Elaboration par implantation ionique de nanoparticules de cobalt dans la silice et modifications de leurs propriétés sous irradiation d'électrons et d'ions de haute énergie

L'objectif de ce travail est d'explorer les possibilités offertes par les faisceaux énergétiques pour élaborer des nanoparticules magnétiques dans la silice et d'en modifier les propriétés.Des ions Co+ ont été implantés à 160 keV à 2.1016,5.1016 et 1017 at.cm-2,à des températures de 77, 295 et 873K.Nous avons montré la dépendance de la taille des particules de la fluence,et de façon plus prononcée,de la température d'implantation.La MET révèle la présence de particules d'un diamètre de l'ordre de 1 nm qui augmente jusqu'à 9,7 nm pour les implantations à 2.1016 Co+.cm-2 à 77K,et à 1017 Co+.cm-2 à 873K,respectivement.Les traitements thermiques induisent un faible mûrissement des particules.L'irradiation à haute énergie provoque le mûrissement des particules pour des faibles fluences,et une déformation pour les fortes fluences induisant une anisotropie magnétique.Ces modifications ont été expliquées par des processus similaires à ceux impliqués dans le modèle de la pointe thermique.This work aims to investigate the capability of ion irradiations to elaborate magnetic nanoparticles in silica layers, and to modify their properties. Co+ ions have been implanted at 160 keV at fluences of 2.1016, 5.1016 and 1017 at.cm-2, and at temperatures of 77, 295 and 873K. The dependence of the particle size on the implantation fluence, and more significantly on the implantation temperature has been shown. TEM observations have shown a mean diameter varying from 1 nm to 9.7 nm for implantations at 2.1016 Co+.cm-2 at 77K, and at 1017 Co+.cm-2 at 873K respectively. Thermal treatments induce the ripening of the particles. Swift heavy ion irradiations also induces the ripening of the particles for low fluences, and an elongation of the particles for high fluences, resulting in a magnetic anisotropy. Mechanisms invoked in thermal spike model could also explain this anisotropic growth.STRASBOURG-Sc. et Techniques (674822102) / SudocSudocFranceF

Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape

Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au(+9 )ions at a fluence of 5 × 10(13 )ions/cm(2). The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au(+9 )ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (H(c)) and remanence ratio (M(r)/M(s)) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction

Ion beam-induced shaping of Ni nanoparticles embedded in a silica matrix: from spherical to prolate shape

Abstract Present work reports the elongation of spherical Ni nanoparticles (NPs) parallel to each other, due to bombardment with 120 MeV Au+9 ions at a fluence of 5 &#215; 1013 ions/cm2. The Ni NPs embedded in silica matrix have been prepared by atom beam sputtering technique and subsequent annealing. The elongation of Ni NPs due to interaction with Au+9 ions as investigated by cross-sectional transmission electron microscopy (TEM) shows a strong dependence on initial Ni particle size and is explained on the basis of thermal spike model. Irradiation induces a change from single crystalline nature of spherical particles to polycrystalline nature of elongated particles. Magnetization measurements indicate that changes in coercivity (Hc) and remanence ratio (Mr/Ms) are stronger in the ion beam direction due to the preferential easy axis of elongated particles in the beam direction.</p

Sputtering of LiF and other halide crystals in the electronic energy loss regime

International audienceSputtering experiments were performed by irradiating LiF, NaCl, and RbCl crystals with various swift heavy ions like S, Ni, I, Au with energies between 60 and 210 MeV, C$_{60}$ clusters between 12 and 30 MeV or Pb ions between 730 and 6040 MeV. Sputtered species are collected on arc-shaped catchers and subsequently analyzed by elastic recoil detection analysis or Rutherford backscattering analysis. The study focuses on angular distributions and total yields for LiF and covers a broad range of experimental parameters including cleaved or rough sample surfaces, ion fluence, beam incident angles, and different ion velocities leading to electronic energy loss (S$_{e}$) values from 5 to 45 keV/nm. In most cases, the angular distribution has two components, a jet-like peak perpendicular to the surface sample superimposed on a broad isotropic cosine distribution whatever is the beam incident angle. The observation of the jet depends mainly on the surface flatness and angle of ion incidence. However, the jet does not appear clearly when irradiated with C$_{60}$ cluster. The sputtering yield is stoichiometric and characterized by huge total yields of up to a few 10$^{5}$ atoms per incident ion. The yield follows a power law as function of electronic energy loss, Y follows an exponential law with S$_{e}^{n}$ with n ~ 4. While the azimuthal symmetry for sputtering is observed at low ion velocity (~1 MeV/u), it seems to be lost at high velocity (>4 MeV/u). The data provide a comprehensive overview how the angular distribution and the total sputtering yield scale with the energy loss, beam incidence angle and ion velocity. Complementary experiments have been done with NaCl and RbCl targets confirming the observation made for LiF.[graphic not available: see fulltext][graphic not available: see fulltext