Nucleation, growth, and self-assembly of cobalt nanoparticles
Abstract
Cobalt nanoparticles have been well recognized for the potential application as ultradense memory storage units. However, a reliable synthesis method is still lacking with the capability of size tuning in a large range. We developed a seeded synthesis procedure with nucleation and growth separation by using cobalt calixarene complex as nucleation agent to produce Co NPs from 10 nm to 30 nm with narrow size distributions. First, the influence of calixarenes as multivalent ligands on cobalt calixarene complexes’ thermal decomposition behaviors was studied by comparison with that of their monovalent counterparts. Upon thermal activation, cobalt calixarene complexes decompose quickly to form capped clusters, which coalesce into small cobalt nanoclusters without further growth if no additional growth reagent. The special property of the cobalt calixarene complexes inspired us to design a synthesis procedure that can separate the nucleation and growth based on the formation of capped clusters from cobalt calixarene complexes. We chose 1–pentyne–Co4(CO)10 (PTC) as growth reagent after testing three different cobalt compounds. A great correlation between the amount of PTC introduced and the final NP size, indicating it is a good growth reagent under the reaction conditions because of its low self– nucleation rate and high solubility. The system of cobalt calixarene complex and PTC produced uniform Co NPs in a large size range. A novel growth mechanism separating nucleation and growth in the synthesis procedure is proposed based on the thermochemical profiles of the nucleation and growth reagents. We indentified an amorphous intermediate from incomplete decomposition of PTC may play an important role in separating the nucleation and growth procedures. Finally, data on visualization of magnetism of self–assembled cobalt nanoring structures was reported, and a theoretical model was provided to explain the switching of flux closure states supported on the cobalt nanorings by off–axis magnetic pluses.
Degree
Ph.D.
Advisors
Wei, Purdue University.
Subject Area
Analytical chemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.