Energetic Heavy Ion Irradiation Research Articles

Amorphization of Intermetallic Compounds by Energetic Heavy Ion Irradiation

Amorphous alloys are expected to be useful for various applications because they have superior mechanical properties such as strength, hardness and corrosion resistance. So far, the only method for production of amorphous metals is to quench from the liquid state. When materials are exposed to high-energy ions, the lattice structures of the materials tend to be metastable or non-thermally equilibrium, and in some cases, they lose the crystallinity, resulting in amorphization. However, the alloy types and irradiation conditions that cause amorphization by irradiation have never been well clarified yet. In order to study the amorphization by particles irradiation as one of the material processes such as strength control, we have studied the structural changes and the accompanying hardness changes of the bulk crystalline alloys due to various irradiation conditions. In this paper, we discuss the correlation between amorphization and hardness change when heavy ion irradiation is applied to several intermetallic compounds.

Structure and magnetic properties of Fe nanoparticles in amorphous silica implanted with Fe ions and effect of subsequent energetic heavy ion irradiation

Amorphous silicon dioxide (hereafter SiO2) samples were implanted with 380 keV Fe ions at room temperature. After the implantation, some samples were irradiated with 16 MeV Au ions. The magnetic property was investigated by using a SQUID magnetometer, and the morphology of Fe-implanted SiO2 samples was examined by using a transmission electron microscope and x-ray absorption spectroscopy (extended x-ray absorption fine structure and x-ray absorption near edge structure). The size of Fe nanoparticles increases with an increase in the amount of Fe implantation. A part of Fe nanoparticles consists of Fe oxides, and with an increase in the amount of Fe implantation, the valence state of Fe atoms and the structure of Fe nanoparticles gets close to those of metallic α-Fe. The room temperature magnetism was observed in Fe-implanted SiO2 samples. The magnetization–magnetic field curves for samples implanted with a small amount of Fe are reproduced by the Langevin equation, implying that Fe nanoparticles present the superparamagnetic behavior. For a large amount of Fe implantation, the magnetization–magnetic field curve shows the ferromagnetic state. Such a result of magnetic property is consistent with the results of the x-ray absorption. By the subsequent 16 MeV Au irradiation, the Fe nanoparticles were fragmentated, resulting in the decrease in magnetization. The optical absorption property of the SiO2 samples is briefly discussed.

Chemical reactions in H2O:CO interstellar ice analogues promoted by energetic heavy-ion irradiation

ABSTRACT H2O:CO, at concentrations of (3:2) and (10:1), was condensed on CsI substrate at 15 K and irradiated with 46-MeV 58Ni11 + ion beam. Radiolysis induced by fast heavy ions was analyzed by infrared spectroscopy (FTIR). The formation of nine molecular species: CO2, H2O2, HCOOH, HCO, H2CO, 13CO2, CH3OH, O3, and C3O2 was observed. For both concentrations, carbon dioxide (CO2), formaldehyde (H2CO), formic acid (HCOOH), and hydrogen peroxide (H2O2) are the most abundant products species, and tricarbon dioxide (C3O2) is much less abundant. Precursor destruction cross-sections and formation cross-sections of products are determined. The CO destruction cross-section for the (3:2) concentration is almost five times higher than that of water, while those for the (10:1) concentration are practically the same. Atomic sputtering yields are estimated for the two ice films, the total mass sputtered is approximately 2.5 × 106 u per impact. These results contribute to figure out the chemical pathways of compounds synthesized from the two most abundant organic species (H2O and CO) observed in the ices of grain mantles of the circumstellar envelopes and interstellar medium. In additional, the finding results reveal that molecular astronomical percentages are comparable to those obtained after 15 eV molec−1 of deposited dose in current experiments compared with the relative concentration of molecules in solid phase observed in MYSO, LYSO, BG Stars, and Comets.

Non-radiative luminescence decay with self-trapped hole migration in strontium titanate: Interplay between optical and transport properties

A novel model for the non-radiative decay of self-trapped excitons (STEs) in the advanced functional oxide SrTiO3 is proposed and supported by experimental observations. The study is based on the initial ionoluminescence stage for STE emission at 2.5 eV, and its dependence on temperature and electronic excitation rate under energetic heavy-ion irradiation. For all temperatures, this initial stage reaches rapidly a quasi-steady level, and then decreases as induced-structural damage increases. The quasi-steady luminescence exhibits a linear dependence on the excitation rate, suggesting a constant efficiency for STEs formation. An activation energy of 55 meV, essentially independent of the incident ion mass and energy of projectile-ion, is deduced from an Arrhenius-type relationship with irradiation temperature. This energy is in good agreement with experimental values, measured for non-radiative STE decay under ns-laser pulse excitation, and reasonably consistent with density functional theory calculations for migration of self-trapped holes (STHs) described by a small-polaron adiabatic hopping model. A new mechanism dealing with a non-radiative contribution to the STE transition is discussed, consisting of STH migration through thermally-activated hopping and annihilation with the STE-electron. Luminescence kinetics from the chromium intrinsic impurity strongly supports this model, being consistent with the annihilation of Cr3+ centers through recombination with migrating STHs.

Ti3AlC2, a candidate structural material for innovative nuclear energy system: The microstructure phase transformation and defect evolution induced by energetic heavy-ion irradiation

For the structure materials applied in the innovative nuclear energy system, the strongly environment radiation source is always a big concern which will severely degrade the materials performance especially at high temperature. To explore the mechanisms of the anti-irradiation properties in Ti3AlC2, a typical MAX phase material showing excellent irradiation damage tolerance and resistance to amorphization, we conducted a series of 1 MeV C4+ ions irradiation experiments on them at different temperatures (RT, 300°C, 500°C and 800°C). Through Grazing Incidence X-ray Diffraction (GIXRD), Raman spectra (Raman), slow positron annihilation Doppler Broadening Spectroscopy (DBS) and high resolution Transmission Electron Microscopy (HRTEM), the anti-irradiation properties were systematically investigated. For the first time, an entire microstructure phase transformation process of Ti3AlC2 from α to β to γ and to perfect fcc structure phase induced by irradiation at RT and it is inverse (recovery) process of phase transformation under high temperature (≥300 °C) irradiation conditions are found and confirmed. And lots of simple vacancies are induced by irradiation and the density of them gets saturated above 5 × 1015 ions/cm2 fluences. These processes of phase transformation and recovery and vacancy saturation phenomenon are the primary reasons for why Ti3AlC2 has excellent irradiation damage tolerance and resistance to amorphization. In addition, the micro strain and lattice parameters are also affected by microstructure transformation and have been discussed. In a word, Ti3AlC2 materials show good anti-irradiation properties especially at high temperature, and now it is a primary candidate as the coating of the cladding material and the spallation target beam windows material in Chinese ADS project. And studies on this kind of materials provide a promising new concept and way for designing the structural materials for innovative nuclear energy system.

Mechanism of the defect formation in supported graphene by energetic heavy ion irradiation: the substrate effect.

Although ion beam technology has frequently been used for introducing defects in graphene, the associated key mechanism of the defect formation under ion irradiation is still largely unclear. We report a systematic study of the ion irradiation experiments on SiO2-supported graphene, and quantitatively compare the experimental results with molecular dynamic simulations. We find that the substrate is, in fact, of great importance in the defect formation process, as the defects in graphene are mostly generated through an indirect process by the sputtered atoms from the substrate.

Artificially modified magnetic anisotropy in interconnected nanowire networks.

Interconnected or crossed magnetic nanowire networks have been fabricated by electrodeposition into a polycarbonate template with crossed cylindrical nanopores oriented ±30° with respect to the surface normal. Tailor-made nanoporous polymer membranes have been designed by performing a double energetic heavy ion irradiation with fixed incidence angles. The Ni and Ni/NiFe nanowire networks have been characterized by magnetometry as well as ferromagnetic resonance and compared with parallel nanowire arrays of the same diameter and density. The most interesting feature of these nanostructured materials is a significant reduction of the magnetic anisotropy when the external field is applied perpendicular and parallel to the plane of the sample. This effect is attributed to the relative orientation of the nanowire axes with the applied field. Moreover, the microwave transmission spectra of these nanowire networks display an asymmetric linewidth broadening, which may be interesting for the development of low-pass filters. Nanoporous templates made of well-defined nanochannel network constitute an interesting approach to fabricate materials with controlled anisotropy and microwave absorption properties that can be easily modified by adjusting the relative orientation of the nanochannels, pore sizes and material composition along the length of the nanowire.

Microstructure evolution and hardness change in ordered Ni3V intermetallic alloy by energetic ion irradiation

Ni3V bulk intermetallic compounds with ordered D022 structure were irradiated with 16MeV Au ions at room temperature. The irradiation induced phase transformation was examined by means of the transmission electron microscope (TEM), the extended X-ray absorption fine structure measurement (EXAFS) and the X-ray diffraction (XRD). We also measured the Vickers hardness for unirradiated and irradiated specimens. The TEM observation shows that by the Au irradiation, the lamellar microstructures and the super lattice spot in diffraction pattern for the unirradiated specimen disappeared. This TEM result as well as the result of XRD and EXAFS measurements means that the intrinsic D022 structure of Ni3V changes into the A1 (fcc) structure which is the lattice structure just below the melting point in the thermal equilibrium phase diagram. The lattice structure change from D022 to A1 (fcc) accompanies a remarkable decrease in Vickers microhardness. The change in crystal structure was discussed in terms of the thermal spike and the sequential atomic displacements induced by the energetic heavy ion irradiation.

Enhancement of Curie temperature of barium hexaferrite by dense electronic excitations

Curie temperature of polycrystalline barium hexaferrite (BaFe12O19), prepared by conventional solid state technique, is anomalously and significantly enhanced (by nearly 15%) by energetic heavy ion irradiation (150 MeV, Ag12+) at ambient temperature due to dense electronic excitations Moderate fluence (1 × 1012 ions/cm2) induces structural defects giving rise to above enhancement. As established by X-ray diffraction, scanning electron microscopy and Raman studies, higher fluence (1 × 1013 ions/cm2) has structurally transformed the sample to amorphous phase with marginal change in magnetization and Curie temperature.

Study on ferromagnetic ordering of FeRh thin films induced by energetic heavy ion irradiation by means of X-ray Magnetic Circular Dichroism

We investigated the ion irradiation induced ferromagnetic state of FeRh thin films with 10MeV I ion beam by the measurements of a superconducting quantum interference device (SQUID) magnetometer as well as of soft X-ray Magnetic Circular Dichroism (XMCD). It was clearly shown in the magnetization loops by SQUID measurements that the ion irradiation induced the ferromagnetic state in the FeRh thin films even below room temperature. This was also confirmed by the Fe L2,3-edge XMCD measurements for the irradiated FeRh film samples. However, we found that the irradiation ion fluence dependence on the magnetization was totally different between two measurement techniques. We also revealed by XMCD sum rule analysis that the ferromagnetism in the ion irradiated FeRh thin films was mainly dominated by the spin moment.

Effects of energetic heavy ion irradiation on hardness of Al–Mg–Si alloys

Al–Mg–Si alloys were irradiated with 5.4MeV Al ions, 7.3MeV Fe ions, 10MeV I ions, and 16MeV Au ions at room temperature and the Vickers microhardness was measured. The hardness of Al–Mg–Si alloys increases with increasing the ion fluence. In a viewpoint of ion fluence, hardness change of the Al alloys is different by the kind of irradiating ions. But, in a viewpoint of the density of elastically deposited energy, the effect of the four kinds of them on hardness is almost the same. This result means that the effect of irradiation on hardness of Al–Mg–Si alloys is dominated by the elastically deposited energy. The microstructure of the ion-irradiated specimens were investigated by means of three-dimensional atom probe (3DAP). The experimental result was compared with the microstructure and the hardness for thermally aged specimens. We also discuss the difference in ion-irradiation induced change in hardness between Al–Mg–Si alloys and Al–Cu–Mg alloys (duralumin).

Hardness modification of aluminum-alloys by means of energetic ion irradiation and subsequent thermal aging

So far, we have found that the hardness of Al–Cu–Mg alloy (JIS2017, Duralumin) increases by energetic heavy ion irradiation at room temperature. Observations by using the three-dimensional atom probe (3DAP) have revealed that nano-meter sized precipitates are homogeneously distributed in the irradiated specimens, which are produced through the irradiation enhanced diffusion of solute atoms. The small precipitates contribute to the increase in hardness. In this report, we show the results for the hardness modification of Al–Cu–Mg alloy by the combination of energetic ion irradiation and thermal aging treatment. The hardness of the specimens pre-irradiated and thermally aged at 423 K is much larger than that without the pre-irradiation. The present result indicates that the combination of energetic ion irradiation and subsequent thermal aging can be used as an effective tool for the hardness modification of Al–Cu–Mg alloy.

Structure alterations in microporous (Mg,Fe) 2Al 4Si 5O 18 crystals induced by energetic heavy-ion irradiation

The microporous framework structure of (Mg 1− x Fe x ) 2Al 4Si 5O 18 (=cordierite) has been subject to a comparative study on the effect of structural alterations originating from exposure to high-energy heavy ions. Oriented samples (with x=0.061, 0.122, and 0.170) were irradiated with swift 124Xe, 197Au and 96Ru ions with 11.1 MeV per nucleon energy and fluences of 1×10 12 and 1×10 13 ions/cm 2. Irradiated and non-irradiated samples were investigated by means of X-ray diffraction, Mössbauer spectroscopy and optical absorption spectroscopy. Structural investigations reveal an essentially unchanged Al,Si ordering, which appears to be unaffected by irradiation. The most remarkable macroscopic change is the ion-beam induced colouration, which could be assigned to electronic charge transfer transitions involving the Fe cations. Mössbauer spectra indicate an increased amount of [4]Fe 3+ for the irradiated sample. The most noticeable structural alteration concerns irradiation-induced dehydration of extra-framework H 2O, which is accompanied by a reduction in the molar volume by ∼0.2 vol%.

Effects of energetic heavy ion irradiation on the structure and magnetic properties of FeRh thin films

Fe–54at.%Rh thin films were irradiated with 10 MeV iodine ions at room temperature. Before and after the irradiations, the changes in magnetic properties and the lattice structure of the samples were studied by means of a SQUID magnetometer and X-ray diffraction. For the low fluence irradiation, the SQUID measurement at 20 K shows that the anti-ferromagnetic region of the thin film is changed into ferromagnetic region by the irradiation. As the film thickness is much smaller than the ion range, we can discuss the relationship between the density of energy deposited by ions and the change in magnetization quantitatively. For the high fluence irradiation, the magnetization of the film is strongly decreased by the irradiation, which can be explained as due to the change in lattice structure from B2 into A1 structure by the irradiation.

Control of the first-order antiferromagnetic–ferrimagnetic phase transition in Cr-modified Mn2Sb thin films by energetic ion irradiation

Thin films of Mn2−xCrxSb with x=0.06 were synthesized by solid-state reaction of the ion beam sputtered Mn/Cr/Mn/Sb multilayers on SiO2 substrates. The films were irradiated at room temperature with 10MeV iodine ions by using a tandem accelerator at JAEA-Takasaki. The temperature dependence of the magnetization measured at 10kOe apparently showed the antiferromagnetic-ferrimagnetic phase transition at around 200K for the unirradiated x=0.06 samples. After the samples were irradiated up to 1.0×1014ions/cm2, the transition temperature was apparently shifted toward a higher temperature side for about 12.8K. However, notable structural changes could not be found due to the ion irradiations. These results suggest that the energetic heavy ion irradiation for the magnetic thin films with a first-order phase transition significantly affects the phase transition temperature with the transferred energy by the ion irradiation process.

Spectroscopic and TSDC analysis of 100 MeV Ag ion irradiated polyetherimide

The energetic heavy ion irradiation effects in polymers have drawn considerable attention for the application of polymers in radioactive environment. In the present paper, we report the Fourier transform infrared (FTIR) and UV–visible spectroscopic analysis and thermally stimulated depolarization current (TSDC) investigations in polyetherimide (PEI) samples (25 μm) irradiated with 100 MeV Ag ion at different fluences (5.6×1010, 1.8×1011, 1.8×1012 ions/cm2). The FTIR spectra of irradiated samples show an overall decrease in the intensity of all the typical bands, whereas the UV–visible spectra show a hyperchromic and bathochromic shift attributed to the formation of new defect sites. The radiation induced dehydrogenation of the methyl pendent group, opening of imide rings and the formation of carbonyl radicals and unsaturated C ˭ C bonds are the major conclusion drawn from the FTIR analysis. The TSDC spectra of pristine PEI comprises two current maxima termed as β- and α-peak with their respective locations around 80° and 190 °C. These are attributed to dipole-orientation and space charge relaxation, respectively. A significant effect of irradiation is observed on the whole TSDC spectrum. The β-peak vanishes due to demerization of carbonyl groups. Enhancement in the α-peak has been associated to the formation of new deep traps. Some new radiation induced relaxation processes have also been identified.

Thermally stimulated depolarization current behaviour of 75 MeV oxygen ion irradiated Kapton-H polyimide film

The thermally stimulated depolarization current (TSDC) technique has been used to investigate the various dielectric relaxation processes in high-energy ion irradiated Kapton-H polyimide. The 25 μm thick Kapton-H samples were irradiated with 75 MeV oxygen ions (fluences: 1.88×1011, 1.88×1012, 1.88×1013, 5.63×1012 ions/cm2) at the Nuclear Science Center (Pelletron Facility), New Delhi. The TSDC characteristics were obtained at a linear heating rate of 2 °C/min for different poling temperatures varying from 80 to 250 °C and poling fields from 160 to 400 kV/cm. The TSDC spectra mainly consist of four current maxima, viz. γ, β, α and ρ in the increasing order of temperature. The γ-relaxation has been attributed to the increased water absorptivity in Kapton-H due to irradiation. The demerization of carbonyl groups, cross-linking of imide groups and formation of free radicals due to energetic heavy ion irradiation in Kapton-H polyimide have been held responsible to govern the behaviour of β, α and ρ relaxations. In the vicinity of the β-relaxation, a new relaxation process, termed as δ-relaxation, is also observed. The activation energy values (0.78, 0.60, 1.04 and 1.32 eV for γ, β, α and ρ relaxations, respectively) for different relaxations were calculated by the Bucci plot method.

Interplay of Self-Doping and Disorder in Epitaxial Bi2Sr2Can-1CunO2n+4+x (n=1,2) Thin Films under Heavy-Ion Irradiation

We propose a novel mechanism for the modification of T(c) in Bi(2)Sr(2)Ca(n-1)Cu(n)O(2n+4+x) epitaxial thin films (2212 and 2201) under energetic heavy-ion irradiation. By irradiating films with various oxygen content, we show from the temperature dependence of the resistance that irradiation always produces a doping effect superimposed on the damage caused to the sample. The effect is larger in 2201 than in 2212 thin films. The T(c) decrease observed by irradiating optimally doped films is partially due to this doping effect. Irradiation of semiconducting samples restores metallic superconducting behavior.

Combination of electrochemical hydrogenation and Mössbauer spectroscopy as a tool to show the radiation effect of energetic heavy ions in Fe–Zr amorphous alloys

Radiation effects of energetic heavy ion irradiation in Fe–Zr amorphous alloys were investigated by the help of Mössbauer spectroscopy, X-ray diffraction and electrolytical hydrogenation. The electrolytical hydrogenation of non-irradiated and irradiated samples was carried out by a unique cathodic potential (−1000 mV versus SHE). The combination of electrolytical hydrogenation and Mössbauer analysis gives a very sensitive method for detecting structural changes of these amorphous alloys. It was found that the structural changes in the amorphous state, which are undetectable without hydrogenation by Mössbauer spectroscopy, modify the localization and the concentration of introduced hydrogen, and are reflected in a significant change of magnetic hyperfine interaction. The results can be associated with structural changes due to the effect of energetic heavy ion irradiation.

Energetic heavy ion irradiation effect in Fe layers studied by Mössbauer spectroscopy

Mössbauer spectroscopy was applied to study radiation damage in evaporated Fe layers irradiated with 209 MeV 84Kr ions at room temperature. Significant differences have been shown between the Mössbauer spectra of the unirradiated and the irradiated samples. The increase of a nonmagnetic component of the spectra as well as a magnetic component around 270 kOe was observed due to the irradiation. The changes were also analysed using the hyperfine field distribution obtained from the spectra. The results can be interpreted as the formation and the increase of proportion of highly disordered phases in Fe layer due to irradiation with energetic heavy ions.