Irradiation-induced Structural Changes Research Articles

Structural modification mechanism of Fe-based amorphous alloys by high-energy particle irradiation

High-energy particle irradiation-induced crystallization technology presents remarkable potential for precise nanostructure design. However, the fundamental mechanism behind this process remains a long-standing unsolved puzzle. In this paper, we used a high-energy electron beam as the irradiation source and amorphous Fe85B15 alloy as a model system to investigate the behavior of irradiation-induced structural changes. Our experimental results show that the nucleation barrier in irradiation-induced crystallization ranges from 0.5 to 0.8 eV, depending on the temperature, much smaller than that observed in thermal-induced crystallization. Additionally, the nucleation entropy observed is −1.60 × 10−3 eV/K, and the entropic contribution to the nucleation barrier dominates over the enthalpic contribution. This paper provides compelling experimental evidence demonstrating that nucleation in irradiation-induced crystallization is not a thermally activated effect; instead, it is a process in which the amorphous state progresses through a series of intermediate short-range ordering configurations toward a crystalline state with the assistance of irradiation-induced atomic rearrangement.

Influence of the Change of Phase Composition of (1 - x)ZrO2-xAl2O3 Ceramics on the Resistance to Hydrogen Embrittlement.

The article describes the influence of the change in the phase composition of ceramics on the stability of the crystal structure and retention of thermo-physical parameters during hydrogenation of the surface layer in the proton irradiation process. The selection of irradiation conditions allows modeling the degradation processes of ceramics associated with gas swelling during hydrogenation, as well as revealing the patterns of the effect of phase composition on embrittlement, de-strengthening, and structural degradation resistance. In the course of the conducted studies, dose-dependencies of irradiation-induced structural changes and consecutive accumulation of radiation-induced damage in ceramics as a result of hydrogenation of the damaged near-surface layer were established. It was found that the maximum structural changes are observed at doses above 1015 protons/cm2. Dependencies of the change in the degree of structural order as a function of the dose of accumulated damage and the concentration of accumulated protons were obtained. It was established that the variation of the ceramics phase composition due to the formation of solid solutions of ZrO2/Al2O3 and ZrO2/Al2O3/AlZr3 type leads to an enhancement of resistance to swelling by 3-5 times in comparison with monoclinic ZrO2 ceramics. The general analysis of the variation of strength and thermo-physical parameters of ceramics as a function of irradiation fluence for ceramics with different phase compositions showed a direct dependence of the decrease in hardness, resistance to cracking, and thermal conductivity on the concentration of deformation structural distortions caused by irradiation.

New measurement system based on small-angle neutron scattering for structural analysis of light-responsive materials

With the increasing importance of light-responsive materials, it is vital to analyze the relationship between function and structural changes induced by light irradiation. Small-angle scattering (SAS) is effective for such structural analysis. However, quantitatively capturing local molecular structure formation and molecular reactions at a scale of less than 1 nm via SAS is difficult. In this study, to analyze the structure of non-equilibrium phenomena in light-responsive materials, a new sample environment has been developed for a time-of-flight small- and wide-angle neutron scattering instrument (TAIKAN), comprising a UV–Vis irradiation system, UV–Vis absorption measurement equipment and photodetector. Simultaneous measurement of small-angle neutron scattering and UV–Vis absorption was achieved. This system was used to demonstrate the in situ observation of UV–Vis irradiation-induced structural change of micelles formed by 4-butylazobenzene-4′-(oxyethyl)trimethylammonium bromide, which is a light-responsive surfactant, in an aqueous solution. The results showed that the present measuring system provides direct information on the interplay between changes in micelle structure and changes in molecular configuration.

Anomalous structural phase transformation in swift heavy ion-irradiated δ-Sc4Hf3O12

Swift heavy ion irradiation was carried out to examine the ionization effects on structural changes of δ-Sc4Hf3O12 in which oxygen vacancies are regularly arranged. The specimens were irradiated at room temperature with 92 MeV xenon ions to fluences ranging from 3 × 1012 to 1 × 1014/cm2 and characterized by grazing (glancing) incidence x-ray diffraction, transmission electron microscopy, and scanning transmission electron microscopy. It was found that the pristine long-range ordered rhombohedral δ-phase undergoes a reconstructive transformation toward a long-range disordered cubic oxygen-deficient fluorite phase promoted by ionization effects. In addition, an ordered phase with a short-range structure different from the δ-type was formed in a layer going from the surface to a depth of ∼4.5 μm in the specimen irradiated to a fluence of 1 × 1014/cm2. It was found that the ordered phase is formed from the disordered cubic fluorite phase. This structural change is anomalous, because it is the opposite process of the usual irradiation-induced structural change, the order-to-disorder phase transformation. Electron diffraction experiments revealed that short-range ordered regions in this layer possess an oxygen-excess bixbyite organization (C-type heavy rare-earth oxides) with randomly filled anion vacant sites to account for the different stoichiometry and a long-range average oxygen-deficient fluorite phase.

Hyperstoichiometric Uranium Dioxides: Rapid Synthesis and Irradiation-Induced Structural Changes.

Uranium dioxide (UO2), the primary fuel for commercial nuclear reactors, incorporates excess oxygen forming a series of hyperstoichiometric oxides. Thin layers of these oxides, such as UO2.12, form readily on the fuel surface and influence its properties, performance, and potentially geologic disposal. This work reports a rapid and straightforward combustion process in uranyl nitrate-glycine-water solutions to prepare UO2.12 nanomaterials and thin films. We also report on the investigation of the structural changes induced in the material by irradiation. Despite the simple processing aspects, the combustion synthesis of UO2.12 has a sophisticated chemical mechanism involving several exothermic steps. Raman spectroscopy and single-crystal X-ray diffraction (XRD) measurements reveal the formation of a complex compound containing the uranyl moiety, glycine, H2O, and NO3- groups in reactive solutions and dried combustion precursors. Combustion diagnostic methods, gas-phase mass spectroscopy, differential scanning calorimetry (DSC), and extracted activation energies from DSC measurements show that the rate-limiting step of the process is the reaction of ammonia with nitrogen oxides formed from the decomposition of glycine and uranyl nitrate, respectively. However, the exothermic decomposition of the complex compound determines the maximum temperature of the process. In situ transmission electron microscopy (TEM) imaging and electron diffraction measurements show that the decomposition of the complex compound directly produces UO2. The incorporation of oxygen at the cooling stage of the combustion process is responsible for the formation of UO2.12. Spin coating of the solutions and brief annealing at 670 K allow the deposition of uniform films of UO2.12 with thicknesses up to 300 nm on an aluminum substrate. Irradiation of films with Ar2+ ions (1.7 MeV energy, a fluence of up to 1 × 1017 ions/cm2) shows unusual defect-simulated grain growth and enhanced chemical mixing of UO2.12 with the substrate due to the high uranium ion diffusion in films. The method described in this work allows the preparation of actinide oxide targets for fundamental nuclear science research and studies associated with stockpile stewardship.

Microstructural evolution in ZrCu metallic glass under neutron irradiation

A detailed numerical investigation has been conducted on the microstructural evolution of a Zr2Cu metallic glass (MG) model under neutron irradiation by extensive molecular dynamics simulations. It was discovered that at the melted zone of the irradiated MG model, an irradiation-induced cascades region was prominent, where there exists a significant atomic-to-cluster structural changes in terms of the coordination numbers, atomic packing efficiency, cluster distribution and regularity. These features effectively were responsible for the transformation of disordered local structures from a densely-packed to a loosely-packed arrangement and largely, the underlying chaos within the structure. Eventually, it was highly remarkable to discover that when the model was fully relaxed at 20 ns, the irradiation-induced structural changes completely vanished and the entire structure was effectively and fully self-recovered. The results of this study will potentially facilitate the development of advanced materials with high irradiation resistance.

Simulated self-irradiation effects of Gd2Ce2O7 nuclear waste form

To simulate self-irradiation effects of nuclear waste forms in long period of deep geological disposal, Gd2Ce2O7 as simulated An4+ matrix was chosen to be irradiated using 0.5 MeV alpha ions to fluences ranging from 1 × 1015 to 1 × 1017 ions cm−2. Irradiation-induced structural change and microstructural evolution were examined using grazing incidence X-ray diffraction, Raman spectroscopy and scanning electron microscopy. Lattice swelling and amorphization in irradiated layer indicated an enhanced disordering degree with increased ion fluences. Main Raman peaks broaden and intensity decrease indicated a significant bonds distortion. In addition, no element aggregation about Gd, Ce and O occurs after He2+ irradiation.

γ-ray Irradiation-Induced Chemical and Structural Changes in CVD Monolayer MoS2

Two dimensional (2D) materials are the ideal choice for highly efficient, lightweight, low power consumption nanoelectronics in space science applications. Therefore, investigation of radiation hardness of 2D-materials is of great interest. Herein, we report the effect of gamma irradiation on chemical vapor deposition (CVD) synthesized crystalline monolayer (1 L) molybdenum disulfide (MoS2) flakes on the sapphire substrate at various doses, viz., 1–1000 kGy. We estimated that the temperature of MoS2 increases by 1.3 °C per kGy of gamma-ray dose. It was observed that up to 130 kGy (∼195 °C), gamma exposure has no significant impact on the morphology and chemical properties of MoS2. However, X-ray photoelectron spectroscopy (XPS) shows that from 275 kGy (∼385 °C), MoS2 starts converting into MoOx. Raman spectroscopy shows that at low gamma doses, the crystallinity of MoS2 increases while at higher doses, a traceable amount of MoS2 starts converting into amorphous MoS3. Our findings show that both E1 2g and A1g Raman mode of MoS2 blue shift as gamma dose increases owing to the combined effect of sulfur vacancies creation and strain caused by thermal expansion of MoS2.

Laser irradiation-induced structural, microstructural and optical properties change in Bi-doped As40Se60 thin films

ABSTRACTThe laser irradiation with band gap light of thermally evaporated As40Se55Bi5 and As40Se45Bi15 thin films was found to be accompanied by structural changes which in turn changed the optical constant. The thin films under investigation were characterized by the X-ray diffraction method to study the structural change and the surface morphology was checked by field emission scanning electron microscope. The composition of the films was verified from the energy dispersive X-ray analysis. The changes in optical properties due to the influence of laser irradiation were calculated from the transmission spectrum recorded by UV–Visible spectrometer in the wavelength region 400–1200 nm. The decrease in optical band gap (photodarkening) is explained on the basis of density of state model proposed by Mott–Davis. The Raman analysis showed the Raman shift and symmetric stretching vibration of As–Se.

Irradiation-induced structural changes in ZnO nanowires

It is a misunderstanding that higher energy ion irradiation on nanomaterials has only detrimental effects on their properties. Recent research reveals that higher energy irradiation on nanostructure materials is favorable with advantageous effects. Light, medium, heavy ions, and high energy photons serve as a veritable tool to synthesized nanowires for these effects. In this article, experimental research on the impact of ion species and high energy photons irradiation on structured ZnO nanowires (ZnO-NWs) and at different ion energies (keV to MeV), ion fluences, and substrate temperatures are discussed. The study has revealed that ZnO-NWs structures were damaged at high irradiation fluence under room temperature. Moreover, the porous structures of ZnO-NWs are created by light ions irradiation at a higher temperature. It is noteworthy that the effect of these irradiation beams induced-cutting of ZnO-NWs and fabrication of nano-holes in ZnO-NWs valuable for nano-devices in space technology under harsh environment.

Monte Carlo simulation of the corrosion of irradiated simplified nuclear waste glasses

Ballistic effects due to recoil nuclei will be the predominant mode of long-term radiation damage of nuclear waste glass in disposal facilities. While these ballistic effects are known to modify the glass structure in ways that have been quantified using molecular dynamics (MD) simulations, the effect of irradiation-induced structural changes on glass corrosion is not understood. Monte Carlo (MC) simulations were therefore performed to quantify the effects of structural changes determined from MD simulations on the corrosion of simplified nuclear waste glasses, namely sodium borosilicate and sodium alumino-borosilicate glasses. MC simulations were first performed to determine separately the effects of irradiation-induced changes in boron coordination, the number and nature of Qn species, and the angular distribution of SiOSi linkages, that is, changes to the short-range order of the glass. Generally, the MC simulations showed the resulting effects on the kinetics (B release rate) and extent (B leached thickness) of corrosion were correlated to the extent of depolymerization of the glass network introduced by these local structural changes. The combined effects of these structural changes, as parameterized using the results of MD simulations, were then determined using a glass composition for which relevant experimental data were available for comparison. Here, the combined effect of local changes was lower than the increase in alteration depth observed upon irradiation. This insight from the MC simulations highlighted the need to consider changes in the medium-range order to completely account for experimental observations.

Electron beam irradiation-induced structural changes increase the antioxidant activities of egg white protein

Electron beam irradiation (EBI) is a widely applied non-thermal technology for food processing. To investigate the influence of EBI on the antioxidant activities and the structure of proteins, we treated egg white protein (EWP) with EBI and tracked the changes in antioxidant activities as well as in the structure of EWP. The ABTS+ free radical scavenging rate significantly increased from 30.16 ± 1.45% to 49.48 ± 1.53% (P < 0.05) after the EBI treatment. The α-helix content decreased from 26.7% to 17.4%, while the β-parallel content increased from 35.1% to 56.6%. Additionally, the particle size of EWP increased, while the absolute Zeta potential decreased. The surface hydrophobicity and the free –SH and total –SH contents increased simultaneously. These results indicate that the buried hydrophobic amino acids and the –SH group become exposed to the environment after EBI treatment. This study can provide a basis for further exploration of the mechanism of EBI applications to improve antioxidant capability.

Mechanics of Irradiation-Induced Structural Changes in a Lipid Vesicle

Irradiation-induced oxidation of lipid membranes is implicated in diseases and has been harnessed in medical treatments. Irradiation induces the formation of oxidative free radicals, which attack double bonds in the hydrocarbon chains of lipids. Studies of the kinetics of this reaction suggest that the result of the first stage of oxidation is a structural change in the lipid that causes an increase in the area per molecule in a vesicle. Since area changes are directly connected to membrane tension, irradiation-induced oxidation affects the mechanical behavior of a vesicle. Here, we analyze shape changes of axisymmetric vesicles that are under simultaneous influence of adhesion, micropipette aspiration, and irradiation. We study both the equilibrium and kinetics of shape changes and compare our results with experiments. The tension–area relation of a membrane, which is derived by accounting for thermal fluctuations, and the time variation of the mechanical properties due to oxidation play important roles in our analysis. Our model is an example of the coupling of mechanics and chemistry, which is ubiquitous in biology.

Surface Potential Decay of Negative Corona Charged Epoxy/Al2O3 Nanocomposites Degraded by 7.5-MeV Electron Beam

Surface potential decay on negative corona charged epoxy/Al2O3 nanocomposites irradiated with high-energy electron beam has been investigated in this paper. 2-mm-thick laminate nanocomposite samples were irradiated with electron beam at an average energy of 7.5 MeV, and the total accumulated dose was up to 500 kGy. After the irradiation, the nanocomposites were corona charged with dc voltage at −10 kV through a pair of needle to plate electrode. Surface potential of the sample was then measured by means of an electrostatic voltmeter through which trap distribution and carrier mobility were calculated. Differential scanning calorimetry curve for the each sample was measured to understand the change in chemical and physical structures induced by the irradiation. Results obtained indicated that the presence of nanofiller in the nanocomposites played a role in limiting the charge transportation both before and after the irradiation, and the charge transportation behavior was remarkably dependent upon the total irradiation dose. It is found that when irradiated with a certain total dose of electron beam, electron migration within epoxy and its nanocomposites is restricted, which should be attributed to the high-energy irradiation-induced structural change of the material.

Raman investigation of laser-induced structural defects of graphite oxide films

Since the beginning of intensive studies on graphene and graphitic materials, Raman spectroscopy has always been used as a characterisation technique. This is due to two main reasons: the non-destructive nature of this experimental technique and its ability to distinguish between the plethora of existing carbon materials. One of the most challenging research activities concerns the production of graphene microcircuits. To address this issue, a possible strategy is to directly reduce and pattern graphite oxide (GO) film by laser irradiation. The objective of this study is to evaluate the laser irradiation-induced structural changes on thin GO films by using Micro-Raman spectroscopy. We used as a source a Nd:YAG laser (1064 nm) and different laser fluences: 15 J/cm2, 7.5 J/cm2 and 5 J/cm2. We have analyzed the modifications of the main Raman contributions of these graphitic materials: the D band (defect induced band), the G band (band due to sp2 hybridized carbon atoms) and the 2D band (D band overtone). In particular, we found out that our figure of merit (FOM) parameters, i.e. the intensity ratio ID/IG (for the D band and G band) and I2D/IG (for the 2D band and G band), change with the laser fluences, revealing a different effect induced by the laser irradiation. The best results are found in the sample irradiated with 5 J/cm2, suggesting that higher fluences do not lead to better results.

Metal passivation effect on focused beam-induced nonuniform structure changes of amorphous SiOx nanowire

In this paper, the passivation effect of Au nanoparticles (AuNPs) on the focused electron beam (e-beam) irradiation-induced nonuniform structure changes of amorphous SiOx nanowire (a-SiOx NW) is in-situ investigated at room temperature in a transmission electron microscope. It is found that the pristine a-SiOx NW demonstrates an accelerated necking at the nanoscale along with a fast, plastic elongation and a local S-type deformation in the axial direction. However, when the surface of a-SiOx NW is modified with uniform AuNPs, it becomes remarkably passivated and the processing transfers from a diffusion (or plastic flow)-dominated status to an evaporation (or ablation)-dominated status. As a result, the necking of the AuNPs-modified a-SiOx NW is greatly retarded with a much lower shrinking rate and there is no visible elongation and bending deformation observed. Further, the combined effects of nanocurvature and beam-induced soft mode and instability of atomic vibration are applied to elucidate the observed new phenomena.

Micro to nanostructural observations in neutron irradiated nuclear graphites PCEA and PCIB

The neutron irradiation-induced structural changes in nuclear grade graphites PCEA and PCIB were investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED) and electron energy loss spectroscopy (EELS). The graphite samples were irradiated at the Advanced Test Reactor at the Idaho National Laboratory. Received doses ranged from 1.5 to 6.8 displacements per atom and irradiation temperatures varied between 350 °C and 670 °C.XRD and Raman measurements provided evidence for irradiation induced crystallite fragmentation, with crystallite sizes reduced by 39–55%. Analysis of TEM images was used to quantify fringe length, tortuosity, and relative misorientation of planes, and indicated that neutron irradiation induced basal plane fragmentation and curvature. EELS was used to quantify the proportion of sp2 bonding and specimen density; a slight reduction in planar-sp2 content (due to the buckling basal planes and the introduction of non-six-membered rings) agreed with the observations from TEM.

X-ray irradiation-induced structural changes on Single Wall Carbon Nanotubes

Dosimetry devices based on Carbon Nanotubes are a promising new technology. In particular using devices based on single wall Carbon Nanotubes may offer a tissue equivalent response with the possibility for device miniaturisation, high scale manufacturing and low cost. An important precursor to device fabrication requires a quantitative study of the effects of X-ray radiation on the physical and chemical properties of the individual nanotubes. In this study, we concentrate on the effects of relatively low doses, 20cGy and 45cGy, respectively. We use a range of characterization techniques including scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy to quantify the effects of the radiation dose on inherent properties of the nanotubes. Specifically we find that the radiation exposure results in a reduction in the sp2 nature of the nanotube bond structure. Moreover, our analysis indicates that the exposure results in nanotubes that have an increased defect density which ultimately effects the electrical properties of the nanotubes.

Irradiation-induced intermixing effects at the interfaces of titanium and titanium-dioxide thin films and Fe-12%Cr substrate

Irradiation-induced compositional and structural changes at the interfaces between Fe-12%Cr binary alloy substrate and thin films of titanium and titanium-dioxide have been investigated. Irradiations were performed with 5MeV Ni2+ ions at 300°C and 500°C, up to damage levels of 35dpa (displacements per atom). For the 300°C irradiation case, irradiation enhanced the interdiffusion coefficient by a factor over twenty for the titanium film samples, but by a factor of only 1.2 for the titanium dioxide film samples. At 500°C, significant intermixing was observed in the titanium film samples and resulted in the formation of a wide Fe2Ti reaction zone. For the titanium dioxide film samples, chromium was observed to diffuse into sub-stoichiometric regions of the film. Irradiation caused the formation of chromium-rich nanoprecipitates within the oxide film and promoted a phase transformation in the film from anatase TiO2 to the Ti2O3 phase.

Ion irradiation-induced crystal structure changes in inverse spinel MgIn2O4

400keV Ne and 200keV He ion irradiations were performed on fully inverse MgIn2O4 samples at cryogenic temperature (~77K), in order to examine the influence of radiation-induced cation disordering on crystal structure. In the case of MgIn2O4 samples irradiated with Ne ions to a peak displacement damage dose of 4 displacements per atom (dpa), a spinel-to-rocksalt phase transformation was observed. By contrast, for MgIn2O4 samples irradiated with He ions to a peak displacement damage dose of 5dpa, the only observed structural effect involved cation rearrangements from an inverse to a “random” spinel structure.