Formation Of Radiation-induced Defects Research Articles

Understanding Formation of Irradiation-Induced Defects through 4D-STEM, Electron Tomography, and WBDF-STEM

Understanding Formation of Irradiation-Induced Defects through 4D-STEM, Electron Tomography, and WBDF-STEM

Extension of the scope of the photoluminescence method after electron irradiation for quantifying low-level carbon in silicon

We have extended the applicability of the photoluminescence method after electron irradiation for quantifying low-level C impurities in Si crystals. The intensity ratio of the G-line to the intrinsic emission normalized by the ratio of the reference sample is used as an index of the C concentration. The calibration curves have already been established for Czochralski-grown crystals with resistivity higher than 50 Ω·cm (n-type) and higher than 5 kΩ·cm (p-type). We showed that the method was extendable to the resistivity range down to 30 Ω·cm in n-type samples with the O concentration in the range 1–6 × 1017 cm−3. The extension to float-zone (FZ) crystals was realized by using the theoretical relationship between the C concentration and the G-line intensity ratio normalized by the ratio of the FZ reference sample. Regarding the extension to conductive p-type B-doped samples, the formation of B-related radiation-induced defects was found to be an obstacle.

Radiation-Induced Defect Formation Kinetics in Inconel–Cu Multimetallic Layered Composites

This study investigates the stability of Inconel–Cu Multimetallic Layered Composites (MMLCs) in nuclear reactor applications using Molecular Dynamics simulations. The focus is on understanding the underlying mechanisms governing the properties of MMLCs for advanced nuclear reactors, specifically, the mechanochemistry of the interface between Inconel and copper alloys. The selection of Inconel–Cu MMLCs is primarily due to copper’s superior thermal conductivity, enhancing heat management within reactors by preventing hotspots and ensuring uniform temperature distribution. This research examines Incoloy 800H and two Inconel variants (718 and 625), assessing their stability at 1000 K after exposure to 10 keV collision cascades up to 0.12 dpa. Notable findings include defect clustering on the {1 2 0} family of planes of Inconel and Cu, with Stacking Faults and Lomer–Cottrell locks on the Inconel side.

Development of an interatomic potential for L12 precipitates in Fe–Ni–Al alloys

Fe–Ni-based alloys have been considered as candidate structural materials for advanced nuclear reactors, and some of their excellent properties are particularly associated with L12 precipitates dispersed in the alloys. For a better understanding of the irradiation response, classical molecular dynamics is an essential tool to simulate the irradiation-induced defect formation and subsequent microstructural evolution. We here develop an interatomic potential for L12(Ni,Fe)3Al precipitates in the ternary Fe–Ni–Al system. The fitting parameters are tuned to describe the lattice and elastic constants of NiFe solid solutions and defect formation/vacancy migration energies in the fcc matrix. Furthermore, the lattice properties and defect energies of L12(Ni,Fe)3Al are considered for the fitting. We demonstrate the developed potential reproduces the lattice and defect properties with reasonable accuracy by comparison with density functional theory calculations, existing empirical potentials, and experimental data. This potential will be useful to investigate the defect formation and evolution of (Ni,Fe)3Al precipitates in the alloys under irradiation, which would provide critical insights into the materials design strategy to achieve enhanced properties.

Nanocomposites based on porous silicon and reduced graphene oxide for ionizing radiation sensing

In this study, the field-effect transistor (FET) based on the oxidized porous silicon (PS) – reduced graphene oxide (rGO) sandwich-like composite has been created. The electrical characteristics of the obtained FET were studied in both DC and AC modes. I-V curves and switching characteristics of the PS–rGO-based FET were analyzed. An increase in resistance and a decrease in capacitance of the experimental structures have been found in the 25 Hz − 1 MHz frequency range due to the joint action of α-, β-, and γ-radiation. The parameters of the equivalent circuit model of the PS–rGO-based FET before and after irradiation with 226Ra isotope have been determined using the impedance spectra. The formation of radiation-induced defects and the charge accumulation in the PS layer is considered a possible mechanism of the ionizing radiation influence on the graphene FET conductivity. The FET based on the PS–rGO structures has a high potential for application in ionizing radiation sensors due to the linear dependencies of resistance and capacitance on the irradiation duration.

Люминесцентная спектроскопия фосфатов, легированных ионами Pr-=SUP=-3+-=/SUP=-, облученных быстрыми электронами и реакторными нейтронами

This paper reports the spectroscopic properties of phosphates KLuP2O7, Sr9Sc(PO4)7, K3Lu(PO4)2, doped with Pr3+ ions. Photoluminescence (PL) spectra under selective excitation with UV photons, PL excitation spectra, and decay kinetics of pulsed cathodoluminescence are studied. Recordings of luminescence spectra were done with non-irradiated samples and after their irradiation with fast electrons (E = 10 MeV) or fast reactor neutrons. Three typical channels of electronic excitations radiative relaxation have been identified: interconfigurational d−f transitions, intraconfigurational f−f transitions in Pr3+ ions and luminescence associated with defects. After irradiation, significant changes in the luminescence characteristics were observed: a redistribution of the intensity of the intraconfigurational d−f transitions, an increase in the luminescence yield of defects and the manifestation of new emission centers. The formation of radiation-induced defects presumably occurs due to the formation of complexes consisting of phosphorus and oxygen atoms.

Recrystallization effects in spray-pyrolyzed Nb2O5 thin films induced by 100 MeV O7+ swift heavy ion beam irradiation

In this work, the influence of 100 MeV O7+ high energy swift heavy ion beam irradiation at varied fluences on the modification of properties of spray-deposited thin niobium pentoxide (Nb2O5) film is reported. The XRD patterns indicate tetragonal structure for pristine polycrystalline Nb2O5 film and partial amorphous nature for the irradiated samples in corroboration with the Raman spectra of the respective samples. The crystallite size is observed to reduce overall compared to that of the pristine film, however, a peaking is observed for 5x1012 ions/cm2 fluence within the irradiated films which is due to the high energy irradiation-induced defect formation and recrystallization effects. It is important to note that the defect density increases with fluence and recrystallisation occurs at 5x1012 ions/cm2, with further amorphization induced at much higher fluences. The generation of additional defect levels lowers the optical band gap. The direct and indirect band gaps were found to reduce upon irradiation compared to that of the pristine Nb2O5 film. The atomic force microscopic analysis reveals decrease in surface roughness of the irradiated samples from 5.9 nm to 10.1 nm compared to the pristine sample. Oxygen ion beam changes their morphology into network-like structures in a controllable manner which mainly depends on electronic energy loss occurring within the Nb2O5 lattice. Variations in transport parameters measured using Hall effect reveal that lower fluence yields less damage accumulation and does not cause significant change in properties of the sample. As fluence increases, vivid modifications originate from the production of significant density of point defects. At the critical fluence, recrystallisation is observed. These results are discussed in detail using the calculated parameters like crystallite size, Urbach energy, defect density and by correlating them with the observed optical and electrical data obtained from different techniques.

Effect of differently oriented interlayer phases on the radiation damage of Inconel-Ni multimetallic layered composite

Multimetallic layered composites (MMLCs) have shown an excellent potential for application under extreme environments, e.g., accident-tolerant fuel cladding, because of their low oxidation tendency and high corrosion resistance. Interfacial phases or complexions in nanocrystalline materials accelerate the annihilation of defects and enhance the radiation resistance of materials, making MMLCs with engineered interlayer phases compelling to deploy in extreme conditions. However, implementation of MMLCs in full capacity remained a challenge due to a lack of fundamental understanding of the underlying mechanisms governing the characteristics of the interface between the metallic layers. The precise role of interlayer phases in MMLCs and their interaction with defects, specifically under extreme conditions, is still unexplored. Pursuing atomistic simulations for various Inconel-Ni MMLCs model materials, we revealed accelerated defect mobility in interlayers with larger crystalline misorientation and the inverse relationship between the interface sink strength to the misorientation angle. Furthermore, we found a linear relation between interlayer misorientation angle with the density of radiation-induced defects and radiation enhanced displacements. Finally, our results indicate that radiation-induced material degradation is accelerated by the higher defect formation tendency of MMLCs with a high-angle interlayer interface. • The misoriented interlayer phase makes the radiation-induced diffusion anisotropic. • Radiation-induced defect formation and diffusion increase as the misoriented angle increases. • Interphase defect sink strength is higher for the interstitials than vacancies. • Defect recombination hampers due to vacancy-interstitial imbalance at higher doses. • Radiation-induced structural degradation is more acute for structures with a high misorientation angle interface.

Physical mechanisms of the influence of γ-ray surface treatment on the characteristics of close AuNi/n–n+-GaN Schottky contacts

The results obtained here suggest that low-dose 60Co γ-irradiation (Dγ ∼ 140 Gy) has a complex effect on close AuNi/n–n+-GaN{0001} Schottky contacts. This manifests in the disappearance of current steps in the initial section of the forward current–voltage curve, improvement in the average values of the ideality factor n, a decrease in the average values of the true Schottky barrier height ϕ bn in the middle section and an increase in series resistance R S and enhancement of the inhomogeneous metal–semiconductor contact series resistance effect in the final section. In all cases, the observed changes are sustainable. A combination of the Zur–McGill–Smith close Schottky contact defect model, the inhomogeneous contact model and the radiation-induced defect formation model provides an explanation for the physical mechanisms of changes observed in electrophysical and instrumental characteristics after γ-irradiation. Such mechanisms are associated with changes in the electrophysical nature of GaN structural defects (dislocations and interface states) and degradation of the homogeneity of contact conductivity. This paper shows that the low-temperature anomaly also manifests itself in close AuNi/n–n+-GaN Schottky contacts subjected to γ-irradiation.

Comparison of formation and evolution of radiation-induced defects in pure Ni and Ni–Co–Fe medium-entropy alloy

High-entropy alloys (HEAs) and medium-entropy alloys (MEAs) have attracted a great deal of attention for developing nuclear materials because of their excellent irradiation tolerance. Herein, formation and evolution of radiation-induced defects in NiCoFe MEA and pure Ni are investigated and compared using molecular dynamics simulation. It is observed that the defect recombination rate of ternary NiCoFe MEA is higher than that of pure Ni, which is mainly because, in the process of cascade collision, the energy dissipated through atom displacement decreases with increasing the chemical disorder. Consequently, the heat peak phase lasts longer, and the recombination time of the radiation defects (interstitial atoms and vacancies) is likewise longer, with fewer deleterious defects. Moreover, by studying the formation and evolution of dislocation loops in Ni–Co–Fe alloys and Ni, it is found that the stacking fault energy in Ni–Co–Fe decreases as the elemental composition increases, facilitating the formation of ideal stacking fault tetrahedron structures. Hence, these findings shed new light on studying the formation and evolution of radiation-induced defects in MEAs.

Photoluminescence of sapphire irradiated by low-energy electrons and ions

Photoluminescence (PL) of sapphire single crystals as received and preirradiated by low energy Ar+ ions and electrons has been studied to reveal a relationship between sapphire charging under electron beam irradiation and radiation-induced defect formation. The photoluminescence spectra were obtained using a confocal microscope excitation wavelength of 445 nm as well as by a nonconfocal method with excitation at a wavelength of 355 nm. The lines observed in PL spectra for all samples are associated with both intrinsic and impurity defects. It has been established that preliminary ion irradiation leads to disordering of the near-surface region of the sample resulting in a significant increase in the photoluminescence intensity. Preliminary electron irradiation can lead to a change in the charge state of defects that initially exist in the crystal. Keywords: radiation-stimulated defects, sapphire photoluminescence, ion and electron irradiation.

Фотолюминисценция сапфира, облученного электронами и ионами низких энергий

Photoluminescence (PL) of sapphire single crystals as received and preirradiated by low energy Ar+ ions and electrons has been studied to reveal a relationship between sapphire charging under electron beam irradiation and radiation-induced defect formation. The photoluminescence spectra were obtained using a confocal microscope wavelength of 445 nm as well as by a nonconfocal method with excitation at a wavelength of 355 nm. The lines observed in PL spectra for all samples are associated with both intrinsic and impurity defects. It has been established that preliminary ion irradiation leads to disordering of the near-surface region of the sample resulting in a significant increase in the photoluminescence intensity. Preliminary electron irradiation can lead to a change in the charge state of defects that initially exist in the crystal.

Effect of irradiation with heavy Xe22+ ions with energies of 165–230 MeV on change in optical characteristics of ZrO2 ceramic

The aim of this work is to study the effect of irradiation with heavy Xe22+ ions with energies of 165 MeV, 200 MeV, and 230 MeV on the change in the optical properties of ZrO2 ceramic. The choice of ion energies, as well as irradiation fluences of 1013-1014 ion/cm2, is primarily due to the possibility of simulating radiation damage in ceramics that occurs when overlapping damaged areas in the material, comparable to damage from fission fragments of uranium nuclei in an atomic reactor. Using UV–Vis spectroscopy methods, changes in the throughput of ceramics were evaluated depending on the irradiation fluence and the energy of incident ions. It was found that a change in the irradiation conditions leads to the formation of irradiation-induced defects with an energy of 2.4–2.45 eV in the structure, the concentration of which increases with the irradiation dose. Changes in the band gap and refractive index depending on irradiation fluence and incident ions energy indicate a change in the electronic and optical density of ceramics, as well as the formation of additional absorbing centers in the structure.

The influence of rhenium addition on the distribution of vacancy-type defects in tungsten

To investigate the influence of transmutation rhenium on the irradiation-induced defects in tungsten , H + and He + irradiation of 50 keV with a fixed fluence of 1 × 10 16 atoms·cm −2 were conducted on W x Re ( x =0, 3, 5 and 25 wt.%) alloys, respectively. Doppler Broadening Spectroscopy and Coincidence Doppler Broadening Spectroscopy both based on slow positron beam were employed in the current work to characterize the depth distribution and the chemical surroundings of the irradiation-induced defects. The results showed that under 723K irradiation, Re addition suppressed the accumulation of vacancy-type defects compared with pure W. This suppression was enhanced by increasing Re content in W. An obvious Re-related peak from (7-28) × 10 −3 m 0 c was observed in CDB spectra of well-annealed W-Re alloys. The irradiation effect led to the height deviation of Re-related peak. The decrease of the Re-related peak could be attributed to the formation of irradiation-induced defects in irradiated samples, and the reduction of positron annihilation fraction with core electrons of Re.

MWCNT-based surfaces with tunable wettability obtained by He+ ion irradiation

A study of He+ ion irradiation influence on the wettability of the multi-walled carbon nanotubes is presented. Tablets of pressed nanotubes of two types with different diameters were prepared and irradiated by 80 keV He+ ions. Raman and X-ray photoelectron spectroscopies showed the differences in the rate of radiation-induced defect formation for different types of nanotubes. The formation of cross-links between the layers of nanotubes under ion irradiation was demonstrated by the molecular dynamics simulation. Contact angle changes drastically with an increase in the fluence for both types of nanotubes: at low fluences superhydrophobic surfaces are formed, with an increase in the fluence a significant reduction in contact angle is observed, especially for the nanotubes of smaller diameters.

Selective patterning of out-of-plane piezoelectricity in MoTe2 via focused ion beam

Two-dimensional transition-metal dichalcogenides (TMDs) have a strain-sensitive nature and can only exhibit in-plane piezoelectricity, owing to their in-plane inversion symmetry breaking, which limits their practical applications for vertical stimulations. In this study, we demonstrated the capability of focused ion beams to create out-of-plane piezoelectricity on multi-layered MoTe 2 . We utilized a focused helium ion beam to selectively pattern the out-of-plane piezoelectricity via defect engineering in a layered MoTe 2 flake. The generated out-of-plane piezoelectricity in the desired area was quantitatively examined using atomic force microscopy, and ion beam irradiation-induced defect formation that gave rise to inversion symmetry breaking was confirmed. These results indicated that the out-of-plane piezoelectricity can be selectively patterned through a focused helium ion beam, and it is expected that this approach can also be applied to other classes of TMDs and can expand the application fields of TMD-based devices. • Selective patterning of out-of-plane piezoelectricity in 2D TMDs. • Generation/improvement of piezoelectricity using ion beam unlike usual reports on the ion beam irradiation. • Atomic-scale inversion symmetry breaking via local defect formation.

The formation and accumulation of radiation-induced defects and the role of lamellar interfaces in radiation damage of titanium aluminum alloy irradiated with Kr-ions at room temperature

A transmission electron microscopy (TEM) specimen of a titanium aluminide (TiAl) alloy was irradiated in-situ, at the IVEM-TANDEM facility, with 1 MeV Kr ions to a maximum fluence of 1.25 × 1019 ions m−2 at room temperature. The irradiated microstructure was then investigated ex-situ using advanced analytical TEM in combination with TEM image simulations and molecular dynamics (MD) simulations. The TEM examination showed that dot-like defects first formed in both the α2-Ti3Al and γ-TiAl phases of the irradiated microstructure. With increasing irradiation dose planar defects formed and propagated within the γ phase, and most of the planar defects were accompanied by the dot-like defects. The TEM image simulations and MD irradiation simulations revealed that the origins of the dot-like and planar defects were interstitial clusters and stacking faults, respectively, and large interstitial clusters were surrounded by dislocation loops. The interstitial clusters formed and grew in the irradiated microstructure due to much faster diffusion of interstitials than that of vacancies at room temperature. Local stress concentrations increased near large interstitial clusters and lamellar interfaces, which resulted in the nucleation and propagation of stacking faults. Moreover, the configurations of the lamellar interfaces in the start microstructure were found to play an important role in the formation and accumulation of the radiation-induced interstitial clusters and stacking faults at room temperature.

Effects of proton irradiation on microstructure and mechanical properties of nanocrystalline Cu–10at%Ta alloy

Duplex nanocrystalline Cu–10at%Ta is attractive for extreme environments because of its grain size stability at high homologous temperatures, owing to dispersed Ta nanoclusters. This study is an initial investigation into the microstructural and mechanical stability of Cu–10at%Ta under irradiation. Proton irradiation is carried out to 1 displacement per atom (dpa) at 500 °C. The Cu–10at%Ta exhibits grain size stability throughout irradiation and resistance to the formation of irradiation-induced defects. However, Ta nanoclusters undergo ballistic dissolution. Nanoindentation reveals there is no significant irradiation hardening, consistent with the relatively irradiation-stable microstructure. Ballistic dissolution of Ta nanoclusters is discussed in the context of Orowan strengthening.

Features of changes in the structure and properties of titanium nickelide irradiated with MeV xenon ions

The effect of irradiation with 141 MeV and 231 MeV xenon ions and irradiation temperatures T = 100 and 250 °C on the structural-phase state and properties of titanium nickelide in its initial martensitic-austenitic and austenitic states was experimentally studied. The radiation effects revealed are as follows: changed phase composition caused by B19′ → B2, B2 → R transformations and recovery of the martensitic phase B19′ at 250 °C; increased nanohardness, microhardness and electrical resistance at 100 °C due to formation of track nanostructures and radiation-induced defects; radiation-induced accumulation of xenon in the near-surface layer. In addition, softening of the near-surface area and decreased electrical resistance were found for the martensitic-austenitic state at irradiation temperature of 250 °C, which was caused by the changed content of the Ni-Ti phase with the B2 phase and R phase.

New optical oxygen-deficient centers in 80 keV Re-implanted amorphous silica

The formation of radiation-induced defects in amorphous SiO2 under the implantation with Re ions was studied by optical absorption and photoluminescence spectroscopies. A new type of oxygen-deficient center, denoted as ODC/Re, has been discovered. The origin of ODC/Re is associated with disturbing influence of Re ions located in the nearest environment of ODCs and causing a change in their energy structure. The absorption and emission bands of Re-modified ODC occur with participation of singlet S1 and triplet T1 excited states, adiabatic terms for which are shifted relative to those for typical Si-ODC. Spectral characteristics of absorption and photoluminescence of ODC/Re along with emission kinetic parameters allow us supposing that the structure of center is close to the ODC(II)-type. Thermal annealing leads to an increase in the emission intensities by a factor of three for both Si-ODC and ODC/Re.