In Situ Redox Microfluidic Synthesis of Core–Shell Nanoparticles and Their Long-Term Stability

Abstract

An in situ redox process in microfluidic reactors was developed to synthesize hybrid nanoparticles with amorphous metallic cores and uniform metal oxide shells embedded with nanocrystallites at large scale. For example, the fabricated Fe(B)@iron oxides nanoparticles (NPs) exhibit permanent ferromagnetic properties at room temperature due to the strong magnetic coupling between different parts and the nanocrystalline pinning effect, providing an alternative design of nanostructures to break out the superparamagnetic limit in ultratiny particles. The NPs with amorphous metallic cores and uniform metal oxide shells can be well maintained over 4–5 months. The dictated novel microfluidic process provides a large-scale synthetic strategy for metal@metal oxide core–shell NPs with uniform shells and long-term stability and can be extended to a variety of material systems.

Magneto-Plasmons in Periodic Nanoporous Structures

“…This result is consistent with previous studies on similar films [44][45][46][47] , and can be attributed to the confined out-of-plane direction that impedes the nucleation and motion of domain walls and forces the magnetic moments to reverse through rotation. The OP H e values of all samples are higher than for the IP case, suggesting that an effective magnetic anisotropy energy (E A ) larger than the interface exchange energy (E int ) can be achieved in the OP direction rather than in the IP direction 33,48 . The nanopores cause only a small change in H e in the CoFeB film consistent with similar result in Permalloy films 45 .…”

“…H K is obtained from the magnetization curves as the crossing point of linear extrapolations of the low field magnetization curve and the saturation curve 43 . When the curves do not pass through the origin, the mean value of the crossing points of the increasing and decreasing external magnetic field curves is used 33,43 . The rather square shape IP loops (high M r /M s ) shows that the magnetization easy axis (low H c ) is in-plane, while the magnetization hard axis (high H c ) is along the out-of-plane direction.…”

“…Applications of new types of multi-functional nanoparticles (NPs) based on hybridization require control over the mismatch among different components and a good understanding of the interface-coupling and proximity effects in the constituent parts 3,5,7,8,25 . It is also essential to develop controlled processes for large scale fabrication of well-defined nanoentities with long-term stability in desired media 10,[26][27][28][29][30][31][32][33][34][35] .For hybrid nanomaterials with magnetic components, both the magnetic properties and dielectric constants can be tuned by IFMEC effects, leading to enhanced magnetic, electronic, optical and acoustic properties 1,5,23,24 . Recent investigations indicate that active magneto-plasmonic nanomaterials formed by noble metals and magnetic metals can improve the interaction between magnetic field, electric field, electromagnetic waves and the localized surface plasmon resonance (LSPR), leading to applications for efficient switching and transmission of electrical, magnetic, optical and acoustic signals based on active plasmonics 1,2,5,23,[36][37][38] .…”

“…Applications of new types of multi-functional nanoparticles (NPs) based on hybridization require control over the mismatch among different components and a good understanding of the interface-coupling and proximity effects in the constituent parts 3,5,7,8,25 . It is also essential to develop controlled processes for large scale fabrication of well-defined nanoentities with long-term stability in desired media 10,[26][27][28][29][30][31][32][33][34][35] .…”

“…Therefore, it is essential either to characterize single nanostructures or to develop controlled fabrication processes for size homogeneity [26][27][28][29][30][31][32][33][34]42 .…”