Depth profiling of Al2O3 + TiO2 nanolaminates by means of a time-of-flight energy spectrometer

Atomic layer deposition (ALD) is currently a widespread method to grow conformal thin films with a sub-nm thickness control. By using ALD for nanolaminate oxides, it is possible to fine tune the electrical, optical and mechanical properties of thin films. In this study the elemental depth profiles and surface roughnesses were determined for Al₂O₃ + TiO₂ nanolaminates with nominal single-layer thicknesses of 1, 2, 5, 10 and 20 nm and total thickness between 40 nm and 60 nm. The depth profiles were measured by means of a time-of-flight elastic recoil detection analysis (ToF-ERDA) spectrometer recently installed at the University of Jyväskylä. In TOF-E measurements ⁶³Cu, ³⁵Cl, ¹²C and ⁴He ions with energies ranging from 0.5 to 10 MeV, were used and depth profiles of the whole nanolaminate film could be analyzed down to 5 nm individual layer thickness.     

Study on effects of swift heavy ion irradiation on the crystal structure in CeO2 doped with Gd2O3

To simulate the effects of Gd₂O₃-doping and high-energy fission products in UO₂, Gd₂O₃-doped CeO₂ pellets were irradiated with 200-MeV Xe¹⁴⁺ ions. Doping and irradiation effects were analyzed using X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS). The lattice constant of CeO₂ decreases and the local structure is disordered with increased doping levels. However, the irradiation induces an expansion of the lattice and a disordering of atomic arrangement near the Gd atoms. The effects of the irradiation become more pronounced with increasing Gd₂O₃-dopant levels. Our results are compared with those of a study involving Er₂O₃-doped CeO₂.     

Effects of swift heavy ion irradiation on the structure of Er2O3-doped CeO2

In order to simulate the effects of burnable poison doping on the fission fragment damage of UO₂ nuclear fuels, Er₂O₃-doped CeO₂ pellets were irradiated with 200 MeV Xe¹⁴⁺ ions. The irradiation effect was measured by means of X-ray diffraction (XRD). The expansion of lattice and the disordering of atomic arrangement due to the irradiation become more remarkable with increasing the concentration of the Er₂O₃ dopant.     

Ion guiding through capillaries in uncoated Al2O3 membranes

We made an experimental study on ion guiding through capillaries in uncoated Al₂O₃ membranes using a variety of ions such as O¹⁺, O³⁺, and O⁶⁺. The incident energy was varied within the range of 30-150 keV. The results were compared with others using coated PET and Al₂O₃ capillary membranes as well as with the so-called scaling law discovered by Stolterfoht and his co-workers. Good agreement of our results with the scaling law was found. However, our membranes showed extraordinarily strong guiding ability. The reason lies in that our membranes were uncoated. A slower charge drift speed along the insulating capillary wall and a much larger equilibrium charge Q_∞ seems to exist in our experiment.     

Mössbauer study and structural characterization of UO2–Gd2O3 sintered compounds

Samples of UO₂and up to 10 wt% of Gd₂O₃ were prepared by solid-state reaction under a reducing atmosphere, in a thermal path comprising ramps and dwell times in the temperature range of 900–1750 °C. The sintered material was analyzed by X-ray diffraction and ¹⁵⁵Gd Mössbauer spectroscopy. The results showed that for samples annealed up to 900 °C, the gadolinium sesquioxide remained unreacted. However, when the temperature was increased to 1300 °C, a solid-state reaction took place forming mixed oxides. For the more severe sintering condition, at 1750 °C, gadolinia left urania partially unreacted producing a material consisting of two compositions, UO₂ (with no dissolved gadolinium) and (U, Gd)O₂. The proposed heating cycle provided pellets free from Gd₂O₃ phase and may be used by the nuclear fuel industry as a suitable sintering process.     

Vacuum plasma etching of 1 wt% La2O3 dispersed tungsten

Vacuum plasma etching of 1 wt% La₂O₃ doped tungsten alloy surfaces were carried out to refine the surface morphology for enhancing its bonding characteristics with copper for fusion reactor components. Three different gas compositions containing argon with zero, 14.3 and 25 vol% hydrogen were used to carry out the plasma etching from 30 to 120 s on the given samples. Mitutoyo surface roughness (R_a) measurement, FORM TALYSURF and scanning electron microscopy (SEM) were employed to measure the changes in the surface roughness. Plasma etching with 14.3 vol% hydrogen mixture was found to be the best in micro-roughening the alloy surface. The maximum increase of 44% in R_a value was obtained with this gas mixture, when etched for 90 s.     

Nanoparticles of Al2O3:Cr as a sensitive thermoluminescent material for high exposures of gamma rays irradiations

Aluminum Oxide (Al₂O₃) doped with proper activators is a highly sensitive phosphor commonly used for radiation dosimetry using thermoluminescence (TL) technique. Nanoparticles of this material activated with Chromium (Cr) have been synthesized using the propellant chemical combustion technique and studied for their TL response. They were characterized by X-ray diffraction and scanning electron microscope. The synthesized material has spherical nanoparticles with grain size around 25 nm. These nanoparticles were exposed to heavy doses from γ-rays of ¹³⁷Cs. The TL glow curves show a prominent peak at around 474 K. This peak is found to be sensitive for high exposures of γ-rays and has linear response in the range of 100 Gy-20 kGy without showing saturation. This remarkable result suggests that Al₂O₃:Cr nanoparticles might be used for the dosimetry of food and seed irradiations.     

Study of the magnetic modifications of Fe3O4 ferrite thin films induced by 2.03 GeV Kr ions irradiation

The effect of 2.03 GeV Kr²⁶⁺ ions irradiation on antiphase boundaries (APBs) of polycrystalline Fe₃O₄ ferrite thin films has been investigated. The structure, magnetic and electrical transport properties of samples were characterized. The initial crystallographic structure of the Fe₃O₄ remains unaffected after Kr-ion irradiation, but the magnetic and electrical transports properties are sensitive to swift heavy ions (SHI) irradiation and exhibit different behaviors depending on the Kr-ion fluence range. The energy deposition is mainly due to the electronic energy loss (S_e) and the large value of energy transferred induces an unusual density of defects, stress and heat annealing effect in the samples, which can affect on the arrangement of magnetic moments and APBs density strongly. On the basis of our observations we conclude that the production, accumulation and free of the defects and stress induced by SHI irradiation is more dominant in the case of the magnetic and electrical transport properties modifications of the Fe₃O₄ thin films.     

Development and evaluation of a new Eu/SmPd3 source for use with Gd Mössbauer spectroscopy

A ¹⁵⁵Eu/¹⁵⁴SmPd₃ (about 231 MBq) source for use with ¹⁵⁵Gd Mössbauer spectroscopy was developed by a novel method. In the novel method, the isotopically enriched ¹⁵⁴SmPd₃ compound was prepared by the conventional solid state reaction of ¹⁵⁴Sm(HCOO)₃ and PdH_x in a hydrogen atmosphere at 1273 K for 18 h, which is simpler than the previously reported method. In order to increase the reaction areas, palladium fine particles used to synthesize the PdH_x hydride were prepared by a chemical solution process. Performance of the newly developed source was evaluated by observing the ¹⁵⁵Gd Mössbauer spectra of known compounds, GdPd₃ and cubic Gd₂O₃ at 12 K. The obtained results indicated that the developed source is fine enough to investigate the structural characteristic of various materials containing gadolinium.     

Clarification of high density electronic excitation effects on the microstructural evolution in UO2

In order to understand the properties of ion tracks and the microstructural evolution under accumulation of ion tracks in UO₂, 100 MeV Zr¹⁰⁺ and 210 MeV Xe¹⁴⁺ ions irradiation examinations have been done at a tandem accelerator facility of JAEA-Tokai, and it has been observed the microstructure by means of a transmission electron microscope (TEM) and a scanning electron microscope (SEM) in CRIEPI.Comparison of the diameter of ion tracks between UO₂ and CeO₂ under irradiation with 100 MeV Zr¹⁰⁺ and 210 MeV Xe¹⁴⁺ ions at room temperature clarify that the sensitivity on high density electronic excitation of UO₂ is much less than that of CeO₂. By the cross-sectional observation of UO₂ under irradiation with 210 MeV Xe¹⁴⁺ ions at 300 °C, elliptical changes of fabricated pores that exist till ∼6 μm depth and the formation of dislocations have been observed in the ion fluence over 5 × 10¹⁴ ions/cm². The drastic changes of surface morphology and inner structure in UO₂ indicate that the overlapping of ion tracks will cause the point defects, enhance the diffusion of point defects and dislocations, and form the sub-grains at relatively low temperature.     

Localised modifications of anatase TiO2 thin films by a Focused Ion Beam

A Focused Ion Beam (FIB) has been used to implant micrometer-sized areas of polycrystalline anatase TiO₂ thin films with Ga⁺ ions using fluencies from 10¹⁵ to 10¹⁷ ions/cm². The evolution of the surface morphology was studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM). In addition, the chemical modifications of the surface were followed by X-ray photoelectron spectroscopy (XPS). The implanted areas show a noticeable change in surface morphology as compared to the as-deposited surface. The surface loses its grainy morphology to gradually become a smooth surface with a RMS roughness of less than 1 nm for the highest ion fluence used. The surface recession or depth of the irradiated area increases with ion fluence, but the rate with which the depth increases changes at around 5 × 10¹⁶ ions/cm². Comparison with implantation of a pre-irradiated surface indicates that the initial surface morphology may have a large effect on the surface recession rate. Detailed analysis of the XPS spectra shows that the oxidation state of Ti and O apparently does not change, whereas the implanted gallium exists in an oxidation state related to Ga₂O₃.     

Influence on the structural characteristic of defect solid solution GdxZr1−xO2−x/2 with 0.18 ? x ? 0.62 under longer term annealing studied by Gd Mössbauer spectroscopy

Three kinds of defect solid solution Gd_xZr_1−xO_2−x/2 with 0.18 ? x ? 0.62, including the three single crystal samples with x = 0.21, 0.26 and 0.30, were investigated by ¹⁵⁵Gd Mössbauer spectroscopy at 12 K. Difference in the structural characteristic under longer term annealing were confirmed by comparing the ¹⁵⁵Gd Mössbauer parameters of the polycrystalline samples sintered one time and twice at 1773 K for 16 h in air, respectively. The results indicated that the polycrystalline samples sintered twice have relatively equilibrated structure by comparing with the three single crystal samples. After being sintered twice, basically the local structure around the Gd³⁺ ions does not change, but the degree of the displacements of the six 48f oxygen ions from positions of cubic symmetry becomes slightly smaller, and distribution of the Gd³⁺ ions in the system becomes more homogeneous.     

Amorphisation of ZnAl2O4 spinel under heavy ion irradiation

ZnAl₂O₄ spinels have been irradiated with several ions (Ne, S, Kr and Xe) at the IRRSUD beamline of the GANIL facility, in order to determine irradiation conditions (stopping power, fluence) for amorphisation. We observed by transmission electron microscopy (TEM) that with Xe ions at 92 MeV, individual ion tracks are still crystalline, whereas an amorphisation starts below a fluence of 5 × 10¹² cm⁻² up to a total amorphisation between 1 × 10¹³ and 1 × 10¹⁴ cm⁻². The coexistence of amorphous and crystalline domains in the same pristine grain is clearly visible in the TEM images. All the crystalline domains remain close to the same orientation as the original grain. According to TEM and X-ray Diffraction (XRD) results, the stopping power threshold for amorphisation is between 9 and 12 keV nm⁻¹.     

Secondary electron yield of Au and Al2O3 surfaces from swift heavy ion impact in the 2.5-7.9 MeV/amu energy range

We report on the secondary electron yields of Au and oxidized aluminum (Al₂O₃) by impact of heavy ions with energies ranging from 7.92 MeV/amu (¹²C₆) to 2.54 MeV/amu (¹⁰⁷Ag₄₇). The obtained results, the first in this energy range using medium-heavy ions, extend the validity of proposed scaling laws obtained with lighter ions. Measurements have been performed using the SIRAD irradiation facility at the 15 MV Tandem of the INFN Laboratory of Legnaro (Italy), to evaluate the performance of ion electron emission microscopy at SIRAD.     

Effect of Ag and Li ion irradiation on superconducting Tl2Ca2Ba2Cu3O10 single crystals

The effect of irradiation by 50 MeV Li³⁺ and 200 MeV Ag¹⁵⁺ ions on single crystals of Tl₂Ca₂Ba₂Cu₃O₁₀ (Tl2223) superconductor has been investigated at different fluences. Isothermal magnetization hysteresis loops have been recorded at different temperatures using a SQUID magnetometer and the effect of irradiation on the critical current density, irreversible field, second magnetization peak and pinning force has been studied. Irradiation by 200 MeV Ag¹⁵⁺ ions resulted in increased hysteresis and irreversibility field while no change in second magnetization peak position and critical temperature was observed. A broadening in the hysteresis loop before the second magnetization peak was also observed for the crystals irradiated by Li³⁺ ions. Annealing of irradiated crystals at 500 °C resulted in reduction of point defects created by Li³⁺ ions.     

Effect of 200 MeV Ag ion irradiation on structural and electrical transport properties of Fe3O4 thin films

Thin films of Fe₃O₄ have been deposited on single crystal MgO(1 0 0) and Si(1 0 0) substrates using pulsed laser deposition. Films grown on MgO substrate are epitaxial with c-axis orientation whereas, films on Si substrate are highly 〈1 1 1〉 oriented. Film thicknesses are 150 nm. These films have been irradiated with 200 MeV Ag ions. We study the effect of the irradiation on structural and electrical transport properties of these films. The fluence value of irradiation has been varied in the range of 5 × 10¹⁰ ions/cm² to 1 × 10¹² ions/cm². We compare the irradiation induced modifications on various physical properties between the c-axis oriented epitaxial film and non epitaxial but 〈1 1 1〉 oriented film. The pristine film on Si substrate shows Verwey transition (T_V) close to 125 K, which is higher than generally observed in single crystals (121 K). After the irradiation with the 5 × 10¹⁰ ions/cm² fluence value, T_V shifts to 122 K, closer to the single crystal value. However, with the higher fluence (1 × 10¹² ions/cm²) irradiation, T_V again shifts to 125 K.     

Bulk-compositional changes of Ni2Al3 and NiAl3 during ion etching

Bulk-compositional changes of Ni₂Al₃ and NiAl₃ in a Ni-50 wt% Al alloy during ion etching have been investigated by transmission electron microscopy and energy dispersive X-ray spectroscopic analyses. After etching with 7, 5 and 3 keV Ar⁺ ions for 15, 24 and 100 h nickel contents in both Ni₂Al₃ and NiAl₃ exceeded greatly those in the initial compounds and increased with the decrement of the sputtering energy. After 100 h etching with 3 keV Ar⁺ ions the compositions of these two compounds reached a similar value, about Ni_80-83Al_12-15Fe_3-4Cr_1-2 (at%). A synergistic action of preferential sputtering, radiation-induced segregation and radiation-enhanced diffusion enables the altered-layers at the top and bottom of the film extend through the whole film. The bulk-compositional changes are proposed to occur in the unsteady-state sputtering regime of ion etching and caused by an insufficient supply of matter in a thin film.     

Alpha-decay induced amorphization of Cm-doped Gd2TiZrO7

The sample of pyrochlore-based ceramic doped with a ²⁴⁴Cm isotope with a target composition Gd_1.935Cm_0.065 TiZrO₇ was prepared by cold pressing and sintering. The pyrochlore structure phase was predominant in the sample but minor perovskite and gadolinium zirconate (ideally Gd₂Zr₂O_7−x) were also present. The Ti/Zr pyrochlore phase was rendered amorphous at a dose of 4.6 × 10¹⁸ α-decays/g (0.60 dpa). Volume expansion of the pyrochlore lattice was found to be 2.7 vol.% at a dose of 3.85 × 10¹⁸ α-decays/g.     

Swift heavy ion irradiation-induced microstructure modification of two delta-phase oxides: Sc4Zr3O12 and Lu4Zr3O12

Swift gold ions (185 MeV) were used to systematically investigate the radiation damage response of delta phase compounds Sc₄Zr₃O₁₂ and Lu₄Zr₃O₁₂ in the electronic energy loss regime. Ion irradiation-induced microstructural modifications were examined using X-ray diffraction (XRD) and transmission electron microscopy (TEM). XRD investigations indicate a phase transformation from ordered rhombohedral to disordered fluorite (O-D) in both compounds, with the Sc compound transforming at a higher ion fluence compared with the Lu compound. This result is consistent with our previous study on Sc₄Zr₃O₁₂ and Lu₄Zr₃O₁₂ under displacive radiation environment in which the nuclear energy loss is dominant. High resolution TEM revealed that individual ion tracks maintain crystalline structure, while the core region experiences an O-D phase transformation. TEM observations also suggest that for the doses in which the tracks overlap, the O-D phase transformation occurs across the entire ion range.     

Microstructural evolution in irradiated uranium-bearing delta-phase oxides A6U1O12 (A = Y, Gd, Ho, Yb, and Lu)

Irradiation-induced microstructural evolution in uranium-bearing delta-phase oxides of A₆U₁O₁₂ (A = rare earth cations) were characterized using grazing incidence X-ray diffraction and transmission electron microscopy. Polycrystalline Y₆U₁O₁₂, Gd₆U₁O₁₂, Ho₆U₁O₁₂, Yb₆U₁O₁₂, and Lu₆U₁O₁₂ samples were irradiated with 300 keV Kr⁺⁺ to a fluence of 2 × 10²⁰ ions/m² at cryogenic temperature (∼100 K). The crystal structure of these compounds was determined to be an ordered, fluorite derivative structure, known as the delta-phase, a rhombohedral symmetry belonging to space group . Experimental results indicate that all these compounds are resistant to amorphization to a displacement damage dose of ∼60 displacements per atom. In these experiments, we sometimes observed an irradiation-induced order-to-disorder phase transformation, from an ordered rhombohedral to a disordered fluorite structure.