title: Self-Assembly of Crystalline Structures of Magnetic Core-Shell Nanoparticles for Fabrication of Nanostructured Materials.
abstract: A theoretical study is presented of the template-assisted formation of crystalline superstructures of magnetic-dielectric core-shell particles. The templates produce highly localized gradient fields and a corresponding magnetic force that guides the assembly with nanoscale precision in particle placement. The process is studied using two distinct and complementary computational models that predict the dynamics and energy of the particles, respectively. Both mono- and polydisperse colloids are studied, and the analysis demonstrates for the first time that although the particles self-assemble into ordered crystalline superstructures, the particle formation is not unique. There is a Brownian motion-induced degeneracy in the process wherein various distinct, energetically comparable crystalline structures can form for a given template geometry. The models predict the formation of hexagonal close packed (HCP) and face centered cubic (FCC) structures as well as mixed phase structures due to in-plane stacking disorders, which is consistent with experimental observations. The polydisperse particle structures are less uniform than the monodisperse particle structures because of the irregular packing of different-sized particles. A comparison of self-assembly using soft- and hard-magnetic templates is also presented, the former being magnetized in a uniform field. This analysis shows that soft-magnetic templates enable an order-of-magnitude more rapid assembly and much higher spatial resolution in particle placement than their hard-magnetic counterparts. The self-assembly method discussed is versatile and broadly applies to arbitrary template geometries and multilayered and multifunctional mono- and polydisperse core-shell particles that have at least one magnetic component. As such, the method holds potential for the bottom-up fabrication of functional nanostructured materials for a broad range of applications. This work provides unprecedented insight into the assembly process, especially with respect to the viability and potential fundamental limitations of realizing structure-dependent material properties for applications.
authors.affiliation: Department of Chemical and Biological Engineering and ‡Department of Electrical Engineering, University at Buffalo SUNY , Buffalo, New York 14260, United States.
authors.forename: Xiaozheng
authors.initials: X
authors.lastname: Xue
authors.affiliation: Department of Chemical and Biological Engineering and ‡Department of Electrical Engineering, University at Buffalo SUNY , Buffalo, New York 14260, United States.
authors.forename: Jianchao
authors.initials: J
authors.lastname: Wang
authors.affiliation: Department of Chemical and Biological Engineering and ‡Department of Electrical Engineering, University at Buffalo SUNY , Buffalo, New York 14260, United States.
authors.forename: Edward P
authors.initials: EP
authors.lastname: Furlani
keywords: assembly of core−shell particles; assembly of crystalline superstructures; field-directed assembly; magnetic dipole−dipole interactions; magnetic template-assisted self-assembly