Helium Ion Irradiation Research Articles

Electron transport tuning of graphene by helium ion irradiation

This article reviews charge carrier transport phenomena in single-layer graphene, in which crystalline defects are generated by helium-ion-beam irradiation using a helium-ion microscope. Crystalline defects work as electron scatterers, and the conductivity drastically decays as ion dose increases. Moreover, real-time conductivity monitoring during ion beam scans over the graphene surface is demonstrated. In cryogenic measurements under magnetic fields, defective graphene exhibits negative magnetoresistance, suggesting that strong localization occurred in this two-dimensional electron system, which survived even at room temperature. The localized state contributes to inducing a transport gap around the Dirac point, where the density of states is at its minimum, and it enables field-effect control of the carrier transport by tuning the carrier density. The fabrication and operation of field-effect transistors with defective graphene channels are demonstrated.

Modulating properties by light ion irradiation: From novel functional materials to semiconductor power devices

In this review, the application of light ion irradiation is discussed for tailoring novel functional materials and for improving the performance in SiC or Si based electrical power devices. The deep traps and electronic disorder produced by light ion irradiation can modify the electrical, magnetic, and optical properties of films (e.g., dilute ferromagnetic semiconductors and topological materials). Additionally, benefiting from the high reproducibility, precise manipulation of functional depth and density of defects, as well as the flexible patternability, the helium or proton ion irradiation has been successfully employed in improving the dynamic performance of SiC and Si based PiN diode power devices by reducing their majority carrier lifetime, although the static performance is sacrificed due to deep level traps. Such a trade-off has been regarded as the key point to compromise the static and dynamic performances of power devices. As a result, herein the light ion irradiation is highlighted in both exploring new physics and optimizing the performance in functional materials and electrical devices.

Investigating the effect of helium ion irradiation on deformation behaviour of Ni-Mo-Cr alloy via in-situ micro-tensile testing

In this study, α particle radiation damage through transmutation of Ni anticipated in a Molten Salt Reactor (MSR) core candidate material is simulated through irradiation of nickel-based alloy, GH3535, with 5 MeV helium ion dose of 1.5 dpa at room temperature via use of a degrader wheel to ensure near-uniform radiation damage throughout a 10 µm depth. For both the unirradiated and irradiated samples, micro tensile specimens 5 × 5 µm in cross sectional area and ∼17 µm in length are fashioned (using focused ion beam milling) out of regions having single crystals and those including grain boundaries and subsequently tested in tension to failure. Surprisingly, micro-tensile results reveal that voids and displacement damage introduced via irradiation did not embrittle the GH3535 appreciably as there was not a statistically significant difference in their elongation to failure, despite an increase of the Critical Resolved Shear Stress (CRSS) from 200 MPa to 361 MPa. It was also observed that all samples including both unirradiated and irradiated grain boundary micro-tensile samples failed within a grain rather than along the grain boundary proving GH3535 fails trans-granularly even after helium ion irradiation. The implication of the results and comparison with existing literature data are discussed further in this paper.

Space Weathering Effects in Troilite by Simulated Solar-Wind Hydrogen and Helium Ion Irradiation.

Space weathering is a key process in the interpretation of airless planetary surfaces. As we engage new missions to planetary objects with potentially novel surfaces such as 16 Psyche, there is renewed interest in expanding our knowledge of space weathering effects to a wider variety of analog materials, including the physical/chemical effects of solar‐wind ions on planetary regoliths. We have experimentally simulated the effects of solar ions on two polished thick sections of meteoritic troilite (FeS) via irradiation with 1 keV hydrogen (H+) and 4 keV helium (He+), to investigate effects resulting from different ion species. We detected depletion of sulfur over the course of each irradiation using in situ X‐ray photoelectron spectroscopy. Sulfur depletion rates were surprisingly similar for H+ and He+, interpreted as a function of subsurface ion‐activated diffusion. By comparing XPS‐derived elemental abundances with SDTrimSP computer simulations, we further quantified sulfur diffusion, sputtering yield, and altered‐layer composition with respect to incident‐ion fluence, and accounted for the influence of surface oxidation due to atmospheric sample storage. Using scanning electron microscopy, we detected an increase in nanoscale surface roughness resulting from the irradiation, which we quantified using atomic force microscopy. Based on these results, we estimate that an exposure time of order 103 Earth‐years is required for troilite on Psyche to reach equilibrium sulfur depletion within the first atomic layer.

Microstructural and mechanical evolution of amorphous Zr-Si with irradiation induced atomic reconfiguration and free volume variation

Amorphous materials have a promising application in irradiation environment. However, the mechanism of irradiation-induced mechanical property changes is not clear yet. In this work, Zr-Si amorphous films were sputtered and the bonding status was optimized based on sputtering parameters. Helium ion irradiation was introduced to study the microstructural evolution as well as the mechanical behavior changes in Zr55Si45 amorphous film. The change of bonding status and the increase of free volume in amorphous material were identified. The elastic modulus increased with the formation of Zr-Si covalent bonds after irradiation. Combined with changes of internal free volume, the plasticity of amorphous materials was improved. No helium bubbles were found in the interior. Thus the bonding states and free volume can synergeticly affect the mechanical properties of Zr55Si45 amorphous film.

Improved spin\u2013orbit torque induced magnetization switching efficiency by helium ion irradiation

Increasing the efficiency of spin–orbit torque (SOT) is of great interest in spintronics devices because of its application to the non-volatile magnetic random access memory and in-logic memory devices. Accordingly, there are several studies to alter the magnetic properties and reduce the SOT switching current with helium ion irradiation, but previous researches are focused on its phenomenological changes only. Here, the authors observe the reduction of switching current and analyze its origins. The analyzed major reasons are improved spin Hall angle represented as the changed resistivity of heavy metal layer and the reduction of surface anisotropy energy at interface between heavy metal and ferromagnet. It is confirmed that almost linear relation between changed SHA and Pt resistivity by helium ion irradiation, which is attributed because of the increase in the scattering sources induced by structural distortion during ion penetration. From the calculated power consumption ratio based on the derived parameter, the requiring power decreases according to the degree of ion irradiation. Our results show that helium ion penetration induced layer and interfacial disturbance affects SOT induced magnetization switching current reduction and may provide possibility about helium ion irradiation based superior SOT device engineering.

Evolution of helium bubbles in SLM 316L stainless steel irradiated with helium ions at different temperatures

The temperature dependence of helium bubble evolution in 316L stainless steel (SS) fabricated by selective laser melting (SLM) has been studied by performing 500 keV helium ion irradiation at temperatures between 350 and 900 °C. The number density of helium bubbles decreased steadily whereas the bubble diameter gradually increased with increasing temperature. The material swelling caused by helium bubbles had no obvious change at the temperature below 800 °C. However, at the maximum temperature of 900 °C, the swelling sharply increased to 0.17% mainly due to the rapidly growing bubble diameter. In particular, heterogeneous nucleation of bubbles occurred in the vicinity of dislocation structures at high temperatures of 700–900 °C, and the formed helium bubbles rapidly grew at the oxide-matrix interface at 900 °C. It was confirmed various intrinsic structures (dislocation structures or oxide particles) differently affected the bubble evolution process. The apparent activation energy (Eact) of helium bubbles determined by the Arrhenius model were used to elucidate the most probable helium bubble evolution mechanisms at various temperatures, as it is an experimentally observed activation energy, which contained information about the activity of helium atoms. It was found that the low-temperature regime with low apparent activation energies (ECbact=0.15eV,ERbact=0.04eV) and high-temperature regime with high apparent activation energies (ECbact=1.50eV,ERbact=0.58eV) favored different helium bubble evolution mechanisms. In the low-temperature regime, helium bubble evolution was controlled by the diffusion of helium atoms via a vacancy mechanism in the SLM 316L SS. On the other hand, the migration and coalescence of helium bubbles also occurred in the high-temperature regime which caused the apparent activation energy of density was higher than the theoretical value of helium atoms diffuse via a replacement mechanism.

Transient thermal shock and helium ion irradiation damage behaviors of ODS-W/CuCrZr joints

The transient thermal shock and helium ion irradiation damage behaviors of oxide dispersion-strengthened tungsten (ODS-W)/CuCrZr alloy joints prepared by direct diffusion bonding and by improved diffusion bonding via surface nano-activation and Cu electroplating were studied. The surface morphologies and interface structures of the ODS-W/CuCrZr joints after thermal shock and He+ irradiation were investigated by atomic force microscopy, scanning electron microscopy, focused ion beam/scanning electron microscopy, and high-resolution transmission electron microscopy. The joint of ODS-W and CuCrZr prepared by the improved diffusion bonding method exhibited superior resistance to crack formation. No obvious plastic deformation was found on the ODS-W surfaces of the ODS-W/CuCrZr joints obtained by either bonding method after transient thermal shock (power density = 0.6 GW/m2). Interfacial debonding was observed to occur at the interface of W and Cu in the direct diffusion-bonded ODS-W/CuCrZr joint where Y2O3 particles exist, but did not occur in the joint prepared using the improved method. The nanostructures formed at the interface of the joint via the improved diffusion bonding method therefore elevated the radiation resistance of the joint. These results should be of relevance for the development of plasma-facing components in future nuclear fusion reactors.

The superior thermal stability and irradiation resistance capacities of tungsten composites synthesized by simple second-phase particle component modulation

W-Y2O3-ZrO2 composite materials were fabricated by a combination of wet chemical method and spark plasma sintering. We systematically studied the W-Y2O3-ZrO2 composite materials at different Y and Zr doping atomic ratios. The ultrafine tungsten-based composites with a dispersed distribution of Y2Zr2O7 particles can be prepared by appropriate Y and Zr doping atomic ratios for this experiment. The surface evolution behavior of W-5Y-5Zr composites induced by high temperature annealing and helium ion irradiation was investigated. The nano-Y2Zr2O7 second-phase particles greatly increased the resistance of the material to grain growth. The dispersed and fine of Y2Zr2O7 particles in the tungsten-based composites effectively improved the resistance to helium ion irradiation. These findings can serve as a reference for the fabrication of tungsten-based materials in fusion engineering.

Tailoring interfacial effect in multilayers with Dzyaloshinskii\u2013Moriya interaction by helium ion irradiation

We show a method to control magnetic interfacial effects in multilayers with Dzyaloshinskii–Moriya interaction (DMI) using helium (He^{+}) ion irradiation. We report results from SQUID magnetometry, ferromagnetic resonance as well as Brillouin light scattering results on multilayers with DMI as a function of irradiation fluence to study the effect of irradiation on the magnetic properties of the multilayers. Our results show clear evidence of the He^{+} irradiation effects on the magnetic properties which is consistent with interface modification due to the effects of the He^{+} irradiation. This external degree of freedom offers promising perspectives to further improve the control of magnetic skyrmions in multilayers, that could push them towards integration in future technologies.

Excellent performance of W–Y2O3 composite via powder process improvement and Y2O3 refinement

In this article, Y2O3-reinforced tungsten composites are fabricated by using an improved wet chemical method combined with the spark plasma sintering (SPS). Triethanolamine (TEA) surfactant addition and an appropriate calcination process are innovatively introduced into this wet chemical method. The results show that ultrafine composite powders with nano-sized Y2O3 dispersions in the tungsten matrix can be obtained through the improved wet chemical method. Using the SPS, the average sizes of Y2O3 particles within tungsten grains and at grain boundaries are identified to be 13.5 and 50 nm, respectively. It is found that the phase interface between W and Y2O3 is a typical semicoherent interface. We observe that the W-Y2O3 composites possess superior mechanical properties compared with the pure tungsten counterparts. The results inferred from atomistic simulations reveal that the added Y2O3 particles can effectively pin the dislocation and impede the dislocation movement, thus enhancing the mechanical performances of W-Y2O3 composites. In addition, the addition of Y2O3 particles is also able to improve the helium ion irradiation resistance of tungsten-based composites. This study is expected to provide a certain reference for the manufacture of large-sized tungsten-based materials.

Evaluating surface damage behavior of W-(Y0.9La0.1)2O3 composites during spark plasma sintering process improvement

In this study, W-(Y0.9La0.1)2O3 composite powders are fabricated by means of a combination of wet chemical method and spark plasma sintering. We systematically study the sintering and densification behavior of W-(Y0.9La0.1)2O3 composite powders at different temperatures and pressures. The results indicate that ultrafine tungsten-based composites with a dispersed distribution of (Y0.9La0.1)2O3 particles can be achieved under optimized temperature and pressure conditions. The optimized pressure and sintering temperature for W-(Y0.9 La0.1)2O3 composites are identified to be 75 MPa and 1600 °C, respectively. In addition, the surface damage behavior of W-(Y0.9La0.1)2O3 composites induced by the laser thermal shock and helium ion irradiation are also investigated. It is shown that the presence of holes greatly enlarges the helium retention during helium ion irradiation and promotes the melting caused by local overheating during laser thermal shock. We find that the fine-dispersed distribution of (Y0.9La0.1)2O3 particles in the tungsten-based composites can effectively improve the resistance of helium ion irradiation and laser thermal shock. We hope that these findings could provide some guidance and reference for the fabrication of large-sized tungsten-based materials in fusion engineering.

High energy density pulsed argon plasma synthesized nanostructured tungsten for damage mitigation under fusion relevant energetic he ion irradiation

Tungsten (W) is considered as one of the promising candidates for plasma facing components in fusion reactors since it has high threshold energy, high melting point, low threshold shock resistance, and resistance against formation of co-deposits with tritium. Despite these commendable features, helium ions produced during fusion reaction are known to alter the microstructure of tungsten. In this work, dense plasma focus (DPF) device is used to study the effect of helium ion flux on double forged tungsten samples delivering a heat load of 6.27×104J/m2 per shot. The irradiation of virgin W samples is carried out at 5, 10, and 15 DPF helium shots. High heat loads resulted in blisters and micro-cracks on the sample surface. With an increase in the number of shots, the density of the blisters increased and craters on the W surface burst followed by re-solidification of the melted and sputtered surface. Surface nano-structurization, with nanoparticle formation, of W samples (nano-W) is realized by high-energy argon ion exposure of virgin samples in an argon filled DPF device. The average size of nanoparticles is found to increase with the number of shots and also leads to particle agglomeration. At 10 shots, uniformly distributed highly dense nanoparticles of 20–50 nm size have been synthesized. The nano-W samples are then irradiated by instability-accelerated high-energy helium ions in helium filled DPF device for 5, 10, and 15 shots to simulate fusion relevant conditions. The presence of the trapped helium bubbles in virgin-W and nano-W are examined by BSE imaging and XRD, respectively. The nanostructured tungsten shows improved structure and surface properties against Helium ion irradiation.

Wetting Property Modification of Al2O3 by Helium Ion Irradiation: Effects of Beam Energy and Fluence on Contact Angle.

In imparting wetting properties, a fabrication process without the addition of new compounds and deposition of coating layers would be the most desirable because it does not introduce additional complexities. Hence, the ion beam irradiation technique is used as it enables the chemistry of materials to be modified through simple adjustments of irradiation parameters such as the type of accelerated particles, beam energy, and fluence. In this study, the hydrophilicity of alumina surfaces was weakened by irradiating He ion beams of different energy levels (200 keV and 20 MeV). These transitions become more pronounced as the total beam fluence increases. In low-energy irradiation, the effect of irradiation is predominant near the surface, and hydrophilicity is weakened by the increase in carbon adsorption and suppression of dissociative adsorption of water molecules owing to the introduction of oxygen vacancies. In contrast, nuclear transmutations are induced by irradiation with high-energy beams. Consequently, fluorine is generated, and hydrophobic functional groups are formed on the surface. By varying the beam conditions, the wetting properties of the target ceramic can be controlled to the desired level, which is required in various industries, via appropriate adjustments of the beam parameters. In addition, the beam irradiation technique may be applicable to all ceramic materials, including lattice oxygen and alumina.

Nanoscale friction of CVD single-layer MoS2 with controlled defect formation

Two-dimensional (2D) layered nanomaterials such as graphene, molybdenum disulfide (MoS2), or tungsten disulfide offer a promising solution in areas of solid-state lubrication, due to their excellent mechanical properties as well as low friction. However, defects can influence their friction and reduce their superior tribological properties. Thus, it is crucial to understand the effects of defects on sliding behavior in 2D nanomaterials, to foster a functional strategy for utilizing 2D nanomaterials as solid-state tribological films. In this study, frictional effects of defects, grain boundaries, and atomic-scale structural defects were explored on chemical vapor deposition (CVD) grown single layer MoS2. Selective patterning of defects into MoS2 was accomplished via controlled irradiation of helium ions with varying ion doses. The friction of MoS2 was characterized by friction force microscopy (FFM) and was found that friction depends on the defect formation controlled by helium ion irradiation. This approach offers a correlation between surface topography, defects and friction. Understanding the relative friction of MoS2 in the presence of different levels of defects is foundational to studying tribological properties of a single layer MoS2 at both nanoscales and macroscales.

Ion irradiation and implantation modifications of magneto-ionically induced exchange bias in Gd/NiCoO

Magneto-ionic control of magnetic properties through ionic migration has shown promise in enabling new functionalities in energy-efficient spintronic devices. In this work, we demonstrate the effect of helium ion irradiation and oxygen implantation on magneto-ionically induced exchange bias effect in Gd/Ni0.33Co0.67O heterostructures. Irradiation using He+ leads to an expansion of the Ni0.33Co0.67O lattice due to strain relaxation. At low He+ fluence (≤2 × 1014 ions cm−2), the redox-induced interfacial magnetic moment initially increases, owing to enhanced oxygen migration. At higher fluence, the exchange bias is suppressed due to reduction of pinned uncompensated interfacial Ni0.33Co0.67O spins. For oxygen implanted samples, an initial lattice expansion below a dose of 5 × 1015 cm−2 is subsequently dominated at higher dose by a lattice contraction and phase segregation into NiO and CoO-rich phases, which in turn alters the exchange bias. These results highlight the possibility of ion irradiation and implantation as an effective means to tailor magneto-ionic effects.

Effect of helium ion irradiation on short-time corrosion behavior of two novel high-entropy alloys in simulated PWR primary water

The effect of helium ion irradiation on the short-time corrosion behavior of two novel high-entropy alloys (HEAs) was investigated in simulated PWR primary water. The results revealed that a double-layer oxide film consisting of Ti, Nb and V oxides was formed on both HEAs, including outer oxide particles and a protective inner oxide layer with a maximum depth of ∼500 nm. Irradiation up to 10.5 dpa may hardly promote corrosion kinetics since severe lattice distortion and sluggish diffusion in HEAs. The corrosion processes with and without irradiation were discussed in detail.

Investigation of the effect of helium ion (He+) irradiation on the fluorescence properties of microdiamonds grown by chemical vapour deposition

Investigation of the effect of helium ion (He⁺) irradiation on the fluorescence properties of microdiamonds grown by chemical vapour deposition

Synthesis of magnesiowüstite nanocrystallites embedded in an amorphous silicate matrix via low energy multiple ion implantations

A synthesis process is presented for experimentally simulating modifications in cosmic dust grains using sequential ion implantations or irradiations followed by thermal annealing. Cosmic silicate dust analogues were prepared via implantation of 20–80 ​keV Fe−, Mg−, and O− ions into commercially available p-type silicon (100) wafers. The as-implanted analogues are amorphous with a Mg/(Fe ​+ ​Mg) ratio of 0.5 tailored to match theoretical abundances in circumstellar dusts. Before the ion implantations were performed, Monte-Carlo-based ion-solid interaction codes were used to model the dynamic redistribution of the implanted atoms in the silicon substrate. 600 ​keV helium ion irradiation was performed on one of the samples before thermal annealing. Two samples were thermally annealed at a temperature appropriate for an M-class stellar wind, 1000 ​K, for 8.3 ​h in a vacuum chamber with a pressure of 1 ​× ​10−7 torr. The elemental depth profiles were extracted utilizing Rutherford Backscattering Spectrometry (RBS) in the samples before and after thermal annealing. X-ray diffraction (XRD) analysis was employed for the identification of various phases in crystalline minerals in the annealed analogues. Transmission electron microscopy (TEM) analysis was utilized to identify specific crystal structures. RBS analysis shows redistribution of the implanted Fe, Mg, and O after thermal annealing due to incorporation into the crystal structures for each sample type. XRD patterns along with TEM analysis showed nanocrystalline Mg and Fe oxides with possible incorporation of additional silicate minerals.

The dependence of Mo ratio on the formation of uniform black silicon by helium plasma irradiation

Reducing the optical reflection of silicon (Si) material is a crucial issue on the surface of solar cells and other photonic applications. Fabrication of nanocone structures on the Si surface (black Si) by plasma (helium or argon) irradiation is a novel technique in recent decades with advantages, such as simple, economical, and harmless to the Si substrate. However, the uniformity and controllability of the surface remain problematic. In this study, uniform black silicon was obtained by low energy (<50 eV) helium ion irradiation with auxiliary Mo co-deposition. The characteristics of the nanocone show a clear relation with the Mo ratio. Deposited Mo was found to accumulate on the cone body, especially on the tip, and it worked as a nano mask to induce the formation of the nanocone and protect it from sputtering. The surface with high and large diameter nanocones possesses low reflectances of roughly 2%. The study of the relation between Mo ratio, characteristics of the nanostructure, and the reflectance of the surface raises a potential method of surface tailoring.