Silver/Gold Heterometallic Nanostructures and Their Surface Plasmon-Related Behaviors
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1257-O01-04
Silver/Gold Heterometallic Nanostructures and Their Surface Plasmon-Related Behaviors Hyunjoon Song Department of Chemistry, Korea Advanced Institute of Science and Technology, Daejeon, 305701, Republic of Korea
ABSTRACT A combination of silver and gold is demonstrated in nanoscale objects. Silver and gold have similar but distinct chemical and physical properties. We employed three main chemistry related to silver and gold – underpotential deposition, epitaxial growth, and Galvanic replacement. Selective underpotential deposition of silver guided the growth direction of gold and generated gold octahedrons, cuboctahedrons, cubes, and rods. Epitaxial growth of silver on gold decahedral seeds formed silver-gold-silver heterometallic nanorods and wires. Galvanic replacement of silver for gold yielded asymmetric single hollow and symmetric double hollow structures. All silver/gold nanostructures exhibited characteristic optical features in the UV-visNIR ranges. Such structural variation and corresponding optical properties are useful for diverse applications in electronics, photonics, biology, and catalysis. INTRODUCTION Heterometallic superlattice structures are particularly of interest because of their multifunctional properties. Since metallic barcodes were synthesized by electrochemical deposition of distinct metal salts inside anodic aluminum oxide templates [1], heterometallic nanorods with various components were fabricated and employed for protein separation, bioassay, and catalytic nanomotors [2]. Compared to the hard template method, synthesis without templates has many advantages including structural variation more than rods, simple process without template dissolution, and large scale production. However, such synthesis has only recently developed, because the reaction condition must be strictly controlled to balance reduction rates of distinct components [3]. In this aspect, silver and gold are excellent components that match together very well. Silver and gold are in Group 11, and have close lattice constants with a small lattice mismatch of 0.2%, which leads to heteroepitaxy on the surface. These two metals also show intense surface plasmon extinctions. There are some differences in chemical reactivity and electrochemical potentials between them, but these make the silver/gold system more exciting. Herein, our recent results related to the coupling of silver and gold components in nanoscale objects are summarized. Gold polyhedrons and rods were synthesized by selective underpotential deposition of silver onto a gold surface in a controlled manner. Silver nanorods and wires were prepared from gold decahedral seeds, which yielded silver-gold-silver heterometallic superlattices through epitaxial growth. Partial Galvanic replacement of gold from silver provided asymmetric and symmetric single and double hollow rods. All these nanostructures showed interesting optical features in the range from visible to near infrared.
EXPERIMENT Control of gold polyhedral shapes by silver underpotential depos
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