Patterned arrays of assembled nanoparticles prepared by interfacial assembly and femtosecond laser fabrication

Creating shape-defined structures of inorganic nanoparticles in a maskless and template-free fashion would advance the engineering of nanoparticle-based devices and structures with desired configurations for various applications. In this work, a novel fabrication protocol combining bottom-up interfacial assembly and subtractive laser patterning was developed for creating patterned arrays of assembled nanoparticles. A solid film of magnetic nanoparticles (10 nm, monodisperse CoFe₂O₄) was assembled as a nanoparticle film (thickness less than 100 nm) on liquid interface under guiding field, and it was further transferred to Si substrate followed by selective material removal using femtosecond laser pulses, producing patterned arrays (typical size of 3 μm) of assembled nanoparticles. The size, shape, and arrangement of the patterned arrays were finely regulated by adjusting the laser pulse energy and laser scanning path. The magnetization behavior and magnetic anisotropy of the patterned arrays differ from those of the nanoparticle-assembled film, as reflected by the changes of coercivity and squareness along the out-of-plane direction. The presented fabrication protocol is compatible with microelectronic fabrication techniques and can be applied to various inorganic nanoparticles.