Jin-Seung Jung

CoFe2O4 nanostructures with high coercivity

Nanometer-sized ferrite magnetic materials are the subject of intense research interest due to their potential applications in high-density magnetic information storage. One of the most explored ferrite materials is the cobalt ferrite (CoFe2O4). We have synthesized cobalt ferrite nanowires using cobalt ferrite nanoparticles in a porous anodic alumina template (AAT). The process of embedding ferrimagnetic particles into the pores was assisted by the magnetic field of a permanent magnet placed in vacuum directly under the substrate. Particles synthesized in the template were subsequently annealed at 600°C for 2h in Ar gas forming arrays of cobalt ferrite nanowires inside the AAT. The morphology of the ferrite before and after annealing was observed using a field-emission scanning electron microscope. The crystallographic structure of the nanowires was analyzed using x-ray diffraction and transmission electron microscopy. The magnetization was measured by a superconducting quantum interference device. The co...

Microwave absorption of patterned arrays of nanosized magnetic stripes with different aspect ratios

Arrays consisting of nanosized stripes of Permalloy with different length-to-width ratios have been fabricated using electron beam nanolithography, magnetron sputtering, and lift-off process. These stripes have a thickness of 100nm, a width of 300nm, and different lengths ranging from 300nmto100μm. The stripes are separated by a distance of 1μm. Magnetization hysteresis loops were measured using a superconducting quantum interference device susceptometer. Microwave absorption at 9.8GHz was determined by means of ferromagnetic resonance technique. The dependence of the resonant field on the angle between the nanostructure and the in-plane dc magnetic field indicates the presence of uniaxial magnetic anisotropy associated with the aspect ratio of the stripes. A maximum change of the resonant field of 1600Oe was observed in the longest stripes, yet it was only 200Oe for square shaped stripes. The linewidth of the resonant curve varied with the angle, in the range from 120to300Oe. Most of the ferromagnetic re...

A Facile Fabrication of Fe

Monodispersed superparamagnetic magnetite submicron particles were synthesized by using a one-step solvothermal method. Increasing the volume ratio of ethylene glycol/diethylene glycol (EG/DEG) shows a gradual increase in the size of primary nanograin and secondary Fe3O4 submicroparticles. To induce the photo-magnetic functionality, we have successfully synthesized the multifunctional core-shell (Fe3O4/ZnO) submicron particles by atomic layer deposition (ALD) method. Microstructure and magnetic properties of the multifunctional core/shell submicron particles are investigated by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), and photoluminescence spectroscopy.

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Nanomedicine, which involves the use of magnetic nanoparticles such as Fe3O4, has provided novel technical solutions for cancer diagnosis and treatment. Most studies in nanomedicine have focused on the use of nanoparticles with magnetic resonance imaging and hyperthermia. However, to achieve optimum anticancer effects, it is important to understand the physicochemical properties of magnetic nanoparticles and their interactions with biological entities. In this study, we synthesized Fe3O4 particles of various sizes and conjugated them with hematoporphyrin (HP) molecules by using a simple surface-modification method. HP molecules were covalently bound to the surface of Fe3O4 particles by a wet chemical process, resulting in Fe3O4@HPs particles that were uniform in size, were nontoxic, and exhibited strong anticancer effects on human prostate cancer (PC-3) and breast cancer (MDA-MB-231) cell lines. The Fe3O4@HPs particles showed remarkable and efficient photodynamic anticancer activity, depending on their particle size. These results indicate that all size of Fe3O4@HPs particles can be useful for photodynamic anticancer therapy, although the smaller size is better than the larger size and further studies will be needed to confirm the potential for clinical anticancer treatment.

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Several Fe nanostructures with different lengths, diameters, and separations of the constituting magnetic components have been synthesized using anodized alumina membranes (AAMs) to understand the influence of these parameters on their magnetic properties. Fe nanostructures with high crystallinity and (110) orientation were synthesized by electrodeposition at room temperature in regular AAMs and mild-hard AAM (Mi-Ha AAM). Fe nanostructures with different aspect ratios (1:1, 1:10, and 1:75) in the form of nanodots, nanorods, or nanowires were synthesized in regular AAMs with the 100 nm interpore distance. Mi-Ha AAMs with two different pore sizes (70 and 120 nm) and 250 nm interpore distances were used to investigate the effect of the interactions and of the diameter of the wires on their magnetic behavior. Nearly linear magnetization characteristics with small coercivity, observed for Fe nanowires, suggest the magnetization rotation to be the predominant magnetization process for the field applied transver...

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For the photooxidative reaction of olefin, colloidal CdS nanoparticles (NPs) show enhanced efficiency of photocatalytic activity compared to bulk CdS. We find that the enhanced activity is due to the enlarged surface area of the colloidal CdS NPs as well as enhanced energetic coupling between the colloidal CdS NPs and the olefin molecules. Photocatalytic activity is reduced in the case that CdS NPs are encapsulated in mesoporous silica nanopores.

/ZnO Core-Shell Submicron Particles With Controlled Size

It has been shown that the deposition of magnetoresistive multilayers on stepped, corrugated or V-grooved surfaces can increase the magnitude of giant magnetoresistance (GMR). The primary reason for this enhancement of GMR is that the in-the-substrate-plane current crosses multiple magnetic layers which results in the mixed current-in-plane and current perpendicular to plane modes called current at an angle to the plane mode. In our studies, we use a novel substrate consisting of nano-hemispheres organized in a regular hexagonal array. The substrate was produced by anodization of Al and subsequent etching of alumina membrane. Scanning electron microscopy was used to investigate larger areas and cross-sectional images of the embossed surface, whereas detailed analysis of the surface structure was made by high resolution atomic force microscopy. We deposited uncoupled Co/Cu multilayers on the alumina substrate with an 8-nm-thick Fe buffer using magnetron sputtering. Our preliminary studies of the magnetotransport using a physical property measurement system (quantum design) demonstrated that the samples on the new substrate have an enhanced GMR effect compared to the samples with similar composition deposited on smooth (100) Si wafers. Because of the inexpensive method of fabrication of the embossed substrate, the GMR structures deposited on this substrate have a potential for use in magnetic sensors.

Particle size dependent photodynamic anticancer activity of hematoporphyrin-conjugated Fe 3 O 4 particles

We have fabricated bimodal porous gold skeletons by double-templating routes using poly(styrene) colloidal opals as templates. The fabricated gold skeletons show a bimodal pore-size distribution, with small pores within spheres and large pores between spheres. The templated bimodal porous gold skeletons were applied in Raman scattering experiments to study sensing efficiency for probe molecules. We found that the bimodal porous gold skeletons showed obvious enhancement of Raman scattering signals versus that of the unimodal porous gold which only has interstitial pores of several hundred nanometers.

Fabrication and magnetic properties of Fe nanostructures in anodic alumina membrane

Abstract For ternary chalcogenide, Ni3(SbTe3)2, with the potential applications of magnetic and opto-magnetic storage media, we investigated the properties induced by the incorporation of ternary chalcogenide into long range ordered mesoporous AlMCM-41. Structural confinement in the mesoporous channel induces the enhanced crystallinity of the ternary chalcogenide and is possibly responsible for the observed weak ferromagnetic transition (∼70 K). Such confinement also causes the suppression of phonon coupling to photoexcited carriers in the confined ternary chalcogenide, resulting narrower photoluminescence (PL) band and slower PL lifetime than those of the bulk ternary chalcogenide.

Photocatalytic Efficiency Analysis of CdS Nanoparticles with Modified Electronic States

In this study, newly designed biocompatible multifunctional magnetic submicron particles (CoFe2O4-HPs-FAs) of well-defined sizes (60, 133, 245, and 335 nm) were fabricated for application as a photosensitizer delivery agent for photodynamic therapy in cancer cells. To provide selective targeting of cancer cells and destruction of cancer cell functionality, basic cobalt ferrite (CoFe2O4) particles were covalently bonded with a photosensitizer (PS), which comprises hematoporphyrin (HP), and folic acid (FA) molecules. The magnetic properties of the CoFe2O4 particles were finely adjusted by controlling the size of the primary CoFe2O4 nanograins, and secondary superstructured composite particles were formed by aggregation of the nanograins. The prepared CoFe2O4-HP-FA exhibited high water solubility, good MR-imaging capacity, and biocompatibility without any in vitro cytotoxicity. In particular, our CoFe2O4-HP-FA exhibited remarkable photodynamic anticancer efficiency via induction of apoptotic death in PC-3 prostate cancer cells in a particle size- and concentration-dependent manner. This size-dependent effect was determined by the specific surface area of the particles because the number of HP molecules increased with decreasing size and increasing surface area. These results indicate that our CoFe2O4-HP-FA may be applicable for photodynamic therapy (PDT) as a PS delivery material and a therapeutic agent for MR-imaging based PDT owing to their high saturation value for magnetization and superparamagnetism.