Ion beam induced modifications in electron beam evaporated aluminum oxide thin films

Al₂O₃ thin films find wide applications in optoelectronics, sensors, tribology etc. In the present work, Al₂O₃ films prepared by electron beam evaporation technique are irradiated with 100 MeV swift Si⁷⁺ ions for the fluence in the range 1 × 10¹² to 1 × 10¹³ ions cm⁻² and the structural properties are studied by glancing angle X-ray diffraction. It shows a single diffraction peak at 38.2° which indicates the γ-phase of Al₂O₃. Further, it is observed that as the fluence increases up to 1 × 10¹³ ions cm⁻² the diffraction peak intensity decreases indicating amorphization. Surface morphology studies by atomic force microscopy show mean surface roughness of 34.73 nm and it decreases with increase in ion fluence. A strong photoluminescence (PL) emission with peak at 442 nm along with shoulder at 420 nm is observed when the samples are excited with 326 nm light. The PL emission is found to increase with increase in ion fluence and the results are discussed in detail.     

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

We have investigated morphology change of FePt nanogranular films (FePt)₄₇(Al₂O₃)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 × 10¹⁴ ions/cm², 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 × 10¹⁵ Xe ions/cm². The particle center is enriched with Pt, while Fe is slightly redistributed to the periphery.     

Electrical properties of silicon diodes with pn junctions irradiated with Au swift heavy ions

Electrical properties of silicon diodes with p⁺n junctions irradiated with ¹⁹⁷Au⁺²⁶ swift heavy ions (energy E = 350 MeV, fluences of 10⁷ cm⁻² and 10⁸ cm⁻²) and silicon diodes irradiated with electrons (energy E = 3.5 MeV, fluences of 10¹⁵ cm⁻², 5 × 10¹⁵ cm⁻² and 10¹⁶ cm⁻²) have been investigated. Frequency dependences of the impedance, current-voltage characteristics and switching characteristics of these devices have been studied. Irradiation of the diodes with ¹⁹⁷Au⁺²⁶ ions at a fluence of 10⁸ cm⁻² leads to the formation of a quasi-continuous layer of irradiation-induced defects that enable a combination of characteristics such as a reverse resistance recovery time and direct voltage drop that are better than those for electron-irradiated diodes. Still, the irradiation of high-energy ions results in an increase in recombination currents that are larger than those obtained with electron irradiation, and causes more complicated frequency dispersion of the diode parameters.     

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.     

Flux dependent MeV ion induced modification of nano-Ag/Si system

Thin films of Ag (1.5 nm thick) are grown on Si (1 1 1) substrates using evaporation method in high vacuum condition and due to non-wetting nature of silver, isolated islands of mean size ≈12.0 nm have been formed on the surface. Au²⁺ (1.5 MeV) ions have been used to irradiate the above systems at various fluences (5 × 10¹³-1 × 10¹⁵ cm⁻²) at an impact angle of 5° and at a flux of 6.3 × 10¹² cm⁻² s⁻¹ (corresponding to a beam current density of 2.0 μA cm⁻² for Au²⁺ ions). Ion beam induced embedding is observed to begin at a fluence of 1 × 10¹⁴ cm⁻² for this high flux whereas low flux irradiations (current density ≈ 0.02 μA cm⁻²) of Au²⁺ ions under similar irradiation conditions did not yield embedding (impact angle 5°). High resolution transmission electron microscopy measurement showed no mixing in the form of silicide formation. These results are compared with high flux modifications in Au/Si system.     

PIXE and RBS analysis of Tl-1223 superconducting phase substituted by scandium

Ion beam analysis techniques (IBA) were performed to determine the elemental stoichiometry of superconducting samples of type TlBa₂Ca_2−xSc_xCu₃O_9−δ, with 0 ? x ? 0.6, prepared via solid-state reaction technique. By combining particle induced X-ray emission (PIXE) with Rutherford backscattering spectrometry (RBS), the stoichiometry of the samples is determined. However, the oxygen content is obtained by using non-Rutherford backscattering cross-section at 3 MeV proton beam. Furthermore, the prepared samples were also characterized using X-ray powder diffraction (XRD) and electrical resistivity measurements. The X-ray data indicate that the partial substitution of Ca²⁺ by Sc³⁺ ions does not affect the tetragonal structure of Tl-1223 superconducting phase. The superconducting transition temperatures T_c, determined from electrical resistivity measurements, was found to be highly correlated to the Sc-content.     

Mass spectrometric study of collision interactions of fast charged particles with water and NaCl solutions

A new experimental technique has been developed for the investigation of secondary particle emission from liquid targets resulting from collision interactions with fast charged particles. Secondary ion mass spectra are presented for the first time for liquid water and 0.1 M, 1 M and 5 M NaCl aqueous solutions bombarded by 2.0 MeV He⁺ ions. The mass spectra exhibit a series of negative cluster ions of the form of X_mY_nR⁻, where X and Y stand for neutral molecules such as H₂O, NaCl and NaOH and R⁻ stands for a negative charged ion such as O⁻, OH⁻ and Cl⁻. Intensities of negative ions are found to change significantly as a function of the concentration. The results imply evidently that the cluster structure in liquid targets changes drastically depending on the abundance of NaCl in solutions.     

Structural studies of silicon oxynitride layers formed by low energy ion implantation

Silicon oxynitride (Si_xO_yN_z) layers were synthesized by implanting ¹⁶O₂⁺ and ¹⁴N₂⁺ 30 keV ions in 1:1 ratio with fluences ranging from 5 × 10¹⁶ to 1 × 10¹⁸ ions cm⁻² into single crystal silicon at room temperature. Rapid thermal annealing (RTA) of the samples was carried out at different temperatures in nitrogen ambient for 5 min. The FTIR studies show that the structures of ion-beam synthesized oxynitride layers are strongly dependent on total ion-fluence and annealing temperature. It is found that the structures formed at lower ion fluences (∼1 × 10¹⁷ ions cm⁻²) are homogenous oxygen-rich silicon oxynitride. However, at higher fluence levels (∼1 × 10¹⁸ ions cm⁻²) formation of homogenous nitrogen rich silicon oxynitride is observed due to ion-beam induced surface sputtering effects. The Micro-Raman studies on 1173 K annealed samples show formation of partially amorphous oxygen and nitrogen rich silicon oxynitride structures with crystalline silicon beneath it for lower and higher ion fluences, respectively. The Ellipsometry studies on 1173 K annealed samples show an increase in the thickness of silicon oxynitride layer with increasing ion fluence. The refractive index of the ion-beam synthesized layers is found to be in the range 1.54-1.96.     

Effects of Mg-ion implantation in α-Al2O3 and α-Al2O3:Mg crystals: Electrical conductivity and electronic structure changes

Undoped and Mg-doped α-Al₂O₃ single crystals were implanted with Mg ions, with an energy of 90 keV and a fluence of 10¹⁷ ions/cm². DC electrical measurements using the four-point probe method, between 295 and 428 K, were used to characterize the electrical conductivity of the implanted area. Measurements in this temperature range indicate that the electrical conductivity after implantation is thermally activated with an activation energy of about 0.03 eV both in undoped and in reduced Mg-doped α-Al₂O₃ crystals, whereas the activation energy in oxidized Mg-doped α-Al₂O₃ crystals remains close to that before implantation. The I-V characteristics of the latter samples reveal a blocking behavior of the electrical contacts on the implanted area in contrast to the ohmic contacts observed in α-Al₂O₃ single crystals with the c-axis perpendicular to the broad face, where the Mg ions were implanted. We conclude that the enhancement in conductivity observed in the implanted regions is related to the intrinsic defects created by the implantation, rather than to the implanted Mg ions. The relationship between the oxygen vacancy concentrations at different stages of etching and the changes in the electronic structure, the chemical bonding, and the Al³⁺(2p)/O²⁻(1s) and Mg²⁺(1s)/O²⁻(1s) relative intensities was studied by X-ray Photoemission Spectroscopy.     

Effect of ion beam irradiation on magnetic and structural properties of Pt/Cr/Co multilayers

This paper discusses the effect of ion beam irradiation on the magnetic and structural properties of Pt/Cr/Co multilayers. We observe Co-Cr-Pt ternary alloy phase formation in 1 MeV N⁺ ion irradiated [Pt (2.5 nm)/Cr (0.8 nm)/Co (3.0 nm)]_×6/Si multilayers for a fluence of 1 × 10¹⁶ ions cm⁻² and beyond. The observed phase formation is accompanied by an enhancement in the average grain size, surface roughness and coercivity. Monte Carlo simulation has been performed to study ion-induced defect evolution and atomic displacements to correlate the above observed effects.     

Ag/Fe:TiO2 nano-catalysts prepared by Fe ion implantation and Ag nanoparticle deposition by electron beam irradiation

TiO₂ nano-catalysts made by the sol-gel method were modified by ion implantation and electron beam irradiation to obtain a more efficient photocatalytic function. The results of photodegradation of methyl orange in aqueous solution demonstrate firstly that the films have a photocatalytic activity which responds to visible light. Secondly, it demonstrates that under ultraviolet excitation the sample with a fluence of 6 × 10¹⁵ ions/cm² and electron beam irradiated with concentration of AgNO₃ aqueous solution at 1 × 10⁻³ M gives a more efficient photodegradation ability than pure TiO₂ film and other Fe-doped films display almost the same photodegradation ability as TiO₂ film. Thirdly it demonstrates that under sunlight, all modified films exhibit more photodegradation activity than TiO₂ film.     

Development of a high intensity Al beam from SiC targets for accelerated beam experiments at ISAC

An intense beam of ^26gAl has been developed for accelerated beam experiments at TRIUMF’s ISAC facility. Studies of the on-line production of Al radionuclides from thick silicon carbide targets have been performed as part of a program of beam development for astrophysical reaction studies at ISAC. While the release of short-lived Al nuclides from SiC was found to be slow, development of new target material forms and high-power target containers has allowed operation of SiC targets with proton currents of up to 70 μA on target. In addition, operation with the TRIUMF resonant ionization laser ion source (TRILIS) has produced ^26gAl beam intensities of 5.1 × 10¹⁰ s⁻¹.     

Formation of silicon hydride using hyperthermal negative hydrogen ions (H) extracted from an argon-seeded hydrogen sheet plasma source

An E × B probe (a modified Wien filter) is constructed to function both as a mass spectrometer and ion implanter. The device, given the acronym EXBII selects negative hydrogen ions (H⁻) from a premixed 10% argon-seeded hydrogen sheet plasma. With a vacuum background of 1.0 × 10⁻⁶ Torr, H⁻ extraction ensues at a total gas feed of 1.8 mTorr, 0.5 A plasma discharge. The EXBII is positioned 3 cm distance from the sheet core as this is the region densely populated by cold electrons (T_e ∼ 2 eV, N_e ∼ 3.4 × 10¹¹ cm⁻³) best suited for H⁻ formation. The extracted H⁻ ions of flux density ∼0.26 A/m² are segregated, accelerated to hyperthermal range (<100 eV) and subsequently deposited into a palladium-coated 1.1 × 1.1 cm², n-type Si (1 0 0) substrate held at the rear end of the EXBII, placed in lieu of its Faraday cup. The palladium membrane plays the role of a catalyst initiating the reaction between Si atoms and H⁻ ions simultaneously capping the sample from oxidation and other undesirable adsorbents. AFM and FTIR characterization tests confirm the formation of SiH₂. Absorbance peaks between 900-970 cm⁻¹ (bending modes) and 2050-2260 cm⁻¹ (stretching modes) are observed in the FTIR spectra of the processed samples. It is found that varying hydrogen exposure time results in the shifting of wavenumbers which may be interpreted as changes in the frequencies of vibration for SiH₂. These are manifestations of chemical changes accompanying alterations in the force constant of the molecule. The sample with longer exposure time exhibits an additional peak at 2036 cm⁻¹ which are hydrides of nano-crystalline silicon.     

Damage recovery and optical activity in europium implanted wide gap oxides

In this study we compare and discuss the defects and optical behaviour of sapphire and magnesium oxide single crystals implanted at room temperature with different fluences (1 × 10¹⁵-1 × 10¹⁶ cm⁻²) of europium ions.Rutherford backscattering channelling shows that for fluences above 5 × 10¹⁵ cm⁻² the surface disorder level in the Al-sublattice reaches the random level. Implantation damage recovers fast for annealing in oxidizing atmosphere but even for the highest fluence we recover almost completely all the damage after annealing at 1300 °C, independently of the annealing environment (reducing or oxidizing). Annealing above 1000 °C promotes the formation of Eu₂O₃ in the samples with higher concentration of Eu. The optical activation of the rare earth ions at room temperature was observed after annealing at 800 °C by photoluminescence and ionoluminescence. In Al₂O₃ lattice the highest intensity line of the Eu³⁺ ions corresponds to the forced electric dipole ⁵D₀ → ⁷F₂ transition that occurs ∼616 nm. For the MgO samples the Eu³⁺ optical activation was also achieved after implantation with different fluences. Here, the lanthanide recombination is dominated by the magnetic dipole ⁵D₀ → ⁷F₁ transition near by 590 nm commonly observed for samples were Eu³⁺ is placed in a high symmetry local site. The results clearly demonstrate the possibility to get Eu incorporated in optical active regular lattice sites in wide gap oxides.     

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.     

Behaviour of chromium steels in liquid Pb-55.5Bi with changing oxygen content and temperature

The behaviour of protective oxide layers on P122 steel and its welds and of ODS steel in liquid Pb_44.5Bi_55.5 (LBE) is examined under conditions of changing temperatures and oxygen concentrations. P122 (12Cr) and its welded joints are exposed to LBE at 550 °C for 4000 h with oxygen concentrations of 10⁻⁶ and 10⁻⁸ wt% (p(O₂) = 8.1 × 10⁻²³ bar and 5.2 × 10⁻²⁷ bar) which change every 800 h. It is found that like in case of constant oxygen concentration of 10⁻⁶ wt% a protective spinel layer (Fe(Fe_1−xCr_x)₂O₄) was maintained on P122 and also on its welded joint. Two experiments with exposure times of 4800 h are conducted on ODS steel, both with temperatures changing from 550 to 650 °C and back every 800 h, one experiment with 10⁻⁶ the other with 10⁻⁸ wt% oxygen in LBE. Both experiments show strong local dissolution attack after 4800 h which is in agreement with the behaviour of ODS in LBE at a constant temperature of 650 °C. However, dissolution attack is less in LBE with 10⁻⁸ wt% oxygen (p(O₂) = 3.0 × 10⁻²⁵ bar).     

Radiation effects on PbO-Al2O3-B2O3-SiO2 glasses by FTIR spectroscopy

The infrared absorption spectra of PbO-Al₂O₃-B₂O₃-SiO₂ glasses have been measured in the spectral range 600-4000 cm⁻¹ before and after absorbed dose of 50 Gy, 4 kGy and 50 kGy to investigate the structural change due to irradiation. The structural change due to composition has also been discussed. The experimental results clearly indicate that after irradiation, a significant change in structure of lead alumino borosilicate glass network is observed. It was shown that BO₄ groups decreases and BO₃ groups increases with the increase of Al₂O_3.     

Ion induced segregation in gold nanostructured thin films on silicon

We report a direct observation of segregation of gold atoms to the near surface regime due to 1.5 MeV Au²⁺ ion impact on isolated gold nanostructures deposited on silicon. Irradiation at fluences of 6 × 10¹³, 1 × 10¹⁴ and 5 × 10¹⁴ ions cm⁻² at a high beam flux of 6.3 × 10¹² ions cm⁻² s⁻¹ show a maximum transported distance of gold atoms into the silicon substrate to be 60, 45 and 23 nm, respectively. At a lower fluence (6 × 10¹³ ions cm⁻²) transport has been found to be associated with the formation of gold silicide (Au₅Si₂). At a high fluence value of 5 × 10¹⁴ ions cm⁻², disassociation of gold silicide and out-diffusion lead to the segregation of gold to defect - rich surface and interface regions.     

On the radiolysis of iodide, nitrate and nitrite ions in aqueous solution: An experimental and modelling study

High radiation fields are predicted in the atmospheres in the reactor containment under postulated severe accident conditions. In particular, an experimental and modelling project (PARIS) has provided results, which show that nitrogen dioxide was the dominant measured species at high doses (>1 kGy) in air/steam mixtures. In addition, nitrite and nitrate ions were measured in the post-test containment sumps in some Phebus FP in-reactor integral experiments; but their separate effects on iodine volatility from irradiated aqueous solutions of iodide using appear unreported in open literature.To address this issue, this paper presents an overview of the results of an experimental and modelling study carried out at PSI, Switzerland. The experimental study consisted of small-scale irradiations of CsI, boric acid and tracer containing aqueous solutions. Tests were first carried out without nitrate or nitrite ions to obtain results to confirm expected iodine behaviour by correlation with predicted results, which were generated by concurrently developed code (PSIodine). The solutions were sparged with N₂O, argon and air to provide different net oxidation systems and to remove volatile iodine for measurement. Since the radiation chemistry of N₂O-saturated iodide solutions is well established and the measured I₂ yields and final pH correlate very well with the PSIodine code predictions, the effect of added nitrite ions to these solutions has provided results, which support the correct choice of relevant reactions for inclusion in the nitrate-model.Both experimental and predicted results clearly show that nitrate or nitrite ions in argon-sparged and irradiated iodide solutions (conc., 10⁻⁴ mol dm⁻³) containing boric acid lower % I₂ yields up to an initial NO₃⁻ concentration of ∼5.0 × 10⁻³ mol dm⁻³. Using a low CsI concentration (4.0 × 10⁻⁵ mol dm⁻³) estimated in containment sump during a postulated severe-accident, an initial nitrate concentration (10⁻³ mol dm⁻³) and pH 7.1, ∼3.6% I₂ was produced by argon sparging at a dose of 20.5 kGy. In contrast, 80% I₂ was formed at a dose of 12 kGy in the absence of nitrate ions.Irradiated and air-sparged CsI solutions, due to the lower net oxidation, gave the expected lower % I₂ yields than their argon-sparged counterparts. However, the reduction of volatile iodine species by radiation products of nitrate ions was enhanced. For example, using CsI solutions (conc., 10⁻⁴ mol dm⁻³), initial pH 4.6 and a range of nitrate ion concentrations (0, 10⁻⁴, 10⁻³ and 10⁻² mol dm⁻³), the % I₂ yields at a dose of 2 kGy have lowered from 26.9% to 25.6%, 3.2% and 2.8%, respectively. In the latter experiment, only ∼6% I₂ at a dose of ∼20 kGy was produced. In the absence of nitrate ions, a yield of ∼93% I₂ at only 5 kGy dose was obtained. By comparison, the % I₂ yields from their Ar-sparged counterpart experiments were lowered from ∼88% to ∼72%, 11% and 22% in the same nitrate concentration range. Therefore, apart from the lower net oxidation in O₂-containing solutions, the results indicate that the reduction of volatile iodine species by products of nitrate ion irradiation is enhanced in the presence of dissolved O₂.