Colloidal Synthesis and Self-Assembly of CoPt₃ Nanocrystals

Reduction of platinum acetylacetonate and thermodecomposition of cobalt carbonyl in the presence of 1-adamantanecarboxylic acid were employed in different coordinating mixtures to produce monodisperse, highly crystalline CoPt₃ nanoparticles. The mean particle size can be varied from 1.5 to 7.2 nm by controlling the reaction conditions and the type of coordinating mixture. As-synthesized CoPt₃ particles represent single crystal domains and have chemically disordered face-centered cubic (fcc) structure. Nearly spherical CoPt₃ nanocrystals were found to assemble into two- (2D) and three-dimensional (3D) structures. An AB₅ type superlattice is observed by TEM after mixing two nanoparticle samples with different mean sizes. Slow precipitation led to the formation of facetted colloidal crystals with sizes up to 20 μm.