):  
Point Defects ◽  
Resonant Tunneling ◽  
Room Temperature ◽  
Defect Density ◽  
Atomic Layer ◽  
Negative Resistance ◽  
Atomic Layer Epitaxy ◽  
Tunneling Diode ◽  
Order Of Magnitude ◽  
Stoichiometry Control

ABSTRACTWe investigate the intrinsic point defects in epilayers grown by atomic layer epitaxy (ALE). Ga vacancies and antisite As atoms in the epilayers are detected by photoluminescence spectroscopy. This shows that the ALE epilayer was grown under As-rich conditions. We propose increasing the TMG flux to reduce the number of point defects. With this method, the number of point defects in ALE epilayers can be decreased to less than that in conventionally grown epilayers. Moreover, it is'found that these point defects are formed by the incomplete Ga coverage, not by the steric hindrance as previously suggested. The carbon concentration is decreased by one order of magnitude by using nitrogen instead of hydrogen as the carrier gas. As an application of this low defect density, we fabricated a GaAs/AlAs resonant tunneling diode and observed the negative resistance at room temperature.

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