Fabrication of multilayered superparamagnetic particles based on sequential thermal deposition method

Abstract

A simple method for the fabrication of superparamagnetic particles was developed. Polystyrene spheres were used as templates, and their surfaces were coated with a magnetic element (Ni) by thermal deposition, controlling their thicknesses strictly. Magnetic properties of fabricated particles depended on the Ni layer thickness; the fabricated particles were typically superparamagnetic for a Ni layer thinner than 3 nm and ferromagnetic for a Ni layer thicker than 4 nm. For the improvement of the force generated on a particle in a magnetic field, the formation of multiple Ni layers on a particle was examined by sequential depositions of Ni and SiO 2 , isolating two Ni layers with a SiO 2 layer. The SiO 2 layer thickness should be larger than 10 nm for a sufficient isolation of two Ni layers to maintain the superparamagnetic properties of the particle, and the magnetic charge of the particle increased proportionally with the number of Ni layers on a particle. These results indicate that enhanced superparamagnetic particles with various diameters can easily be fabricated by the suggested method.

Application-driven multi-layered particles – The role of polymers in the architectural design of particles

“…Qualitative confirmation of superparamagnetic properties of particle achieved by tuning the layer thickness of Ni[48].…”

“…An attractive thermal deposition method has been utilized by Kim et al for the fabrication of multi-layered superparamagnetic particles [48], which can be utilized as a magnetically cell sorting device. Polystyrene spheres are used as a template, and their surfaces were coated with a magnetic element (i.e.…”

Depletion effect on concave microstructure upon size-specific target particle collection

“…For experimental confirmation of the contribution of the depletion effect to target bead capture by concave structures of magcups, two differently sized beads (10 and 20 µm in diameter) were mixed simultaneously with magcups of a certain size (10,15,20,30,40, or 50 µm in diameter). Figure 3 shows typical examples of target beads captured by 30-µm-diameter magcups.…”

“…14,15,[24][25][26][27][28][29][30] First, commercially available suspensions of polystyrene spheres of 10 to 50 µm diameter [JSR DYNOSPHERES: nominal diameters of 10.14, 15.62, and 20.31 µm and coefficients of variation (CVs) of 1.20, 1.17, and 1.17% and Duke Standards (Thermo Scientific): nominal diameters of 29.75, 39.94, and 50.2 µm and CVs of 1.4, 1.3, and 1.0%, respectively] were dropped onto clean flat silicon (Si) substrates as one diameter of the sphere on a substrate, and dried. Next, the polystyrene spheres were placed into a vacuum evaporator (ULVAC VPC-1100) to coat elements onto their surfaces, and nickel (Ni) and silicon dioxide (SiO 2 ) were sequentially coated onto the spheres alternately and sufficiently thinly to convey superparamagnetism, 30) typically, 2 nm thick for Ni and 15 nm thick for SiO 2 . Finally, the element-coated spheres were placed into an electric furnace (Asone MMF-2) and incubated at 500 °C for 17 h to remove the polystyrene sphere templates.…”