Synthesis of Highly Uniform Nickel Multipods with Tunable Aspect Ratio by Microwave-Power Control.

As the importance of anisotropic nanostructures and their unique surfaces continues to rise in applications including catalysis, magneto-optics and electromagnetic interference shielding, there is a need for efficient and economical synthesis routes for such nanostructures. The manuscript describes the application of cycled microwave-based heating for the rapid synthesis of highly branched pure phase fcc crystalline nickel mulitpods nanostructures with >99% multipod population. By controlling the power delivery to the reaction mixture through cycling, superior control is achieved over the growth kinetics of the metallic nanostructures allowing formation of multipods consisting of arms with different aspect ratios. The multipod structures are formed under ambient conditions in a simple reaction system comprised of nickel acetylacetonate (Ni(acac)2), oleylamine (OAm) and oleic acid (OAc) in a matter of minutes by selective heating at the (111) overgrowth corners on Ni nanoseeds. The selective heating at the corners leads to accelerated autocatalytic growth along the <111> direction through a 'lightning rod' effect. The length is directly proportional to the number of cycles, while the core size is controlled by continuous power delivery. The roles of heating mode (cycling versus variable power versus convective heating) during synthesis of the materials is explored allowing a mechanism into how cycled microwave energy may allow fast multipod evolution to be proposed.