Light ion irradiation effects on stuffed Lu2(Ti2−xLux)O7−x/2 (x = 0, 0.4 and 0.67) structures

We have recently synthesized “stuffed” (i.e., excess Lu) Lu₂(Ti_2−xLu_x)O_7−x/2 (x = 0, 0.4 and 0.67) compounds using conventional ceramic processing. X-ray diffraction measurements indicate that stuffing more Lu³⁺ cations into the oxide structure leads eventually to an order-to-disorder (O-D) transition, from an ordered pyrochlore to a disordered fluorite crystal structure. At the maximum deviation in stoichiometry (x = 0.67), the Lu³⁺ and Ti⁴⁺ ions become completely randomized on the cation sublattices, and the oxygen “vacancies” are randomized on the anion sublattice. Samples were irradiated with 400 keV Ne²⁺ ions to fluences ranging from 1 × 10¹⁵ to 1 × 10¹⁶ ions/cm² at cryogenic temperatures (∼77 K). Ion irradiation effects in these samples were examined by using grazing incident X-ray diffraction. The results show that the ion irradiation tolerance increases with disordering extent in the non-stoichiometric Lu₂(Ti_2−xLu_x)O_7−x/2.     

Effects of ion irradiation on the mechanical properties of SiNawOxCyHz sol-gel derived thin films

A study of the effects of ion irradiation of hybrid organic/inorganic modified silicate thin films on their mechanical properties is presented. NaOH catalyzed SiNa_wO_xC_yH_z thin films were synthesized by sol-gel processing from tetraethylorthosilicate (TEOS) and methyltriethoxysilane (MTES) precursors and spin-coated onto Si substrates. After drying at 300 °C, the films were irradiated with 125 keV H⁺ or 250 keV N²⁺ at fluences ranging from 1 × 10¹⁴ to 2.5 × 10¹⁶ ions/cm². Nanoindentation was used to characterize the films. Changes in hardness and reduced elastic modulus were examined as a function of ion fluence and irradiating species. The resulting increases in hardness and reduced elastic modulus are compared to similarly processed acid catalyzed silicate thin films.     

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.     

Ferromagnetic modification of GaN film by Cu ions implantation

The structural and magnetic properties of Cu⁺ ions-implanted GaN films have been reported. Eighty kiloelectron-volt Cu⁺ ions were implanted into n-type GaN film at room temperature with fluences ranging from 1 × 10¹⁶ to 8 × 10¹⁶ cm⁻² and subsequently annealed at 800 °C for 1 h in N₂ ambient. PIXE was employed to determine the Cu-implanted content. The magnetic property was measured by the Quantum Design MPMS SQUID magnetometer. No secondary phases or clusters were detected within the sensitivity of XRD. Raman spectrum measurement showed that the Cu ions incorporated into the crystal lattice positions of GaN through substitution of Ga atoms. Apparent ferromagnetic hysteresis loops measured at 10 K were presented. The experimental result showed that the ferromagnetic signal strongly increased with Cu-implanted fluence from 1 × 10¹⁶ to 8 × 10¹⁶ cm⁻².     

Oxygen potential measurements of Am0.5Pu0.5O2−x by EMF method

The dependence of the oxygen potentials on oxygen non-stoichiometry and temperature of Am_0.5Pu_0.5O_2−x has been obtained by the electromotive force (EMF) method with the cell: (Pt) air |Zr(Ca)O_2−x| Am_0.5Pu_0.5O_2−x (Pt). The x value of Am_0.5Pu_0.5O_2−x was changed at 1333 K over 0.02 < x ? 0.25 by the coulomb titration method. The temperature dependence of the oxygen potential was also measured over the range of 1173-1333 K. It was found that the oxygen potential decreased from −80 to −360 kJ mol⁻¹ with increasing x from 0.021 to 0.22 at 1333 K and that it remained almost constant at −360 kJmol⁻¹ around x = 0.23. It was concluded that Am_0.5Pu_0.5O_2−x should be composed of the single fluorite-type phase over 0.02 < x ? 0.22 and the mixed phases of fluorite-type and (Am, Pu)₉O₁₆ at around x = 0.23.     

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.     

HRXRD and Raman study of irradiation effects in InGaN/GaN layers induced by 2.3 MeV Ne and 5.3 MeV Kr ions

In_0.15Ga_0.85N/GaN bilayers irradiated with 2.3 MeV Ne and 5.3 MeV Kr ions at room temperature were studied by high-resolution X-ray diffraction (HRXRD) and micro-Raman scattering. The Ne ion fluences were in the range from 1 × 10¹² to 1 × 10¹⁵ cm⁻², and the Kr ion fluences were in the range from 1 × 10¹¹ to 1 × 10¹³ cm⁻². Results show that the structures of both In_0.15Ga_0.85N and GaN layers remained almost unchanged for increasing fluences up to 1 × 10¹³ and 1 × 10¹² cm⁻² for Ne and Kr ion irradiations, respectively. After irradiation to higher fluences, the GaN layer was divided into several damaged layers with different extents of lattice expansion, while the In_0.15Ga_0.85N layer exhibited homogenous lattice expansion. The layered structure of GaN and the different responses to irradiation of the GaN and In_0.15Ga_0.85N layers are discussed.     

Thermal conductivities of hypostoichiometric (U, Pu, Am)O2−x oxide

The thermal conductivities of (U_0.68Pu_0.30Am_0.02)O_2.00−x solid solutions (x = 0.00-0.08) were studied at temperatures from 900 to 1773 K. The thermal conductivities were obtained from the thermal diffusivities measured by the laser flash method. The thermal conductivities obtained experimentally up to about 1400 K could be expressed by a classical phonon transport model, λ = (A + BT)⁻¹, A(x) = 3.31 × x + 9.92 × 10⁻³ (mK/W) and B(x) = (−6.68 × x + 2.46) × 10⁻⁴ (m/W). The experimental A values showed a good agreement with theoretical predictions, but the experimental B values showed not so good agreement with the theoretical ones in the low O/M ratio region. From the comparison of A and B values obtained in this study with the ones of (U,Pu)O_2−x obtained by Duriez et al. [C. Duriez, J.P. Alessandri, T. Gervais, Y. Philipponneau, J. Nucl. Mater. 277 (2000) 143], the addition of Am into (U, Pu)O_2−x gave no significant effect on the O/M dependency of A and B values.     

The improvement of low-resistance and high-transmission ohmic contact to p-GaN by Zn implantation

The electrical and optical characteristics of Zn⁺ ion-implanted Ni/Au ohmic contacts to p-GaN were investigated. After the preparation of Ni/Au electrode on the surface of p-GaN, the metal/p-GaN contact interface was doped by 35 keV Zn⁺ implantation with fluences of 5 × 10¹⁵-5 × 10¹⁶ cm⁻². Subsequent rapid thermal annealing of the implanted samples were carried in air at 200-400 °C for 5 min. Obvious improvements of the electrode contact characteristics were observed, i.e. the decrease of specific contact resistance and the increase of light transmittance. The lowest specific contact resistance of 5.46 × 10⁻⁵ Ω cm² was achieved by 1 × 10¹⁶ cm⁻² Zn⁺ implantation. The transmission enhancement of the electrodes was found as the annealing temperature rises. Together with the morphology and structure analyses of the contacts by scanning and transmission electron microscope, the corresponding mechanism for such an improvement was discussed.     

Raman spectroscopy characterization of actinide oxides (U1−yPuy)O2: Resistance to oxidation by the laser beam and examination of defects

Structural changes in four (U_1−yPu_y)O₂ materials with very different plutonium concentrations (0 ? y ? 1) and damage levels (up to 110 dpa) were studied by Raman spectroscopy. The novel experimental approach developed for this purpose consisted in using a laser beam as a heat source to assess the reactivity and structural changes of these materials according to the power supplied locally by the laser. The experiments were carried out in air and in water with or without hydrogen peroxide. As expected, the material response to oxidation in air depends on the plutonium content of the test oxide. At the highest power levels U₃O₈ generally forms with UO₂ whereas no significant change in the spectra indicating oxidation is observed for samples with high plutonium content (²³⁹PuO₂). Samples containing 25 wt.% plutonium exhibit intermediate behavior, typified mainly by a higher-intensity 632 cm⁻¹ peak and the disappearance of the 1LO peak at 575 cm⁻¹. This can be attributed to the presence of anion sublattice defects without any formation of higher oxides. The range of materials examined also allowed us to distinguish partly the chemical effects of alpha self-irradiation. The results obtained with water and hydrogen peroxide (a water radiolysis product) on a severely damaged ²³⁸PuO₂ specimen highlight a specific behavior, observed for the first time.     

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.     

Thermal studies on fluorite type ZryU1−yO2 solid solutions

Solid state reactions of UO₂ and ZrO₂ in mild oxidizing condition followed by reduction at 1673 K showed enhanced solubility up to 35 mol% of zirconium in UO₂ forming cubic fluorite type Zr_yU_1−yO₂ solid solution. The lattice parameters and O/M (M = U + Zr) ratios of the solid solutions, Zr_yU_1−yO_2+x, prepared in different gas streams were investigated. The lattice parameters of these solid solutions were expressed as a linear equation of x and y: a₀ (nm) = 0.54704 − 0.021x - 0.030y. The oxidation of these solid solutions for 0.1 ? y ? 0.2 resulted in cubic phase MO_2+x up to700 K and single orthorhombic zirconium substituted α-U₃O₈ phase at 1000 K. The kinetics of oxidation of Zr_yU_1−yO₂ in air for y = 0-0.35 were also studied using thermogravimetry. The specific heat capacities of Zr_yU_1−yO₂ (y = 0-0.35) were measured using heat flux differential scanning calorimetry in the temperature range of 334-860 K.     

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 × 10¹⁴ to 1.0 × 10¹⁷ ions/cm², implanted by 400 keV Xe-ions with 2.0 × 10¹⁴ to 2.0 × 10¹⁶ ions/cm², irradiated by 3.64 MeV Xe-ions with 1.0 × 10¹² to 1.0 × 10¹⁵ ions/cm², or irradiated by 308 MeV Xe-ions with 1.0 × 10¹² to 5.0 × 10¹⁴ ions/cm², 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.     

Band gap controlled H loss from passivated Hg1−xCdxTe (MCT) wafers under intense electronic excitations

We report here loss of H monitored by on-line elastic recoil detection analysis (ERDA) technique from passivated Hg_1−xCd_xTe (MCT) wafers due to irradiation by 80 MeV Ni⁹⁺, 120 MeV Au¹⁵⁺ and 200 MeV Ag¹⁰⁺. The loss of H is more in case of the wafer irradiated by Ag ions as compared to other two because of higher electronic energy loss (S_e). For same S_e value, H loss is more in case of the wafer having x = 0.29 as compared to the one having x = 0.204. This is due to higher band gap of the former as compared to the later, which is an important data for proper use of these materials as IR detector in intense radiation zone. These results are explained on the basis of thermal spike model of ion-solid interaction.     

Corrosion of alkali-borosilicate waste glass K-26 in non-saturated conditions

Experimental data obtained during long term environmental tests of a nuclear waste alkali-borosilicate glass K-26 in an experimental near-surface repository are examined. Average leaching rates of the radionuclides were calculated: the leach rates gradually diminished from 9.4 × 10⁻⁷ g cm⁻² day⁻¹ over the first year to 2.2 × 10⁻⁷ g cm⁻² day⁻¹ over 16 years of tests. Radionuclide losses obey a square root time dependence indicating a diffusion-controlled release mechanism. The main parameters, which control the corrosion of waste glass K-26 in the near-surface repository, are the effective diffusion coefficient of radiocaesium D_Cs and the rate of glass hydrolysis r_h. Analysis of 16 years experimental data gave D_Cs = 4.5 × 10⁻¹² cm² day⁻¹ and r_h = 0.1 μm years⁻¹. Diffusion is predicted to be dominant for 16.4 years after which diffusion and hydrolytic dissolution are expected to be similarly important. This mixed stage is predicted continue for 262 years after which hydrolytic dissolution will be the dominant mechanism.     

Enthalpy measurements of La2Te3O9 and La2Te4O11

Enthalpy increment measurements on La₂Te₃O₉(s) and La₂Te₄O₁₁(s) were carried out using a Calvet micro-calorimeter. The enthalpy values were analyzed using the non-linear curve fitting method. The dependence of enthalpy increments with temperature was given as: H°(T) − H°(298.15 K) (J mol⁻¹) = 360.70T + 0.00409T² + 133.568 × 10⁵/T − 149 923 (373 ? T (K) ? 936) for La₂Te₃O₉ and H°(T) − H°(298.15 K) (J mol⁻¹) = 331.927T + 0.0549T² + 29.3623 × 10⁵/T − 114 587 (373 ? T (K) ? 936) for La₂Te₄O₁₁.     

Light ion irradiation-induced phase transformation in the monoclinic polymorph of zirconia

Ion irradiation damage experiments were performed at ∼80 K on polycrystalline samples of monoclinic, slightly sub-stoichiometric zirconia (ZrO_1.98). Following irradiation with 150 keV Ne⁺ ions, the monoclinic phase was gradually replaced by a new phase. Transmission electron microscopy (TEM) observations in cross-sectional geometry and electron microdiffraction (μD) measurements revealed that the irradiated layer in a sample irradiated to a fluence of 5 × 10²⁰ Ne/m² is partially transformed to a higher symmetry phase of high crystallinity. This phase transformation is accompanied by reduction of the initial micron-sized, highly-twinned grain distribution, to a nano-phased grain structure. Grazing incidence X-ray diffraction (GIXRD) measurements revealed that the radiation-induced phase is a tetragonal polymorph of zirconia. This was verified by the existence of strong (1 0 1) diffraction maxima and weak (1 0 2) reflections (body-centered cell). Raman spectroscopy (RS) measurements were also performed in an attempt to corroborate GIXRD results obtained from the irradiated material. RS measurements in the confocal geometry agreed with GIXRD measurements, although RS was not as definitive as GIXRD. In addition to RS showing the existence of a band corresponding to a tetragonal structure at 262 cm⁻¹, a new mystery band appeared at 702 cm⁻¹ that increased in intensity as a function of irradiation fluence.     

Structural characterization of buried nitride layers formed by nitrogen ion implantation in silicon

The synthesis of buried silicon nitride insulating layers was carried out by SIMNI (separation by implanted nitrogen) process using implantation of 140 keV nitrogen (¹⁴N⁺) ions at fluence of 1.0 × 10¹⁷, 2.5 × 10¹⁷ and 5.0 × 10¹⁷ cm⁻² into 〈1 1 1〉 single crystal silicon substrates held at elevated temperature (410 °C). The structures of ion-beam synthesized buried silicon nitride layers were studied by X-ray diffraction (XRD) technique. The XRD studies reveal the formation of hexagonal silicon nitride (Si₃N₄) structure at all fluences. The concentration of the silicon nitride phase was found to be dependent on the ion fluence. The intensity and full width at half maximum (FWHM) of XRD peak were found to increase with increase in ion fluence. The Raman spectra for samples implanted with different ion fluences show crystalline silicon (c-Si) substrate peak at wavenumber 520 cm⁻¹. The intensity of the silicon peak was found to decrease with increase in ion fluence.     

Crystal structure and magnetic properties of UFe5Ga7

The new ternary compound UFe₅Ga₇ was prepared by an argon arc-melting followed by annealing. This intermetallic compound belongs to the series UFe_xGa_12−x and crystallizes in a structure related with the ThMn₁₂-type, with a = 8.6309 Å and c = 5.0524 Å. EDS elemental analysis yielded the phase composition UFe_4.9(2)Ga_6.8(1), which is very close to the nominal composition. Dc magnetization measurements revealed ferromagnetic type of magnetic ordering in UFe₅Ga₇. The Curie temperature of ∼439 K was estimated by the temperature dependence of magnetization at a low magnetic field of 0.1 T.     

Sputtering and crystalline structure modification of bismuth thin films deposited onto silicon substrates under the impact of 20-160 keV Ar ions

The sputtering of bismuth thin films induced by 20-160 keV Ar⁺ ions has been studied using Rutherford backscattering spectrometry, scanning electron microscopy and X-ray energy dispersive and diffraction spectroscopy. These techniques revealed increasing modifications of the Bi film surfaces with increasing both ion beam energy and fluence up to their complete deterioration under irradiation conditions E = 160 keV and φ = 1.5 × 10¹⁶ cm⁻², leaving isolated islands of preferred (0 1 2) orientation on the Si substrate. The observed surface morphology and crystalline structure evolutions are likely due to a complex interplay of interaction mechanisms involving both elastic nuclear collisions and inelastic electronic ones. The measured Bi sputtering yields versus Ar⁺ ion fluence for a fixed ion energy exhibit a significant depression at very low φ-values followed by a steady state regime above ∼2.0 × 10¹⁴ cm⁻². Measured sputtering yields versus Ar⁺ ion energy with fixing ion fluence to 1.2 × 10¹⁶ cm⁻² in the upper part of the yield saturation regime are also reported. Their comparison to theoretical model and SRIM 2008 Monte Carlo simulation predictions is discussed.