Ferromagnetic cobalt nanodots, nanorices, nanowires and nanoflowers by polyol process
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Various shapes and sizes of colloidal Co nanoparticles were fabricated by the polyol process using Co(acac)3, 1,2-hexadecanediol, oleylamine, and oleic acid within octylether. The rice-shaped Co nanoparticles with size of 30 nm and aspect ratio of 1.8 can be fabricated into a self-assembled form without assistance of surfactants. The addition of oleylamine as surfactant decreased the particle size and aspect ratio, and the addition of oleic acid made the surface of particle faceted without decreasing particle size from that of rice shape. The mixture of oleylamine and oleic acid produce differently shaped Co nanoparticles, including nanoprism, nanowire, and nanoflower according to the ratio of components, total amount of surfactant mixture, and reaction time. The fabricated nanoparticles showed ferromagnetic properties. These results showed that the various size and shape of metallic nanoparticles can be fabricated by the polyol process into controlled forms.
I. INTRODUCTION
Uniform colloidal Co nanoparticles are fascinating due to their outstanding magnetic properties and various promising applications such as high-density recording media, magnetic fluids, drug delivery, and gene therapy.1,2 To fabricate monodispersed Co nanoparticles, several processes and related chemicals have been proposed during the last decade.1–13 The rapid thermal decomposition process, which consists of rapid injection of organometallic precursor into high-temperature solvent with surfactant, is widely used to fabricate Co nanoparticles.1,3 Relatively little attention is paid to slow processes, which take more time for nucleation and growth of nanoparticles than rapid process does due to slow reaction rate and low monomer concentration. However, the slow process has a greater potential for controlling the morphology of nanoparticles because it allows enough time to perform certain treatment during nucleation and growth.2 Among the slow processes, the polyol process is one of the more popular processes for obtaining colloidal nanoparticles; the metallic nanoparticles are obtained by a reduction of metallic salt with polyols having high boiling temperatures.2,4–13 Many metallic nanoparticles, such as Ni, Ag, CoPt, Au, and Co, are fabricated by the polyol process with
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2005.0267 2148
http://journals.cambridge.org
J. Mater. Res., Vol. 20, No. 8, Aug 2005 Downloaded: 07 May 2015
particle sizes ranging from 5 nm to several micrometers.4–13 However, it is relatively difficult to fabricate colloidal Co nanoparticles compared to nanoparticles of noble metals. Also, the shape control of Co nanoparticles into spheres, rods, wires, and disks by polyol process is more difficult than it is with other processes.1–3 Here we show that various sizes, ranging from 6 to 50 nm, and shapes, including rice-shape, dot, prism, wire, and flower-like shape, of ferromagnetic Co nanoparticles can be fabricated by employing polyol process. II. EXPERIMENTAL
Colloidal Co nan
