Energetic Ion Beam Irradiation Research Articles

Swelling as a stabilizing mechanism in irradiated thin films: II. Effect of swelling rate

It has long been observed experimentally that energetic ion-beam irradiation of semiconductor surfaces may lead to spontaneous nanopattern formation. For most ion/target/energy combinations, the patterns appear when the angle of incidence exceeds a critical angle, and the models commonly employed to understand this phenomenon exhibit the same behavioral transition. However, under certain conditions, patterns do not appear for any angle of incidence, suggesting an important mismatch between experiment and theory. Previous work by our group (Swenson and Norris 2018 J. Phys.: Condens. Matter 30 304003) proposed a model incorporating radiation-induced swelling, which is known to occur experimentally, and found that in the analytically-tractable limit of small swelling rates, this effect is stabilizing at all angles of incidence, which may explain the observed suppression of ripples. However, at that time, it was not clear how the proposed model would scale with increased swelling rate. In the present work, we generalize that analysis to the case of arbitrary swelling rates. Using a numerical approach, we find that the stabilization effect persists for arbitrarily large swelling rates, and maintains a stability profile largely similar to that of the small swelling case. Our findings strongly support the inclusion of a swelling mechanism in models of pattern formation under ion beam irradiation, and suggest that the simpler small-swelling limit is an adequate approximation for the full mechanism. They also highlight the need for more—and more detailed—experimental measurements of material stresses during pattern formation.

Effects of varying ion flux on high vacuum evaporated erbium thin films

For the first time, to the best of our knowledge, a comprehensive study has been carried out to investigate the effects of ion beam on erbium thin films. Thin enriched erbium films with areal density ∼50–200 μg/cm2 sandwiched between carbon films were prepared using the high vacuum deposition technique. The samples were bombarded with fluorine ion beam accelerated to 90 MeV energy using a tandem accelerator. Irradiation time was varied for each sample. Accelerator based characterization technique-Rutherford Backscattered Spectrometry (RBS) was used to study the structural changes induced by ion beam irradiation. The morphology and composition of the samples were studied using Field Emission Scanning Electron Microscopy (FE-SEM) and Energy Dispersive x-ray Spectroscopy (EDS), respectively. Comparisons have been drawn between the various samples and with pristine erbium sample. These results show that erbium films are quite stable under energetic ion beam irradiation. This makes their application in various fields dealing with high radiation protection and shielding possible.

Lattice structure transformation and change in surface hardness of Ni3Nb and Ni3Ta intermetallic compounds induced by energetic ion beam irradiation

Ni3Nb and Ni3Ta intermetallic compounds, which show the complicated lattice structures were irradiated with 16MeV Au5+ ions at room temperature. The X-ray diffraction measurement revealed that the lattice structure of these intermetallic compounds changed from the ordered structures to the amorphous state by the ion irradiation. The irradiation-induced amorphization caused the increase in Vickers hardness. The result was compared with our previous results for Ni3Al and Ni3V, and was discussed in terms of the intrinsic lattice structures of the samples.

Hardness modification of Al–Mg–Si alloy by using energetic ion beam irradiation

So far, we have irradiated Al–Mg–Si alloy with 5.4–16MeV several ions at room temperature, and have found that ion irradiation is a useful tool for controlling the surface hardness for Al–Mg–Si alloys. In the present study, we tried several experiments as some applications of ion beam irradiation for hardness modifications of Al–Mg–Si alloy. Main results are as follows; (1) the combination of ion beam irradiation and the subsequent thermal aging can be used as an effective tool for the hardness modification of Al–Mg–Si alloy, and (2) designated regions and areas of the specimen can be hardened by changing the energy of ion beam and producing the irradiated area and unirradiated area of the surface. Then, we can expand the possibility of the ion beam irradiation as a new process for the three-dimensional hardness modification of Al–Mg–Si alloy.

Magnetic modification at sub-surface of FeRh bulk by energetic ion beam irradiation

Ferromagnetic layered structure has been made at sub-surface of the antiferromagnetic FeRh bulk samples by high energy He ion beam irradiation. In accordance with the Transport of Ions in Matter simulation, such ion beam can effectively deposit the elastic collision energy in several μm regions in the depth from the surface. Measurement with a superconducting quantum interference device reveals the irradiated samples to be ferromagnetic. Assuming that only the part the energy deposited can be modified to be ferromagnetic, the corresponding irradiation induced magnetization is consistent with the data that we previously reported. On the other hand, the X-ray magnetic circular dichroism (XMCD) spectra for the irradiated samples are totally unchanged as those for the unirradiated samples. Since XMCD signal in total emission yield method is considered to be surface sensitive with a typical probing depth of several nm, the surface magnetic state is maintained to be antiferromagnetic. By utilizing these phenomena, three-dimensional magnetic patterning of FeRh can be realized, which may potentially be used for future magnetic exchange device application such as nano-scale sensors and memories.

放射光を用いた鉄ロジウム合金のイオンビーム照射誘起構造・磁気変態の研究

放射光を用いた鉄ロジウム合金のイオンビーム照射誘起構造・磁気変態の研究

Modification of microstructure and hardness for Cu–Ti alloy by means of energetic ion beam irradiation

Cu–Ti alloys were irradiated with5.4MeV Al ions, 7.3MeV Fe ions, 10MeV I ions, and 16MeV Au ions at room temperature and the Vickers microhardness was measured. The hardness once increases by the irradiation with a low fluence, and then it remains almost constant even with increasing the ion fluence. The change in hardness was well correlated with the density of energy deposited through the elastic collisions and not the electronic excitation. The observation of atom probe tomography (APT) did not show any Ti clusters in the irradiated specimens. This result suggests that not Ti clusters but lattic defects (interstitial atoms, vacancies and/or their aggregates) contributed to the increase in hardness of Cu–Ti alloys.

Change in magnetic and structural properties of FeRh thin films by gold cluster ion beam irradiation with the energy of 1.67 MeV/atom

The effect of energetic cluster ion beam irradiation on magnetic and structural properties of FeRh thin films have been investigated. The cluster ions used in the present studies consist of a few gold atoms with the energy of 1.67 MeV/gold atom. Saturation magnetization of the sample irradiated with Au3 cluster ion beam (280 emu/cc) is larger than that for the irradiated sample with Au1 ion beam (240 emu/cc) for the same irradiation ion fluence. These results can also be confirmed by the X-ray magnetic circular dichroism (XMCD) measurement; the XMCD signal for Au3 cluster ion irradiation is larger than that for Au1 ion irradiation. Since the ion beam irradiation induced magnetization of FeRh is significantly correlated with the amount of the lattice defects in the samples, cluster ion beam irradiation can be considered to effectively introduce the lattice defects in B2-type FeRh rather than the single ion beam. Consequently, cluster ion irradiation is better than single ion irradiation for the viewpoint of saturation magnetization, even if the same irradiation energy is deposited in the samples.

Improvements in the structural and optical properties of a-Si:H by a dense plasma focus

Crystallization of hydrogenated amorphous silicon thin films with irradiation by using a dense plasma focus ion beam source has been investigated. The effects of the energetic ion beam irradiation on the surface morphological, structural and optical properties of the as-prepared a-Si:H thin films were investigated with field emission scanning electron microscopy, high resolution transmission electron microscopy, Raman scattering spectroscopy and mapping, and photoluminescence (PL) spectroscopy. The results show that irradiation of the energetic ion beam leads to the agglomeration of the Si grains with formation of Si nanocrystallites embedded within the amorphous matrix. This significantly enhances the optical properties of the film that it exhibits a wide range of PL emission spectra at room temperature.

Transition Metal Doped ZnO as a Host of Dilute Magnetic Semiconductor

In the last couple of years, dilute magnetic semiconductor (DMS) has drawn significant interest in the scientific community. Primarily this is due to its potential for application in spintronic devices. The euphoria acquired momentum following the theoretical prediction that diamagnetic ZnO can be made ferromagnetic even at room temperature by doping with transition metal (TM) ions such as Mn. The exact nature of the ferromagnetic coupling of spins in such materials is a matter of debate. Actually the impurity phase assisted ferromagnetism is not intended. The observed ferromagnetism should definitely be intrinsic. Claims and counterclaims in this issue are the key of this debate. However, one important understanding has evolved that defects play crucial role in stabilizing the ferromagnetic state in DMS systems. Some kind of defects or disorder favors ferromagnetism and others compete with this phenomenon. An effort will be made to present the contemporary scenario of research in this field. So far as discussion of synthesis of TM doped ZnO is concerned both bulk pellet and films will be investigated. Emphasis will be made for development of TM doped ZnO nanostructured samples. Low cost simple synthesis route of formation will be highlighted for its cost-effectiveness in comparison to sophisticated physical methods. A thorough investigation will be made for characterization of the samples. Structural, morphological, electrical, optical and the most crucial magnetic properties of TM doped ZnO will be discussed. So far as magnetic properties are concerned a careful analysis will be made from the results of field and temperature-dependent dc magnetization measurements and further from ac susceptibility measurement. The correlation between defects and observed intrinsic ferromagnetism of the samples, the crucial role of valence state of TM in achieving intrinsic ferromagnetism and the analysis of X-ray photoelectron spectroscopy data that is crucial in determining valence state of TM will be discussed. Energetic ion beam irradiation is an efficient tool for introducing defect states in solid materials particularly for semiconductors. There is a wide range of studies of ion irradiation effects on TM doped ZnO. Actually controlled formation of defects along the trajectory of the ion beam modifies chemical and physical properties of the specimens. A careful attempt will be made to explore that formation of defects by ion beam irradiation somehow favors in achieving intrinsic ferromagnetism in the samples or not, since proper correlation of defects and magnetic properties of TM doped ZnO samples can really enhance the potential of this field of scientific research. To develop TM doped ZnO as a perfect DMS system, synthesis and characterization have to be done in a very specific way. Controlled formation of defects is a key in case of synthesis and ion beam irradiation can be manifested suitably in this respect. Characterization of defects for TM doped ZnO would be given prior importance to unfold the role they play.

Optical waveguides in laser crystals produced by energetic ion beam irradiation

Laser crystals are important gain media for solid state lasers. Optical waveguides are basic components in integrated photonics. By using energetic ion beam irradiation techniques, optical guiding structures can be produced in laser crystals, and miniaturized waveguide lasers can be realized. In this paper, the fundamentals and methods for laser crystal waveguide fabrication by using energetic ion beams are reviewed. The influence on the micro-fluorescence properties in the waveguide regions induced by the ion beams is overviewed. The latest progress on the crystalline waveguide lasers is introduced. The prospect on the ion beam irradiated optical waveguides in laser crystals is presented.

Effect of energetic ion beam irradiation on structural and optical properties of a-Si:H thin films

Hydrogenated amorphous silicon (a-Si:H) thin films deposited by radio-frequency plasma enhanced chemical vapor deposition were irradiated by an energetic argon ion beam source from a 3.3kJ Mather type dense plasma focus device. The effect of the energetic ion beam irradiation on the structural and optical properties of a-Si:H thin films has been studied. The results show that irradiation of the energetic ion beam leads to the formation of Si nano-crystallites embedded within the amorphous matrix. This significantly improves the optical properties of the films, which include widening of the optical band gap and exhibiting wide range of photoluminescence (PL) emission spectra at room temperature. The correlations of the PL peak energy and intensity with the optical energy gap and crystalline volume fraction in the variation of number of shots are discussed.

Response of synthetic coffinite to energetic ion beam irradiation

Coffinite, USiO 4, is one of the two most abundant and important naturally occurring U 4+ phases (the other is UO 2), and it is an alteration product of the UO 2 in spent nuclear fuel when in contact with silica-rich groundwater under reducing conditions. Despite its ubiquity, there are very limited data on the response of coffinite to radiation. Here, we present the results of the first systematic investigation of energetic ion beam irradiation (1 MeV Kr 2+) of ultra-fine, synthetic coffinite (20–50 nm). In situ transmission electron microscopy (TEM) showed that the crystalline-to-amorphous transformation occurs at a relatively low dose, ∼0.27 displacements per atom (dpa) at room temperature. The critical temperature, T c , above which coffinite cannot be amorphized, is low (∼608 K). Synthetic coffinite is more stable as compared with isostructural zircon (ZrSiO 4; T c = 1000 K) and thorite (ThSiO 4; T c above 1100 K) upon ion beam irradiation at elevated temperature, suggesting enhanced defect annealing behavior in nano-sized synthetic coffinite. Irradiation was found to decrease the temperature required to induce phase decomposition process in coffinite upon thermal annealing. A good correlation among the critical amorphization temperature, T c , phase decomposition temperature, T f , and the temperature range of the two-phase (ZrO 2 and SiO 2) co-existed region was identified.

Radiation Effects on Materials in the Near-Field of a Nuclear Waste Repository

ABSTRACTThe long-term radiation effects on materials in the near-field of a nuclear waste repository have been evaluated using accelerated laboratory experiments with energetic electron or ion beam irradiation. The materials studied include: zeolites, layered silicates (smectite clay and mica), as well as crystalline silicotitanate (CST) which is an important ion exchange material for the chemical separation of high-level liquid radioactive wastes.In situ transmission electron microscopy (TEM) during irradiation by energetic electrons and ions has shown that all of the studied materials are susceptible to irradiation-induced amorphization. At room temperature, complete amorphization was observed after ionizing doses of 1010 ∼ 1012 Gy or displacement doses on the order of 0.1 dpa (equivalent to doses received in 400-1,000 years for a high-loading nuclear waste form). Amorphization may be preceded or accompanied by dehydration, layer spacing reduction and gas bubble formation. In the case of zeolites, CST and some layered silicates, radiation effects are significantly enhanced at higher temperatures. Our experiments have shown that amorphization or even partial amorphization will cause a dramatic reduction in ion exchange and sorption/desorption capacities for radionuclides, such as Cs and Sr. Because the near-field or chemical processing materials (e.g. zeolites or CST) will receive a substantial radiation dose after they have incorporated radionuclides, our results suggest that radiation effects may, in some cases, retard the release of sorbed or ion-exchanged radionuclides.

Amorphous-crystal silicon interfaces: structure and movement under ion beam irradiation

Our recent work on the kinetics of the crystal Si/amorphous Si (c-Si/a-Si) interface motion induced by energetic ion beam irradiation is reported. Ion beam irradiation may result in either epitaxial crystallization or planar layer-by-layer amorphization depending on the substrate temperature. In both cases the interface motion has been characterized by in situ reflectivity measurements and by ex situ Rutherford backscattering and channeling. At temperatures ⩾ 150°C crystallization occurs. In this regime the interface motion depends linearly on the energy deposited into elastic collisions by the impinging ions, is ∼ 4 times faster onto 〈100〉 than onto 〈111〉 oriented substrates and is influenced by the presence of impurities at the c-a interface. As soon as the temperature is lowered below 150°C the interface motion is reversed and amorphization occurs. In this regime both substrate orientation and impurities have a negligible effect on the kinetics of the process. The data will be discussed and analyzed in terms of a phenomenological model in which competitive processes between defect generation and annihilation at the c-a interface determine the evolution of the transition.

Influence of doping on ion-induced growth and shrinkage of partial damage in silicon

In this work we report the first experimental evidence that the balance between dynamic crystallization and amorphization is influenced by the presence of dopants through a detailed study on the effects produced by energetic ion beam irradiation on partially damaged, doped Si crystals. Predamaging was produced by room temperature 150 keV Au + implantations to a dose of 2 × 10 13/cm 2 onto undoped, B-doped, and P-doped 〈100〉 oriented Si single crystals. The doping species were present in the samples at concentrations in the range 1.5 × 10 20−2 × 10 21/cm 3. The low dose Au implants resulted in the formation of small damage clusters embedded in a defect-free crystal matrix. Samples were subsequently irradiated by 600 keV Kr2 + ions at different doses and at temperatures in the range 350–500 K. In the case of undoped samples a reordering of the damage clusters is observed for substrate temperatures above 420 K (critical temperature). At lower temperatures damage accumulation is observed. Doping strongly influences the balance between damage accumulation and reordering: the critical temperature becomes 390 K for P-doped samples at a concentration of ∼ 2 × 10 20 P/cm 2 and 360 K for P-doped samples at a concentration of ∼ 2 × 10 21/cm 3. This behavior is discussed and explained on the basis of a phenomenological model.

Effects of heavy ion irradiation on amorphous hydrogenated (diamondlike) carbon films

Energetic ion-beam irradiation of diamondlike carbon thin films induces a decrease of 5–6 orders of magnitude in the resistivity of the films from their as-grown value of 107 Ω cm. Diagnostics used to characterize the nature of the transformation included optical absorption measurements (band gap), Raman spectroscopy (microcrystalline structure), Rutherford backscattering spectroscopy (hydrogen content of the films), and measurements of the temperature dependence of the conductivity (electronic structure). It was found that the initial decrease in resistivity with an increasing ion dose is due to the loss of hydrogen from the films, with a concomitant decrease in the optical band gap. Heating the films during the irradiation greatly accelerates the rate of hydrogen loss as a function of dose. Once the hydrogen removal is complete, further irradiation increases the film conductivity by inducing the growth of microcrystallites of graphite.

Ion beam induced conductivity and structural changes in diamondlike carbon coatings

Energetic ion beam irradiation of diamondlike carbon thin films induces a decrease of 4–5 orders of magnitude in the resistivity of the films from their as-grown value of 107 Ω cm. The initial decrease in resistivity with increasing ion dose is due to the loss of hydrogen from the films with a concomitant decrease in the optical band gap. Heating the films during the irradiation greatly accelerates the rate of hydrogen loss as a function of dose. Once the hydrogen removal is complete, further irradiation increases the film conductivity by inducing the growth of microcrystallites of graphite.