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S. Bouffard

Bio: S. Bouffard is an academic researcher from Centre national de la recherche scientifique. The author has contributed to research in topics: Ion & Irradiation. The author has an hindex of 29, co-authored 60 publications receiving 2364 citations. Previous affiliations of S. Bouffard include University of Caen Lower Normandy.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the effect of the irradiation temperature, the crystallographic orientation, the initial electrical resistivity and the oxygen stoichiometry on the damage morphology of oxide materials has been investigated.
Abstract: Damage induced in several oxide materials by swift heavy ions is presented. The discussion is based on results obtained on the following materials [Y3Fe5O12, AFe12O19 (A = Ba, Sr), BFe2O4 (B = Ni, Mg, Zn), ZrSi2O4, SiO2 quartz, Al2O3, high Tc superconductors (YBa2Cu3O7 − δ and Bi2Sr2CaCu2O8)] which have been irradiated by ions with atomic number ranging between 6 (12C) and 92 (238U) and energies between 0.05 GeV and 6 GeV. The damage cross section A has been deduced using several physical characterisations like Mossbauer spectrometry, saturation magnetisation measurements, channeling Rutherford backscattering, infrared absorption and electrical resistance measurements. Depending on the material and on the value of the electronic stopping power (dE/dx) the damage cross section varies between 10−17 and 10−12 cm2. Using medium and high resolution transmission electron microscopy and chemical etching of the latent track, an electronic stopping power evolution of the damage morphology has been observed leading to the definition of an effective radius Re of the latent track which can be linked to the damage (amorphous) cross section A by the relation Re = √A/π. Moreover there is a direct correlation between these values and the damage morphology: for Re > 3 nm the latent tracks are long and cylindrical, conversely for Re < 3 nm the damage is inhomogeneous along the latent track. The effect of the irradiation temperature, of the crystallographic orientation, of the initial electrical resistivity and of the oxygen stoichiometry will be presented. In opposition to what has been usually believed it will be shown that alumina (Al2O3) is indeed sensitive to the electronic stopping power. Moreover the velocity of the incident ion has a direct influence on the damage production: the lower the velocity, the higher the damage.

295 citations

Journal ArticleDOI
TL;DR: These observations are the first images of nanometric changes of elastic properties in mica observed through atomic force microscopy as hollows which are associated with softer areas in the mica surface.
Abstract: For the first time, latent tracks induced by swift Kr ions have been directly observed in mica. These tracks are imaged by atomic-force microscopy as hollows which are associated with softer areas in the mica surface. The track core is formed by disordered mica. The mean diameter of the observed hollows increases with the electronic stopping power of the ions. The track shape along the ion path is deduced from the analysis of both the number of the tracks per unit area and their diameter distribution. These observations are the first images of nanometric changes of elastic properties.

147 citations

Journal ArticleDOI
TL;DR: In this paper, the effects of dense electronic excitations on vinyl linear polymers, by performing swift heavy ion, SHI, irradiations, were studied using different ion beams, from C to Pb, provided by the GANIL accelerator at energies of a few MeV/u.
Abstract: We have studied the effects of dense electronic excitations on vinyl linear polymers, by performing swift heavy ion, SHI, irradiations We used different ion beams, from C to Pb, provided by the GANIL accelerator at energies of a few MeV/u We mainly studied the physico-chemical modifications induced in polyethylene (PE), but the role of chemical substitutions has also been investigated by studying the swift heavy ion induced damage in polyvinylidene fluoride (PVDF) and polystyrene (PS) The irradiated samples were analysed ex-situ by means of Fourier transform infrared spectroscopy in the transmission mode Any contact with air was avoided: oxidation does not occur Swift heavy ion irradiations are characterised by a significant increase of the yield of chain scission associated with unsaturated end groups Moreover, we have evidences for specific modifications, ie modifications which are never observed when using low ionising particles as electrons or gamma-rays; namely the creation of alkyne and allene end groups These specific modifications are little sensitive to chemical substitutions For instance, alkyne formation is observed in PE, PVDF and PS A simultaneous ionisation of the different atoms of a constituting monomer is likely needed for triggering the formation of the specific swift heavy ion induced modifications On the other hand, if we pay attention to the physico-chemical modifications which are easily induced by low ionising particles, it is observed that increasing the electronic stopping power does not significantly modify the creation yield of, for instance in PE, trans-vinylene or trans-trans diene groups

145 citations

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TL;DR: In this paper, a Monte Carlo method is used to describe event by event the interactions of the projectile with the target electrons as well as the evolution of the electronic subsystem of the target.
Abstract: In this paper the swift heavy ion interactions with condensed matter are studied from the point of view of the modifications induced in the electronic subsystem of the target. A Monte Carlo method is used to describe event by event the interactions of the projectile with the target electrons as well as the evolution of the electronic subsystem. The validity of the method and the results are discussed. This detailed picture of the excited target could be used for further explanations and calculations of the damage creation by electronic excitation. We have focused our attention on two materials whose electronic properties are different: graphite and quartz. For both materials a quantitative analysis of the energy deposition mechanism is given.

128 citations

Journal ArticleDOI
TL;DR: In this article, the radial dose distribution was calculated using a Monte Carlo simulation code and it was found that for homogeneous track etching the energy loss of the ions has to surpass a threshold of about 450 eV/A.
Abstract: Tracks of various heavy ions with energies up to 13 MeV/u were studied using the technique of selective chemical etching. It was found that for homogeneous track etching the energy loss of the ions has to surpass a threshold of about 450 eV/A. In a transition regime between 180 and 450 eV/A etching was possible but the mean diameter of the resulting pores showed a wider distribution than pores at higher energy losses. In order to describe this observation, the radial dose distribution was calculated using a Monte Carlo simulation code. Inhomogeneous etching is interpreted as due to the spatial fluctuations of the deposited energy along the ion path.

99 citations


Cited by
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TL;DR: In this paper, nuclear tracks in solids (Principles and Applications) nuclear technology: Vol. 30, No. 1, pp. 91-92, were discussed and discussed in detail.
Abstract: (1976). Nuclear Tracks in Solids (Principles and Applications) Nuclear Technology: Vol. 30, No. 1, pp. 91-92.

973 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of the electronic stopping power (Se) in metals irradiated by swift heavy ions was investigated in the framework of the thermal-spike model, and the effect on the lattice temperature induced by swift-heavy ion irradiation was calculated.
Abstract: In the framework of the thermal-spike model the present paper deals with the effect of the electronic stopping power (Se) in metals irradiated by swift heavy ions. Using the strength of the electron-phonon coupling g(z) with the number of valence electrons z as the unique free parameter, the increment of lattice temperature induced by swift-heavy-ion irradiation is calculated. Choosing z=2, the calculated threshold of defect creation by Se for Ti, Zr, Co and Fe is about 11, 27.5, 28 and 41 keV nm-1, in good agreement with experiment. Taking the same z value, the calculation shows that Al, Cu, Nb and Ag are Se insensitive. Moreover, in Fe, the differences in the damage created by U ions of different energies but exhibiting the same value of Se may be interpreted by a velocity effect. Using z=2, other calculations suggest that Be (Se>or=11 keV nm-1), Ga (Se>or=5 keV nm-1) and Ni (Se>or=49 keV nm-1) should be sensitive to Se but Mg should not. These examples put the stress on the effect of the physical parameters governing the electron-phonon coupling constant apart from z determination: the sound velocity linked to the Debye temperature and the lattice thermal conductivity. Furthermore, a simple criterion is proposed in order to predict the Se sensitivity of metals.

493 citations

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TL;DR: In this article, the authors predict the composition of water subjected to electron irradiation in the electron microscope and reinterpret available experimental data, such as beam-induced variations in pH and colloid aggregation, in light of their predictions.
Abstract: Liquid cell electron microscopy enables direct in situ imaging of processes in liquids and objects suspended in liquids with nanoscale resolution. However, the irradiating electrons affect the chemistry of the suspending medium, typically an aqueous solution, producing molecular and radical products such as hydrogen, oxygen, and hydrated (solvated) electrons. These may impact the imaged structures and phenomena. A good understanding of the interactions between the electrons and the irradiated medium is necessary to correctly interpret experiments, minimize artifacts, and take advantage of the irradiation. We predict the composition of water subjected to electron irradiation in the electron microscope. We reinterpret available experimental data, such as beam-induced variations in pH and colloid aggregation, in light of our predictions and show new observations of crystallization and etching as functions of dose rate, resolving conflicting reports in the scientific literature. We make our computer code avai...

472 citations

Journal ArticleDOI
Ch. Jooss, Joachim Albrecht1, H Kuhn, S. Leonhardt1, H. Kronmüller1 
TL;DR: In this paper, a review of the magneto-optical imaging technique and experiments on thin films, single crystals, polycrystalline bulk ceramics, tapes and melt-textured HTS materials is presented.
Abstract: In the past few years magneto-optical flux imaging (MOI) has come to take an increasing role in the investigation and understanding of critical current densities in high-Tc superconductors (HTS). This has been related to the significant progress in quantitative high-resolution magneto-optical imaging of flux distributions together with the model-independent determination of the corresponding current distributions. We review in this article the magneto-optical imaging technique and experiments on thin films, single crystals, polycrystalline bulk ceramics, tapes and melt-textured HTS materials and analyse systematically the properties determining the spatial distribution and the magnitude of the supercurrents. First of all, the current distribution is determined by the sample geometry. Due to the boundary conditions at the sample borders, the current distribution in samples of arbitrary shape splits up into domains of nearly uniform parallel current flow which are separated by current domain boundaries, where the current streamlines are sharply bent. Qualitatively, the current pattern is described by the Bean model; however, changes due to a spatially dependent electric field distribution which is induced by flux creep or flux flow have to be taken into account. For small magnetic fields, the Meissner phase coexists with pinned vortex phases and the geometry-dependent Meissner screening currents contribute to the observed current patterns. The influence of additional factors on the current domain patterns are systematically analysed: local magnetic field dependence of jc(B), current anisotropy, inhomogeneities and local transport properties of grain boundaries. We then continue to an overview of the current distribution and current-limiting factors of materials, relevant to technical applications like melt-textured samples, coated conductors and tapes. Finally, a selection of magneto-optical experiments which give direct insight into vortex pinning and depinning mechanisms are reviewed.

430 citations

Journal ArticleDOI
TL;DR: In this paper, a review of matter transformation induced in crystalline inorganic insulators by swift heavy ions is presented, with the emphasis on new results obtained for amorphizable materials such as Gd3Ga5O12, GeS, and LiNbO3 and for nonamorphizable crystals such as SnO2, LiF and CaF2.
Abstract: A review of matter transformation induced in crystalline inorganic insulators by swift heavy ions is presented. The emphasis is made on new results obtained for amorphizable materials such as Gd3Ga5O12, GeS, and LiNbO3 and for non-amorphizable crystals such as SnO2, LiF and CaF2. Assuming that latent tracks result from a transient thermal process, a quantitative development of a thermal spike is proposed. The only free parameter is the electron–lattice interaction mean free path λ. With this parameter it is possible to quantitatively describe track radii, whatever the bonding character of the crystal is, in a wide range of ion velocities assuming two specific criteria: tracks may result from a rapid quenching of a cylinder of matter in which the energy deposited on the lattice has overcome either the energy necessary to reach a quasi-molten phase in the case of amorphizable materials or the cohesion energy in the case of non-amorphizable materials. The evolution of the λ parameter versus the band gap energy of the considered insulator will be presented. On the basis of this discussion some predictions are developed.

425 citations