Synthesis, directed-assembly and characterization of magnetic nanoparticles

Abstract

Forced Assembly of Nanoparticles and Their Micro Patterning An easy and reliable method for the fabrication of patterned monolayer of Co nanoparticles is described. Two-dimensional monolayer of Co nanoparticles has been prepared by spreading of nanoparticles solution on an air-water interface and transferred it to a hydrophobic substrate by the Langmuir-Blodgett (LB) method. Transmission electron microscopy (TEM) showed that on increasing the surface pressure, the Co nanoparticles were well organized into a Langmuir monolayer with a hexagonal close-packed structure. By controlling the pH of the subphase, long range ordered monolayer of Co nanoparticles was obtained. In particular, by stamping after transferring a Langmuir monolayer onto a polydimethoxysilane (PDMS) mold, micro-patterning of Co nanoparticles was achieved selectively on a patterned electronic circuit. Electronic transport properties of Co nanoparticles showed metallic characteristic with ohmic I-V curve. Binary Superlattices of Nanoparticles The structuring of binary superstructure of two nanoparticles with different diameters is new issue in assembly. AB type binary superstructures are formed after mixing of Co and $Fe_3O_4$ nanoparticles with size ratio of 0.416. An AB type binary superstructure is the same structure as NaCl structure which revealed by TEM analysis. $AB_2$ type binary superstructures are also formed by changing the molar ratio to 1:2. When the similar sized Co and $Fe_3O_4$ nanoparticles were used, a randomly mixed binary superstructure was produced. These binary structures showed intermediate properties of native Co and $Fe_3O_4$ nanoparticles in magnetism. In case of Ag and CdSe nanoparticles, $AB_2$ type binary superstructures are also formed where the size ration is 0.53. The photoluminescence of $AB_2$ type binary superstructure of Ag and CdSe quantum dots was quenched by charge transfer of CdSe quantum dots due to the surrounding of Ag nanoparticles around CdSe quantum d...