Chemical Synthesis of Gold Micro-Bars for Optical Circuitry Applications
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Chemical Synthesis of Gold Micro-Bars for Optical Circuitry Applications Erik W. Hobbs1 and Mary Sajini Devadas2 1 Department of Physics Astronomy and Geosciences, Towson University 8000 York Road, Towson, MD 21252, U.S.A. 2 Department of Chemistry, Towson University 8000 York Road, Towson, MD 21252, U.S.A. ABSTRACT The aim of this research was to establish a reliable chemical synthesis route to produce plasmonic gold micro-bars. Gold micro-bars have been synthesized through chemical reduction in the presence of surfactants: polyvinylpyrrolidone (PVP) and sodium dodecylsulfonate (SDS), and in the presence of a metal cation. Synthesis was executed by varying the concentration of PVP and SDS, and introducing copper ions, and performing seeded growth. Resulting plasmonic gold micro-bars were viewed under dark field microscopy and scanning electron microscopy (SEM) to visualize the nanoparticle product mixture. Energy Dispersive Spectroscopy (EDS) was used to determine composition of the micro-bars. The results indicate that the copper additive method yields the longest micro-bars. INTRODUCTION Gold based anisotropic structures are of great interest for their intrinsic optical properties as they differ from bulk materials. They have demonstrated applications in catalysis[1] and optics. Plasmonic gold nano-particles have been previously synthesized using a modified polyol method[2, 3]. Protocols to synthesize 1D and 2D plasmonic nanostructures (100 nm to 1000 nm) that decreases polydispersity is important from a standpoint of interferometric optical trapping[4], plasmonic waveguides[5] and logic circuitry[3, 6]. The El-Sayed[7], Murphy[8] and the Xia[9] groups have done extensive research on the synthesis of Au based 2D and 3D objects[10]. Other longitudinal structures have been grown using seeded growth[11]. Gold nanoparticle morphology can also be controlled through the addition of metal ions[12]. Gold longitudinal nanostructures and gold micro-bars have been demonstrated to exhibit plasmonic properties[3]. Plasmonic properties make gold micro-bars useful for wave guides in optical circuitry applications. Plasmonic wave guides can channel light whose wavelength is considerably larger than the wave guide[13]. These materials are of great interest because they support the transfer of polaritons at half the speed of light despite suffering from Joule losses[14]. This research was focused on the development of a one pot synthesis of gold micro-bars in relatively high yield, exhibiting plasmonic properties. In this report, three strategies have been taken which include (a) varying the concentration of a dual surfactant mediated synthesis on a nanobelt protocol developed by Zhang et al.[15]; (b) metal additive concentration variation; (c) seeded growth using copper. The synthesis protocol was tested by considering relative yield of gold micro-bars using histogram data obtained from dark field microscopy. XRD was implemented to identify the growth direction, and to probe the crystallinity of synthesized gold micro-bars. SEM i
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