Creation of High-Density and Low-Defect Single-Layer Film of Magnetic Nanoparticles by the Method of Interfacial Molecular Films

A technique to solubilize fine magnetic inorganic particles in general organic solvents is proposed via surfaces modification by long-chain carboxylic acids. This organic modification should overcome the relatively weak van der Waals interactions between the nanoparticles, allowing the formation of ordered arrangements of the modified Fe₃O₄ and CoFe₂O₄ materials. Using nanodispersions of these organo-modified magnetic nanoparticles as “spreading solutions”, Langmuir monolayers of these particles were formed. Multiparticle layered structures were constructed by the Langmuir–Blodgett (LB) technique. The fabrication of single- and multiparticle layers of organo-modified magnetic nanoparticles was investigated using surface pressure–area (π–<i>A</i>) isotherms, out-of-plane X-ray diffraction (XRD), in-plane XRD, and atomic force microscopy (AFM). The out-of-plane XRD profile of a single-particle layer of organo-modified Fe₃O₄ clearly showed a sharp peak which was attributed to the distance between Fe₃O₄ layers along the <i>c</i>-axis. The AFM image of single-particle layer of organo-modified CoFe₂O₄ revealed integrated particle organization with a uniform height; these aggregated particles formed large two-dimensional crystals. For both nanoparticle species, regular periodic structures along the <i>c</i>-axis and high-density single-particle layers were produced via the Langmuir and LB techniques