Activation Energy For Recovery Research Articles

Irradiation damages in lithium oxide

Irradiation defects in lithium oxide, irradiated by oxygen ions with energies of 0.5, 0.75, 1.25 and 100 MeV, were studied by an optical absorption technique. In the optical absorption spectra, a dominant absorption band at about 310 nm in wave length and weak bands at about 375 and 570 nm were observed. The 310 nm band corresponds to F +-centers, and the 375 and 570 nm bands may be due to F aggregate centers. The intensity of the 310 nm band increased with the incident ion energy as well as the fluence. From the considerably large dependence of the intensity on the incident ion energy, the irradiation defect production due to the electron excitation process was conjectured to occur during the oxygen-ion irradiation. Isochronal and isothermal annealing experiments were carried out and the activation energy for recovery of the F +-centers was the same as that for lithium oxide irradiated with thermal neutrons.

Activation Energies of Oxide Charge Recovery in SOS or SOI Structures after an Ionizing Pulse

MOS transistors in either SOS technology with oxidation temperature varations or laser-recrystallized SOI have been exposed to ionizing pulse in order to derive activation energy of oxide charge recovery. It is found a direct dependence of annealing activation energy on oxidation or on highest temperature, and on electric field. In case of SOI, substrate oxide must also be considered. Models are discussed, based on an exponential distribution of states above the valence band and/or on polaron effect.

Recombination enhanced defect annealing in n-InP

The first example of a recombination enhanced defect reaction in InP is reported. The major defect E(0.79 eV) introduced by 1-MeV electron irradiation of p+n junctions, formed by Zn-doped epilayers on undoped n-type substrates, is not observed with Schottky barrier structures on similar material. The defect exhibits a reduction in activation energy of recovery from 1.3 eV under pure thermal annealing to 0.42 eV with minority-carrier (hole) injection. The enhanced reaction rate is proportional to the square of the injected current showing that the process results from two particle capture.

Transition from regular oscillations in flow stress to single peak during high-temperature torsional deformation of a low-alloy steel

AbstractThe high-temperature deformation of a low-alloy steel has been studied by torsion testing at temperatures in the range 850–1150°C and at constant strain rates in the range 0·6 × 10−3 to 5·3 S−1. The stress-strain curves obtained were characteristic of the occurrence of dynamic recrystallization over the entire range of testing conditions. Analysis of flow-stress data before the peak, at the peak, and during steady state gives a constant activation energy for deformation of 315 kJ mol- 1, indicating that the activation energies for dynamic recovery and dynamic recrystallization are the same. Correlations of the strains to the peak flow stress and to steady state and also of the dynamically recrystallized grain size with the Zener-Hollomon parameter and original grain size have been obtained. By using these correlations the interrelating parameter between the strain to the peak flow stress and the critical strain for the onset of recrystallization has been obtained. It is shown that the ‘relative gr...

Creation and annealing kinetics of magnetic oxygen vacancy centers in SiO2

Dose and energy dependence of the E′1 defect density/cm2 created in SiO2 by implantation of Ar ions has been determined by electron paramagnetic resonance. A dose dependent region followed by a saturated, dose independent region is found for all energies studied (50–150 keV). In the low dose limit for 100-keV Ar ions we estimate E1 creation to be 35/implant ion. The defect density/cm2 is found to be a linear function of the longitudinal atomic collisional damage distribution consistent with a picture of overlapping lateral damage distributions. A simple model for defect creation and annihilation gives a good quantitative explanation of the observed energy and dose dependence of the defect density. Isothermal annealing studies have been performed and the results do not follow those expected for a simple exponentially activated process. A model assuming correlated defect/interstitial recovery gives a better description of the experimental results and suggests an activation energy for recovery of approximately 0.85 eV.

Sputter Etching Effects on GaAs Schottky Junctions

The electrical properties of Schottky junctions with rf sputter etching, immediately before sputter deposition of metals, and their thermal recovery characteristics are described. Sputter etching not only results in removal of surface layers, but also in formation of a thin (∼100Å) damage layer, which decreases the Schottky junction effective barrier height. Thermal recovery characteristics strongly depend on sputter‐etching conditions, such as rf‐power and etching time. The activation energy for thermal recovery is continuously distributed, even in one sample. The results suggest that the damage is in lattice disorder and the degree of disorder depends on energy and/or dose of incident ions. The damage introduced during low power (50W) sputter‐etching is completely annihilated by thermal annealing at 350°C. The barrier height uniformity after annealing is improved by sputter etching at low power. It has been confirmed that sputter etching is a useful technique for surface treatment in the fabrication of Schottky junctions with uniform barrier height.

分散強化型Al-Be合金の高温クリープにおける加工硬化率と回復速度

Work hardening and recovery during high temperature creep of aluminum strengthened by dispersed beryllium particles have been investigated by means of the stress relaxation method. It was found that the proportion of the internal stress to the flow stress is nearly 100 percent and hence that the deformation is governed by a recovery process. Under the chosen condition of stress and temperature (10−4≤σ⁄E≤10−3, 0.51≤Tm⁄T≤0.69), the work hardening rate, h, showed no dependence on temperature and increased only slightly with an increase in stress. The recovery rate, r, is related to stress and temperature by(This article is not displayable. Please see full text pdf.) \ oindentHere the stress exponent, nr (9.5∼10.0), is close to that for the steady-state creep rate and the activation energy for recovery, Qr (138∼152 kJ/mol), is in agreement with that for volume self-diffusion in pure aluminum. The results are in contrast to those reported for pure aluminum in which h depends both on stress and temperature and the temperature dependence of r does not agree with that of volume self-diffusion, suggesting that the recovery in Al-Be alloys may be controlled by a unique thermally activated process. It is also shown that the effect of interparticle spacing on the work hardening rate is much smaller than that on the recovery rate, and hence that the increase in creep strength is brought about by the decrease in the recovery rate.

High-temperature deformation characteristics of free-machining steels

AbstractThe high-temperature deformation of three as-cast free-machining steels with different lead contents and Mn : S ratios has been studied by torsion testing at temperatures in the range 900°-1 150°C and at constant strain rates in the range 6·9 x 10−3–5·3 S−l. The stress-strain curves obtained were characteristic of the occurrence of dynamic recrystallization over the entire range of testing conditions. Analysis of flow-stress data before the peak, at the peak, and during steady state gives a constant activation energy for deformation of 310 kJ mol−1, indicating that the activation energies for dynamic recovery and dynamic recrystallization are the same. Correlation of the strains to the peak flow stress and to steady state with the Zener-Hollomon parameter shows agreement with previously published work on mild steel, with minor variations between the experimental steels that are attributable to differences in grain size.

Study of radiation damage inLi2O by means of electron-spin resonance

ESR spectra with a hyperfine structure consisting of more than 20 peaks were observed in Li/sub 2/O single crystals, irradiated by energetic tritons and helium ions formed by 6 x 10/sup 22/ to 6 x 10/sup 25/ /sup 6/Li(n,..cap alpha..)-/sup 3/H reactions per m/sup 3/ introduced with the order of 10/sup 20/ to 10/sup 23/ thermal neutrons per m/sup 2/. The g value of the spectra was 2.002 +- 0.001, and the hyperfine structure depended on the orientation of the specimens relative to the applied magnetic field. From the angular dependence the spectra were attributed to F/sup +/ centers (an oxygen vacancy trapping an electron). In Li/sub 2/O single crystals irradiated to the order of 10/sup 23/ thermal neutrons per m/sup 2/, colloidal Li metal centers were not observed, in direct contrast with the situations in sintered Li/sub 2/O pellets. Isochronal and isothermal annealing experiments were done and the recovery behavior of the F/sup +/ centers was observed. From the isothermal annealing experiments, the activation energy for recovery of the F/sup +/ centers was determined to be about 135 kJ/mol (1.4 eV).

Recovery of X-ray radiation damage in anthracene single crystals

Imperfections are introduced in anthracene single crystals by low energy (⩽ 20 keV) X-ray irradiation. About 60% of these imperfections can be recovered by annealing. The activation energy for recovery of the structural defects is measured to be 1.12 eV, using triplet excitons as a probe.

Effects of shock-loading on Young's Modulus and activation energy of recovery in 1018 steel

The effects of shock-loading on Young's Modulus of 1018 carbon steel and the activation energy of recovery were studied. The shock pressures employed were 104 and 304 kbars respectively. The results are explained in terms of Mott's defect Modulus theory and the theory of ageing hardening. It was found that the activation energy of diffusion during recovery is different between the specimens shock-loaded to 104 and to 304 kbars. This difference in activation energies is attributed to the difference in vacancy concentrations.

A phenomenological structural approach to high-temperature creep

1. Relationships have been derived within a structural phenomenological approach to describe high-temperature plastic deformation; examples have been taken for pure nickel, nickel-iron alloys, and chromium-nickel steel to confirm the model and the method of calculation. 2. High-temperature plastic deformation at constant stress is determined by the following: a) the kinetic coefficients\(\bar t\) and\(\bar \tau \), which characterize the rates of hardening and recovery together with the exponential dependence on stress and temperature; b) the deformation capacity of the material e1 in the absence of recovery. 3. Methods have been proposed for calculating the true activation energies of hardening and recovery, as well as the microscopic elastic limit\(\bar \sigma \).

Effects of shock loading on Young's modulus and activation energy of recovery in 1018 steel

Synthesis of the new (disordered) compound CaFe(CO3)2 has been achieved with the use of Fe-substituted CaCO3(Cc ss) + Ca-substituted FeCO3(Sid ss) as starting materials, and high CO2 pressures. High pressure (20–30 kbar) is needed to stabilize FeCO3 to sufficiently high temperatures for disordered CaFe(CO3)2 to form. Experiments provide reversed compositions of coexisting disordered phases in the CaFe join and locate the solvus temperature for CaFe(C)3)2 between 815 and 845°C at 30 kbars. Calculated phase relations predict that the stability of ordered CaFe(CO3)2 is limited to T < ∼450°C by the breakdown to Cc ss + Sid ss. A comparison of the unit-cell volume measured for disordered CaFe(CO3)2 vs. that estimated for ordered CaFe(CO3)2 suggests that increasing pressure stabilizes the disordered phase.

Electrical conductivity of disordered layers in GaAs crystal produced by ion implantation

The electrical conductivity of disordered layers in GaAs produced by ion implantation has been studied as a function of ion species, dose level, energy of implanted ions, and anneal temperature. The resistivity of the implanted layer, ρ, at room temperature can be expressed by a single relation, ρ=const×NDD−3, even for different masses and energies of implanted ions, where NDD is the total number of displacements of host atoms per unit volume due to nuclear collisions with implanted ions. At a temperature above 180 K the resistivity is proportional to exp(B/T) and below 180 K it changes as exp(B/T1/4). The conduction mechanism of the implanted layers is discussed based upon the hopping conduction in disordered or amorphous semiconductors. The annealing behavior of the implanted layers was also studied. The activation energy for recovery of the resistivity ρ was about 0.35 eV, which is quite small compared with the migration energies of stray atoms in ordered crystals. These results indicate that the implanted layer is in a disordered state rather than in a crystalline state containing the point defects.

Electron irradiation dilatation in SiO2

Negative dilatation (shrinkage) induced by 10-keV electron bombardment of SiO2 films thermally grown on Si has been studied. Measured deflection changes in continuous SiO2 bridges etched following irradiation showed a maximum shrinkage of [inverted lazy s] 0.8%, which occurred at 0.2 C/cm2, followed by a slight expansion, and subsequent saturation at higher exposures. Exposures up to 3 C/cm2 were utilized. Isochronal annealing studies show the activation energy for recovery to be approximately 1 eV with 2% recovery occurring in 1 h at 400°C.

An interpretation of steady state creep

Abstract Effective stress in steady state creep in aluminum was measured by the strain transient dip test technique with the aim to analyse the creep in terms of two separate kinetic processes driven by different components of the applied stress [sgrave]: the effective stress [sgrave]∗ and the internal stress [sgrave]i (Ahlquist, Gasca-Neri and Nix 1970). The analysis has led to values of’ the apparent activation energy of slip ‘, Q∗, and ‘the apparent activation energy of recovery’, Qi, which generally differ from the apparent activation energy of creep and, therefore, also from the activation enthalpy of lattice self-diffusion, and cannot be correlated with the process controlling dislocation glide velocity and recovery rate, respectively. This supports the contention that if [sgrave]∗ is measured by a dip test technique [sgrave]i, obtained as [sgrave]—[sgrave]∗, cannot be identified with the internal stress taking part in processes other than the dislocation glide. Assuming that the recovery is driven by the applied stress the creep in aluminum can be described in terms of recovery due to dislocation climb as a rate-controlling process.

Annealing of Electron-Irradiated n-Type Silicon: Illumination and Fluence Dependence

The effects of strong illumination and radiation fluence on the annealing behavior of the E center in electron-irradiated phosphorus-doped float-zoned silicon were studied by Hall-effect measurement. Illumination of the sample during anneal increased the rate of recovery significantly. Increasing the radiation fluence and, hence, the level of the induced-carrier compensation, also increased the rate of anneal. These results were found to be consistent with a previously proposed model in which the charge state of the defect was found to be a major determinant of the activation energy of recovery.

Dynamic recovery in aluminum

Dynamic recovery was studied in pure aluminum specimens deformed in tension at temperatures between 200° and 573° K, and strain rates between 0.004 and 2 min −1. The dislocation interactions and substructures were observed by means of thin-foil transmission electron microscopy. Activation energies were obtained for dynamic recovery and for tensile deformation. The values for deformation are ΔH d = 22.5 ± 3.5 kcal/ mol (at low temperatures) and ΔH d = 37.5 ± 2.5 kcal/ mol (at high temperatures). These two activation energies are related to the rate-controlling controlling processes of cross-slip and dislocation processes of cross-slip and dislocation climb, respectively. Thus, the activation energy for dynamic recovery, ΔH r = 22 ± 2.8 kcal/ mol, corresponds to the cross-slip of screw dislocations, which leads to the formation of stable dislocation networks and dislocation-free subgrains. At higher deformation temperatures, dislocation climb predominates, and subboundary disintegration and coalescence of subgrains are observed.

Annealing of Electron-Irradiatedn-Type Silicon. I. Donor Concentration Dependence

The annealing behavior of electron-irradiated phosphorus-doped silicon of low oxygen content (float zoned and Lopex) was studied by monitoring changes in the carrier concentration with Hall-effect measurements. In isochronal anneals, the $E$-center annealing stage was observed to shift to higher temperatures as the donor concentration was increased. This behavior was found to be consistent with a charge-state influence on the stability of the $E$ center. Analysis of the experimental data with respect to a charge-state model suggests an activation energy for recovery of the neutrally charged $E$ center of 0.9-1.2 eV. This value is in good agreement with previous annealing studies of Watkins and Corbett and Hirata et al.

High-temperature creep of polycrystalline graphite

A theory describing the high-temperature creep of polycrystalline graphite is developed. Equations are derived which describe the creep of graphite produced by the climb of edge dislocations distributed near the tips of basal plane cracks. These dislocations are characterized as follows: (i) their Burgers vectors are parallel to the c-axis, and (ii) they force the crack faces apart. The theory predicts and experimental results agree with the following: (1) cracks are observed microscopically; (2) the creep strain in the early stage of creep is proportional to the square root of time; (3) the creep strain at a given moment in time is proportional to the third power of stress; (4) the creep rate at a given creep strain is proportional to the 6th power of the stress; (5) the apparent activation energy of creep is appreciably larger than the self-diffusion activation energy and the creep recovery activation energy; and (6) extensive recovery creep based on reverse dislocation climb is predicted and observed.