Effect Of He Ion Irradiation Research Articles

Solid-State Transformation of Uranyl Peroxide Materials through High-Level Irradiation.

The solid-state transformation of sodium uranyl triperoxide (Na4(UO2)(O2)3·9H2O, NaUT) to sodium uranyl tricarbonate (Na4(UO2)(CO3)3) by radiolysis was observed for the first time. The exposure of NaUT to 3 MGy gamma irradiation resulted in partial breakdown of the peroxides forming a mixed peroxide and carbonate species. The effects of He-ion irradiation on NaUT were also investigated up to 225 MGy using both hydrated argon and dry argon. The complete conversion to the uranyl tricarbonate phase by 56 MGy was done using hydrated argon, while dry argon did not fully convert showing the importance of water in the system. He-ion irradiated NaUT samples all convert to the tricarbonate phase with time in air post radiation exposure. This transition was monitored via Raman spectroscopy, infrared spectroscopy (IR), and powder X-ray diffraction (PXRD) to further confirm the identity of the final product as the sodium uranyl tricarbonate, čejkaite. This transformation outlines a mechanism for the mobility of uranyl in natural environments and in the Hanford tanks.

Effects of He-ion irradiation on microstructures of low activation Ti-Ta-V alloy from atomic simulations and irradiation experiments

Most conventional titanium alloys contain nuclides with long half-lives, which is not conductive to material recovery after decommissioning. To recover components from post-service reactors safely and effectively, it is necessary to use materials with low activation and rapid induction of radioactive decay. In this work, a low-activation α-titanium alloy Ti-5Ta-1.6 V was prepared and irradiated with 80 keV helium ions to 6.8 dpa at room temperature. The mechanical properties and irradiation swelling properties of Ti-5Ta-1.6 V alloy were mainly investigated. The results showed that compared with the commercially pure titanium alloy (CP-Ti), the mechanical properties of Ti-5Ta-1.6 V were substantially improved. After ion irradiation, the irradiation swelling rate of Ti-5Ta-1.6 V (in mass ratio) was found to be significantly lower than that of CP-Ti by atomic force microscopy (AFM) technology. Molecular dynamic (MD) simulations were used to study the irradiation behavior and cascade collisions process, and the Ti-5Ta-1.6 V produced a small number of stable defects with cluster size and number density, which is consistent with the results of irradiation experiments. The results indicate that Ti-5Ta-1.6 V is expected to be a promising new titanium alloy for nuclear applications, which provides a new idea for the selection and optimization of low-activation and radiation-resistant nuclear materials.

Effects of He ion irradiation on the structural stability and deformation behavior in Zr63.5Cu23Al9Fe4.5 and Fe80B13Si7 metallic glasses

The effects of He2+ irradiation on the structural stability and deformation behavior in Zr63.5Cu23Al9Fe4.5 and Fe80B13Si7 metallic glasses (MGs) were investigated by TEM and nano-indenter. He bubbles in Fe80B13Si7 MG distributed more narrowly along the depth direction, packed more densely and exhibited larger size. At 4 × 1017/cm2 dose, Fe3B nanocrystals generated in Fe80B13Si7 MG caused by enhanced atomic diffusion due to increased excess free volume and larger compressive stress on atoms of bubbles gaps, while Zr63.5Cu23Al9Fe4.5 MG could maintain the amorphous structure. According to serrated flow phenomenon and bubbles distribution, the underlying mechanism of the transformation in deformation behavior of MGs with increasing He dose was analyzed as follows: localized inhomogeneous deformation in as-cast MGs, homogeneous deformation in the rejuvenated stage, localized inhomogeneous deformation in the stage where small bubbles act as weak pinning, homogeneous deformation in the stage where large bubbles act as strong pinning, localized fracture in the stage where bubbles collapse.

Effects of He-ion irradiation on the microstructures and mechanical properties of the novel Co-free VxCrFeMnNiy high-entropy alloys

High-entropy alloys (HEAs), as a promising candidate structural material for advanced nuclear energy system, have been widely studied recently due to the combination of the outstanding irradiation tolerance and enhanced mechanical properties at elevated temperatures. In this study, an FCC-structured CrFeMnNi2 HEA and a BCC-structured VCrFeMn HEA without Co element were designed and prepared. The effects of He-ion irradiation on the microstructures and mechanical properties were investigated, so as to preliminarily evaluate the irradiation tolerance of the novel Co-free HEAs. At fluences of 3 × 1016 and 6 × 1016 ions/cm2, the CrFeMnNi2 and VCrFeMn HEAs showed good structural stability at 1023 K; the transmission electron microscope results revealed no amorphization/precipitations. The average sizes and number densities of He bubbles increased as the fluence improved for the two alloys. At each fluence, the average size of the He bubbles in the VCrFeMn HEA was larger than that in the CrFeMnNi2 HEA, while the number density and volume fraction were lower. The CrFeMnNi2 HEA possessed a higher hardening fraction (77%), and an irradiation-induced hardening saturation was observed in the VCrFeMn HEA with a lower hardening fraction of 33%. The experimental results indicated that the novel low-activation VCrFeMn HEA might be a competitive candidate structural material for advanced reactors. The mechanisms of the irradiation tolerance of Co-free HEAs were also discussed.

Anisotropic He-ion irradiation damages in nanocolumnar W thin films

The effects of He-ion irradiation on the microstructures and the mechanical, thermal properties of sputter-deposited nanocolumnar tungsten thin films have been studied. 200 keV He+ ion irradiation with a fluence of 2x1017 ions/cm2 was performed in the growth direction of the W thin films. Small scale mechanical testing methods, such as nanoindentation and square membrane deflection experiments, were carried out, and the thermal conductivity measurement was performed based on the electrical resistivity measurement and the Wiedemann–Franz law for the unirradiated and irradiated W thin films. It was revealed that the properties in the out-of-plane direction are not changed much, but a significant degradation occurs in the in-plane direction after the He-ion irradiation. The microstructure of the film and the distribution of He-ion induced damages are responsible for the anisotropic property changes by He-ion irradiation.

Effect of He ion irradiation on microstructure and electrical properties of graphene

Graphene is a planar two-dimensional material composed of sp<sup>2</sup>-bonded carbon atoms with extraordinary electrical, optical and mechanical properties, and considered as one of the revolutionary electronic component materials in the future. Some studies have shown that the inert gas ion irradiation as a defect introducing technique can change the structure and properties of graphene without introducing additional effects. In this paper, the 5.4 keV He ion irradiation at the dose ranging from 0.7 × 10<sup>13</sup> cm<sup>–2</sup> to 2.5 × 10<sup>13</sup> cm<sup>–2</sup> has a strong effect on graphene deposited by CVD technology. The X-ray photoelectron spectroscopy (XPS), Raman spectroscopy (Raman) and semi-conductor parameter analysis instrument are used to study the changes in the microstructure and electrical properties of graphene before and after irradiation. Detailed analysis shows that the defect density increases gradually with the irradiation dose increasing. Raman spectrum shows that when the irradiation dose increases to 1.6 × 10<sup>13</sup> cm<sup>–2</sup>, the value of <i>I</i><sub>D</sub>/<i>I</i><sub>G</sub> begins to decrease, and XPS shows that the irradiation changes the structure of C chemical bond in graphene which causes the bonding state of C—C sp<sup>2</sup> to be destroyed and partly converted into the C—C sp<sup>3</sup> bonding state. Therefore, the structure of graphene begins to transform from nano-crystalline structure into sp<sup>3</sup> amorphous structure. Simultaneously, increasing defects causes the graphene conductivity to continuously decrease, and also gives rise to the electrical transition from defect scattering mechanism based on Boltzmann transport to the hopping transport. The positive voltage direction offset of <i>V</i><sub>dirac</sub> increases nearly in direct proportion, which is due to the enhancement of graphene’s p-type doping effect caused by defects and adsorbed impurities. This work conduces to the understanding the mechanism of He ion interaction with graphene, and also provides an effective way of controlling the electronic properties.

Channeling effects in gold nanoclusters under He ion irradiation: insights from molecular dynamics simulations

The interpretation of helium ion microscopy (HIM) images of crystalline metal clusters requires microscopic understanding of the effects of He ion irradiation on the system, including energy deposition and associated heating, as well as channeling patterns. While channeling in bulk metals has been studied at length, there is no quantitative data for small clusters. We carry out molecular dynamics simulations to investigate the behavior of gold nanoparticles with diameters of 5–15 nm under 30 keV He ion irradiation. We show that impacts of the ions can give rise to substantial heating of the clusters through deposition of energy into electronic degrees of freedom, but it does not affect channeling, as clusters cool down between consecutive impact of the ions under typical imaging conditions. At the same time, high temperatures and small cluster sizes should give rise to fast annealing of defects so that the system remains crystalline. Our results show that ion-channeling occurs not only in the principal low-index, but also in the intermediate directions. The strengths of different channels are specified, and their correlations with sputtering-yield and damage production is discussed, along with size-dependence of these properties. The effects of planar defects, such as stacking faults on channeling were also investigated. Finally, we discuss the implications of our results for the analysis of HIM images of metal clusters.

Effects of He ion irradiation on the corrosion performance of alloy GH3535 welded joint in molten FLiNaK

In present study, the influence of He irradiation on the corrosion performance of a GH3535 welded joint has been investigated. A welded joint was irradiated with 300 keV He ions and corroded in FLiNaK molten salt at 700 °C for 400 h. The microstructures after corrosion were characterized by SEM, EPMA and TEM. The corrosion produced cavities and created Cr depletion. He bubbles were formed and grew during corrosion. Although He irradiation did not obviously deteriorate corrosion-induced Cr depletion, the combination effect of He bubbles and corrosion attack caused severe damage to the joint, enlarging bubbles and/or cavities into large holes.

Effects of He ion irradiation on the microstructures and mechanical properties of t' phase yttria-stabilized zirconia ceramics

Abstract The dense ZrO2-8 wt.% Y2O3 ceramics with tetragonal (t') phase were prepared by spark plasma sintering (SPS). The micro-structure modification in poly-crystalline t' phase YSZ ceramics irradiated with 60 KeV He ions over a wide fluence range were studied. It is found that, the t' → t + c phase transformation was detected for the samples irradiated at the fluence above 2 × 1017 cm−2. In addition, a three-steep model for damage stages has been proposed and discussed for interpreting the evolution of mechanical properties of t'-YSZ ceramics after irradiated, mainly revealed by the analysis from HRTEM results. Firstly, as the He+ fluences range from 0.5 × 1017 cm−2 to 1 × 1017 cm−2, the hardening effects were confirmed in t'-YSZ owing to the irradiation induced defects serve as obstacles to resist slipping of dislocations. As the fluence was increased to 2 × 1017 cm−2, the degradation of mechanical properties was evidenced, which could be ascribed to the deterioration effect of aggregated He bubbles inside t' YSZ grains. While the fluence increased to 10 × 1017 cm−2, a seriously damaged region was approximately located at 250 nm in depth, at which a great number of He bubbles with different shape and dislocation loops were evidenced, leading to a further reduction of hardness and elastic modulus. No micro-cracks emerge even for He+ fluences as high as 10 × 1017 cm−2, indicating high irradiation stability and resistance to micro-crack propagation in t'-YSZ.

Effect of He ion irradiation on the microstructure of t′ phase yttria-stabilized zirconia ceramic coatings

Abstract Yttria-stabilized zirconia (YSZ) films with tetragonal (t′) phase was prepared on China Low Activation Martensitic steel (CLAMs) substrates by supersonic atmospheric plasma spraying (SAPS) with ZrO2-8 wt% Y2O3 nano-powders as feedstock. This study deals with the subject of the structural modifications and phase transformations in t′ phase YSZ coatings induced by implantation of low-energy (60 keV) He ions. It is found that the phase transformation in t′ phase YSZ coatings during helium ion-irradiation as a function of fluence can be divided into a two-stage process based on the microstructural evolution as follows: (i) In the case of He ions at 0.5 × 1017 cm2 (∼1.5 dpa), no obvious volume swelling can be detected, suggesting the irradiation-induced defects is primarily associated with a positive relaxation volume. Therefore, only t′ → t phase transformation was observed for the samples implanted at a fluence of 0.5 × 1017 cm−2. (ii) While increasing the fluence from 0.5 × 1017 cm−2 to 2 × 1017 cm−2, an increase in the defect concentrations can be observed, leading to an exponential growth in volume swelling from 3.2% to 9.7% observed. These high- density extended defects can induce a plastic deformation in the lattice structure, resulting significant lateral compressive stress. Correspondingly, the t′ → t + c phase transformation was detected for the samples implanted at the fluence of 2 × 1017 cm−2. At a fluence of 10 × 1017 cm−2, the formation of the He bubbles, and ellipsoidal cavities can be observed by TEM, inducing the further volume swelling. Meanwhile, the intensity of (4 0 0)c peak increases while fluence increase from 2 × 1017 cm−2 to 10 × 1017 cm−2. Based on the experimental results, a reasonable mechanism for the phase transformation of t′ phase YSZ samples during He ions irradiation is proposed.

Evolution of the multi-walled carbon nanotubes structure with increasing fluence of He ion irradiation

Abstract Effects of He ion irradiation on the structural properties of multi-walled carbon nanotubes (MWCNT) are presented in this study. We carry out MWCNT ion irradiation gradually increasing the fluence. As grown MWCNTs possess a relatively large diameter (∼80 nm) and a significantly defective structure of the external walls. This paper shows how ion irradiation affects MWNTs Raman spectra. Quantitative analysis of the deconvoluted spectral components, together with the XPS and SEM data, help to suggest changes in the MWNTs crystal lattice.

Morphological change in FePt nanogranular films induced by irradiation with 100 keV He ions

Abstract We have investigated the effects of He-ion irradiation on structures of FePt nanoparticles dispersed in thin films with amorphous Al 2 O 3 matrix. The coarsening of FePt nanoparticles is suppressed under irradiation with 100 keV He + ions at an elevated temperature, such as 923 K. The delay of particle growth is also recognized in the post-irradiation annealing. On the other hand, He-irradiation is of little assistance in promoting L1 0 ordering in the nanogranular films at a temperature as low as 573 K.

Tuning exchange bias and coercive fields in ferromagnet/antiferromagnet bilayers with ion irradiation

The effect of He ion irradiation on the magnetic properties of NiFe exchange coupled to different antiferromagnetic alloys (FeMn, CrMn, and PtMn) with the same layer thickness is investigated. All systems exhibit an enhanced coercivity prior to irradiation. An exchange bias field is only observed for FeMn and PtMn. Upon ion irradiation the FeMn-based system shows with increasing ion dose an enhancement followed by a decrease and finally a full suppression of the exchange bias field. For systems exchange coupled to PtMn only a decrease and suppression of the bias field is found. This can be attributed to the ion induced chemical disordering of the antiferromagnetic phase in the latter case. In the case of CrMn the antiferromagnetic layer thickness is too small to induce an exchange bias field, but an enhanced coercivity is observed which is caused by the exchange coupling between the antiferromagnetic and ferromagnetic layers. For all systems, this enhanced coercivity of the exchange coupled bilayer system is modified by ion irradiation.

He ion radiation effects in high electron mobility transistors

The effects of He ion irradiation have been investigated in high electron mobility transistors. Heterojunctions have been also used to monitor the two-dimensional electron-gas degradation. Devices with different layer structures have been employed for the better understanding of failure mechanism sources. Finally, introduction of a charge control model allowed the determination of buffer layer degradation.

Ion irradiation effects in EuBa2Cu3O y thin film

The effect of He ion irradiation on the pinning potential in EuBa2Cu3O y , thin film was investigated by measuring the temperature dependence of resistivity in magnetic fields. The pinning potential decreased as the ion fluence increased. A slower decrease of pinning potential was observed in higher magnetic field in the fluence region <3.5×1015 cm−2.

Physico-chemical changes in a-C:H by MeV He ion irradiation

The effect of He ion irradiation on the hydrogen content and structure of a-C:H films has been examined. Comparison of elastic recoil detection and Fourier transform infrared spectroscopy results have shown that significant hydrogen depletion occurs in conjunction with an equally significant change in the structure of the films. Examination of the films’ hydrogen profiles also indicates that the diffusion length of molecular hydrogen in these materials during bombardment may be between 160–320 nm.