Nanoparticles of metallic Cobalt and Nickel prepared by ion implantation into SiO 2

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Nanoparticles of metallic Cobalt and Nickel prepared by ion implantation into SiO2 O. Cíntora-González1, 2, C. Estournès1, D. Muller2, M. Richard-Plouet1, A. Traverse3, J. L. Guille1 and J.J. Grob2 1 Groupe des Matériaux Inorganiques Institut de Physique et Chimie des Matériaux de Strasbourg (UMR7504 CNRS-ULP-ECPM) 23 rue du Loess 67037 Strasbourg Cedex France ; 2 Laboratoire PHASE (UPR292 CNRS), 23 rue du Loess 67037 Strasbourg, France ; 3 Lure (UMR130 CNRS), Bâtiment 209A, Université de Paris-Sud, 91405 Orsay Cedex France.

ABSTRACT The structural and magnetic properties of nano-sized particles of transition metals (Co and Ni) implanted into amorphous SiO2 are investigated. The SiO2 substrates used were as grown on a silicon (100) wafer under wet O2 atmosphere. The metals were implanted as singly charged atoms energized to 30 or 160 keV. Transmission Electron microscopy (TEM) observations and X-ray absorption spectroscopy (XAS) show that M+ implantation results in the formation of metallic nanoparticles at the vicinity of the surface whereas oxide particles (< 1 nm) are formed in a deeper region. After thermal treatment under hydrogen, TEM evidences the disappearance of the oxide region and an increase in the size of the metallic particle. XAS shows that cobalt and nickel are entirely in the metallic form and saturation magnetization becomes close to the theoretical value.

INTRODUCTION The design and synthesis of materials of nanometer size are currently the subject of intense research because their properties differ considerably from those of the corresponding bulk materials. In particular, the nanoparticles can exhibit novel magnetic, optical and chemical properties due to their large surface to volume ratio. Nanoparticles can be prepared by physical methods (inert gas evaporation, sputtering, laser vaporization) [1,2] or by chemical methods (solgel, inverse micelle technique) [3-6]. An important challenge in studies of the physical properties of such composites is to obtain well characterized samples of controllable size and surface of particles, as it is known that such particles are not very stable. We have recently shown that the use of an inorganic matrix like glasses or a SiO2 xerogel [7,8] is a good host for crystalline metallic nanoparticles. However, due to the low solubility of transition metals in these matrices only a low volume fraction can be obtained in the form of monolithic samples. Ion implantation of metallic ions into an insulating matrix is a powerful technique for the elaboration of nanosized metal particles [9-15]. The purpose of the present study is to investigate the physico-chemical properties of Nickel and Cobalt implanted into amorphous silica and the magnetic properties of these nanocomposites.

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EXPERIMENTAL DETAILS Transition metal ions (Ni+ and Co+) have been implanted into 300 nm thick silica layers prepared by oxidation of wafers of Si (100) at 1100°C under water/oxygen mixture. The samples were implanted at 30 and 160 keV with nominal dose of 1017 ions cm-2 and curren

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