Magnetic nanoparticle assembly arrays prepared by hierarchical self-assembly on a patterned surface

Abstract

Inverted pyramid hole arrays were fabricated by photolithography and used as templates to direct the growth of colloidal nanoparticle assemblies. Cobalt ferrite nanoparticles deposit in the holes to yield high quality pyramid magnetic nanoparticle assembly arrays by carefully controlling the evaporation of the carrier fluid. Magnetic measurements indicate that the pyramid magnetic nanoparticle assembly arrays preferentially magnetize perpendicular to the substrate.

Magnetic nanoparticles: material engineering and emerging applications in lithography and biomedicine

“…Self-assembly of nanoparticles can be affected by a variety of factors, including drying front movement, nanoparticle movement in solution, evaporation rate, and directions of carrier fluids, etc. Here, we discuss controlling nanoparticle self-assembly by manipulating the evaporation of carrier solvent and the movement of drying front [41, 55, 56]. …”

“…They are also of interest for many other applications such as nanoparticle lithography [136], discussed later in §3.1. Besides the large area 2D monolayer or bilayer, it is also often required to self-assemble nanoparticles into complex hierarchical structures [137, 138], such as nanoparticle assembly arrays, where assemblies composed of ~millions of nanoparticles are spatially organized in 2D arrays [56]. The combinations of lithographic techniques and convective self-assembly can be used to fulfill requirements of hierarchical self-assembly [43, 48, 50, 56, 120, 139].…”

“…Besides the large area 2D monolayer or bilayer, it is also often required to self-assemble nanoparticles into complex hierarchical structures [137, 138], such as nanoparticle assembly arrays, where assemblies composed of ~millions of nanoparticles are spatially organized in 2D arrays [56]. The combinations of lithographic techniques and convective self-assembly can be used to fulfill requirements of hierarchical self-assembly [43, 48, 50, 56, 120, 139]. Here the lithographic techniques have two important roles, namely, (1) to generate the first layer of the hierarchical structures on the substrates, and (2) affect the movement of the contact line by the lithographic features [48, 56].…”

“…The combinations of lithographic techniques and convective self-assembly can be used to fulfill requirements of hierarchical self-assembly [43, 48, 50, 56, 120, 139]. Here the lithographic techniques have two important roles, namely, (1) to generate the first layer of the hierarchical structures on the substrates, and (2) affect the movement of the contact line by the lithographic features [48, 56]. The patterns can be generated by photolithography and e-beam lithography.…”

“…By controlling these factors, magnetic nanoparticles can be self-assembled into different patterns and morphologies [42, 52-54]. Instead of discussing the broad topic of self-assembly, we mainly concentrate on magnetic nanoparticle monolayers [55] and hierarchical nanoparticle assembly arrays [56]. To obtain long-range order in nanoparticle assembly, the nanoparticles should be made monodisperse, which can be realized by controlling the nucleation and growth of nanoparticles [57-59].…”