Ion Irradiation Experiments Research Articles

Co-evolution of M23C6 precipitates and cavities in a boron-free Ni-based alloy GH3617 under high-temperature He ion irradiation: Effects on cavity swelling and mechanical properties

Ni-based alloys are promising materials for advanced nuclear reactors operating at high temperatures due to their exceptional resistance to high temperatures and corrosion. Understanding the synergy of phase stability and helium effects is crucial for assessing the long-term performance and reliability of these alloys in advanced nuclear reactors. This study has investigated the co-evolution behavior of M23C6 precipitates and cavities in a boron-free solid solution strengthened Ni-based alloy GH3617 under high-temperature He ion irradiation, and its impact on alloy swelling and mechanical properties, by He ion irradiation experiments with the highest fluence of 1 × 1017 He/cm2 up to 800 °C. Transmission Electron Microscopy (TEM) and Nanoindentation are employed to investigate microstructural evolution and mechanical properties, respectively. The findings show that at room temperature and 500 °C, cavities and dislocation loops were the dominant irradiation defects, whereas at 800 °C, the density of cavities and dislocations reduced while the formation of M23C6 precipitates increased. These precipitates act as effective trapping sites for He and point defect, leading to cavity formation at the interfaces or within the precipitates. Moreover, increased irradiation fluence accelerates the co-evolution process, resulting in an increase in the density and size of both precipitates and cavities, ultimately leading to enhanced swelling. The {111} planes are favored interfaces between intragranular M23C6 precipitates and the matrix due to their minimal misfit, while the preferred interface planes between cavities with octahedral or cubo-octahedral shapes and the precipitate/matrix are also {111}, owing to their lower surface energy as well. The co-evolution of cavities and precipitates was found to influence mechanical properties, resulting in an irradiation hardening effect at lower fluences, while softening at higher fluences. This study provides novel insights into the degradation mechanisms of Ni-based alloys under coupling effect of He and high-temperature irradiation.

Study on the Single-Event Burnout Effect Mechanism of SiC MOSFETs Induced by Heavy Ions

As a prominent focus in high-voltage power devices, SiC MOSFETs have broad application prospects in the aerospace field. Due to the unique characteristics of the space radiation environment, the reliability of SiC MOSFETs concerning single-event effects (SEEs) has garnered widespread attention. In this study, we employed accelerator-heavy ion irradiation experiments to study the degradation characteristics for SEEs of 1.2 kV SiC MOSFETs under different bias voltages and temperature conditions. The experimental results indicate that when the drain-source voltage (VDS) exceeds 300 V, the device leakage current increases sharply, and even single-event burnout (SEB) occurs. Furthermore, a negative gate bias (VGS) can make SEB more likely via gate damage and Poole–Frenkel emission (PF), reducing the VDS threshold of the device. The radiation degradation behavior of SiC MOSFETs at different temperatures was compared and analyzed, showing that although high temperatures can increase the safe operating voltage of VDS, they can also cause more severe latent gate damage. Through an in-depth analysis of the experimental data, the physical mechanism by which heavy ion irradiation causes gate leakage in SiC MOSFETs was explored. These research findings provide an essential basis for the reliable design of SiC MOSFETs in aerospace applications.

Synergistic Effects of Total Ionizing Dose and Single-Event Upset in 130 nm 7T Silicon-on-Insulator Static Random Access Memory

The exposure of spaceborne devices to high-energy charged particles in space results in the occurrence of both a total ionizing dose (TID) and the single-event effect (SEE). These phenomena present significant challenges for the reliable operation of spacecraft and satellites. The rapid advancement of semiconductor fabrication processes and the continuous reduction in device feature size have led to an increase in the significance of the synergistic effects of TID and SEE in static random access memory (SRAM). In order to elucidate the involved physical mechanisms, the synergistic effects of TID and single-event upset (SEU) in a new kind of 130 nm 7T silicon-on-insulator (SOI) SRAM were investigated by means of cobalt-60 gamma-ray and heavy ion irradiation experiments. The findings demonstrate that 7T SOI SRAM is capable of maintaining normal reading and writing functionality when subjected to TID irradiation at a total dose of up to 750 krad(Si). In general, the TID was observed to reduce the SEU cross-section of the 7T SOI SRAM. However, the extent of this reduction was influenced by the heavy ion LET value and the specific writing data pattern employed. Based on the available evidence, it can be proposed that TID preirradiation represents a promising avenue for enhancing the resilience of 7T SOI SRAMs to SEU.

Oxygen ion irradiation: Insights into the structural modifications of CVD-grown graphene

To enhance graphene's functionalities and explore potential applications, modifying its structure through ion irradiation has evolved as a favorable method. In the present study, graphene film grown on a copper substrate was transferred to a SiO2/Si substrate for conducting oxygen ion irradiation experiment at 100-keV. The research investigates the impact of varying oxygen ion fluences on CVD-grown graphene films. Characterization through Raman spectroscopy, confirmed increased D peak intensity and alterations in the 2D peak at higher fluences, indicating defects and lattice distortion induced by irradiation.

Novel integrated structure and function of Mg–Gd neutron shielding materials

Abstract As the lightest metal structural materials, magnesium (Mg) alloys offer extensive application potential. Gadolinium (Gd), as the primary alloying element in Mg alloys and recognized for its notable thermal neutron capture cross-section, is considered one of the most efficient neutron absorbers. Thus, the Mg–Gd alloy is highly expected to emerge as a material with remarkable neutron absorption capacity. Hence, in this study, the thermal neutron-shielding capabilities of Mg–Gd alloys were comprehensively examined by fabricating four as-cast Mg–xGd alloys with varying compositions (x = 0, 5, 10, and 15 wt%). The obtained results were further corroborated by sophisticated modeling and calculations using SuperMC. The results revealed a direct correlation between the thermal neutron absorption capacity of the Mg–Gd alloys and the increase in Gd content, with a noteworthy neutron attenuation factor of 22.33. Moreover, in an Au ion irradiation experiment conducted at 200°C, the Mg–15Gd alloy exhibited exceptional radiation resistance, with a displacement per atom (dpa) of 10. The matrix and second-phase regions were devoid of any cavity formation. Instead, a finite number of dislocation rings were observed, forming both leaf-like and granular Gd-rich nanoscale precipitates. This study underscores the versatility of Mg–Gd alloys as efficient neutron shielding materials and structural materials tailored for applications demanding radiation resistance in diverse environments.

Automated analysis of grain morphology in TEM images using convolutional neural network with CHAC algorithm

The shape and size of grains significantly impact the properties of polycrystalline materials. In particular, high temperature and radiation exposure in nuclear reactors can lead to considerable grain growth of UO2, thereby substantially modifying the fuel performance. Transmission electron microscopy (TEM) has been used to characterize the grain morphology of polycrystalline materials, but the manual analysis of TEM images is a time-consuming and labor-intensive process, which cannot meet the increasing demand for high-throughput data analytics.This study presents an automated approach we developed for characterizing grain morphology recorded in bright field TEM images during ion irradiations performed in situ. Our approach combines a machine learning model for detecting grain boundaries and a computer vision algorithm named CHAC for selecting well-labeled grains for statistical analysis. Using TEM images acquired from in-situ ion irradiation experiments on nanocrystalline UO2, we demonstrate that this automated approach can achieve comparable results to human experts while significantly reducing the analysis time. Moreover, the machine learning model functions as a "few-shot" model, requiring only a modest number of training images to perform effectively on a specific task. Consequently, researchers in need can efficiently train their own models following the procedures described in this study to automate grain morphology analysis of their own TEM images.

Heavy Ion Single Event Effects in CMOS Image Sensors: SET and SEU

High-energy particles in space often induce single event effects in CMOS image sensors, resulting in performance degradation and functional failure. This paper focuses on the formation and morphology of transient bright spots in CMOS image sensors and analyzes the formation process of transient bright spots by conducting heavy ion irradiation experiments to obtain the variation law of transient bright spots with heavy ion linear energy transfer values and background gray values; in addition, we classify the single event upset that occurred in the experiments according to the state of transient bright spots and extract the characteristics of different single event upsets. The failure mechanisms of different single event upsets are analyzed according to their characteristics and are combined with the information given by transient bright spots. This provides an essential reference for rapidly evaluating single event effects and the reinforcement design of CMOS image sensors.

Evaluating the effects of space weathering on magnetite on airless planetary bodies

Magnetite is a relevant mineral component of asteroids as it has been identified in carbonaceous chondrites, on the surface of asteroid Bennu through remote sensing observations, and in samples returned from asteroid Ryugu. However, the effects of space weathering processes on magnetite have not yet been explored. To investigate how this mineral phase responds to space weathering, here we simulate micrometeoroid bombardment and solar wind irradiation of magnetite using pulsed laser and ion irradiation experiments. We performed X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), and visible to near-infrared (VNIR) reflectance spectroscopy analyses to characterize the chemical, microstructural, and spectral response of magnetite to simulated space weathering. In addition, we carried out ion impact simulations using the SDTrimSP software to evaluate the calculated response of magnetite to 1 keV H+ and 4 keV He+ ions and compared these results to our XPS and TEM results. Ion irradiation simulated ∼750 years on the surface of asteroid Bennu, with a solar-wind appropriate total H:He fluence ratio (∼24). Within this time, depletion of O was observed with H+ and He+ ion irradiation, with significantly greater change via protons due to the larger fluence, where preferential sputtering promotes the formation of a metallic iron layer at the magnetite surface. This suggests that solar wind ions act as reducing agents on Fe oxides, with a fraction remaining implanted in these phases. Indeed, we observe elongated defects contained in a crystalline rim created by He+ implanted ions in the TEM. Pulsed laser irradiation, analogous to micrometeoroid impacts, generates melts on the surface of the magnetite grains. The impact melts and H+-generated metallic iron rims both result in increased VNIR spectral reflectance, but lower fluence He+ implantation has no significant spectral effect. These results suggest that space weathered magnetite could contribute to bright regions detected in remote sensing analyses of the Ryugu and Bennu surfaces by the Hayabusa2 and OSIRIS-REx missions and will contribute to the identification and interpretation of space weathered magnetite in returned samples retrieved from both asteroids.

Ion Beam as an External and Dynamic Metal Reservoir to Induce Nanoparticle Exsolution in Oxides

Nanoparticle exsolution is a recently developed method to produce oxide-supported metal nanoparticles via phase precipitation. It has attracted significant attention in the field of solid oxide fuel cells and electrolyzers (SOFC/SOEC) due to its potential for producing active and nanostructured electrodes. However, conventional exsolution methods face challenges in reaching the solubility limit of metal ions in the oxide matrix. To overcome this issue, here we propose a new approach to induce exsolution by using ion beams as an external and dynamic metal reservoir. We demonstrate the effectiveness of this method by using thin-film Zr0.5Ce0.5O2 (CZO) as a model system. Through ion irradiation experiments, 10 keV Ni ions were implanted into the near-surface regions of CZO films, and then exsolved as nanoparticles on the surface. This research offers a promising new avenue for developing next-generation SOFC/SOEC electrode materials using irradiation-tailored exsolution.

Effect of local chemical order on the irradiation-induced defect evolution in CrCoNi medium-entropy alloy

High- (and medium-) entropy alloys have emerged as potentially suitable structural materials for nuclear applications, particularly as they appear to show promising irradiation resistance. Recent studies have provided evidence of the presence of local chemical order (LCO) as a salient feature of these complex concentrated solid-solution alloys. However, the influence of such LCO on their irradiation response has remained uncertain thus far. In this work, we combine ion irradiation experiments with large-scale atomistic simulations to reveal that the presence of chemical short-range order, developed as an early stage of LCO, slows down the formation and evolution of point defects in the equiatomic medium-entropy alloy CrCoNi during irradiation. In particular, the irradiation-induced vacancies and interstitials exhibit a smaller difference in their mobility, arising from a stronger effect of LCO in localizing interstitial diffusion. This effect promotes their recombination as the LCO serves to tune the migration energy barriers of these point defects, thereby delaying the initiation of damage. These findings imply that local chemical ordering may provide a variable in the design space to enhance the resistance of multi-principal element alloys to irradiation damage.

Microstructure and defect evolution of nuclear graphite under temperature-dependent ion irradiation

Nuclear graphite plays a vital role in GEN-IV reactors and is expected to function in the harsh environments such as high temperature and high-dose irradiation. The ion irradiation behaviour of ET-10 nuclear graphite in comparison with highly orientated pyrolytic graphite (HOPG) was reported in this work, to explore the combined effects of ion irradiation and temperature. Ion irradiation experiments were carried out using 190 keV H+ and 1.8 MeV Ar+ at different doses. SRIM simulation, scanning electron microscopy (SEM) and Raman spectroscopy were employed to characterize the microstructural changes and defect evolution of graphite specimens under different irradiation conditions. The vein structure in HOPG graphite and the vertical scale-like structure in ET-10 graphite caused by ion irradiation were observed. The effects of temperature on ion irradiation could be divided into two stages of recovering and saturation according to mutual analysis of SEM and Raman. It was also found that the recovery degree of the half-width at half maximum (HWHM) for the G band was greater than that of ID/IG, probably because the deformed or ruptured graphite layers were difficult to recover at rising temperatures and/or could even be enhanced. HWHM(G), ID/IG, and La was comprehensively discussed, giving an overall perspective of defect evolution and crystallite size changes under temperature-dependant ion irradiation.

An in-situ TEM investigation of microstructure evolution in Cr-coated zirconium alloy under heavy ion irradiation: Simultaneous evolution of both Cr coating and Zr-4 matrix

Cr-coated zirconium (Zr) alloy is one of the potential candidate materials for accident tolerant fuel (ATF) cladding. However, little attention has been paid in the simultaneous microstructure evolution of Cr coating and Zr alloy matrix under irradiation, which is necessary for comprehensive evaluation of the alloy irradiation performance. In the present work, in-situ ion irradiation experiment was conducted to capture the major features during simultaneous microstructure evolution of Cr coating and Zr alloy at various temperatures. It is found that at 300 ℃ the size and number density of dislocation loops increase with irradiation dose, but at higher temperature the tendency seems different, which is related to the formation of dislocation networks. Besides, the extent of precipitate amorphization in Zr alloy matrix decreases with temperature due to the recovery of irradiation defects. The present work may provide useful insights into the irradiation property of the Cr-coated Zr alloy for ATF applications.

Irradiation Effects on Stability of δ-UZr2 phase in U-50 wt% Zr Alloy

U-50wt%Zr is a candidate metallic nuclear fuel with potential application in light water reactors due to its excellent thermal properties and high radiation tolerance. The Zr-rich UZr fuels possess greater swelling resistance and fission gas release characteristics compared with U-rich UZr fuels. In this current study, the δ-phase U-50wt%Zr is proton irradiated at room temperature to 1 displacement per atom (dpa) to provide insights on phase stability under irradiation conditions. High resolution characterization of Transmission Electron Microscopy (TEM) and Atom Probe Tomography (APT) characterization techniques are used to elucidate microstructural changes due to irradiation. TEM and APT results show highly oriented bcc β-Zr-rich platelet precipitates nucleating adjacent to α-U phases inside the UZr2 matrix. Formation of this platelet morphology is characteristic of Widmänstatten structure which can be attributed to a variety of factors such as differences in thermal expansion coefficient between the phases, grain size, alloy composition, and cooling rate. The phases present are distinctly different than those observed through in situ annealing, but irradiation accelerates diffusion and phase separation kinetics. These microstructural changes in U-50wt%Zr are different from those achieved by pure thermodynamic or high temperature heavy ion irradiation experiments. Our work, together with previous ones, highlight the necessity to study the U-Zr phase diagram under non-equilibrium thermodynamics conditions to support this material's deployment as a viable nuclear fuel form.

Role of structural ordering on the radiation response of Gd2Zr2O7 pyrochlore

Complex oxides with pyrochlore and fluorite phases offer several advantages for the Immobilization of actinides or high-level radioactive wastes. In this report, we present the different behavior of structural ordering/crystallinity of Gd2Zr2O7 (GZO) ceramics upon sintering at two different temperatures (1400°C–1500 °C). XRD and Raman spectroscopy studies revealed the enhancement of structural ordering/crystallinity with the increase of sintering temperature. Further, the ion irradiation experiments using 100 MeV iodine at the fluence of 1.0 × 1014 ions/cm2 were performed to investigate the radiation effects on both GZO ceramics. The irradiation studies insinuate that the GZO ceramic sintered at 1500 °C possesses relatively better radiation resistance than GZO ceramic sintered at 1400 °C. The variation in the radiation resistance response of GZO ceramics seems associated with the different degrees of structural ordering. These results suggest the role of structural ordering in the radiation resistance response of GZO ceramics. The relatively better radiation tolerance of GZO15 ceramic with some extant pyrochlore phase ordering may be suitable for applications in harsh environments.

An investigation of angle effect on heavy ion induced single event effect in SiC MOSFET

The angle impact on the single event effect in SiC Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) has been evaluated by Ta ion irradiation experiments. Two bias voltages of 275 V and 350 V were chosen to analyse the oxide and the body damages of the 900 V-rated devices, respectively. Two different angles of along and vertical to the stripes were tested for SiC MOSFETs with stripe-cell structures. The results show that the leakage degradation of the devices reduced with the angle increasing. The leakage paths changed from the drain-source dominating at normal incidence to the drain-gate at 30° for 350 V irradiations. The weakening of the combined effect between the charge deposition and electric filed in angular irradiation is the main reason of body damage attenuation. The results would help comprehend the single event effect characteristics and mechanisms of SiC MOSFET.

Room temperature fabrication of poly-crystalline Si thin films via Al-induced crystallization under 500 keV Xe+ ion irradiation

Poly-crystalline Si film is an important material for its applications in microelectronics and solar cells. In order to realize poly-crystalline Si for practical application with high performance, it needs to be fabricated at room temperature. In this paper, we present a novel technique to develop poly-crystalline Si thin films at room temperature using 500 keV Xe+ ion irradiation. Here, the Al-induced crystallization process is employed to reduce the crystallization temperature. For that, c-Al (50 nm)/a-Si (150 nm) bilayer thin films have been used for ion irradiation experiments. Structural studies show that crystallization of Si starts at a threshold fluence of 3 × 1015 ions cm−2, and crystallinity is found to increase with increasing ion fluence. The results are explained in terms of displacement spike and thermal spike due to the interaction of energetic ions with target atoms. The transport of ions in matter Monte Carlo computer simulation code has been used to estimate the number of displacements due to ion irradiation. Generation of a sufficient amount of free Si atoms at threshold fluence and diffusion of these free Si atoms along the Al grain boundary starts the nucleation process.

Thermal diffusivity in ion-irradiated single-crystal iron, chromium, vanadium, and tungsten measured using transient grating spectroscopy

The speed-up of radiation science development with the advent of ion-irradiation experiments has, until recently, been omitted in the post-irradiation examination technique. This paper reports the results of transient grating spectroscopy—a rapid, non-destructive, in situ photothermal surface technique—of ion-irradiated single-crystals of iron, chromium, vanadium, and tungsten at room temperature. Thermal diffusivity was used to track damage development throughout irradiation, with 5 MeV self-ion irradiated iron, chromium, and vanadium showing little to no change up to damages of the order of 1 dpa. 5 MeV Si3+-ion irradiated tungsten exhibits a reduction of thermal diffusivity from 0.78(7) to 0.29(2) cm2 s−1 with logarithmically increasing dose over a similar damage range. A comparison to literature of transient grating spectroscopy thermal diffusivity values past and present shows good agreement; radiation-induced change can be clearly distinguished from differences between mono- and poly-crystalline tungsten.

Effect of Post-irradiation Annealing on Microstructure Evolution and Hardening in GH3535 Alloy Irradiated by Au Ions

The Au ion-irradiation experiments of GH3535 alloy, a candidate alloy structural material for molten salt reactor, was carried out in this study. Herein, isochronous annealing experiments were conducted from 200 to 850 °C to clarify the evolution behavior of damage defects with increasing temperature. The coarsening of dislocation loops and formation and dissolution of precipitates with increasing annealing temperature were characterized by transmission electron microscopy. Nanoindentation was performed to measure the variation of hardness caused by irradiation. Additionally, the relationship between irradiation hardening and microstructure evolution was established. This study lays a foundation for the evaluation of irradiation damage properties of GH3535 alloy at different annealing temperatures.

Structure and radiation response of anion excess bixbyite Gd2Ce2O7

The crystal structure analysis of ${\mathrm{Gd}}_{2}{\mathrm{Ce}}_{2}{\mathrm{O}}_{7}$ reveals that it crystallizes in a bixbyite-type symmetry ($I{2}_{1}3$). Analysis of the structure suggests a randomly occupied cation sublattice with infinite correlation length associated with long-range ordered anion sublattice with half of the vacant sites of an ideal bixbyite filled, hence the name anion-excess bixbyite. Ion irradiation experiments and quantitative x-ray diffraction analysis were used to study the separate response of the anion sublattice to swift heavy ion radiation. Analysis of anion and cation correlation lengths as a function of fluence shows that the topological disorder on the anion sublattice grows faster than that on the cation sublattice. The microstructural response at increasing radiation fluences leads to a decrease of the strain after an initial increase, while the variance of the strain increases following the increase of the microdomain wall density. This particular behavior seems responsible for the exceptional radiation resistance of this system that does not display any significant amorphization, even at the highest fluence.

Influence of Au2+ ions irradiation on the structure and wear resistance of amorphous MoS2 films

The former work proved that ion irradiation causes the amorphization of the crystalline MoS2 film and leads to the degradation of the lubricating performance. In this work, in order to investigate the influence of irradiation damage on the amorphous structure, MoS2 film with amorphous structure was prepared and ion (Au2+) irradiation experiment was performed with damage level up to 5 dpa. The results show that after irradiation, the short-range order structure in the amorphous MoS2 film is interrupted, and the degree of disorder of its internal atoms increases. With the increase of the irradiation fluence, although the hardness and elastic recovery of the film increases significantly, the wear lives of the film reduce by two third. Further friction interface analyses reveal that the irradiation damage MoS2 film formed less reordered transferred layer at counter face, which leads to the higher friction coefficient and the shorter wear life.