Synthesis of Cobalt Nanoparticles, Nanorods and Nanowires assisted by Oleic Acid and Oleylamine based Mixtures

摘要

In this paper we report on the synthesis in solution of cobalt nanoparticles, nanorods and nanowires achieved through the decomposition of an organometallic precursor Co(η~3-C_8H_(13))(η~4-C_8H_(12)) and stabilized by carboxylic acid / amine based mixtures. Through decomposition of the precursor in the presence of a 1/1 mixture of oleylamine / oleic acid during 3 hours, the formation of 3 nm spherical nanoparticles is observed while hep-cobalt nanorods are obtained if the reaction is pursued for 48 hours. Increasing the amount of oleic acid to 2 equivalents with respect to the amine results in the formation of hep-cobalt nanowires, micrometers in length and 6 nm mean diameter.. By using amines with various chain lengths we have observed a modification of the aspect ratio of the cobalt nanorods. For example, the decomposition of Co(η~3-C_8H_(13))(η~4-C_8H_(12)) in the presence of octadecyl-, hexadecyl-, dodecyl- and octylamine in association with oleic acid allows to selectively produce nanorods of varying aspect ratio. Physical characterization using TEM and HRTEM, shows that the nanoparticles, nanorods and nanowires are all hcp single crystals. The magnetic properties reveal a saturation magnetization similar to that of bulk and a ferromagnetic behavior at room temperature for the nanorods and nanowires while the 3 nm nanoparticles remain super-paramagnetic.