Fabrication and Properties of Self-Assembled Nanosized Magnetic Particles
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Fabrication and Properties of Self-Assembled Nanosized Magnetic Particles G. Salazar-Alvarez, M. Mikhailova, M. Toprak, Y. Zhang, and M. Muhammed. Materials Chemistry Division, Royal Institute of Technology. SE-100 44 Stockholm, Sweden. ABSTRACT The synthesis and characterisation of gold-coated cobalt nanoparticles, as well as their chemically- and magnetically-induced self-organisation have been studied. Metallic core-shell nanoparticles were prepared using two different experimental techniques: bulk reductive precipitation, with average particles size ~15 nm, and microemulsion confining method, with average particle size of ~6 nm. The self-assembly of prepared nanoparticles on flat substrates was achieved by derivatising the substrate and particle surfaces with bifunctional organic molecules that attaches to both particles and substrates. Examination of the self-assembled systems was carried out by a number of characterisation techniques including transmission electron microscopy (TEM), UV-visible spectrophotometry (UV-VIS), and atomic force microscopy (AFM). INTRODUCTION Over the last decade, control and design of nanoparticles and, in particular, core-shell structured materials have drawn the attention of physicist, chemists and material scientists. The tailoring of the surface properties combined with those shown by the core provides a number of applications that range from catalysis, and coatings to spintronics and magneto-resistants, among others.[1-3] Furthermore, during the last few years, it has been observed that the quantum size effects in low dimensional systems of such materials vary considerably than those in the bulk. Such behaviour has been associated with the degree of organisation, i.e., 0D, 1D, 2D, and 3D self-assembled arrays.[4] The understanding, control, and design of such systems open a true supramolecular engineering of materials, where a defined nanophase grain boundary plays a major role. Among the prospective applications for self-organised systems are: photonic bandgap crystals,[5] ultra high-density data storage,[6] and biomedical applications.[7] In this work, attempt has been made at studying the controlled preparation of superstructures based on magnetic particles and the chemical parameters that affect them. EXPERIMENTAL Reagents All the salts used were purchased from Aldrich with ACS grade. As solvents c-Hexane (cHex, +99.5%), n-decane (C10, 97%), and n-octane (C8, 97%) were used as obtained without any further purification. Triton-X 100 (TX100), n-Hexanol (HxOH), and n-Butanol (BuOH) were purchased from Fluka and were used as obtained. 3-aminopropyl trimethoxy silane (APTMS) and 3-mercaptopropyl trimethoxy silane (MPTMS) were purchased from Aldrich. High purity water was used with a specific resistivity of 18 MΩ·cm (Milli-Q, Millipore Inc.).
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Colloidal system Microemulsions were prepared by solubilising aqueous solutions of the salts and aqueous solution of NaBH4 into a TX100-HxOH/cHex system. The control of size was achieved by adjusting the water to surfactant molar ra
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