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International audience; The photo-annealing of colour centres in yttria-stabilized zirconia (YSZ) was studied by electron paramagnetic resonance spectroscopy upon UV-ray or laser light illumination, and compared to thermal annealing. Stable hole centres (HCs) were produced in as-grown YSZ single crystals by UV-ray irradiation at room temperature. The numbers of HCs decays to non-zero asymptotic values when UV light is set off. The HCs produced by 200-MeV Au ion irradiation are partially bleached by UV light, whereas the F$^+$-type centres (involving oxygen vacancies) were left unchanged. In contrast, a significant photo-annealing of the latter point defects was achieved in 1.4-MeV electron-irradiated YSZ by 553-nm laser light irradiation, inside the absorption band of F$^+$-type centres centred at a wavelength $\sim$550 nm. Thermal annealing of F$^+$-type centres was also followed by UV-visible absorption spectroscopy. Almost complete photo-bleaching by laser irradiation was achieved like for thermal bleaching at $\sim$500K. Kinetic rate models of colour-centre evolution are proposed for the photo-induced processes and correlated to the thermally-activated ones.

Electron paramagnetic resonance (EPR) spectroscopy is used to study the point defect production in yttria-stabilized zirconia (YSZ) (1 0 0) single crystals by swift heavy ion, electron and X-ray irradiations. A common color center known as the “T center” (for “trigonal” center) with an axial 〈1 1 1〉 symmetry is produced in all cases. We show that this defect is likely an intrinsic one with concentrations much larger than the major impurities. The growth curves of this point defect versus fluence for ion and electron irradiations can be on the whole rescaled as a function of the absorbed dose. This confirms that T centers are produced by the electronic excitations, either at low density with X-rays and electrons, or at high density with heavy ions. A kinetic model depending on fluence is proposed to account for the saturation behavior of growth curves. The production rate, corresponding to the initial slope of growth curves, increases steeply versus the average volume density of electron–hole pairs that are generated by ions and electrons in the irradiated volume.

Cubic yttria-stabilized zirconia (YSZ) can be used for nuclear applications as an inert matrix for actinide immobilization or transmutation. Indeed, the large amount of native oxygen vacancies leads to a high radiation tolerance of this material owing to defect recombination occurring in the atomic displacement cascades induced by fast neutron irradiation or ion implantations, as showed by molecular dynamics (MD) simulations. Amorphization cannot be obtained in YSZ either by nuclear-collision or electronic-excitation damage, just like in urania. A kind of polygonization structure with slightly disoriented crystalline domains is obtained in both cases. In the first steps of damage, specific isolated point defects (like F + -type color centers) and point-defect clusters are produced by nuclear collisions with charged particles or neutrons. Further increase of damage leads to dislocation-loop formation then to collapse of the dislocation network into a polygonization structure. For swift heavy ion irradiations, a similar polygonization structure is obtained above a threshold stopping power value of about 20–30 keV nm −1 .

A simple model for the nucleation and growth of single wall carbon nanotubes from a graphene sheet at the surface of a metallic catalyst saturated in carbon is developed. It enables to predict the geometry and energy of tube embryos of all possible chiralities, as well as the way that they can grow. It is shown that armchair-like chiralities are energy preferred for geometrical reasons. This result is discussed and compared to experimental literature., 8 pages, 7 figures

Sodium fluoride crystals were bombarded with MeV electrons near room-temperature or at 21 K and their EPR spectra measured. While after RT-irradiation one observes the spectrum of the classical cubic F-center, the low-T irradiation introduces a new low-symmetry defect which transforms reversibly into the F-center above ≈200 K. We suggest for the new center a triplet V K -type defect stabilized during irradiation by the nearby created F-center. While the ordinary V K -center as observed after low-T X-ray and γ-irradiation vanishes at 200 K the present electron-induced defect is stable and reappears upon cooling; it is still discernible after anneals up to 200 °C.

We have studied the color center production in yttria-stabilized zirconia single crystals (i.e. ZrO2: Y with 9.5 mol% Y2O3) with the (100) orientation, by electron irradiations at energies ranging between 1.0 and 2.5 MeV. Electron paramagnetic resonance (EPR) measurements show that three paramagnetic centers are stable at room-temperature: i) an F+-type center (singly ionized oxygen vacancy), ii) the so-called T-center (Zr3+ in a trigonal oxygen environment), and iii) a hole center. The growth curves of F+-type centers at variable electron energy cannot be rescaled versus the absorbed dose. These data confirm that F+-type center production is primarily governed by elastic collision processes with a threshold electron energy about 1.0 MeV. This can be correlated to a threshold displacement energy either about 120 eV for the O-atoms in the collision cascades, or about 80 eV for the Zr- (or Y-) atoms. In contrast, the growth curves of T-centers at variable electron energy are rescaled versus the absorbed dose. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; Pure and (Ca and Si)-substituted yttrium iron garnet (Y3Fe5O12 or YIG) epitaxial layers and amorphous films on gadolinium gallium garnet (Gd3Ga5O12, or GGG) single crystal substrates were irradiated by 50 MeV (32)Si and 50 MeV (or 60 MeV) (63)Cu ions for electronic stopping powers larger than the threshold value (~4 MeV μm(-1)) for amorphous track formation in YIG crystals. Conductivity data of crystalline samples in a broad ion fluence range (10(11)-10(16) cm(-2)) are modeled with a set of rate equations corresponding to the amorphization and recrystallization induced in ion tracks by electronic excitations. The data for amorphous layers confirm that a recrystallization process takes place above ~10(14) cm(-2). Cross sections for both processes deduced from this analysis are discussed in comparison to previous determinations with reference to the inelastic thermal-spike model of track formation. Micro-Raman spectroscopy was also used to follow the related structural modifications. Raman spectra show the progressive vanishing and randomization of crystal phonon modes in relation to the ion-induced damage. For crystalline samples irradiated at high fluences (⩾10(14) cm(-2)), only two prominent broad bands remain like for amorphous films, thereby reflecting the phonon density of states of the disordered solid, regardless of samples and irradiation conditions. The main band peaked at ~660 cm(-1) is assigned to vibration modes of randomized bonds in tetrahedral (FeO4) units.

We have used X-band electron paramagnetic resonance (EPR) measurements at room-temperature (RT) to study the thermal annealing and RT ageing of color centers induced in yttria-stabilized zirconia (YSZ), i.e. ZrO2:Y with 9.5 mol% Y2O3, by swift electron and ion-irradiations. YSZ single crystals with the 〈1 0 0〉 orientation were irradiated with 2.5 MeV electrons, and implanted with 100 MeV 13C ions. Electron and ion beams produce the same two color centers, namely an F+-type center (singly ionized oxygen vacancy) and the so-called T-center (Zr3+ in a trigonal oxygen local environment) which is also produced by X-ray irradiations. Isochronal annealing was performed in air up to 973 K. For both electron and ion irradiations, the defect densities are plotted versus temperature or time at various fluences. The influence of a thermal treatment at 1373 K of the YSZ single crystals under vacuum prior to the irradiations was also investigated. In these reduced samples, color centers are found to be more stable than in as-received samples. Two kinds of recovery processes are observed depending on fluence and heat treatment.

Lithium oxide (Li 2 O) has been studied in various contexts for more than two decades. Previous work on electron-irradiated Li 2 O crystals has demonstrated a simultaneous formation of two populations of colloids of metallic lithium, one of which is associated with oxygen bubbles and a typical size of >10 μm, the other one consisting of nanoclusters in the range of

We present experimental results on the nucleation of nanoscale metallic lithium colloids, of well-controlled diameter (2–5 nm), in MeV electron-irradiated LiF single crystals. Conduction electron spin resonance experiments show a clear-cut quantum effect in these colloids: the spin susceptibility follows a mixed Curie–Pauli law, characteristic for tiny metallic particles in which the mean level spacing is comparable to kT. The behavior of the spin relaxation times (T1 and T2) is presented and a discussion of quantum size effect in small metallic particles is proposed.

Like in lithium oxide, it is easy to nucleate very pure metallic lithium precipitates by electron-irradiation of lithium fluoride crystals. Irradiations performed near room temperature give metallic colloids which are characterized by electron spin resonance (ESR). The metallic character of the precipitates is demonstrated by the temperature behaviour of the ESR line intensity, which follows the temperature-independent Pauli law. A typical value for the metal concentration is about a few percent. Varying the irradiation parameters, i.e. the total fluence and/or the instantaneous flux, affects considerably the ESR properties of the colloids: first, the ESR line width changes by almost two orders of magnitude, indicating that the sizes of the precipitates strongly depend on these irradiation conditions. Second, when measuring the variation of the ESR intensity, proportional to the metal content, two very different behaviours are observed during recovery (dynamic or isochronal). When the flux is high, an intense and narrow metallic line is obtained, which disappears rapidly with annealing (300 °C). For lower flux, the colloids have a broader ESR signal, i.e. a much smaller size, and are not destroyed by annealing until the LiF crystal melts (870 °C). 7 Li NMR measurements extending earlier NMR experiments on neutron-irradiated LiF indicate that the Knight-shifted signal is split into two components with different widths. The position of the narrower component seems to correspond to big lithium particles having the features of bulk metallic lithium. The second component is likely to regroup particles of different sizes and geometry with different hyperfine interaction strength.

We have used electron spin resonance to study the defects induced in yttria-stabilized zirconia single crystals by 2.5-MeV electron and 2.6-GeV uranium ion irradiations. In addition to the O − and Zr 3+ paramagnetic centers already observed after X-ray irradiation at g =1.98 and g =1.89, we bring clear evidence of an unknown paramagnetic center at g =1.96 induced by charged particles. For the O − center, a maximum of the integrated spin intensity occurs near 50 K, suggesting some antiferromagnetic spin-pairing effect. Respective contributions of the ionization and atomic displacement processes in defect production are addressed.

7 Li MAS NMR spectra of 2.5 v MeV electron-irradiated LiF crystals have been measured in a field of 9.4 v T. Besides the resonance line of the ionic compound, a second well-separated spectrum is observed in the region of the Knight shift value for metallic lithium. At room temperature, the latter can be decomposed into two components with different Knight shift and linewidth values. When the temperature is increased, line narrowing takes place at first, indicating shortening of correlation times for self-diffusion, independently in both components. Above 370 v K, both lines broaden and approach each other before collapsing into a single line. The high ppm component disappears after crossing the melting temperature of metallic lithium (454 v K). The two lines are attributed to different types of metallic Li: one to bulk-like metal, the other to Li present initially under pressure and relaxing to the former under thermal treatment.

We have used electron spin resonance spectroscopy to study the defects induced in yttria-stabilized zirconia (YSZ) single crystals by 2.5-MeV electron irradiations. Two paramagnetic centers are produced: the first one with an axial symmetry is similar to the trigonal Zr 3+ electron center (T center) found after X-ray irradiation or thermochemical reduction, whereas the second one is a new oxygen hole center with an axial symmetry different from the orthorhombic O - center induced by X-ray irradiation. At a fluence around 10 18 e/cm , both centers are bleached out near 600 K, like the corresponding X-ray induced defects. At a fluence around 10 19 e/cm 2 , defects are much more stable, since complete thermal bleaching occurs near 1000 K. Accordingly, ageing of as-irradiated samples shows that high-dose defects at more stable than the low-dose ones.

International audience; Lithium oxide crystals containing metallic Li-colloids created by MeV-electron irradiation around room temperature were analyzed by elastic neutron scattering. High-resolution scans on a triple-axis spectrometer show that the main Bragg peaks of the irradiated Li2O crystals are broadened and exhibit diffuse shoulders due to the introduced lattice damage. Extensive search in reciprocal space reveals the presence of weak, yet well-defined, point-like intensities which can be identified as Bragg reflections of bulk bcc lithium. The Li precipitates are aligned according to the orientational relation [1 1 0]Li//[1 1 1]Li2O and may correspond to the large (>1 µm) Li-colloids observed earlier by conduction electron spin resonance (CESR) and by optical microscopy. Small-angle neutron scattering on the same crystals indicates an anisotropic distribution of non-spherical precipitates whose diameters lie in the range of several hundred angstroms and which possibly represent the small Li-colloids ("1 µm) characterized by CESR.

Magnetization measurements of Li2O crystals between 1.4 and 300 K reveal a diamagnetic-to-paramagnetic transformation of the samples, containing Li-colloids after electron irradiation near room temperature, and exhibit a break near 50 K as well as an antiferromagnetic ordering transition at 38 K. The magnetism is attributed to ⩽1% of molecular oxygen gas, freezing at 50 K, which is contained in micron-size cavities and produced simultaneously with the Li colloids. The earlier 7Li NMR experiments were extended to higher temperatures, in the range 300–520 K. The Knight-shifted Li-metal signal at ∼260 ppm is weakening during heating, due to annealing, but maintains its split double structure. The separation between the two peak components diminishes by ∼10%, after crossing the Li melting point at 453 K. The interpretation of these observations is discussed.

When irradiated with energetic electrons near room temperature, Li 2 O single crystals exhibit metallic Li colloids, as shown by conduction electron spin resonance (CESR) and 7 Li-nuclear magnetic resonance (NMR) experiments. These colloids are established as being of two types represented by two superimposed signals in a CESR spectrum: a Lorentzian line corresponding to small colloids (≪1 μm in diameter); and a Dysonian to much bigger (>1 μm) aggregates. We present isochronal annealing experiments and CESR experiments above room temperature in the range 290–590 K, in which melting of the Li metal is observed. When investigating such colloid-containing crystals by 7 Li-NMR we observe a Knight-shifted signal to the metallic colloids, which consists of two components. This duality is due to a result either of the presence of two types of colloids, or of one type having two different orientations inside the crystal. In the latter case the colloids should exhibit anisotropic properties as was already suggested by dielectric constant measurements. Thin Li 2 O crystals investigated by transmission optical microscopy after irradiation contained disc-like structures of up to 30 μm in diameter, which possibly represent oxygen gas bubbles surrounded by metallic Li corresponding to the large colloids detected by magnetic resonance: this confirms the strong anisotropy of the metallic colloids.

When irradiated with energetic electrons near room temperature Li2O single crystals exhibit metallic Li colloids, as shown by ESR (electron spin resonance) and 7Li-NMR experiments. These colloids were established as being of two types of very different sizes. ESR experiments performed above room temperature, in the range up to 300°C, show melting of the metallic colloids as observed on the line parameters, affecting simultaneously the width and the intensity of the ESR signal. The phenomenon is complicated by the fact that annealing effect of the metallic colloids are superimposed on the purely thermal behaviour. We performed also DSC (differential scanning calorimetry) experiments which are manifesting directly the reversible melting of the colloids; from the integrated intensity of the DSC peaks, we could deduce the lithium metal concentration, which is in good agreement with the value obtained from the ESR signal intensity.

Bismuth has been irradiated with swift xenon and tantalum ions at several temperatures between 20 K and 300 K, in the electronic stopping power regime. From in situ electrical resistivity measurements as a function of the ion fluence, damage efficiency and track radii have been deduced. It is shown in this paper that the damage efficiency and the track radii are all the higher as the irradiation temperature is high. This fact is in agreement with the thermal spike model: the energy deposited by a given ion on the target electrons is independent of the target temperature, but the energy necessary to melt a material depends on its initial temperature especially in the case of low melting point materials. The thermal spike is shown to be able to describe quantitatively the evolution of the track radii as a function of the irradiation temperature. The values used for the electronic thermal diffusivity (38 cm2 s−1 at 300 K) and for the electron-phonon coupling (1.3·1011 W cm−3 s−1) are in agreement with the semi-metallic characteristic of bismuth, i.e. its small number of electrons participating in the energy transport.

Poly- and monocrystalline Li2O samples have been irradiated by 1 and 2.5 MeV electrons at various doses and temperatures and their EPR spectra measured. At low doses, less than 1019 e−/cm2, and for Tirr

When irradiated with energetic electrons near room temperature Li2O single crystals exhibit metallic Li colloids of two types. These are represented by two superimposed signals in an electron paramagnetic resonance (EPR) spectrum: a Lorentzian line, corresponding to small colloids (≪1 μm in diameter), and a Dysonian, due to much bigger (>1 μm ) aggregates. We have investigated such colloid-containing crystals by 7Li-NMR and observe, in addition to the main ionic line, a Knight-shifted signal due to the metallic colloids, which appears to consist of two components, one at 265(3) ppm and the other at 246(3) ppm. In an annealing treatment, the principal peak remains observable up to 450–500∘C, while the secondary peak disappears at 300∘C. We attribute the former to the large Li colloids and the latter to the smaller ones. The difference of ΔK=19(4) ppm is possibly a signature for the presence of two phases, considering the Knight-shift variation due to the pressure-induced martensitic transformation observed in bulk Li. Thin Li2O crystals investigated by transmission optical microscopy, after irradiation, contained disc-like (1 1 1)-oriented structures of up to 20 μm in diameter which possibly correspond to oxygen gas bubbles surrounded by metallic Li.

AlH3 powder was bombarded with energetic electrons at 20 K and at room temperature and investigated by EPR, NMR, X-ray diffractometry, and microwave dielectric-constant measurements. The EPR spectra of the irradiated powder and of a selected single crystal cuboid of $$ \sim {10^{ - 1}}$$ mm edge show a complex asymmetric line centered at g = 2.009, with a Curie-like temperature dependence, attributed to radiation-induced color centers and/or their agglomerates. At the same time, the grains, which have become shiny black after irradiation, exhibit an increase of both the real and the imaginary part of e. 27Al-NMR spectra of the irradiated powder present a Knight-shifted line at 1600(50) ppm, close to the position of bulk metallic Al, and corresponding to a concentration of c(Al) $$ \sim {10^{ - 1}}$$ . In addition, the main hydride line differs from that before irradiation, demonstrating an alteration of environmental symmetry. The irradiation induces also a change in shape and width of the 1H-NMR line, another indication of symmetry change in the lattice. Finally, a refined X-ray single-crystal structure analysis of the irradiated cuboid indicates a change of structure from trigonal R -3 c to R -3, with a loss of mirror symmetry for the two Al sites caused by the introduction of Al-defects in the vicinity of one of them.

International audience; Yttria-stabilized zirconia (YSZ) single crystals (for 9.5 and 18 mol% yttria)were irradiated at room temperature (RT) by X-rays (W white spectrum) and2.5-MeV electrons. The growth curves of the so-called T-centre (for trigonalcentre, i.e. Zr3+ sitting in a trigonal symmetry site) were studied as a functionof absorbed dose, or irradiation time, by UV–visible optical absorption (OA)spectroscopy and X-band electron paramagnetic resonance spectroscopy. Thedefect concentration at saturation and the production rate are increased by afactor around two for 18 mol% yttria with respect to 9.5 mol%. Defect decaywas then followed after irradiation by OA spectroscopy as a function ofageing time at RT. Growth and decay curves of the T-centre are modelled onthe basis of rate equations of charge-exchange reactions with the zirconiumlattice ions. Increase in yttrium content is thought to decrease hole trappingon Zr3+ ions, thereby enhancing T-centre formation.

The two kinds of lithium metal colloids created in single crystals of lithium oxide by electron irradiation near 0 \ifmmode^\circ\else\textdegree\fi{}C manifesting themselves as two electron paramagnetic resonance metallic lines [see F. Beuneu and P. Vajda, Phys. Rev. Lett. 76, 4544 (1996)] are investigated as a function of impinging electron fluence and after an isochronal annealing treatment. The small (1\ensuremath{\mu}m) colloids, responsible for the narrow Lorentzian line, anneal near 300 \ifmmode^\circ\else\textdegree\fi{}C, while the large (\ensuremath{\gg}:1\ensuremath{\mu}m) colloids, giving rise to the Dysonian signal, recover above 400 \ifmmode^\circ\else\textdegree\fi{}C. Dielectric-constant measurements in the microwave frequency range reveal a substantial increase of both real and imaginary parts of \ensuremath{\epsilon}, corroborating the metal colloid formation. An effective medium analysis of the \ensuremath{\epsilon} variation after irradiation suggests nonspherical shapes for the metal colloids. The recovery of the irradiation-induced \ensuremath{\epsilon} increase occurs in the same range as that of the colloid lines, with a peak of \ensuremath{\Delta}${\mathrm{\ensuremath{\epsilon}}}^{|\mathrm{I}\mathrm{J}}$ near 400 \ifmmode^\circ\else\textdegree\fi{}C, probably indicating a colloid shape redistribution before decomposition. Finally, electron and optical microscopy results are presented, confirming the existence of two sizes of nonspherical, anisotropically distributed lithium colloids.

International audience; Poly(acrylic acid) (PAA) was grafted into the nanochannel walls of track-etched β-PVDF membranes in a controlled manner by RAFT polymerization. PAA-g-PVDF copolymers with various degrees of grafting from 5% to 63% were characterized by ATR-FTIR, X-ray photoelectron spectroscopy and atomic force microscopy (AFM). The controlled fashion of RAFT mediated grafting was demonstrated by size exclusion chromatography (SEC) and AFM. It was observed that the pore diameter decreases steadily with the degree of grafting (DOG) and pores start to be filled by the grafted PAA beyond $ 40 wt% DOG, based on AFM measurements and $ 15 wt% DOG, based on electrochemical analysis. The synthesized nanoporous membranes were later transformed into highly sensitive functionalized membrane electrodes (FMEs) by deposition of a thin gold ($ 50 nm) layer onto the membrane surfaces without blocking the nanochan-nels. The synthesized FMEs have been found to be sensitive to sub-ppb concentrations of Pb 2+ in square-wave anodic stripping voltammetry (SW-ASV) measurements. The sensitivities of RAFT mediated FMEs compared to those synthesized by conventional free-radical polymerization were found to be almost three times higher at sub-ppb concentrations of Pb 2+ in SW-ASV analysis. &

Poly- and monocrystalline samples of Li2O were irradiated with 1 MeV electrons at different temperatures, Tirr, and their EPR spectra measured. The created defects manifest a strong Tirr-dependence: (a) at low temperatures, Tirr ≤ 200 K, mainly F+-centers (O-vacancies with a trapped electron) are formed; (b) at room temperature, we observe, for the first time, a T-independent narrow signal (ΔH ∼ 10−2 mT) at g = 2.00235(2), characteristic for metallic lithium colloids. The microwave dielectric constant, e = e′ - ie″, was measured on the same speciment; both components increased very notably after the room temperature irradiation, emphasizing the presence of metallic particles, while remaining unchanged for lower Tirr. Thermal annealing of the specimens led to simultaneous vanishing of the colloid line and of Δe′, Δe″ above Tann ≈ 250°C. For case (a) irradiation, the recovery of the F+-centers near Tann ≈ 400°C is accompanied by the emergence of a new signal near g = 2.003, possibly due to their agglomeration into small clusters; the latter disappear at 600–700°C, depending on Tirr.

Polycrystalline samples of ${\mathrm{Li}}_{2}$O were irradiated with 1-MeV electrons at different temperatures, ${T}_{\mathrm{irr}}$, in the range 21 to 275 K, and their electron paramagnetic resonance spectra measured. The created defects manifest a strong ${T}_{\mathrm{irr}}$ dependence. (i) At low temperatures, ${T}_{\mathrm{irr}}l~200$ K, mainly ${F}^{+}$ centers (O vacancies with a trapped electron) are formed; thermal annealing leads to their recovery near ${T}_{\mathrm{ann}}=400\ifmmode^\circ\else\textdegree\fi{}$C, which is accompanied by the emergence of a new signal near $g=2.003$, possibly due to their agglomeration into small ${F}^{+}$ clusters. The latter disappear at 600-700 \ifmmode^\circ\else\textdegree\fi{}C. (ii) At ${T}_{\mathrm{irr}}=200$ K, the ${F}^{+}$ spectra are superimposed by the $g=2.003$ line and by a new narrow signal at $g=2.0023$, probably already caused by small metallic colloids. (iii) At ${T}_{\mathrm{irr}}=275$ K, finally, only a narrow $T$-independent line ($\ensuremath{\Delta}H\ensuremath{\sim}{10}^{\ensuremath{-}2}$ mT) is observed at $g=2.00235(2)$, characteristic for metallic Li colloids. The microwave dielectric constant, $\ensuremath{\varepsilon}$, measured on the same specimens increased notably after the room-temperature irradiation emphasizing the presence of metallic particles, while remaining unchanged for lower ${T}_{\mathrm{irr}}$. Both the colloid line and the radiation-induced $\ensuremath{\Delta}\ensuremath{\varepsilon}$ vanish simultaneously above ${T}_{\mathrm{ann}}\ensuremath{\approx}250\ifmmode^\circ\else\textdegree\fi{}$C.

Unusually narrow electron spin resonance lines can give birth to spectacular and interesting phenomena. We use here very pure lithium metal colloids created in electron-irradiated LiF, giving rise to a very narrow Li metal line. In these samples, three interesting phenomena are discussed and interpreted: signal saturation in particularly good conditions; oscillations appearing on strongly overmodulated lines; signal bistability, when the signal shape seems to depend on the sample magnetic history.

International audience; Hydrogen selenide is a recurrent metabolite of selenium compounds. However, few experiments studied the direct link between this toxic agent and cell death. To address this question, we first screened a systematic collection of Saccharomyces cerevisiae haploid knockout strains for sensitivity to sodium selenide, a donor for hydrogen selenide (H(2)Se/HSe(-/)Se(2-)). Among the genes whose deletion caused hypersensitivity, homologous recombination and DNA damage checkpoint genes were over-represented, suggesting that DNA double-strand breaks are a dominant cause of hydrogen selenide toxicity. Consistent with this hypothesis, treatment of S. cerevisiae cells with sodium selenide triggered G2/M checkpoint activation and induced in vivo chromosome fragmentation. In vitro, sodium selenide directly induced DNA phosphodiester-bond breaks via an O(2)-dependent reaction. The reaction was inhibited by mannitol, a hydroxyl radical quencher, but not by superoxide dismutase or catalase, strongly suggesting the involvement of hydroxyl radicals and ruling out participations of superoxide anions or hydrogen peroxide. The (*)OH signature could indeed be detected by electron spin resonance upon exposure of a solution of sodium selenide to O(2). Finally we showed that, in vivo, toxicity strictly depended on the presence of O(2). Therefore, by combining genome-wide and biochemical approaches, we demonstrated that, in yeast cells, hydrogen selenide induces toxic DNA breaks through an O(2)-dependent radical-based mechanism.

We have studied the colour centre production in yttria-stabilized zirconia (ZrO(2):Y(3 +)) by heavy ion irradiation in the GeV range using on-line UV-visible optical absorption spectroscopy. Experiments were performed with 11.4 MeV amu(-1) (127)Xe, (197)Au, (208)Pb and (238)U ion irradiations at 8 K or room temperature (RT). A broad and asymmetrical absorption band peaked at a wavelength about 500 nm is recorded regardless of the irradiation parameters, in agreement with previous RT irradiations with heavy ions in the 100 MeV range. This band is de-convoluted into two broad Gaussian-shaped bands centred at photon energies about 2.4 and 3.1 eV that are respectively associated with the F(+)-type centres (involving a singly ionized oxygen vacancy, VO· and T centres (i.e. Zr(3+) in a trigonal symmetry) observed by electron paramagnetic resonance (EPR) spectroscopy. In the case of 8 K Au ion irradiation at low fluences, six bands are used at about 1.9, 2.3, 2.7, 3.1 and 4.0 eV. The three bands near 2.0-2.5 eV can be assigned to oxygen divacancies (i.e. F(2)(+) centres). No significant effect of the irradiation temperature is found on the widths of all absorption bands for the same ion and fluence. This is attributed to the inhomogeneous broadening arising from the static disorder due to the native charge-compensating oxygen vacancies. However, the colour centre production yield is strongly enhanced at 8 K with respect to RT. When heating irradiated samples from 8 K to RT, the extra colour centres produced at low temperature do not recover completely to the level of RT irradiation. The latter results are accounted for by an electronically driven defect recovery process.

International audience; Yttria-stabilized zirconia (ZrO2:Y3+) single crystals (with 9.5 mol% Y2O3) were irradiated with ions (from 1 MeV He to 2.6 GeV U). Electron paramagnetic resonance (EPR) data show that two kinds of colour centres (F+-type and T centres) are produced. Thermo-stimulated luminescence (TSL) data exhibit a quite strong peak at ∼500–550 K in the glow curves of all irradiated samples regardless of the ion species and energy. Moreover, the 3D-TSL measurements reveal that this peak is correlated with a light emission at a wavelength of ∼620 nm (i.e. photon energy ∼ 2 eV). The TSL peak maximum temperatures are consistent with characteristic temperatures of about 500 K of annealing stages of colour centres. However, the trap-depth energies (ranging between 0.7 and 1.4 eV) deduced from the initial rise of partially cleaned TSL peaks, or from a rough approximation using Urbach's formula, are rather larger than the activation energies for defect recovery, ranging between 0.3 and 0.7 eV, as deduced from the EPR data. The processes involved in TSL are discussed in relation to available photoluminescence and defect energy-level data.

International audience; We present an extensive study of point-defect creation in yttria-stabilized zirconia (ZrO2:Y) exposed to 2.5 MeV electrons and various heavy ions (from C to U) covering an energy range from 100 MeV to several GeV. A synthesis of results from UV–visible optical absorption spectroscopy and electron paramagnetic resonance spectroscopy is provided with special emphasis on the respective roles of elastic collisions and electronic excitations. The colour centre production and recovery are the main focus in this survey. It is concluded that F+-type centres (involving singly ionized oxygen vacancies) are produced by elastic-collision processes. The large threshold displacement energy and defect volume hint that these colour centres might actually be small paramagnetic oxygen vacancy clusters, most probably divacancies (i.e. F+2 centres). Such a picture is consistent with the (100) axial symmetry, inhomogeneous broadening of the optical absorption band, lack of hyperfine splitting, and weak spin–lattice coupling found for this defect.

Pure bismuth samples were irradiated at 20 K with swift heavy ions from 18O to 238U in the GeV range. The rate of the induced damage was deduced from in situ electrical resistance measurements. Above a threshold in the electronic stopping power Se equal to 24 keV nm-1, the damage is due to electronic slowing down. Above 30 keV nm-1, the electronic slowing down is efficient enough to induce latent tracks attributed to the appearance of a high-resistivity phase. The induced latent tracks radii can be up to 21.9 nm for Se=51 keV nm-1 which is the largest value reported so far for non-radiolytic materials. The evolution with Se of the latent tracks radii is calculated on the basis of the thermal spike model, assuming a realistic value for the electron-phonon coupling constant. A rather good agreement is obtained which supports the idea that the thermal spike could be operative in the observed radiation damage.

(1993). High resistivity bismuth produced by heavy ion irradiations in the electronic stopping power regime. Radiation Effects and Defects in Solids: Vol. 126, No. 1-4, pp. 181-184.

We present a study of point-defect creation in yttria-stabilized zirconia (ZrO2: Y) or YSZ exposed to various heavy ions (from C to U) covering an energy range from 100 MeV to several GeVs. It is concluded that F+-type centers (involving singly-ionized oxygen vacancies) are produced by elastic-collision processes. The ion-induced out-of-plane expansion is found to be small (< 0.2%) and to increase linearly as a function of the average F+-type center concentration with a large slope compatible with small oxygen vacancy clusters. The large defect volume and axial symmetry of the F+-type centers hint that these color centers might actually be divacancies (i.e. F2+centers).

Via a direct coupling between the order parameter and the singlet Josephson supercurrent we detect spin-wave resonances and their dispersion in ferromagnetic Josephson junctions in which the usual insulating or metallic barrier is replaced with a weak ferromagnet. The coupling arises within the Fraunhofer interferential description of the Josephson effect because the magnetic layer acts as a time-dependent phase plate. A spin-wave resonance at a frequency ${\ensuremath{\omega}}_{s}$ implies a dissipation that is reflected as a depression in the current-voltage curve of the Josephson junction when $\ensuremath{\hbar}{\ensuremath{\omega}}_{s}=2eV$. We have thereby performed a resonance experiment on only ${10}^{7}$ Ni atoms.

International audience; The lattice damage was investigated by x-ray diffraction techniques in yttria-stabilized zirconia single crystals with the (100) or (110) orientation upon irradiation with swift heavy ions (from 100-MeV C to 2.6-GeV U) in a broad electronic stopping power range (from about 0.3 to 48 keV nm−1). The -2 scans show that no amorphization or change to a new crystalline phase occurs regardless of the ion and crystal features. However, the rocking curves ( scans) and reciprocal space mappings show evidence of the mosaicity of the crystals, which is produced above a threshold electronic stopping power between 18 and 27 keV nm−1. This threshold is in agreement with our previous Rutherford backscattering spectroscopy/channeling spectroscopy data. Two kinds of damage phenomena are found: (i) nuclear-collision induced clusters of point defects which generate Bragg peak shifts and broadening in the 2- and -2 scans, and (ii) electronic-excitation induced lattice damage yielding broad peaks in the scans above the stopping power threshold at high fluences

We compare the G and G′2D bands of single-, double- and triple-wall carbon nanotubes (CNTs). We observe that the band shape is sensitive to the number of walls of the CNTs. For single-wall carbon nanotubes (SWCNTs), the G band is composed of two distinct contributions G+ and G−, while the G band for double-wall nanotubes is composed of one band with two main contributions from the inner and the outer tube. The G′2D band can be fitted with one Lorentzian for single-wall tubes, while two distinct contributions are observed for double-wall carbon nanotubes (DWCNTs). Considerable variations of the G′2D band are found with similar first order Raman spectra. Annealing influences the D- and RBM-band intensities. Electron irradiation has the effect of decreasing the G- and D-band wavenumbers but does not enhance the D-band intensity considerably. The down-shifts of the G- and D-band wavenumbers are correlated and are the same for two excitation wavelengths. This is consistent with the scattering of phonons around the K-point. Copyright © 2007 John Wiley & Sons, Ltd.

International audience; Yttria-stabilized zirconia single crystals were irradiated with a variety of different swift heavy ions from 145 MeV C to 2.6 GeV U in a broad fluence range between 1011 and 1015 cm-2. Surface profilometry measurements show that the out-of-plane expansion of the samples increases versus ion fluence up to an asymptotic value of about 0.2%; the larger the ion mass, the smaller the fluence needed to reach saturation. Rutherford backscattering spectrometry data on irradiated crystals under channeling conditions give clear evidence of lattice damage creation for ions heavier than Br corresponding to a threshold electronic stopping power about 20 keV nm-1. In contrast, no threshold is found for the swelling data which scale fairly well with the number of displacements per atom except for the irradiation with U ions. In all cases we find a linear increase of the out-of-plane expansion versus the concentration of F+-type centers singly ionized oxygen vacancies measured by electron paramagnetic resonance spectroscopy in as-received and thermochemically reduced samples, regardless of crystal orientation. The nature of the lattice disorder and the respective effects of elastic collisions and electronic excitations on the ion-induced volume expansion and damage are discussed.

Sintered samples of monoclinic zirconia (alpha-ZrO2) have been irradiated at room temperature with 6.0-GeV Pb ions in the electronic slowing down regime. X-ray diffraction (XRD) and micro-Raman spectroscopy measurements showed unambiguously that a transition to the 'metastable' tetragonal phase (beta-ZrO2) occurred at a fluence of 6.5x10^12 cm-2 for a large electronic stopping power value (approx 32.5 MeV $\mu$m-1). At a lower fluence of 1.0x10^12 cm-2, no such phase transformation was detected. The back-transformation from beta- to alpha-ZrO2 induced by isothermal or isochronal thermal annealing was followed by XRD analysis. The back-transformation started at an onset temperature around 500 K and was completed by 973 K. Plots of the residual tetragonal phase fraction deduced from XRD measurements versus annealing temperature or time are analyzed with first- or second-order kinetic models. An activation energy close to 1 eV for the back-transformation process is derived either from isothermal annealing curves, using the so-called "cross-cut" method, or from the isochronal annealing curve, using a second-order kinetic law. Correlation with the thermal recovery of ion-induced paramagnetic centers monitored by EPR spectroscopy is discussed. Effects of crystallite size evolution and oxygen migration upon annealing are also addressed.

The nucleation and growth of single wall carbon nanotubes from a carbon-saturated catalytic particle surrounded by a single sheet of graphene is described qualitatively by using a very restricted number of elementary processes, namely Stone-Wales defects and carbon bi-interstitials. Energies of the different configurations are estimated by using a Tersoff energy minimization scheme. Such a description is compatible with a broad variety of size or helicity of the tubes. Several mechanisms of growth of the embryos are considered: one of them is made more favourable when the tubes embryos are arranged in an hexagonal network in the graphene plane. All the proposed mechanisms can be indefinitely repeated for the growth of the nanotubes., Solid state communications, in press

International audience; We have studied the electron spin resonance (ESR) of single-walled carbon nanotubes (SWNTs) both in their pristine state and after irradiation with fast electrons in order to detect the signal of conduction electrons. No metallic Pauli contribution was observed in the global spin susceptibility, the ESR signal of the conduction electrons is undetectable because it is broadened by magnetic impurities. We measured a paramagnetic contribution from localized states, with an effective Curie constant decreasing when the temperature increases, following a deactivation law of the type A-B exp(-E-a/k(B)T). This behavior is supposed to be characteristic of semiconducting SWNTs interacting with metallic impurities from the catalyst

We have studied the colour centre production by swift electron and heavy ion irradiations of yttria-stabilized zirconia (YSZ), i.e. ZrO2:Y with 9.5 mol% Y2O3. For this purpose, we performed irradiations of \langle 100\rangle - or \langle 110\rangle -oriented YSZ single crystals with 2.5 MeV electrons, 145 MeV 13C, 180 MeV 32S, 200 MeV 58Ni, 230 MeV 79Br, 120 MeV 127I, 200 MeV 127I, 200 MeV 197Au, and 2.6 GeV 238U ions. X-band electron paramagnetic resonance (EPR) and UV–visible optical absorption measurements were used to monitor the point defect formation. The EPR line saturations were measured between 6 and 150 K, in order to obtain the spin–lattice relaxation time (T1). Electron and ion beams produce the same two colour centres: (i) the first one is identified as an F+-type centre (singly ionized oxygen vacancy) with an axial \langle 100\rangle symmetry, a small g-factor anisotropy (g_{\bot }=1.972 and g_{\parallel }=1.996 ) and long T1 values, (ii) the second one is similar to the well known T-centre (Zr3+ in a trigonal oxygen environment) with an axial \langle 111\rangle symmetry and a large g-factor anisotropy (g_{\bot }=1.855 and g_{\parallel }=1.986 ), which is also produced by photon irradiations. A broad optical absorption band centred at a wavelength near 500 nm is observed with an absorption coefficient proportional to the volume density of the F+-type centre deduced from the room temperature EPR spectra. Since no change of this band occurs between 10 and 300 K, it indicates that the electron–phonon coupling of this colour centre must be strong, in agreement with an F+-type centre. Owing to the axial \langle 100\rangle symmetry and lack of hyperfine structure of the EPR lines of this defect, it is suggested that the first coordination shell must contain one native oxygen vacancy. The plots of the volume density of this centre versus fluence are on the whole rescaled as functions of the number of displacements per atom induced by elastic collisions.

We have studied the effect of the yttria content on the paramagnetic centers in electron-irradiated yttria-stabilized zirconia (ZrO2: Y3+) or YSZ. Single crystals with 9.5 mol % or 18 mol % Y2O3 were irradiated with electrons of 1.0, 1.5, 2.0, and 2.5 MeV. The paramagnetic center production was studied by X-band electron paramagnetic resonance (EPR) spectroscopy. The same paramagnetic centers were identified for both chemical compositions, namely two electron centers, i.e., (i) F+-type centers (involving singly ionized oxygen vacancies), and (ii) so-called T centers (Zr3+ in a trigonal symmetry site), as well as hole-centers. A strong effect is observed on the production of hole-centers that is strongly enhanced when doubling the yttria content. However, no striking effect is found on the electron centers (except the enhancement of an extra line associated with the F+-type centers). It is concluded that hole-centers are produced by inelastic interactions, whereas F+-type centers are produced by elastic co...

The linewidth of the electron-spin resonance in aluminum has been studied experimentally in many laboratories over the frequency range 1.3-80 GHz and at temperatures from 4 to 100 K. At low temperatures the width is thought to be due to motionally narrowed $g$ anisotropy, and at high temperatures spin-flip scattering by phonons is assumed to dominate. Models are developed in this paper, based on previous calculations of the $g$ anisotropy by Beuneu, which give a good semiquantitative account of the linewidth variation over the full range of frequency and temperature.

Recently it has been shown that the most efficient conduction-electron-spin relaxation mechanism in Al is associated with scattering events to and from certain portions (ridges) of the Fermi surface where the spin-orbit interaction leads to electron wave functions which have a substantial admixture of spin-up and spin-down components. Those ridges arise from intersections of the Fermi surface with Brillouin boundaries and therefore this relaxation mechanism must be common to and prevail in the simple (nontransition) polyvalent metals. Here, we show that in fact this mechanism accounts for the spin-flip processes responsible for the finite Knight shift observed in small Sn and Pb superconducting particles.