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β-Ga2O3 has received widespread attention due to its ultrawide bandgap, which potentially permits applications in extreme conditions. Ultrafast laser irradiation of β-Ga2O3 provides a means for exploring the response of the material under such conditions, which could result in the generation of point defects as well as a localized modification of structural features that could yield properties that differ from the pristine surface. However, an understanding of defects generated by femtosecond laser irradiation in the vicinity of laser-induced periodic surface structures (LIPSS) remains to be explored. We correlate topographic features with optical and electronic properties by combining near-nm scale resolution cathodoluminescence with Kelvin probe force microscopy. Defects are found to correlate with crystalline order and near-surface morphology, as well as changes in work function. They are also suggested to be closely related to the formation of high spatial frequency LIPSS. These results suggest a need for precise tuning of laser irradiation conditions as well as possible post-processing to control defects in future Ga2O3 devices. [ABSTRACT FROM AUTHOR]

β-Ga2O3 has received widespread attention due to its ultrawide bandgap, which potentially permits applications in extreme conditions. Ultrafast laser irradiation of β-Ga2O3 provides a means for exploring the response of the material under such conditions, which could result in the generation of point defects as well as a localized modification of structural features that could yield properties that differ from the pristine surface. However, an understanding of defects generated by femtosecond laser irradiation in the vicinity of laser-induced periodic surface structures (LIPSS) remains to be explored. We correlate topographic features with optical and electronic properties by combining near-nm scale resolution cathodoluminescence with Kelvin probe force microscopy. Defects are found to correlate with crystalline order and near-surface morphology, as well as changes in work function. They are also suggested to be closely related to the formation of high spatial frequency LIPSS. These results suggest a need for precise tuning of laser irradiation conditions as well as possible post-processing to control defects in future Ga2O3 devices. [ABSTRACT FROM AUTHOR]

Nanopore/pillar formation on a Ge substrate can be induced by ion irradiation, which activates the ion beam sputtering and self-organization of point defects. Considering that the size and morphology of nanostructures are dependent on damage production, the irradiation parameters significantly affect nanostructuring. Here, the projected range of incident ions was selected as a parameter to be investigated. The projected range was modified by adding an Au buffer layer on the surface of the substrate, enabling the ions to stop in a shallower layer. The experimental results showed that the deposited Au layer affected the size and morphology of the nanostructures produced by ion irradiation. As a unique morphology, network-like structures were observed on the Au-deposited substrates. These structures were larger than ordinary porous structures. [ABSTRACT FROM AUTHOR]

Vanadium dioxide (VO2) manifests an abrupt metal–insulator transition (MIT) from monoclinic to rutile phases, with potential use for tunable electronic and optical properties and spiking neuromorphic devices. Understanding pathways to modulate electronic transport in VO2, as well as its response to irradiation (e.g., for space applications), is critical to better enable these applications. In this work, we investigate the selective modulation of electronic transport in VO2 films subject to different 10 keV helium ion (He+) fluences. Under these conditions, the resistivity in the individual monoclinic and rutile phases varied by 50%–200%, while the MIT transformation temperature remains constant within 4 °C independent of irradiation fluence. Importantly, different trends in the resistivity of the monoclinic and rutile phases were observed both as a function of total He fluence as well as in films grown on different substrates (amorphous SiO2/Si vs single crystal Al2O3). Through a combination of measurements including majority carrier sign via Seebeck, low frequency noise, and TEM, our investigation supports the presence of different kinds of point defects (V in; O in), which may arise due to grain boundary defect interactions. Our work suggests the utility of He irradiation for the selective modulation of VO2 transport properties for neuromorphic, in contrast to other established but non-selective methods, like doping. [ABSTRACT FROM AUTHOR]

The response of MgO periclase to irradiation is investigated by means of molecular dynamics simulations, mimicking irradiation by Frenkel pairs accumulation. Both the calculated lattice and volume swellings, which refer, respectively, to the lattice and total volume changes reproduce well the experimental measures. The two diverge at around 0.2 dpa, above which lattice and volume swellings follow separate trends. Below this value, dislocation loops nucleate from point defects clusters, built up by progressive aggregation of both magnesium and oxygen interstitials. Very small 1 2 ⟨110⟩ loops lying in {001} planes and made of (MgO)6 interstitials could be characterized. They serve as seeds for the subsequent growth of dislocation loops in all three {110}, {001}, and {111} planes, which then follows a sublinear law. The 1 2 ⟨110⟩ loops lying in the {011} planes become dominant as loop diameters increase beyond 15 nm. Above 0.2 dpa, we observe (i) the relative decrease of lattice swelling mainly because the very dense dislocations loops recombine and stabilize into less dense dislocation forests and, concomitantly, (ii) the fast increase of volume swelling caused by the occurrence of significant voids of up to 32 vacancies. [ABSTRACT FROM AUTHOR]

In this study, the formation of nano-porous/fibrous structures was investigated by spot-ion irradiation on Ge and GaSb substrates to consider the formation range of nanostructures and point defects. Spot-ion irradiation was performed in a focused ion beam system with a beam diameter of 35.1 nm, which is determined by the system. The fluence and ion beam current ranged within 5 × 1019–1 × 1022 ions/m2 and 500–520 pA, respectively. All the irradiated ions were Ga+ with incident energy adjusted at 30 keV, and the angle of incidence to the surface normal was 0°. The interval of the irradiated spot ranged from 100 to 1000 nm. For line-patterned irradiations, these spots overlapped with one another at an overlap ratio of 50%, producing a 35.1 nm × 10 μm irradiated region. Result shows that nanostructured regions followed a spot interval. When an interval was shorter than 200 nm, each nanostructured spot coalesced with neighbors to form large and uniform structures. Furthermore, line-patterned irradiation indicated that the migration distance of vacancy was ∼300 nm at maximum, which is consistent with the coalescence phenomenon. [ABSTRACT FROM AUTHOR]

The spectra of anticrossing of spin sublevels have been recorded and spin-3/2 color centers have been identified for the first time in commercially available 4H-SiC Schottky diodes irradiated with 0.9-MeV electrons or 15-MeV protons. The effect of the irradiation density on the defect formation has been shown. It has been demonstrated that the increase in the temperature at which proton irradiation is carried out acts as a short-term annealing, leading to a decrease in the concentration of point defects. [ABSTRACT FROM AUTHOR]

CVD-SiC and sintered SiC (SPS-SiC) were proton irradiated at 340 ̊C receiving different levels of damage (0.05–0.25 dpa). A novel multi-step machining and measurement method using laser flash analysis (LFA) was developed to derive the thermal conductivity of the irradiated layer (∼46 µm). Before irradiation, the thermal conductivity of SPS-SiC was much lower than CVD-SiC, primarily due to its higher intrinsic defect concentration and smaller grain size which provide a greater density of barriers to phonon transmission. Following irradiation, major thermal conductivity degradation (∼90%) was found to occur to both types of SiC after only a low dose (∼0.1 dpa), with both saturating at a similarly low value (a few W/K⋅m), as the thermal resistivity due to the presence of high density of grain boundaries became less important. Thermal conductivity degradation after irradiation was primarily caused by point defects in both types of SiC, as reflected by Raman spectra. [ABSTRACT FROM AUTHOR]

The tunability of the transition metal dichalcogenide properties has gained attention from numerous researchers due to their wide application in various fields including quantum technology. In the present work, WS2 has been deposited on fluorine doped tin oxide substrate and its properties have been studied systematically. These samples were irradiated using gamma radiation for various doses, and the effect on structural, morphological, optical and electrical properties has been reported. The crystallinity of the material is observed to be decreased, and the results are well supported by x-ray diffraction, Raman spectroscopy techniques. The increase in grain boundaries has been supported by the agglomeration observed in the scanning electron microscopy micrographs. The XPS results of WS2 after gamma irradiation show evolution of oxygen, carbon, C=O, W–O and SO4−2 peaks, confirming the addition of impurities and formation of point defect. The gamma irradiation creates point defects, and their density increases considerably with increasing gamma dosage. These defects crucially altered the structural, optical and electrical properties of the material. The reduction in the optical band gap with increased gamma irradiation is evident from the absorption spectra and respective Tauc plots. The I–V graphs show a 1000-fold increase in the saturation current after 100 kGy gamma irradiation dose. This work has explored the gamma irradiation effect on the WS2 and suggests substantial modification in the material and enhancement in electrical properties. [ABSTRACT FROM AUTHOR]

This paper presents an experimental investigation of irradiation-induced evolutions in three different oxide dispersion strengthening (ODS) alloys. High-dose, dual beam Ni–He ion irradiations are carried out up to 700 °C. The significant dose-dependent changes in the ODS particle size and number density are documented and interpreted in terms of specific point defect transport mechanisms, from small angle neutron scattering, TEM, and pulsed low-energy positron system measurements combined. The corresponding micro-mechanical changes in the alloys are evaluated based on the indentation response, which is, in turn, interpreted in terms of related, sub-grain plasticity mechanisms. The room temperature tests (without dwell time) reveal that the microscale work-hardening rate increases with decreasing the particle number density and pronounced strain localization effect. The elevated temperature tests (up to 600 °C, with dwell time) show that the indentation creep compliance is mostly temperature-independent after irradiation up to 25 dpa at Tirr = 500 °C and markedly temperature-dependent, after irradiation beyond 40 dpa at Tirr = 600 °C. This effect is ascribed to particular creep mechanisms associated with indent-induced plasticity, i.e., high stress and high dislocation density conditions. [ABSTRACT FROM AUTHOR]

There are several applications for irradiating materials with protons that could provide alternative methodologies to synthesize and induce the formation of new compounds of different size scales. In this study, we explored the effects of proton irradiation oncommercial glass silicate that was previously subjected to a Cu+–Na+ ion exchange (IE) treatment at 600 °C for a duration of 60 min. The ion-exchanged glass samples were irradiated with protons (p+) of 2 MeV energy at doses in the range of thousands of grays (3.3 × 103, 7.9 × 103 Gy) and hundreds of thousands of grays (3.6 × 105 Gy). Significant changes in the optical and structural properties were observed post the radiation treatment. The UV-Visible absorption spectra of the irradiated samples revealed the appearance of overlapping absorption bands, which could be deconvoluted into three Gaussian-shaped bands peaking at 566, 620 and 680 nm. These three bands could be attributed to the surface plasmon resonance (SPR) of copper nanoparticles, non-bridging oxygen hole centers (NBOHCs) and self-trapped hole (STH) defects, respectively. Prominent photoluminescence (PL) was observed in the Cu-exchanged and irradiated samples, mainly induced by the presence of both Cu+ and Cu2O. Increasing the irradiation dose led to an increase in the PL intensity due to the conversion of Cu2+ ions into Cu+. This result was confirmed by electron paramagnetic resonance (EPR) spectroscopy that shows a decrease in the Cu2+ signal when increasing the dose of proton exposure. Transmission electron microscopy (TEM) and high-resolution TEM (TEM and HRTEM) observations confirmed the presence of copper nanoparticles (CuNPs) in the doped and p+ irradiated Cu-exchanged glass silicate samples. These CuNPs were found to be crystalline with an average size of 12.39 nm. [ABSTRACT FROM AUTHOR]

Both irradiation and dislocations have been proposed as routes to rationally manipulate spatial distribution and micromorphology of precipitate. An interesting effect emerges in Fe–10at.%Cu–3at.%Mn–1.5at.%Ni–1.5at.%Al alloy due to the synergistic-competitive roles of dislocation loop and irradiation. Base on cascade mixing, vacancy-interstitial atoms and dislocation stress field model, we examine nucleation and growth dynamics of Cu-rich precipitates, where both dislocation loop and irradiation act in conjunction. Analytical treatments identify regimes, where the distribution of elements and point defects due to irradiation and dislocations are specific to the Cu-rich precipitates. Simulation results reveal that density, size and distribution of Cu-rich precipitates are a manifestation of the competing effects of the dislocation loop and the irradiation rate. More specifically, the dislocation loop preferentially assists the formation of precipitates and new dislocations at lower irradiation rates. Only the irradiation induces the formation of Cu-rich precipitates with the irradiation rate continues to increase. Equipped with molecular dynamics, where reproduces major interaction features of the solutes with point defects under displacement cascade, can verify multi-component morphologies of Cu-rich precipitates. This modeling framework provides an avenue to explore the role of dislocation loop and irradiation on the microstructural evolution of Cu-rich precipitates. [ABSTRACT FROM AUTHOR]

An experimental study on how to reduce the content of singly ionized zinc vacancy (V−Zn) in ZnGeP2 crystals to improve their optical quality is presented. Their electron paramagnetic resonance signal has been studied in samples treated in different ways. The data provide a scheme of the reductions that can be obtained by the different methods or by their combinations. The adding of Sn during the synthesis phase helps the production of large‐size single crystals and the reduction of the V−Zn content. Thermal treatment and electron irradiation are then needed for further reduction. At the fluence of 2 × 1017 e cm−2, the V−Zn decrease does not reach a minimum value, so with higher fluences, additional reduction of V−Zn content is expected. [ABSTRACT FROM AUTHOR]

Swift heavy Ta ions with an ultra-high energy of 2896 MeV are utilized for irradiation of β-Ga2O3 photodetectors. Noteworthy variations in device performance under different wavelengths are observed. Under 254 nm light illumination, the photocurrent of the devices exhibit degradation at low ion fluences but gradually recover and even surpass the performance of non-irradiated devices at the irradiation fluence of 1 × 1010 cm−2. Conversely, under 365 nm light illumination, photocurrent increases at low fluence but slightly decreases at the same high fluence of 1 × 1010 cm−2. Cathodoluminescence spectra and first-principles calculations elucidate the mechanism underlying the evolution of device performance with irradiation fluence. At low irradiation fluence, the introduction of point defects such as oxygen vacancies and gallium vacancies leads to an expansion of the bandgap, resulting in a decline in photocurrent under 254 nm light illumination. Additionally, deep defect levels are generated by these point defects, promoting an enhancement of photocurrent under 365 nm light illumination. Higher fluences transform these point defects into complex defects such as Ga–O pair vacancies, resulting in a reduction in the bandgap. Consequently, an increase in photocurrent is observed for devices illuminated with 254 nm light. However, at high irradiation fluences, charge recombination induced by the presence of deep defect levels becomes more significant, leading to a decrease in photocurrent when exposed to 365 nm light. No matter what, at 1 × 1010 cm−2 fluence, β-Ga2O3 photodetectors still maintain excellent performance, implying their strong radiation resistance and immense potential for application in space environments. [ABSTRACT FROM AUTHOR]

Among two-dimensional (2D) transition metal dichalcogenides (TMDs), MoTe2 is predestined for phase-engineering applications due to the small difference in free energy between the semiconducting H-phase and metallic 1T′-phase. At the same time, the complete picture of the phase evolution originating from point defects in single-layer of semiconducting H-MoTe2 via Mo6Te6 nanowires to cubic molybdenum has not yet been reported so far, and it is the topic of the present study. The occurring phase transformations in single-layer H-MoTe2 were initiated by 40–80 kV electrons in the spherical and chromatic aberration-corrected high-resolution transmission electron microscope and/or when subjected to high temperatures. We analyse the damage cross-section at voltages between 40 kV and 80 kV and relate the results to previously published values for other TMDs. Then we demonstrate that electron beam irradiation offers a route to locally transform freestanding single-layer H-MoTe2 into one-dimensional (1D) Mo6Te6 nanowires. Combining the experimental data with the results of first-principles calculations, we explain the transformations in MoTe2 single-layers and Mo6Te6 nanowires by an interplay of electron-beam-induced energy transfer, atom ejection, and oxygen absorption. Further, the effects emerging from electron irradiation are compared with those produced by in situ annealing in a vacuum until pure molybdenum crystals are obtained at temperatures of about 1000 °C. A detailed understanding of high-temperature solid-to-solid phase transformation in the 2D limit can provide insights into the applicability of this material for future device fabrication. [ABSTRACT FROM AUTHOR]

Validation of multiscale microstructure evolution models can be improved when standard microstructure characterization tools are coupled with methods sensitive to individual point defects. We demonstrate how electronic and vibrational properties of defects revealed by optical absorption and Raman spectroscopies can be used to compliment transmission electron microscopy (TEM) and x-ray diffraction (XRD) in the characterization of microstructure evolution in ceria under non-equilibrium conditions. Experimental manifestation of non-equilibrium conditions was realized by exposing cerium dioxide (CeO2) to energetic protons at elevated temperature. Two sintered polycrystalline CeO2 samples were bombarded with protons accelerated to a few MeVs. These irradiation conditions produced a microstructure with resolvable extended defects and a significant concentration of point defects. A rate theory (RT) model was parametrized using the results of TEM, XRD, and thermal conductivity measurements to infer point defect concentrations. An abundance of cerium sublattice defects suggested by the RT model is supported by Raman spectroscopy measurements, which show peak shift and broadening of the intrinsic T2g peak and emergence of new defect peaks. Additionally, spectroscopic ellipsometry measurements performed in lieu of optical absorption reveals the presence of Ce3+ ions associated with oxygen vacancies. This work lays the foundation for a coupled approach that considers a multimodal characterization of microstructures to guide and validate complex defect evolution models. [ABSTRACT FROM AUTHOR]

Films of α-Ga2O3 grown by Halide Vapor Phase Epitaxy (HVPE) were irradiated with protons at energies of 330, 400, and 460 keV with fluences 6 × 1015 cm−2 and with 7 MeV C4+ ions with a fluence of 1.3 × 1013 cm−2 and characterized by a suite of measurements, including Photoinduced Transient Current Spectroscopy (PICTS), Thermally Stimulated Current (TSC), Microcathodoluminescence (MCL), Capacitance–frequency (C–f), photocapacitance and Admittance Spectroscopy (AS), as well as by Positron Annihilation Spectroscopy (PAS). Proton irradiation creates a conducting layer near the peak of the ion distribution and vacancy defects distribution and introduces deep traps at Ec-0.25, 0.8, and 1.4 eV associated with Ga interstitials, gallium–oxygen divacancies VGa–VO, and oxygen vacancies VO. Similar defects were observed in C implanted samples. The PAS results can also be interpreted by assuming that the observed changes are due to the introduction of VGa and VGa–VO. [ABSTRACT FROM AUTHOR]

Films of α-Ga2O3 grown by Halide Vapor Phase Epitaxy (HVPE) were irradiated with protons at energies of 330, 400, and 460 keV with fluences 6 × 1015 cm−2 and with 7 MeV C4+ ions with a fluence of 1.3 × 1013 cm−2 and characterized by a suite of measurements, including Photoinduced Transient Current Spectroscopy (PICTS), Thermally Stimulated Current (TSC), Microcathodoluminescence (MCL), Capacitance–frequency (C–f), photocapacitance and Admittance Spectroscopy (AS), as well as by Positron Annihilation Spectroscopy (PAS). Proton irradiation creates a conducting layer near the peak of the ion distribution and vacancy defects distribution and introduces deep traps at Ec-0.25, 0.8, and 1.4 eV associated with Ga interstitials, gallium–oxygen divacancies VGa–VO, and oxygen vacancies VO. Similar defects were observed in C implanted samples. The PAS results can also be interpreted by assuming that the observed changes are due to the introduction of VGa and VGa–VO. [ABSTRACT FROM AUTHOR]

ZrN films were irradiated with 2 MeV proton and 91.3 MeV Xe ion. Our aim is to demonstrate the radiation damage tolerance of nanostructured ZrN. Uv–visible spectroscopy revealed localized surface plasmon resonance (LSPR) band at 650 nm of ZrN nanoparticles. After irradiation the LSPR band intensity increases and become larger. The band gap decreases, while Urbach energy increases indicating defect formation. It is found a better crystallinity and no swelling or contraction in the studied fluence range. Therefore, nanostructured ZrN can be used in harsh irradiation environments such as neutron reactors and aerospace without altering its structural and plasmonic properties. [ABSTRACT FROM AUTHOR]

We report here scanning tunneling microscopy (STM) observations of bridge-bonded oxygen vacancies (OVs) on the TiO2(110) surface diffusing under the influence of 266 nm ultraviolet (UV) laser irradiation. OV pairs, and even OV trimers, were formed as a result of UV light-induced OV diffusion. There are two stable STM representations of the OV-pair defects, which are inter-changeable during scanning. An extended irradiation time (68 min) can lead to the formation of a TiO2(110) surface with pre-dominant OV-pair point defects. Our results enrich the understanding of OV behavior upon UV irradiation, and future photocatalytic studies on reduced rutile TiO2(110) surfaces involving 266 nm UV light can benefit from the knowledge of the observed diffusion of OVs and the formation of OV oligomers. We also provide a plausible way to prepare an OV-pair abundant TiO2(110) surface, a requisite for further investigations of the otherwise unapproachable defects. [ABSTRACT FROM AUTHOR]

Atomic-scale defects generated in materials under both equilibrium and irradiation conditions can significantly impact their physical and mechanical properties. Unraveling the energetically most favorable ground-state configurations of these defects is an important step towards the fundamental understanding of their influence on the performance of materials ranging from photovoltaics to advanced nuclear fuels. Here, using fluorite-structured thorium dioxide (ThO2) as an exemplar, we demonstrate how density functional theory and machine learning interatomic potential can be synergistically combined into a powerful tool that enables exhaustive exploration of the large configuration spaces of small point defect clusters. Our study leads to several unexpected discoveries, including defect polymorphism and ground-state structures that defy our physical intuitions. Possible physical origins of these unexpected findings are elucidated using a local cluster expansion model developed in this work. [ABSTRACT FROM AUTHOR]

One of the proposed materials for structural application in compact high-temperature reactors (CHTRs) is Nb-1Zr-0.1C alloy. Using the Variable Energy Cyclotron at the Variable Energy Cyclotron Centre, Kolkata, Nb-1Zr-0.1C alloy was irradiated with a 160-MeV oxygen (O6+) ion up to three different doses. Emulation of neutron irradiation by ion irradiation could be achieved as the weighted recoil spectra of the oxygen ion are found to be similar to the neutron recoil spectra of CHTRs within recoil energy ranging from 100 eV to 100 keV. The irradiated materials along with one as-received sample were characterized using different X-ray diffraction line profile analyses (XRDLPAs) to systematically evaluate microstructural parameters. A decrease in the domain size with an increase in microstrain and dislocation density is observed at first dose and then found to saturate with further irradiation. An increase in the Wilkens arrangement parameter indicates the formation of less correlated dislocations (clusters) after irradiation. Transmission electron microscopy analysis of as-received and highest-dose samples shows the formation of densely populated defect clusters after irradiation. Nanohardness increased after irradiation due to pinning of the dislocation movement by point defects and defect clusters/loops, as well as carbides in the matrix. The results extracted from the XRDLPAs are compared with our earlier studies of light ion–irradiated (H+) Nb-1Zr-0.1C alloy and oxygen-irradiated pure Nb to understand the effect of the type of ion and the alloying elements, respectively, on the evolution of the microstructure. It may be concluded that changes in dose and dose rate affect the movement of point defects toward sinks. Hence, possible correlated dislocation formation is observed in light ion–irradiated Nb alloy, but correlation is found to decrease with dose for heavy ion–irradiated Nb alloy. On the other hand, the presence of finely dispersed carbides restricts the formation of dislocation loops by making complexes with the defects in heavy ion (O6+)–irradiated Nb-1Zr-0.1C alloy, which is in contrast to pure Nb irradiated using the heavy ion (O6+) in a similar environment. [ABSTRACT FROM AUTHOR]

In a fusion environment, tungsten, a plasma-facing material in a reactor, is subject to the irradiation of high-energy neutrons, generating a large amount of displacement damage and transmutation products (such as rhenium, Re). We studied the evolution of defects under irradiation in W and W-Re systems using the density functional theory (DFT) and rate theory (RT) method. The results indicate that the evolution of irradiation defects is mainly affected by the irradiation dose, dose rate, and temperature. During irradiation, loops form first in W, followed by the generation of voids, which are due to the different migration energies of point defects. Higher dose rates result in a higher density and larger size of defects in tungsten. Higher temperatures cause a decrease in void density and an increase in size. The results obtained at 600 °C were in good agreement with the reported TEM data. In W-Re alloys, it is indicated that the formation of loops is delayed because Re suppresses the nucleation of loops. The dynamic introduction of Re in W stabilizes the growth of defects compared to W-Re alloys, suggesting that transmuting elements have less detrimental effects on irradiation than alloying. As defect densities and sizes were quantified under different irradiation conditions, the results provide data for the multi-scale simulation of the radiation damage and thermal/mechanical properties in plasma-facing materials under fusion conditions. [ABSTRACT FROM AUTHOR]

Modern X-ray free-electron lasers (XFELs) produce intense femtosecond X-ray pulses able to cause significant damage to irradiated targets. Energetic photoelectrons created upon X-ray absorption, and Auger electrons emitted after relaxation of core-hole states trigger secondary electron cascades, which contribute to the increasing transient free electron density on femtosecond timescales. Further evolution may involve energy and particle diffusion, creation of point defects, and lattice heating. This long-timescale (up to a microsecond) X-ray-induced dynamics is discussed on the example of silicon in two-dimensional geometry. For modeling, we apply an extended Two-Temperature model with electron density dynamics, nTTM, which describes relaxation of an irradiated sample between two successive X-ray pulses, emitted from XFEL at MHz pulse repetition rate. It takes into account ambipolar carrier diffusion, electronic and atomic heat conduction, as well as electron-ion coupling. To solve the nTTM system of equations in two dimensions, we developed a dedicated finite-difference integration algorithm based on Alternating Direction Implicit method with an additional predictor-corrector scheme. We show first results obtained with the model and discuss its possible applications for XFEL optics, detectors, and for diagnostics tools. In particular, the model can estimate the timescale of material relaxation relevant for beam diagnostic applications during MHz operation of contemporary and future XFELs. [ABSTRACT FROM AUTHOR]

This study aims to learn more about the structure of densified silica with focus on the metamict-like silica phase (density = 2.26 g/cm3) by examining the formation of E' point defects and interstitial molecular oxygen O2 by 2.5 MeV electron irradiation. High-dose (11 GGy) irradiation creates a metamict-like phase and a large amount of interstitial O2, which is destroyed upon subsequent additional lower-dose electron irradiation. The O2 cathodoluminescence (CL) data indicate that the formation of O2 from peroxy linkages Si–O–O–Si in silica network is strongly dependent on the intertetrahedral void sizes. The position and shape of the O2 emission line support the idea that the configuration of these voids in metamict phase is close to that of non-densified silica. Moreover, data support the strong correlation between the formation of 3-membered rings of Si–O bonds and E'-centers when silica density increases from 2.20 to 2.26 g/cm3. [ABSTRACT FROM AUTHOR]

We investigated the nature, optical properties, and decay kinetics of point defects causing large transient attenuation increase observed in silica-based optical fibers exposed to short duration and high-dose rate x-ray pulses. The transient radiation-induced attenuation (RIA) spectra of pure-silica-core (PSC), Ge-doped, F-doped, and Ge + F-doped optical fibers (OFs) were acquired after the ionizing pulse in the spectral range of [∼0.8–∼3.2] eV (∼1500–∼380 nm), from a few ms to several minutes after the pulse, at both room temperature (RT) and liquid nitrogen temperature (LNT). Comparing the fiber behavior at both temperatures better highlights the thermally unstable point defects contribution to the RIA. The transient RIA origin and decay kinetics are discussed on the basis of already-known defects absorbing in the investigated spectral range. These measurements reveal the importance of intrinsic metastable defects such as self-trapped holes (STHs), not only for PSC and F-doped fibers but also for germanosilicate optical fibers as clearly evidenced by our LNT measurements. Furthermore, our results show that fluorine co-doping seems to decrease the RIA related to the strain-assisted STHs absorption bands in both types of optical fibers. Regarding Ge-doped glasses, besides a description of the defects responsible of the RIA, highlighting the STHs' role in their transient response, we provide a clear correlation between the GeX and GeY centers' kinetics. In conclusion, the presented results improve our understanding of the transient RIA origin in the ultraviolet and visible domains. The lack of knowledge about the defects causing the RIA in the near-infrared domain will require future studies. [ABSTRACT FROM AUTHOR]

The crystal orientation effect on the mechanical properties and micro-deformation behavior of single-crystal iron (SC Fe) were revealed by molecular dynamics (MD) simulations. The results show that the surviving defects in the SC Fe models are [110] < [100] < [111], and only the vacancy and interstitial atomic clusters are formed in the [111] SC Fe model. Irradiation leads to the increase of elastic modulus owing to the annihilation of irradiation point defects. However, the non-annihilable irradiation clusters reduced the strength. The decrease of yield strain and yield strength of the [111] SC Fe model is significantly higher than those of [110] and [100] SC Fe models, exhibiting worse radiation damage resistance. This is due to the number and types of operation of slip systems in the [110] and [100] SC Fe after irradiation, which is caused by its poor inhibition of [111] crystal orientation on clusters under irradiation, being much lower than those in the [111] SC Fe. The yield strength of SC Fe increases with the increase of the number and length of 1/2 111 and 100 dislocations, while the plasticity decreases with the increase of the falling gradient of dislocations after yield. The purpose is to provide theoretical guidance for the microstructure design and regulation of radiation-damage-resistant iron-based materials. [ABSTRACT FROM AUTHOR]

A comprehensive statistical treatment is conducted to analyse the outcomes of MD simulations of collision cascades in α-titanium in a wide range of primary knocked-on atoms (PKAs) energy 5 keV 25 keV and irradiation temperature 100 K 900 K. The fractions of vacancies and interstitial atoms in clusters of point defects formed in individual cascades and their average values and , the average sizes of vacancy and interstitial clusters, and the average number of vacancy and interstitial clusters per cascade are evaluated. The physical mechanisms that determine the dependence of , , , , , and on simulation parameters have been proposed. [ABSTRACT FROM AUTHOR]

The authors previously discovered a new optoplastic effect and observed it under the action of a nanosecond UV laser pulse irradiation of subcritical intensity. In this paper it is shown that under this effect no micropores arise in the subsurface layer of metal. This proves the statement that swelling of metal under laser impact of moderate (subcritical) intensity occurs due to interstitial atoms migrating to the surface and not due to melting with formation of bubbles. At a abrupt cooling (for ~20 μs) interstitial atoms migrate to the surface by the Schottky mechanism due to abnormal mass transfer and the less mobile vacancies have no time to coagulate with formation of micropores in the time of the process. [ABSTRACT FROM AUTHOR]

The authors modified BaSO 4 powders with SiO 2 nanoparticles and studied the effect of this modification on powders' structure and optical properties, as well as on the changes of the latter after 5 keV proton irradiation. No significant post-modification changes in structure have been observed. In the IR-spectrum, the authors have recorded the band intensity changes for SiO 2 , Si – O – Si, and Si–Si vibrations, as well as emerging OH group vibration band. Additionally, the authors have noted the appearance of an absorption band in the UV/vis spectra caused by intrinsic point defects in BaSO 4 anionic sublattice. The energy losses induced by displacement and ionization were calculated, as were the proton free paths in the modified powder. It is shown that an increase of radiation stability is provided by solely 1.2% of the proton energy flux absorbed in the nSiO 2 nanolayer contributing to the total energy loss in the entire modified powder. Two mechanisms are proposed for the processes occurring in the nSiO 2 /mBaSO 4 system that determine the increase of its radiation stability compared with the non-modified powder. [ABSTRACT FROM AUTHOR]

We readdress the nature and creation mechanism of the defects absorbing at 4.7 eV in Swift Heavy Ion (SHI)-irradiated AlN semiconductor. Irradiations are performed in different controlled atmospheres (vacuum, oxygen, helium or argon partial pressure) to investigate the coupled effects of (i) the synergy between electronic excitations (S e) and nuclear collisions (S n) for point defect creation and (ii) SHI-induced impurity introduction/diffusion into the AlN layer. We found that the synergy, previously reported, between S e and S n for defect formation must also be related to the presence of oxygen during irradiation. At the same S e , the synergy parameter is indeed increased by up to two orders of magnitude during irradiation under O 2 compared to irradiation under vacuum. By SHI irradiation and by a fine-tuning of the irradiation atmosphere, we then control the activation or inhibition of these light-emitted point defects (oxygen-vacancy complexes) which can be used as qubits for applications in quantum computing. [ABSTRACT FROM AUTHOR]

In our work, the model of self-consistent electron–deformation–diffusion effects in thin films grown on substrate with the mismatch of lattice parameters of the contacting materials is constructed. The proposed theory self-consistently takes into account the interaction of the elastic field (created by the mismatch of lattice parameters of the film and the substrate, and point defects) with the diffusion processes of point defects and the electron subsystem of semiconductor film. Within the framework of the developed model, the spatial distribution of deformation, concentration of defects, conduction electrons and electric field intensity is investigated, depending on the value of the mismatch, the type of defects, the average concentrations of point defects and conduction electrons. It is established that the coordinate dependence of deformation and the concentration profile of defects of the type of stretching (compression) centers, along the axis of growth of the strained film, have a non-monotonic character with minima (maxima), the positions of which are determined by the average concentration of point defects. It is shown that due to the electron–deformation interaction in film with a lattice parameter mismatch, the spatial redistribution of conduction electrons is observed and n-n+ transitions can occur. Information about the self-consistent spatial redistribution of point defects, electrons and deformation of the crystal lattice in semiconductor materials is necessary for understanding the problems of their stability and degradation of nano-optoelectronic devices operating under conditions of intense irradiation. [ABSTRACT FROM AUTHOR]

Atomically thin transition metal dichalcogenides (TMDs), like MoS2 with high carrier mobilities and tunable electron dispersions, are unique active material candidates for next generation opto-electronic devices. Previous studies on ion irradiation show great potential applications when applied to two-dimensional (2D) materials, yet have been limited to micron size exfoliated flakes or smaller. To demonstrate the scalability of this method for industrial applications, we report the application of relatively low power (50 keV) 4He+ ion irradiation towards tuning the optoelectronic properties of an epitaxially grown continuous film of MoS2 at the wafer scale, and demonstrate that precise manipulation of atomistic defects can be achieved in TMD films using ion implanters. The effect of 4He+ ion fluence on the PL and Raman signatures of the irradiated film provides new insights into the type and concentration of defects formed in the MoS2 lattice, which are quantified through ion beam analysis. PL and Raman spectroscopy indicate that point defects are generated without causing disruption to the underlying lattice structure of the 2D films and hence, this technique can prove to be an effective way to achieve defect-mediated control over the opto-electronic properties of MoS2 and other 2D materials. [ABSTRACT FROM AUTHOR]

We report on the nature of charge-neutral exciton emission decay, exciton-trion conversion as well as their phonon coupling in exfoliated WSe2 nanosheets subjected to ~ 1.3 MeV energetic γ-photons. Steady-state photoluminescence (PL) spectra, upon deconvolution, showed prominent emission peaks at ~ 680 nm, ~ 712 nm, and ~ 730 nm and ascribed to 2s, and 1s excitons and trions respectively, while the chalcogen vacancy (VSe) mediated defect emission peak found at ~ 790 nm. From the X-ray photoelectron spectroscopy (XPS) analysis, we noticed a clear shifting of the fundamental peaks due to W and Se toward higher binding energy values and were attributed to the radiation-induced alteration in the oxidation states locally, taking advantage of the manifestation of point defects/vacancies. Moreover, the time-resolved PL spectra signify an anomalous variation in the fast parameter (0.4–0.86 ns), and with slow parameter (2.46–3.82 ns) getting slower with increasing γ-dose. A slight variation in the exciton-phonon coupling factor is noted with Se-ph < 1 indicating a weaker interaction and featuring maximal envelope over all the phonon replica near the zero-phonon line. In contrast, trion-phonon coupling factor, St-ph > 1, or < 1 depending on its spin degeneracy (ζ = 2 s + 1; with 2, for s = 1/2 and 4 for s = 3/2). The highest St-ph value determined was ~ 1.82 ± 0.2 which declines monotonically with increasing dose but remained greater than unity up to a γ-dose as high as 96 kGy. The implication of trion-phonon coupling has immense scope in nano-photovoltaics, and nano-electronics as well as heat sinks in nanogenerators. [ABSTRACT FROM AUTHOR]

• Dependence of crystallite size and morphology of nanocrystalline ZnO on synthesis temperature. • Defect dominated photoluminescence spectra and its assignment. • Dependence of photocurrent response on crystallite size and its wavelength dependence. • Dependence of photocatalytic activity and reuse on crystallite size. Nanocrystalline zinc oxide (ZnO) samples are synthesized through a facile hydrothermal route at different temperatures. Sample synthesized at 80 °C (sample code HT80) has average crystallite size of 32 ± 2 nm and the morphology is not unform with the presence of rods, wires and discs. Sample prepared at 160 °C (sample code HT160) has rod-like morphology with an average crystallite size of 130 ± 5 nm. X-ray photoelectron spectra reveal the presence of hydroxyl groups bonded to Zn2+, oxygen vacancies and adsorbed oxygen species in both the samples. Atomic percentage of the bonded/adsorbed hydroxides and oxygen containing species is higher in HT80. Band gaps values are lower in comparison with bulk ZnO due to band bending. Photoluminescence spectra has a UV peak at ∼381 nm (3.25 eV) and a broad emission band in the visible region centred at ∼550 nm (2.25 eV) respectively corresponding to the band edge emission and defect mediated emission. The emission profile of both samples is similar indicating the presence of similar type of native point defects viz., Zn vacancies, Zn interstitials and oxygen vacancies in different charge states. Sample HT160 has more intense emission due to the better photonic absorption. The photocurrent response under wide light irradiation is also larger for HT160 with a sensitivity of 37 due to the better photonic absorption and larger crystallite size. Wavelength dependent photocurrent response for this sample shows highest sensitivity at 380 nm with a sensitivity of 152 corresponding to the band-to-band excitation. A weak photoresponse for visible light irradiation (∼600 nm) due to the desorption of adsorbed O 2 or hydroxide species caused by the direct photoexcitation of the captured electron to the conduction band is also noted. Photocatalytic efficiency of both the samples are comparable with rate constants 3.1 × 10−2 min−1 and 3.7 × 10−2 min−1 respectively for HT80 and HT160. The reusability is much better for sample HT160 which is attribute to larger average crystallite size and uniform morphology. [ABSTRACT FROM AUTHOR]

We have studied the formation of color centers in magnesium aluminate spinel (MgAl2O4) by X-ray and electron irradiations near room temperature (RT). For this purpose, Cu Kα radiation and three electron energies (1.0, 1.4, and 2.5 MeV) were used for variable fluences (up to 4.2 × 1018 cm−2). Off-line UV-visible absorption spectra were recorded at RT as well as at low temperature down to 27 K after electron irradiation. The dependence of the production rate of F centers (oxygen vacancies) on the electron energy yields a threshold displacement energy of 190 ± 10 eV for oxygen atoms at RT, which is much higher than the determinations by molecular-dynamics simulations. Such a discrepancy is discussed on the basis of available migration data of point defects in spinel. Equipartition of F0 and F+ centers, i.e., the neutral (VOx) and singly ionized (VO.) oxygen vacancies, is reached for high electron fluences. Moreover, the evolution of the width of color-center absorption bands versus temperature is interpreted with the classical theory for F centers (neutral halogen vacancies) in alkali halides. The Stokes shifts are deduced from the temperature dependence of the absorption bandwidths of color centers like for alkali halides and alkaline-earth oxides. Finally, isothermal annealing data for long annealing time show a non-zero asymptotic behavior for both F0 and F+ centers. This uncommon behavior is interpreted by charge exchange processes leading to an equilibrium state between those two color centers. [ABSTRACT FROM AUTHOR]

The effect of fast cluster irradiation on the formation of fibrous structures is investigated for single crystal GaSb surfaces irradiated by Cun+ ions (n =1–3) with an energy of 0.4 MeV/atom at ion fluences up to 5 × 1015 cm−2. We study the cluster size dependence on the growth of fibrous network structures. With increasing cluster size, the shape of the fiber changed from rod-like to spherical. To quantitatively evaluate this cluster effect, a fiber diameter d in rod or spherical portion is examined as a function of ion fluence Φ and cluster size n. We find that the fiber diameter nonlinearly increases and follows the relation d ∝ n α × Φ , with α ≈ 2. This evidently implies that the amount of defects generated by n-sized cluster bombardments varies as n 2 for n ≤ 3. Cluster ion irradiation enhances the defect generation owing to the overlap between cascades of individual cluster constituents and is therefore effective for the growth of nanofibers. [ABSTRACT FROM AUTHOR]

Radiation damage in the nuclear structural components is a stochastic phenomenon in both length and time scales. In this work, molecular dynamics-based numerical simulations were employed to model and investigate the primary radiation damage within irradiated Cu specimens. Here, a single-crystal Cu specimen and two nanocrystalline specimens: hexagonal columnar grain Cu specimen with ∑3 and ∑9 GBs (CG Cu) and Cu specimen randomly oriented grain boundary (GBs) (RG Cu), were irradiated at 600 K at primary knock-on atom (PKA) energy magnitudes, EPKA = 10 keV, 20 keV, 30 keV, respectively. The equilibrium part of the long-range Finnis–Sinclair (FS)-type interatomic potential was smoothly conjoined with the universal short-range repulsive Ziegler–Biersack–Littmark potential to account for simulations of high-energy collisions. By investigating the evolution of point defects, defect cluster distribution, and dislocation analysis, it was observed that the irradiated nanostructured Cu specimens survived with comparatively lower defects at the end of cascade simulations. GB serves as the effective radiation sink junctions for the generated Frenkel pair defects. Secondly, the population of point defects increases with the increase in PKA energy magnitude and the annihilation rate. Therefore, polycrystalline irradiated Cu specimens can be favoured for potential radiation immune candidate in the next-generation nuclear reactor structural materials. [ABSTRACT FROM AUTHOR]

The composition, structure, and diffuse reflectance spectra of ZnO powder modified with SiO2 nanoparticles have been investigated in the range of 0.2−2.2 μm and in the IR range together with the radiation stability under irradiation with electrons at 30 keV and fluence up to 9∙1016 cm−2. It has been found that after modification and irradiation, new compounds are not formed, the intensity of some bands in the IR spectra decreases, and the reflectivity in the range from 0.4 to 2.2 μm decreases. An absorption band appears in the visible range with a maximum at 420 nm caused by intrinsic ZnO point defects; its intensity increases with increasing electron fluence. After irradiation, the induced absorption appears in the near-IR range due to free electrons. A comparison with unmodified ZnO powder showed the effectiveness of modification to increase the radiation stability. [ABSTRACT FROM AUTHOR]

Mechanical exfoliation assisted by gold is applied to obtain good quality large lateral size single‐layer MoS2. The effects of 2.5 MeV electron irradiation are investigated at room temperature on structural and electronic features by Raman and microluminescence spectroscopy. The exciton recombination emission in the direct bandgap of single‐layer MoS2 is affected during irradiation starting from the minimum explored dose of 1 kGy. At higher doses, Raman bands show no relevant modifications whereas the exciton emission is quenched, suggesting that irradiation‐induced point defects affect exciton dynamics. [ABSTRACT FROM AUTHOR]

This paper examined the impact of the isotope effect on the lattice structure of monocrystalline silicon, as well as the defects caused by proton irradiation. First, by using the molecular dynamics simulation, the number of point defects of monocrystalline silicon exposed to protons was calculated, and the number of stable defects in 30Si was 11%–14% lower than that in 28Si. Second, the structures of various isotopes at 300 K were simulated through ab initio molecular dynamics simulations based on the density functional theory. In addition, the thermal stability of the two structures was determined. The results indicated that pure 30Si had superior radiation resistance to pure 28Si, which suggested a new idea for the radiation resistance enhancement of silicon materials. [ABSTRACT FROM AUTHOR]

Atomic configurations and activation energies for diffusion of point defects and point defects clusters are important elements to consider when predicting the microstructural evolution of zirconium-based materials under irradiation. Using Density Functional Theory (DFT) we performed molecular dynamics (MD) calculations to determine the diffusion coefficient of self-interstitials (SIA) clusters containing up to three atoms in the hexagonal close packed (hcp) structure of zirconium. The calculated values of the activation energy for single SIA diffusion are in line with previous DFT studies performed with accurate constrained minimization techniques, which validates the adopted methodology. Diffusion in the basal plane is similar for mono-, di- and tri-SIAs but diffusion along the c → axis is significantly slowed down by the addition of SIA. Quantitative differences with existing empirical potential results highlight the usefulness of the ab initio MD calculations reported in this work. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • A technique for identifying the grain boundary regions in irradiated nano-crystalline configurations has been developed. • The production efficiency of interstitials is significantly lower in nano-crystalline HEA FeCoCrNi/Ni than in their single- crystalline counterparts. • Most defect clusters in irradiated nano-crystalline materials comprise 1/2 〈1 1 0〉 stair-rod dislocation lines. • The nano-crystalline-HEA FeCoCrNi effectively prevents the formation of harmful large defect clusters. Because of remarkable irradiation resistance and mechanical properties, high entropy alloys (HEAs) are expected to be a candidate structural material in the next-generation nuclear power plants. Besides, the nano-crystalline (NC) materials also exhibit excellent radiation tolerance and good thermal stability. The NC-HEAs may have superior irradiation resistance than both NC and HEA materials. However, how the irradiation-resistant effects of HEAs and grain boundary (GB) jointly affect the irradiation damage evolution in NC HEAs is an interesting but rarely reported topic. Considering these, the present work investigated the irradiation defect production and accumulation characteristics in NC-HEA FeCoCrNi and NC-Ni by cascade overlapping simulations. The evolution of irradiation clusters within NC grains was quantitatively analyzed for the first time using a newly developed method. The results show that the irradiation defects produced in NC-HEA are more diminutive and uniformly distributed than those in NC-Ni with a similar irradiation dose despite the total number of survived point defects being very close in the two cases. Further investigation shows that such a better irradiation resistance of NC-HEA can be attributed to the synergy between the severe lattice distortion effect in HEAs and the interstitial sink effect of GBs in NC. The present study may provide some fundamental understanding of the irradiation defect evolution mechanisms for the novel HEAs that potentially serve as structural materials in advanced reactors. [ABSTRACT FROM AUTHOR]

Grain boundaries play a significant role during deformation and can exhibit both beneficial and adverse effects on deformation behaviour during irradiation. For instance, macroscopic irradiation growth is increased by the presence of a high density of grain boundaries. Grain boundaries can act as sinks for point defects and barriers to dislocation motion. Thus, a mechanistic assessment of the impact of grain boundaries is essential for better understanding irradiation-induced deformation. The interplay between irradiation-induced microstructure and mechanical properties has been an area of research for many decades, but many uncertainties remain. In the present work, the deformation fields adjacent to grain boundaries in pure zirconium are investigated by using high angular resolution electron backscatter diffraction (HR-EBSD) after a period of irradiation growth. It is observed that the extent of grain boundary deformation is associated with the crystallographic orientation difference between adjacent grains. High-angle grain boundaries function as a deformation constraint, whereas a significant grain boundary migration occurs at some low-angle grain boundaries, which likely act as an active diffusion path for the irradiation-induced point defects. In addition, the change in residual strain fields associated with the irradiation damage is quantified with respect to a non-irradiated reference. A net change in the state of residual elastic strain in the order of ∼ 10 − 3 has been estimated for ∼8 dpa proton irradiation. Furthermore, the origin of residual elastic strain and lattice misorientation concentration along (0002) traces are discussed. [Display omitted] [ABSTRACT FROM AUTHOR]

Aiming to simulate the radiation damage effect on a dual α+β phase Ti-6Al-4V alloy utilized as high-intensity accelerator beam window material, a series of irradiation experiments were conducted with a 2.8 MeV-Fe2+ ion beam in several dpa regions at room temperature. The nano-indentation hardness increased steeply at 1 dpa and unchanged up to 10 dpa, due to the saturation of defect clusters and tangled dislocations in the dominant α-phase matrix with a size of 2–3 nm and a density of about 1×1023 m−3. In contrast in the intergranular β-phase, larger loops of 20–30 nm diameter were observed with much less density of about 5×1020 m−3. The diffraction pattern showed rectilinear diffuse streaks between the β-phase reflections, corresponding to the ω-phase precursor, without dose dependency in its intensity. FFT/I-FFT analysis of the HREM revealed a sub-nanometer-sized lattice disorder with local fluctuations, not discrete but continuous, and homogeneously distributed within the matrix β-phase stably against the irradiation. The significantly low dislocation density and the absence of phase transformation in the β-phase matrix could be attributed either to the strong sink effect expected for this distinctive sub-nanometer-sized homogeneous lattice disorder or to the anomalous point defect recombination induced by the high mobility of vacancies, both of which are originated from the metastable ω-phase precursors specifically formed in the β(BCC) phase of group-4 transition metals. [Display omitted] • Fe2+ ion irradiation on α+β phase Ti-6Al-4V at RT for accelerator beam windows. • Hardness increment at 1 dpa due to tiny defect cluster saturation in dominant α phase. • A few ten nm dislocations in β-phase were fewer by orders even at 10 dpa. • Homogeneous sub-nanometer-sized lattice disorder of ω-phase precursor in β-phase. • Strong sink effect or anomalous point defect recombination due to ω-phase precursor. [ABSTRACT FROM AUTHOR]

Experimental investigations are carried out on Fe65Ni35 invar alloy after irradiation with copper ions (Cu++) with 2 MeV energy in a fluence range of 1 × 1014–5 × 1015 ions/cm2. The effect of ion irradiation is studied on various parameters and material properties such as structure, lattice parameters, crystallite size, lattice strain, dislocation density, electrical resistivity, thermal properties like Debye temperature, mean square amplitude of vibration, temperature factor and micro-hardness. All irradiated samples exhibit the same single fcc phase found in the un-irradiated reference sample. The lattice parameter of Cu++-irradiated samples decrease as compared to the un-irradiated reference sample indicating the formation of point defects. On the other hand, the lattice strain of Cu++-irradiated samples increases with increasing ion fluence and is found greater than the un-irradiated sample. This is attributed to defect formation as they produce localized strain in the region around defects. The crystallite size of Cu++-irradiated samples shows a minor deviation from the un-irradiated reference. Furthermore, the dislocation density of Cu++-irradiated samples also shows a minor shift from the un-irradiated reference sample values. Similar trends are observed in electrical resistivity, thermal conductivity and micro-hardness properties of the alloy after Cu++ irradiation treatment. The modifications produced as a result of Cu++ irradiation finds applications in various industries needing high-strength materials including aeronautic and aerospace industry. [ABSTRACT FROM AUTHOR]

For the Fe–9 at.% Cr alloy, radiation-induced segregation is simulated in the model based on the first and second Fick’s laws with inverse Kirkendall effect considered. The governing quantitative characteristics of radiation-induced segregation are systematized and calculated. Such characteristics include the following: concentration profiles of Cr atoms and point defects, surface concentration of Cr atoms, the value of surface enrichment (depletion) of Cr atoms, the full width of the concentration profile of Cr atoms at half maximum enrichment (depletion), segregation area of Cr and discriminant of radiation-induced segregation of Cr atoms in a steady state. The effect of the Fe–9 at.% Cr alloy dislocation subsystem on the specified characteristics of radiation-induced segregation is studied due to the absorption of nonequilibrium point defects. The dislocation subsystem is shown to suppress the effects of radiation-induced segregation. The concentration profiles of Cr atoms and point defects at the selected values of dislocation densities in the alloy dislocation subsystem (0, 1012 m−2, 1014 m−2, 1016 m−2) are calculated. For the values of dislocation densities, the dependence of the surface enrichment of Cr atoms on the irradiation dose increased from 10−4 dpa to 10² dpa is studied and the dependences of the governing quantitative characteristics of radiation-induced segregation on temperature changed from 250°С to 650°С are analysed. [ABSTRACT FROM AUTHOR]

Replacement of conventional Zircaloy fuel cladding with silicon carbide (SiC) fuel cladding is expected to significantly decrease the amount of hydrogen generated from fuel claddings by the reaction with steam during severe accidents. One of their critical issues addressed regarding practical application has been hydrothermal corrosion. Thus, the corrosion resistant coating technology using a Ti-Cr multilayer was developed to suppress silica dissolution from SiC fuel cladding into reactor coolant under normal operation. The effect of radiation on adhesion of the coating to SiC substrate and its microstructure characteristics were investigated following Si ion irradiation at 573 K up to 3 dpa for SiC. Measurement of swelling in pure Ti, pure Cr and SiC revealed that the maximum inner stress attributed to the swelling difference was generated between the coating and SiC substrate by irradiation of 1 dpa. No delamination and cracking were observed in cross-sectional specimens of the coated SiC irradiated up to 3 dpa. According to analyses using transmission electron microscopy, large void formation and cascade mixing due to irradiation were not observed in the coating. The swelling in the coating at 573 K was presumed to be caused by another mechanism during radiation such as point defects rather than void formation. [ABSTRACT FROM AUTHOR]

We present a study of the modifications of the electronic properties of β-gallium oxide crystals by 2.5-MeV electron irradiation. This type of irradiation produces exclusively local point defects in Ga2O3, predominantly gallium vacancies, which act as acceptor centers. Starting with a highly n-doped sample, we establish a quantitative linear relation between the irradiation dose and the concentration of generated acceptor centers. This gives the possibility to tune the Fermi level position within the bandgap by choosing an appropriate irradiation dose. At high doses, with a very deep position of the Fermi level, the n-type sample becomes compensated, reaching a semi-insulating state. The downward shift of the Fermi level with irradiation allows us to reveal the presence of latent impurities of transition metals (like Cr and Fe), which are inactive in electron paramagnetic resonance and luminescence spectra of pristine samples. This study confirms the potential of electron irradiation as a tool for tailoring the electronic properties of gallium oxide. [ABSTRACT FROM AUTHOR]

In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reaction of the GLPC with molecular oxygen. Such investigations suggested the stability of the dioxagermirane (DIOG) bulk defect, and its back conversion into GLPC with a local release of O2 under irradiation. Furthermore, it is also inferred that a remarkable portion of the O2 passivated GLPC may form Ge tetrahedra connected to peroxy bridges. Such structures may have a larger resistance to the irradiation and not be back converted into GLPC. [ABSTRACT FROM AUTHOR]