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ABSTRACT: Nano-composite material consisting of Co2C and Co3C nanoparticles has recently been shown to exhibit unusually large coercivities and energy products. Experimental studies that can delineate the properties of individual phases have been undertaken and provide information on how the coercivities and the energy product change with the size and composition of the nanoparticles. The studies indicate that while both phases are magnetic, the Co3C has higher magnetization and coercivity compared to Co2C. Through first principles electronic structure studies using a GGA+U functional, we provide insight on the role of C intercalation on enhancing the magnetic anisotropy of the individual phases.
Applied Physics Letters 07/2012; 101:012409. · 3.84 Impact Factor
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ABSTRACT: We present theoretical and experimental studies that explain the observed strong enhancement of the magneto-optical (MO) Faraday rotation in all-metal core-shell Co-Ag nanoparticles (NPs) attributed to localized surface plasmon resonance (LSPR). We also explain why the optical absorption and MO spectra peaks appear blue-shifted with increased Co core size while keeping the NP size constant. Further, we demonstrate direct correlation between the strong LSPR induced electromagnetic fields and the enhanced MO activity of the NPs.
Nano Letters 02/2011; 11(3):1237-40. · 13.20 Impact Factor
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ABSTRACT: This paper discusses the relationship between synthesis conditions, crystal morphology, and theoretical modeling of copper and nickel nanoparticles prepared by a modified polyol process. The polyol serves as a solvent, a reducing agent, and a capping agent, and we investigate the role several polyol types play in the nucleation and growth of metallic nanoparticles. The nanoparticles are characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Our results demonstrate that changing the solvent system from a short chain polyol (ethylene glycol) to a long chain polyol (tetraethylene glycol) greatly affects the resulting morphology of copper nanoparticles. These results suggest that the polyol is playing a major role as an in situ capping agent and that the various polyol chain lengths in-turn result in various particle morphologies by directly altering the nucleation and growth steps. We were also able to use theoretical modeling to investigate the mechanism for growth to better understand the intermediate structure stability. This work presents an alternative approach in investigating the polyol mechanism by using both theoretical and experimental results and opens new insight for the synthesis of metals and alloys by the polyol process.
01/2011;
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ABSTRACT: This article investigates a facile one-pot method for the synthesis of Fe and Ag core/shell nanoparticles by aqueous reduction under ambient conditions. We have shown that the injection time of silver nitrate into a reaction vessel containing aqueous ferrous salt, sodium borohydride, and sodium citrate is a vital parameter for the precise control of a desired core/shell structure. For example, if silver nitrate is injected one minute after sodium borohydride is added to the reaction vessel, Ag will nucleate first followed by Fe, creating monodisperse Ag/Fe core/shell nanoparticles. In contrast, if the introduction time is prolonged to 5 min, Fe nanoparticles will nucleate followed by Ag producing Fe/Ag nanoparticles. The composition, morphology, and magnetic behavior were investigated by X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), transmission electron microscopy (TEM), and room-temperature vibrating sample magnetometry (VSM). Fe/Ag core/shell nanoparticles with optical and magnetic functionality offer broad opportunities in medicine, catalysis, and chemical detection.
11/2010;
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ABSTRACT: The comprehensive goal of this research is the synthesis and characterization of nanomaterials that are spectrally tunable in terms of their electromagnetic signal, are robust, magnetic (allowing their piloted movement), and have the potential to be functionalized for the detection of CBRNE threats. Various chemical methods were utilized for synthesis of magnetic (iron) and luminescent rare earth (RE) components, and their mixtures. Effects of integrating an iron core into RE luminescent lattices (excited by UV, emit in the VIS) were investigated. The determination of the optimum balances between magnetic and luminescent components such that the magnetism was maximized while maintaining acceptable fluorescence integrity will be discussed. The emphasis of this work is focused on developing a distributed sensor suitable for use in the terrestrial environment. The robust properties of using a RE luminescent shell would allow the particles to be resistant to photobleaching. Additionally the chemical stability of the RE shell would allow operation in a variety of p H conditions. The magnetic core will ultimately allow the distributed particles to be recollected.
Journal of Applied Physics 06/2010; · 2.17 Impact Factor
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ABSTRACT: A one-step polyol method was utilized to prepare a stable aqueous iron/iron oxide ferrofluid. The dried powders were characterized by x-ray diffraction, electron microscopy, x-ray absorption spectroscopy, and vibrating sample magnetometry for the determination of phase, morphology, and magnetic properties. To show its potential for imaging applications, the ferrofluid was also investigated as a magnetic resonance imaging contrast agent.
Journal of Applied Physics 06/2010; · 2.17 Impact Factor
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03/2010;
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ABSTRACT: The ionic title complex, bis(mu-ethylene glycol)-kappa(3)O,O':O';kappa(3)O:O,O'-bis[(ethylene glycol-kappa(2)O,O')(ethylene glycol-kappaO)sodium] bis(ethylene glycolato-kappa(2)O,O')copper(II), [Na(2)(C(2)H(6)O(2))(6)][Cu(C(2)H(4)O(2))(2)], was obtained from a basic solution of CuCl(2) in ethylene glycol and consists of discrete ions interconnected by O-H...O hydrogen bonds. This is the first example of a disodium-ethylene glycol complex cation cluster. The cation lies about an inversion center and the Cu(II) atom of the anion lies on another independent inversion center.
Acta crystallographica. Section C, Crystal structure communications 03/2010; 66(Pt 3):m83-5. · 0.78 Impact Factor
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ABSTRACT: A copolyacrylate with semifluorinated and polydimethylsiloxane side chains (D5-3) was used as a surface modifier for a condensation-cured PDMS coating. The decyl fluorous group is represented by "D"; "5" is a 5 kDa silicone, and "3" is the mole ratio of fluorous to silicone side chains. Wetting behavior was assessed by dynamic contact angle (DCA) analysis using isopropanol, which differentiates silicone and fluorous wetting behavior. Interestingly, a maximum in surface oleophobicity was found at low D5-3 concentration (0.4 wt %). Higher concentrations result in decreased oleophobicity, as reflected in decreased contact angles. To understand this unexpected observation, dynamic light scattering (DLS) studies were initiated on a model system consisting of hydroxyl-terminated PDMS (18 kDa) containing varying amounts of D5-3. DLS revealed D5-3 aggregation to be a function of temperature and concentration. A model is proposed by which D5-3 surface concentration is depleted via phase separation favoring D5-3 aggregation at concentrations >0.4 wt %, that is, the cmc. This model suggests increasing aggregate/micelle concentrations at increased D5-3 concentration. Bulk morphologies studied by scanning electron microscopy (SEM) and atomic force microscopy (AFM) support this model by showing increased aggregate concentrations with increased D5-3 > 0.4 wt %.
Langmuir 12/2009; 26(8):5848-55. · 4.19 Impact Factor
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ABSTRACT: Using two-step (air/argon) thermal processing, sol-gel-derived nickel-iron oxide aerogels are transformed into monodisperse, networked nanocrystalline magnetic oxides of NiFe(2)O(4) with particle diameters that can be ripened with increasing temperature under argon to 4.6, 6.4, and 8.8 nm. Processing in air alone yields poorly crystalline materials; heating in argon alone leads to single phase, but diversiform, polydisperse NiFe(2)O(4), which hampers interpretation of the magnetic properties of the nanoarchitectures. The two-step method yields an improved model system to study magnetic effects as a function of size on the nanoscale while maintaining the particles within the size regime of single domain magnets, as networked building blocks, not agglomerates, and without stabilizing ligands capping the surface.
ACS Nano 05/2008; 2(4):784-90. · 10.77 Impact Factor
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ABSTRACT: Dopamine forms an initial structure coordinated to the surface of the iron oxide nanoparticle as a result of improved orbital overlap of the five-membered ring and a reduced steric environment of the iron complex. However, through transfer of electrons to the iron cations on the surface and rearrangement of the oxidized dopamine, a semiquinone is formed. Because of free protons in the system, oxygens on the surface are protonated, which allows for the Fe2+ to be released into the solution as a hydroxide. This released fragment of the nanoparticle will then eventually oxidize in air to a form of an iron(III) oxyhydroxide. All of the reported results demonstrate that the reactivity between Fe3+ and dopamine quickly facilitates the degradation of the nanoparticles. The energetic modeling studies substantiate our proposed decomposition mechanism and thus conclude that the use of dopamine as a robust anchor for iron oxide or iron oxide shell particles will not fulfill the need for stable ferrofluids in most biomedical applications.
Journal of the American Chemical Society 04/2007; 129(9):2482-7. · 9.91 Impact Factor
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ABSTRACT: We have developed crystalline nanoarchitectures of iron oxide that exhibit superparamagnetic behavior while still retaining the desirable bicontinuous pore-solid networks and monolithic nature of an aerogel. Iron oxide aerogels are initially produced in an X-ray-amorphous, high-surface-area form, by adapting recently established sol-gel methods using Fe(III) salts and epoxide-based proton scavengers. Controlled temperature/atmosphere treatments convert the as-prepared iron oxide aerogels into nanocrystalline forms with the inverse spinel structure. As a function of the bathing gas, treatment temperature, and treatment history, these nanocrystalline forms can be reversibly tuned to predominantly exhibit either Fe(3)O(4) (magnetite) or gamma-Fe(2)O(3) (maghemite) phases, as verified by electron microscopy, X-ray and electron diffraction, microprobe Raman spectroscopy, and magnetic analysis. Peak deconvolution of the Raman-active Fe-O bands yields valuable information on the local structure and vacancy content of the various aerogel forms, and facilitates the differentiation of Fe(3)O(4) and gamma-Fe(2)O(3) components, which are difficult to assign using only diffraction methods. These nanocrystalline, magnetic forms retain the inherent characteristics of aerogels, including high surface area (>140 m(2) g(-1)), through-connected porosity concentrated in the mesopore size range (2-50 nm), and nanoscale particle sizes (7-18 nm). On the basis of this synthetic and processing protocol, we produce multifunctional nanostructured materials with effective control of the pore-solid architecture, the nanocrystalline phase, and subsequent magnetic properties.
Journal of the American Chemical Society 01/2005; 126(51):16879-89. · 9.91 Impact Factor
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ABSTRACT: In an adaptation of sol–gel methods recently described for preparing iron oxide (FeOx) aerogels, we use epichlorohydrin as a proton scavenger to generate mixed metal oxides from ethanol solutions of Mn- and Fe-chloride salts. This reaction forms monolithic gels, which can be processed with supercritical CO2 extraction to form high-surface-area, highly porous Mn–FeOx aerogels. The amorphous as-prepared Mn–FeOx aerogel is transformed into a nanocrystalline form by heating in argon to 300 °C. Elemental analysis shows that a Fe:Mn ratio of 2:1 is attained, and the X-ray diffraction pattern for the nanocrystalline aerogel is consistent with that for spinel MnFe2O4, confirming that Mn(II) from the initial sol–gel mixture is incorporated into the crystal structure of the resulting oxide. The nanocrystalline Mn–FeOx aerogel exhibits magnetic properties consistent with a superparamagnetic material, while still retaining the characteristic morphology of an aerogel nanoarchitecture.
Journal of Non-Crystalline Solids 350:182-188. · 1.54 Impact Factor
