Synthesis and Structural Characterization of Ferromagnetic Au/Co Nanoparticles
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Synthesis and Structural Characterization of Ferromagnetic Au/Co Nanoparticles Nabraj Bhattarai*, Subarna Khanal, Daniel Bahena, Robert L. Whetten, and Miguel JoseYacaman Department of Physics and Astronomy, University of Texas at San Antonio, One UTSA Circle, San Antonio, TX 78249, USA. [email protected] ABSTRACT The synthesis of bimetallic magnetic nanoparticles is very challenging because of the agglomeration and non-uniform size. In this paper, we present the synthesis of monodispersed 35 nm sized thiolated bimetallic alloyed Au/Co nanoparticles with decahedral and icosahedral shape, their characterization using Cs-corrected scanning transmission electron microscopy (STEM) and magnetic measurements using superconducting quantum interference device (SQUID) magnetometer. The Z-contrast imaging and energy dispersive X-ray spectroscopy (EDS) mapping showed an inhomogeneous alloying with minor segregation between Au and Co at nanoscale and the SQUID measurement exhibited the ferromagnetic behavior. INTRODUCTION The study of magnetic bimetallic (BM) nanoparticles (NP) with plasmonic properties is a very fascinating area of nanoscience and nanotechnology because of the presence of both plasmonic and magnetic properties. The magneto-plasmonic nanoparticles give rise to interesting bifunctional properties simultaneously that can be used to enhance the catalytic, magnetic and optical properties. The core-shell magneto-plasmonic nanostructure with magnetic core and plasmonic shell is the model system for targeted drug delivery applications. Moreover, magnetoplasmonic nanoparticles are widely used for applications such as: biomedicine, waste water management, magnetic resonance imaging, magnetic particle imaging, data storage, environmental remediation and many more.1, 2 They can also be used in protein purification, bacterial detection,3 hyperthermia treatment and cell separation.4, 5 Because of its toxicity, the metallic Co nanoparticles cannot be used directly for biological applications. The coating of Co with the noble metals like Au reduces (almost zero) its toxicity. However, the synthesis of small magnetic nanoclusters of deļ¬ned sizes is very challenging because of agglomeration, nonuniform size, shape and narrow size distributions. Despite those challenges, there are some studies have been done in the synthesis and theoretical study of Au-Co nanoparticles.6-8 The fabrication of thiol protected BM magnetic NP is very good system as thiol protected metallic nanoclusters have been studied both theoretically and experimentally.9 Even the problem with non-uniform size and agglomeration can be well controlled with the suitable choice of capping ligands and the reaction environment during synthesis. The phase transfer process at which the metal nanoparticles at aqueous phase are transferred to organic phase is suitable for obtaining very small nanoclusters where the particle size is controlled by low interfacial energy in non-polar organic solvent and the particle is
protected by specific thiols. Moreover, by co
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