Activation Energy For Detrapping Research Articles

Microstructural Evolution and Behavior of Deuterium in a Ferritic ODS 12 Cr Steel Annealed at Different Temperatures

In the present work, an ODS 12 Cr steel was characterized using Electron Microscopy techniques, in an as-received condition and after annealing treatments between 773 K and 1573 K. Results show a complex microstructure, with the presence of fine Y–Ti–O nanoparticles dispersed in the matrix. After annealing at 1573 K, the average diameter of Y–Ti–O nanoparticles increases from ~ 4 to ~ 7 nm and partial recrystallization occurs. The trapping behavior of deuterium in the steel in its as-received state and annealed at 1573 K was investigated. Samples were exposed to low-energy deuterium plasma and analyzed with thermal desorption spectroscopy, after waiting times of 1 day and 25 days. The samples measured 1 day after exposure released a higher total amount of deuterium than the ones measured after 25 days. The effect of waiting time is explained by the release of deuterium, at 300 K, from sites with low activation energy for detrapping, Ed. In the as-received condition, part of the deuterium detrapped at 300 K was re-trapped by high-Ed sites. For the samples in the annealed condition, the redistribution of deuterium from low-Ed to high-Ed sites was not observed, but the total amount of deuterium released was higher.

Hydrogen Diffusion and Trapping in Laser Additively Manufactured Ultra-High Strength AerMet100 Steel

Hydrogen trapping and the permeation behavior of laser additively manufactured (LAM) AerMet100 (UNS K92580) steel with an as-deposited specimen (AD) and after three types of heat-treated specimens (bainite microstructure [BM], tempered bainite and martensite microstructure [TBMM], and tempered martensite [TM]) was investigated. At least three types of different hydrogen traps were identified in each microstructure of the LAM steel, including both reversible and irreversible H traps. For as-deposited microstructure, the main reversible H trap states are related to the precipitation of M3C carbides associated with a detrapping activation energy (Ed) of 17.3±0.2 kJ/mol. After heat treatment, the dominant reversible hydrogen trap states in the tempered martensite microstructure have a different Ed value of 19.3±0.5 kJ/mol, which is attributed to the precipitation of highly coherent M2C carbides. In comparison with the reported Ed value of approximately 21.4 kJ/mol for main reversible hydrogen traps in wrought UNS K92580 steel, the lower Ed value in the LAM steel is closely related to the composition change of M2C carbides. In all of the H precharged samples, the diffusible and total H concentration of the TM specimen and the TBMM specimen are about three to four times higher than that of the AD specimen and the BM specimen. The TM specimen with tempered martensite microstructure has the highest diffusible and total H concentration due to its high density of dominantly reversible H traps. The effective hydrogen diffusion coefficient (Deff) of the LAM steel is on the order of 10−9 cm2/s, and decreases with increasing density of the dominant reversible H traps brought about by heat treatment. The LAM steel has a comparable Deff of about 2.8 × 10−9 cm2/s compared to the wrought steel of a similar yield strength (∼1,750 MPa),

Influence of dynamic annealing of irradiation defects on the deuterium retention behaviors in tungsten irradiated with neutron

Tungsten (W) samples were damaged by neutron and 6.4 MeV Fe-ion irradiation above 1000 K simulating the divertor operation temperature. Deuterium (D) retention properties were examined by decorating the damaged W with D and subsequent thermal desorption spectroscopy (TDS) measurements. Vacancy clusters were the major D trapping site in the W irradiated with Fe-ion at 873 K, although D retention by vacancy clusters decreased in the W irradiated with Fe-ion at 1173 K due to dynamic annealing. The D de-trapping activation energy from vacancy clusters was found to be 1.85 eV. D retention in neutron damage W was larger than that damaged by Fe-ion due to the uniform distribution of irradiation defects. The D desorption behaviors from neutron damaged W was simulated well by assuming the D de-trapping activation energy to be 1.52 eV.

Numerical Analysis of Stress Gradient and Traps Effects on Carbon Diffusion in AISI 316L during Low Temperature Gas Phase Carburization

In order to elucidate the roles of the composition-induced stress gradient and the traps formed by chromium atoms in carbon diffusion in AISI 316L austenitic stainless steel during low temperature gas phase carburization, the carbon concentration-depth profiles were analyzed by a diffusion model considering the composition-induced stress gradient and the trapping effect. The results show that the carbon concentration-depth profiles calculated by this model show good agreement with the experimental results. The composition-induced compressive stress gradient can enhance the carbon diffusion but reduce the surface carbon concentration; these effects are not pronounced. Carbon atoms prefer to occupy the trap sites, and the detrapping activation energy (Qt = 33 kJ·mol−1) was deduced from fitting the experimental carbon concentration-depth profile. Furthermore, this applied diffusion model can be used to interpret the enhanced carbon diffusion in low temperature carburized AISI 316L.

The Influence of Morphology and PbI2 on the Intrinsic Trap State Distribution in Perovskite Films Determined by Using Temperature-Dependent Fluorescence Spectroscopy.

Perovskite films with different particle sizes and PbI2 contents were prepared by using a controlled single or sequential method. By means of temperature-dependent fluorescence spectroscopy, the energetic distribution of intrinsic intragap trap states in perovskite was quantitatively determined, and the radiative charge recombinations through the band edge and via trap states were studied. Furthermore, a series of thermodynamic parameters, such as the demarcation energy between radiative and nonradiative recombination regions, detrapping activation energy, and characteristic temperature, were extracted based on which of the possible radiative and nonradiative recombination mechanisms were proposed. In addition, the correlation between the morphology of the perovskite films, the PbI2 content, and the energetic distribution of the trap states was investigated. Finally, we discuss the structure-function relationship of perovskite films prepared by different methods.

Modeling of Nitrogen Penetration in Medical Grade CoCrMo Alloy during Plasma Nitriding

For analysis of plasma nitriding process and nitrogen penetration into CoCrMo alloy the trapping-detrapping model is applied. This model is commonly used for analysis of stainless steel nitriding, however, in this work it is shown that the same nitrogen penetration mechanism takes place in CoCrMo alloys. From the fitting of experimental curves, taken from literature, it is found by the proposed model that diffusion coefficient depends on nitrogen concentration according to Einstein-Smoluchowski relation D µ 1/ C N . The diffusion coefficients for 400 o C temperature nitriding of in CoCrMo are calculated. The shape of nitrogen depth profile curves are analyzed showing influence of different parameters such as detrapping activation energy, chromium concentration, etc. DOI: http://dx.doi.org/10.5755/j01.ms.20.1.3458

Reliability investigation of AlGaN/GaN high electron mobility transistors under reverse-bias stress

Impact of reverse-bias stress on the reliability of AlGaN/GaN high electron mobility transistors was investigated in this paper. We found that inverse piezoelectric effect could induce noisy characteristics of stress current, and the “critical voltage” increased with the drain–source bias in the step-stress experiments. Although the degradation of the gate leakage current and drain-to-source leakage current are non-recoverable, the maximum output current can recover almost completely through electron de-trapping procedure after stress. The de-trapping activation energy was estimated to be 0.30eV by the dynamic conductance technique. The surface morphology of the electrically stressed devices was investigated after removing the gate metallization by chemical etching, and no pits or cracks under the gate contact were observed.

Modeling of nitrogen penetration in polycrystalline AISI 316L austenitic stainless steel during plasma nitriding

The nitrogen depth profile in polycrystalline AISI 316L austenitic stainless steel after plasma nitriding at temperatures around 400 °C is analyzed by the “trapping–detrapping” model. This model considers the diffusion of nitrogen under the influence of trap sites formed by local chromium atoms. Nitrogen depth profiles in polycrystalline AISI 316L steel simulated on the basis of this model are in good agreement with experimental nitrogen profiles. The enhanced nitrogen diffusivity as well as a plateau-type shape of nitrogen depth profile can be explained. The nitrogen diffusion coefficient at 400 °C is found to be D = 4.81 × 10 −12 cm 2/s and the diffusion pre-exponential factor D 0 (0.837 × 10 −3 cm 2/s) and detrapping activation energy E B (0.28 eV) were deduced from fitting experimental data. It is known that the nitrogen penetration depth (and nitrogen diffusivity) depends on the crystalline orientation and a tentative to take into account this anisotropy effect and describe nitrogen depth profiles in polycrystalline AISI 316L steel is proposed by using different diffusion coefficients characteristic for each crystallite orientation.

Towards a detailed understanding of the mechanisms of hydrogen retention in beryllium

In this paper, we present new temperature-programmed desorption measurements from implanted single and polycrystalline beryllium as well as new computational results on the diffusion of interstitials through an undisturbed beryllium lattice. The threshold fluence for the appearance of a low-temperature desorption region around 460 K after implantation of 1 keV D ions into polycrystalline beryllium is determined to be 1.2×1021 m−2. In the high-temperature release region, an implantation energy-dependent shift in desorption temperatures is observed after implantation to very low fluences. It is explained by the variation of the mean distance from the surface for atoms implanted at different energies rather than by changes in the activation energy for detrapping. Morphological investigations of the surface of polycrystalline beryllium after several implantation and annealing cycles show a strong dependence of the damage on the surface orientation of grains. This dependence correlates with the preferred diffusion of interstitials parallel to basal planes of the beryllium lattice as calculated within the formalism of density functional theory.

Hydrogen Delayed Fracture Properties and Internal Hydrogen Behavior of a Fe–18Mn–1.5Al–0.6C TWIP Steel

The hydrogen delayed fracture (HDF) properties and internal hydrogen behavior were investigated in a Fe–18Mn–1.5Al–0.6C steel, a representative twinning induced plasticity (TWIP) aided steel. Slow strain rate tests (SSRT) were employed on both smooth and notched specimens to evaluate the effects of diffusible hydrogen on the HDF properties of the steel. Results showed that the fracture stress, fracture strain and time to fracture of the hydrogen pre-charged specimens were relatively insensitive to the amount of diffusible hydrogen. Fracture surface exhibited a ductile dimple fracture mode regardless of the diffusible hydrogen concentration. It was found that most hydrogen became non-diffusible after SSRT. The major trapping sites of hydrogen were dislocations, grain boundaries and twins. The activation energies for detrapping of hydrogen were estimated 35 kJ/mol for dislocations or grain boundaries, and 62 kJ/mol for twins. A comparison of the HDF properties of the present steel with those of other high strength steels revealed that the TWIP steel appeared to be relatively immune to hydrogen delayed fracture. This was due to the combined effects of (a) higher hydrogen solubility of austenite matrix (b) negligible portion of diffusible hydrogen to the total hydrogen, (c) decrease of diffusible hydrogen content during the deformation, and (d) no transformation of austenite to either e or α′ martensite.

Electron trapping and detrapping in ion-beam-damaged diamond surfaces

Ion-beam-damaged diamond surfaces subjected to electron irradiation are observed to develop a pronounced negative surface charge. In this study, this effect is shown to be associated with the capture of electrons into traps created by the ion irradiation process. The trapped charge increases with ion dose and incident electron current, and decreases with increasing sample temperature and laser illumination as the traps are depleted of charge. An activation energy for detrapping of about 1.5 eV is deduced from the temperature dependence of the charging.

Hydrogen Trapping Behavior in Vanadium-added Steel

Hydrogen trapping and de-trapping behavior was investigated for steels with and without V. The de-trapping of hydrogen is very slow while the trapping presumably proceeds rapidly for steels containing VC precipitates. The activation energy for de-trapping is in the range of 33 to 35 kJ/mol. The trapped-hydrogen content and diffusible-hydrogen content in the steady state increase with increasing hydrogen entry rate into the steel. The density of hydrogen trapping sites decides the maximum trapped-hydrogen content; 9 ppm for 1 % V steel tempered at peak secondary hardening temperature. Analysis of hydrogen embrittlement cracking tests in terms of hydrogen contents such as the critical hydrogen content should be performed on the specimens with uniform hydrogen distribution and must consider the nature of hydrogen whether it is trapped or diffusible.

Evaluation of Hydrogen Content Trapped by Vanadium Precipitates in a Steel

Hydrogen content trapped by vanadium precipitates was evaluated using vanadium bearing martensitic steels which show single TDA desorption peak. The peak consists of desorption from various sorts of trap site with different detrapping activation energy, even if it appears to be a single peak. Experimentally obtained single desorption profile taken from vanadium bearing martensitic steels was decomposed to multiple profiles with different peak temperature. Form of each desorption profile was approximated to Gaussian function. Area surrounded by each Gaussian function was calculated by integrating the functions to obtain decomposed hydrogen contents related to each peak temperature. It was revealed that decomposed profile with 140°C peak was caused by vanadium precipitates trapping, by comparing an amount of vanadium precipitates with decomposed hydrogen contents. Most of hydrogen in vanadium bearing tempered martensitic steel was revealed to be trapped by vanadium precipitates.

Insulator surface analysis

AbstractCharging an insulator hampers surface analysis techniques from working properly and over a long time has been considered as a spurious effect. Actually it is a physical phenomenon of major importance because its parameters are also those used to describe the macroscopic properties of insulators. This paper explains trapping/detrapping mechanisms where the important points are the calculation of the trap energy and of the energy stored in a charged dielectric material. Experimental techniques are developed for determining the insulator intrinsic properties. It is shown that measurements of permitivity, detrapping activation energy, trapping rate, detrapping space charge field, and power coefficient in the law describing the relationship between the insulator size and the detrapping field, are obtained with an electron beam. Another important finding is that charging significantly modifies the free energy of the sample. The consequence of the dielectric relaxation is investigated. It has been found that electron beam damages is not related to stimulated desorption but to the release of the polarization energy. This new approach to charging and related phenomena is applied to material science. It is shown that many phenomena such as breakdown, friction, fracture, which were believed to be very different are actually all related to dielectric processes. One consequence of the dielectric relaxation is the exoemission of various particles including neutrons in appropriate materials. The enormous energy released during charge detrapping or during polarization switching in ferroelectrics has been used elsewhere to produce electron and ion sources and nuclear fusion.

Elastic Recoil Detection Analysis of the Concentration and Thermal Release of Hydrogen in a-Si:H Films by the ECR Plasma CVD Method

For the a-Si:H films prepared by ECR plasma CVD, the hydrogen content and its variation associated with heat treatment have been studied by means of 6.06 MeV-19F-ERDA. It was found that as the deposition temperature was elevated from room temperature(RT) to 573 K, the hydrogen content in the film abruptly decreased. The activation energy for detrapping was estimated to be 0.84±0.02 eV for the Si-H bonds of two films prepared at RT and at 573 K. For a film prepared on a 5-in.-diameter Si wafer at RT, the film thickness was uniform in the error range of ±3% within the distance from the center to the edge of the wafer, while the hydrogen content fluctuated over the range of 20% near the edge.

Binding energies of triplet excimers in poly(N-vinylcarbazole) solid films from laser-based kinetic spectroscopy between 15 and 55 K

Time-resolved delayed luminescence spectra from solid films of poly(N-vinylcarbazole) have been recorded in the temperature interval between 15 and 55 K. Below 40 K the phosphorescence spectra are primarily nonexcimeric in character but become totally excimeric at 55 K. Rate constants for the phosphorescence decay in this same temperature interval yield linear Arrhenius plots but with a discontinuous change in slope at 40 K. The activation energy above 40 K is 2.0 kJ/mol and is associated with the trapping of nonexcimeric triplets. When combined with previous determinations of the activation energies for detrapping of triplet excimers, binding energies of 2.5 and 12.1 kJ/mol are found for the shallow and deep excimers relative to the energy of the limited free rotor, the energy of which corresponds to the top of the activation barrier.

Temperature Dependence of Positron Annihilation in Plastically Deformed Copper

Doppler-broadened photopeaks resulting from positron annihilation in as-deformed and recovered copper crystals were measured as a function of temperature between 4.2 and 275 K. In the as-deformed state, a significant line narrowing for increasing temperature was observed in the range below about 100 K. This low-temperature effect was removed by recovery annealing up to 573 K, at which the annealing out of dislocations had taken place. The results from the as-deformed state were explained in terms of thermal detrapping of positrons from shallow traps along the dislocation line, with subsequent retrapping either at submicroscopic vacancy clusters or deeper traps associated with dislocations. An activation energy for detrapping was estimated to be less than 0.01 eV.

Electron traps in AℓPO4 substituted zinc silicate phosphors

Recently it has been shown that the incorporation of AlPO4 in a Zn2SiO4 phosphor results in an improved cathodoluminescent efficiency1. We report here on electron trap distributions in the substituted phosphors derived from UV excited thermoluminescent glow curve measurements. It has been found that the glow curve peaks are modified appreciably with AlPO4 addition, but new peaks do not appear to be introduced. This shift, however is largely due to a considerable change in the absolute value of the detrapping rate, while there is only a relatively small change in the activation energies for detrapping. The phosphors were prepared in a silica rich environment and for the present study were not subjected to post preparation annealing treatments.

Luminescence de recombinaison consecutive a la photoionisation d'une solution organique vitreuse-nouvelle methode experimentale

In this paper, we describe a new experimental method which is used to determine the effect of temperature on the mechanisms related to the detrapping of electrons trapped in a glass. The studied samples are organic vitreous solutions of an aromatic molecule (TMPD) inside a non-polar glass (3-MP or MCH). The intensity of the isothermal luminescence (ITL) following the photoionization of the sample at 77K is increased when applying thermal jumps ΔT≲2K (the rise time is ⋍s). A general kinetical theory is used to explain the shapes of the luminescence curves perturbed by thermal jumps. It is shown that the experimental observations can be explained in terms of a slow diffusion of the trapped electrons towards a tunneling detrapping zone. When applying a thermal jump ΔT, the intensity of luminescence is multiplied by X such as: X = exp ΔT T E kT + Y 1+Y . This relationship is in good agreement with experience. The thermal detrapping activation energy E and the tunnelling effect ratio Y can be determined through this formula. The shapes of the kinetic curves at T = 77K and T = 77·50K are compared in the case of 3-MP glassy samples (near the glass transition, T g = 77K). It is concluded that there is a slow diffusion of trapped electrons (as it was already shown); the diffusion activation energy ( E d = 0·65eV) is found to be very close to viscosity activation energy ( E = 0·65eV) as given by Willard. This last result seems to support the hypothesis according to which the diffusion of trapped electrons is the consequence of the diffusion of the trapping cavities (at T g ).