MeV Xe Ions Research Articles

Structural and optical study of irradiation effect in GaN epilayers induced by 308 MeV Xe ions

Wurtzite GaN epilayers irradiated at room temperature with 308 MeV 129Xe 35+ ions to fluences of 1 × 10 13 and 3 × 10 13 cm −2 have been studied by contact mode atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), micro-Raman scattering and photoluminescence (PL) spectroscopy. The AFM images showed that the surface of GaN films was etched efficiently due to the Xe ion irradiation. The initial step-terrace structure on GaN surface was eliminated completely at a fluence of 3 × 10 13 cm −2. HRXRD and Raman results indicated that the Xe ion irradiation led to a homogenous lattice expansion throughout the entire ∼3 μm-thick GaN films. The lattice expansion as well as the biaxial compressive stress of the films was increasing with the increase of ion fluence. PL measurements showed that a dominant yellow luminescence band in the as-grown GaN films disappeared, but a blue and a green luminescence bands were produced after irradiation. Based on these results, the strong electronic excitation effect of 308 MeV Xe ions in GaN is discussed.

Study on ion-irradiation-induced ferromagnetism in FeRh intermetallic compound by means of magnetic Compton scattering

The magnetic Compton profiles of Fe–50 at. % Rh intermetallic compound were measured to study the ferromagnetism induced by 200 MeV Xe ion irradiation. The magnetic effect at 50 K increases with increasing the ion-fluence. The analysis of the experimental result revealed that the values of spin moment induced by the irradiation were close to the values of magnetization obtained by a superconducting quantum interference device magnetometer, suggesting that the ion irradiation mainly induces the spin magnetic moment. The difference in magnetic Compton profiles between the irradiation-induced ferromagnetism and the intrinsic ferromagnetism in pure Fe is also discussed.

Raman investigation of incident N-, Xe-ions induced effects in ZnO thin films

Highly c-axis orientation ZnO thin films with hundreds nanometers in thickness have been deposited on (1 0 0) Si substrate by RF magnetron sputtering. These films are implanted at room temperature by 80 keV N-ions with fluences from 5.0 × 10 14 to 1.0 × 10 17 ions/cm 2, implanted by 400 keV Xe-ions with 2.0 × 10 14 to 2.0 × 10 16 ions/cm 2, irradiated by 3.64 MeV Xe-ions with 1.0 × 10 12 to 1.0 × 10 15 ions/cm 2, or irradiated by 308 MeV Xe-ions with 1.0 × 10 12 to 5.0 × 10 14 ions/cm 2, respectively. Then the ZnO films are investigated using a Raman spectroscopy. The obtained Raman spectra show that a new Raman peak located at about 578 cm −1 relating to simple defects or disorder phase appears in all ZnO films after ion implantation/irradiation, a new Raman peak at about 275 cm –1 owing to N-activated zinc-like vibrations is observed in the N-implanted samples. Moreover, a new Raman peak at about 475 cm −1 is only seen in the samples after 400 keV and 3.64 MeV Xe-ions bombardment. The area intensity of these peaks increases with increasing ion fluence. The effects of ion fluence, element chemical activity, atom displacements induced by nuclear collisions as well as energy deposition on the damage process of ZnO films under ion implantation/irradiation are discussed briefly.

A study of defects in electron- and ion-irradiated ZrCuAl bulk glassy alloy using positron annihilation techniques

Free volume changes in Zr50Cu40Al10 bulk glassy alloys irradiated by 200 and 2.5 MeV Xe ions, 180 keV He ions, and 2 MeV electrons were investigated at room temperature using positron annihilation lifetime and Doppler broadening techniques. In addition, a slow positron beam was used to probe the change in free volume in the 180 keV He ion-irradiated sample. X-ray diffraction revealed that no crystallization took place in any of the irradiated samples. The Doppler broadening spectra from the annihilated gamma rays remained essentially constant in all ion-irradiation cases; however, an extremely minor change of positron mean lifetime was detected in each case. For electron- and He ion-irradiated samples the positron lifetime increased, and the opposite was seen in heavy-ion irradiated samples. The Doppler broadening S parameter increased with He-ion radiation dose, and the depth profile correlated well to the damage profile.

Irradiation Damage in Ti3(Si,Al)C2: a TEM Investigation

Ti3SiC2, belonging to MAX phases, is a potential candidate material, which could be incorporated in core components of future gas‐cooled fast nuclear reactors (GFR). Despite extensive work on mechanical behavior, corrosion resistance, or electrical properties, data concerning the evolution of Ti3SiC2 under irradiation are very limited. In this work, Ti3(Si,Al)C2 was irradiated at room temperature with 92 MeV Xe ions to induce irradiation damage. The samples were investigated by transmission electron microscopy (TEM) through front view and cross‐section observations, which allowed to follow microstructure changes from 0.02 dpa up to 6.67 dpa. Progressive atomic disorder versus dose was highlighted, leading to extinction of some diffraction spots (at 0.15 dpa) and then diffuse patterns (at 3 dpa). The ABABACAC periodicity related to 3‐1‐2 MAX phases was lost but the image fringes of basal plans could still be identified and no amorphous ring occurred. This means that Ti3(Si,Al)C2 was strongly affected by irradiation but did not turn to amorphous even at 6.67 dpa. This important result was correlated to previous conclusions from X‐ray diffraction and nanoindentation analysis and suggests the good behavior of Ti3(Si,Al)C2 under irradiation in the target temperature range assigned to GFR.

Mechanical properties of fluorite-related oxides subjected to swift ion irradiation: Pyrochlore and zirconia

The modifications of the mechanical properties of related-fluorite oxides (cubic zirconia [c-ZrO 2] and pyrochlores [Gd 2(Ti 1− x Zr x ) 2O 7 with x = 0.5 and x = 1]) induced by swift heavy ion irradiation are investigated. Polycrystalline pellets of both materials were irradiated at room temperature with 940 MeV Pb or 870 MeV Xe ions at the GANIL accelerator in Caen at fluences ranging from 2 × 10 11 to 10 13 cm −2. Residual macroscopic stresses induced by irradiation were determined using X-ray diffraction and the sin 2ψ method. The microhardness and the fracture toughness of irradiated samples were studied by Vickers micro-indentation. Amorphization occurs in Gd 2TiZrO 7 and not in Gd 2Zr 2O 7 and c-ZrO 2. The mechanical behavior of materials is found to be closely related to the residual stresses induced in the surface layer by irradiation. Compressive stresses are generated in c-ZrO 2 and Gd 2TiZrO 7 (leading to an increase of fracture toughness), whereas tensile stresses (inducing a large decrease of fracture toughness) are observed in Gd 2Zr 2O 7 due to the lattice contraction related to a pyrochlore fluorite→transition.

Behavior of free volume in ZrCuAl bulk metallic glass after irradiation

Free volumes in Zr50Cu40Al10 bulk metallic glasses irradiated by 100 MeV and 200 MeV Xe ions and 2 MeV electrons at room temperature have been investigated by using positron annihilation techniques, the micro Vickers hardness and X-ray diffraction measurements. No crystallization took place due to both ion and electron irradiations. The coincidence Doppler broadening spectra of annihilation gamma rays also remained unchanged by ion and electron irradiation. Meanwhile, an increase and a decrease of positron lifetimes after electron and ion irradiation, respectively, were observed. This suggests the structural modification of free volumes. The response of positron lifetime to ion and electron irradiations may be connected with the tendency of hardness.

Light-emitting Si nanostructures formed in silica layers by irradiation with swift heavy ions

Thin SiO2 layers were implanted with 140 keV Si ions to a dose of 1017 cm−2. The samples were irradiated with 130 Mev Xe ions in the dose range of 3×1012–1014 cm−2, either directly after implantation or after pre-annealing to form the embedded Si nanocrystals. In the as-implanted layers HREM revealed after Xe irradiations the 3–4 nm-size dark spots, whose number and size grew with increase in Xe dose. A photoluminescence band at 660–680 nm was observed in the layers with the intensity dependent on the Xe dose. It was found that passivation with hydrogen quenched that band and promoted emission at ∼780 nm, typical of Si nanocrystals. In spectra of pre-annealed layers strong ∼780 nm peak was observed initially. Under Xe bombardment its intensity fell, with subsequent appearance and growth of 660–680 nm band. The obtained results are interpreted as the emission at ∼660–680 nm belonging to the imperfect Si nanocrystals. It is concluded that electronic losses of Xe ions are mainly responsible for formation of new Si nanostructures in ion tracks, whereas elastic losses mainly introduce radiation defects, which quench the luminescence. Changes in the spectra with growth of Xe ion dose are accounted for by the difference in the diameters of Xe ion tracks and their displacement cascades.

Electronic and atomic structure modifications of copper nitride films by ion impact and phase separation

We have studied electronic and atomic structure modifications of Cu 3N films under 100 keV Ne and 100 MeV Xe ion impact. Cu 3N films were prepared on R(11–2 surface)-cut-Al 2O 3 substrates at 250 °C by using a RF-magnetron sputter deposition method. X-ray diffraction (XRD) shows that unirradiated films are polycrystalline with (1 0 0) orientation of cubic structure. We find that the electrical resistivity (∼10 Ω cm before ion impact) decreases by more than two orders of magnitude after the Ne impact at a fluence of ∼10 13 cm −2, where no Cu phase separation is observed. For further ion impact (larger than ∼10 15 cm −2), XRD shows Cu diffraction peak (Cu phase separation), and the resistivity decreases further (three orders of magnitude). Decomposition and phase separation are discussed based on these results, as well as temperature dependence of the resistivity and optical absorption. The results of 100 MeV Xe ion impact are compared with those of Ne ion impact.

Morphological change in FePt nanogranular thin films induced by swift heavy ion irradiation

We have investigated morphology change of FePt nanogranular films (FePt) 47(Al 2O 3) 53 under irradiation with 210 MeV Xe ions. Here, electron tomography technique was extensively employed to clarify three-dimensional (3D) structure in irradiated specimens, in addition to conventional transmission electron microscopy (TEM) techniques such as bright-field observation and scanning TEM energy dispersive X-ray spectroscopy (STEM-EDX) analysis. The ion irradiation induces the coarsening of FePt nanoparticles with elongation along the beam direction. Electron tomography 3D reconstructed images clearly demonstrated that when the fluence achieves 5.0 × 10 14 ions/cm 2, well-coarsened FePt balls have been formed on the irradiated surface, and the particles in the film interior have been deformed into rods along the ion trajectory. The alloy particles become inhomogeneous in composition after prolonged irradiation up to 1.0 × 10 15 Xe ions/cm 2. The particle center is enriched with Pt, while Fe is slightly redistributed to the periphery.

Effects of electronic and nuclear interactions in SiC

In this study, we performed irradiation experiments on nanostructured 3C–SiC samples, with 95 MeV Xe ions at room temperature. This energy permits the observation of the combined electronic and nuclear interactions with matter. The grazing incidence X-ray diffraction results do not reveal a complete amorphization, despite value of displacement per atom overcoming the total amorphization threshold. This may be attributed to competing effects between nuclear and electronic energy loss in this material since a total amorphization induced by nuclear interactions was found after low energy ion irradiation (4 MeV Au). Moreover, electronic interactions created by high energy ion irradiations induce no disorder in single crystalline 6H–SiC. But in samples previously disordered by low energy ion implantation (700 keV I), the electronic interactions generate a strong defects recovery.

Study on the behavior of oxygen atoms in swift heavy ion irradiated CeO 2 by means of synchrotron radiation X-ray photoelectron spectroscopy

To study the effects of swift heavy ion irradiation on cerium dioxide (CeO 2), CeO 2 sintered pellets were irradiated with 200 MeV Xe ions at room temperature. For irradiated and unirradiated samples, the spectra of X-ray photoelectron spectroscopy (XPS) were measured. XPS spectra for the irradiated samples show that the valence state of Ce atoms partly changes from +4 to +3. The amount of Ce 3+ state was quantitatively obtained as a function of ion-fluence. The relative amount of oxygen atom displacements, which are accompanied by the decrease in Ce valence state, is 3–5%. This value is too large to be explained in terms of elastic interactions between CeO 2 and 200 MeV ions. The experimental result suggests the contribution of 200 MeV Xe induced electronic excitation to the displacements of oxygen atoms.

Energetic Processing of Interstellar Silicate Grains by Cosmic Rays

While a significant fraction of silicate dust in stellar winds has a crystalline structure, in the interstellar medium nearly all of it is amorphous. One possible explanation for this observation is the amorphization of crystalline silicates by relatively ‘‘low’’ energy, heavy-ion cosmic rays. Here we present the results of multiple laboratory experiments showing that single-crystal synthetic forsterite (Mg2SiO4) amorphizes when irradiated by 10 MeV Xe ions at large enoughfluences.Usingmodeling,weextrapolatetheseresultstoshowthat0.1Y5.0GeVheavy-ioncosmicrayscan rapidly (� 70 Myr) amorphize crystalline silicate grains ejected by stars into the interstellar medium. Subject headingg cosmic rays — dust, extinction Online material: color figures

Effect of ionization rates on dynamic recovery processes during electron-beam irradiation of 6H-SiC

The authors have investigated the effects of 200 and 300keV electron-beam irradiations on amorphization in 6H-SiC at 100 and 295K. Amorphization is induced by the accumulation of defects produced by direct atomic displacements. Dynamic recovery of these defects during irradiation, due to temperature increases and ionization effects, results in increases in the amorphization dose. By comparing with previous data for 2MeV electrons and 1.5MeV Xe ions, the results demonstrate that ionization-enhanced recovery in 6H-SiC dramatically increases above an ionization rate threshold.

Study of damage in ion-irradiatedα-SiC by optical spectroscopy

UV–visible absorption and Raman scattering spectroscopy were used toinvestigate the effects of 4 MeV Xe-ion and 4 MeV Au-ion irradiations onα-SiC single crystals. The evolution of transmission spectra upon irradiation evidences anincrease of the optical absorption. The optical band-gap energy decreases versus fluence,which is linked to band-gap closure attributed to the creation of localized states into theforbidden energy band. A strong effect of the irradiation temperature is observed as aresult of dynamic annealing enhanced by the temperature increase. The Urbach energyincreases versus fluence due to disorder accumulation in the damaged layer. Comparison ofUrbach energy and disorder parameters extracted from Raman spectra shows that theUrbach energy is sensitive to the disorder induced by the accumulation of pointdefects.

Irradiation effects with 100 MeV Xe ions on optical properties of Al-doped ZnO films

Al-doped ZnO (AZO) films are known as n-type transparent semiconductors. We have investigated the effects of 100MeV Xe ion irradiation on the optical and structural properties of AZO films, which were prepared on SiO2 glass at 400°C by using a RF-magnetron sputtering deposition method. We discuss relationships between these property modifications and the recent observations of the conductivity increase by ion irradiation. It is suggested that the band-gap modification has more close relation with the conductivity increase than the structural modification.

Comparative Study of Structural Damage Under Irradiation in SiC Nanostructured and Conventional Ceramics

AbstractIn the context of research on new materials for next generation nuclear reactors, it becomes more and more interesting to know what can be the advantages of nanostructured materials for such applications. In this study, we performed irradiation experiments on microstructured and nanostructured â-SiC samples, with 95 MeV Xe and 4 MeV Au ions. The structure of the samples was characterized before and after irradiation by grazing incidence X ray diffraction and Raman spectroscopy. The results showed the occurrence of a synergy between electronic and nuclear energy loss in both samples with 95 MeV Xe ions, while the nanostructured pellet was found to have a better resistance to the irradiation with 4 MeV Au ions.

Depth-resolved nanostructure and refractive index of borosilicate glass doped with Ag nanocrystals

Abstract We present an investigation of the Ag-nanocrystal depth profile as well as the corresponding refractive index depth profile of borosilicate glass that was first doped with Ag by Na+ ↔ Ag+ ion exchange and subsequently irradiated with 1 MeV Xe ions. By combining RBS, XPS, XE-AES, and transmission and reflection spectroscopy, we show unambiguously that the Ag nanocrystals are formed in a layer with a thickness (90 ± 20 nm) that is significantly smaller than the 1-MeV Xe range (340 nm). The effective refractive index for the highest Xe fluence is n = 2.1 + 0.8 i at the resonance wavelength (λ = 430 nm). The implications for the integration of surface-plasmon-resonance-based functionalities in photonic devices based on the described fabrication method are discussed.

Effect of inclined magnetic field on pinning parameters in YBaCuO thin films with columnar defects

The effect of inclined magnetic field on pinning parameters in YBCO thin films with columnar defects was investigated. The columnar defects were produced by the heavy-ion irradiation with 200 MeV Xe ions parallel to c-axis. The magnetic field was applied inclined to c-axis with angle θ B which was 0°, 10°, and 20°. One of the pinning parameters z, which is also called the dynamic critical exponent, extremely increased near the certain field related to the density of columnar defects in the case of θ B = 0°, that is, a peak in the magnetic field dependence of z appeared near B/ B ϕ = 1/3, while such peak was not observed before irradiation. On the other hand, the peak did not appear and the values of z decreased with the tilting angle θ B . According to the percolation model, the appearance of the peak of z near B/ B ϕ = 1/3 for θ B = 0° originates from the matching effect. When the magnetic field is inclined away from columnar defects, the vortices are not pinned along those defects so that the matching effect is not achieved and the columnar defects take the various values of pinning force to flux lines.

Pressure dependence of the irradiation-induced ferromagnetism in Fe–Ni invar alloys

Pressure dependence of the irradiation-induced ferromagnetism recently found in Fe–Ni invar alloys was investigated under hydrostatic pressures up to 7.5 GPa. A rectangular sheet of Fe–30.2 at% Ni invar alloy was irradiated with 80 MeV Xe ions. The range was much smaller than the thickness of the sample. The Curie temperature of the irradiated part increased by 63 K, and the absolute value of the pressure coefficient, d T C/d p was smaller than that of non-irradiated part. The relation p ≈ ( T C 0 - T C ) n holds with n = 2 for both non-irradiated and irradiated part. The itinerant character was not so much modified by irradiation.