Synthesis of colloidal cobalt nanoparticles with controlled size and shapes

Abstract

A method of producing high quality magnetic colloidal dispersions by the rapid pyrolysis of cobalt carbonyl in an inert atmosphere was employed to produce monodispersed, stabilized, defect-free e-cobalt nanocrystals with spherical shapes and sizes ranging from 3 to 17 nm, as well as cubic and rod-like shaped particles. The size distribution and the shape of the nanocrystals were controlled by varying the surfactant composition (oleic acid, phosphonic oxides and acids), its concentration and the reaction temperature. These particles have been observed to produce 2D self-assemblies when evaporated at low rates in a controlled atmosphere. A combination of X-ray powder diffraction; transmission electron microscopy; and SQUID magnetometry has been used to characterize both the dispersed nanocrystals and the assembled superlattices.