Dr. Yugang G. Sun Profile

Dr. Yugang G. Sun

Scientist at Argonne National Lab

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Publications (4)

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Proceedings Article | 24 November 2003 Paper

Polymer-mediated synthesis of metal nanostructures

Yugang Sun, Younan Xia

Proceedings Volume 5224, (2003) https://doi.org/10.1117/12.504822

KEYWORDS: Silver, Nanostructures, Crystals, Metals, Transmission electron microscopy, Polymers, Nanoparticles, Scanning electron microscopy, Nanowires, Nanorods

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A solution-phase approach has been developed for the large-scale synthesis of metal nanostructures with well-defined shapes in the presence of a polymeric surfactant, i.e., poly(vinyl pyrrolidone) (PVP). As a demonstration, nanowires and nanocubes of silver have been synthesized through a modified polyol process that involved the reduction of silver nitrate with ethylene glycol heated at 160°C. Both reactant concentrations and the molar ratio between PVP and silver nitrate played critical roles in determining the shape and dimension of the final products. Relatively high concentrations of silver nitrate were favorable for the formation of silver nanocubes, while nanowires or nanorods became the dominated products if the concentration of silver nitrate was below 0.1 mM. The edge lengths of nanocubes and the lateral dimensions of nanowires synthesized with this method could be varied in the ranges of 50-180 nm and 30-60 nm, respectively. Nanocubes were single crystals mainly bounded by {100} facets. Each nanowire/nanorod, however, was characterized with a pentagonal cross-section, five straight side edges, and five flat side surfaces. It is believed that these silver nanostructures with well-defined shapes should find uses in a number of areas such as electronics, photonics, and catalysis.

Proceedings Article | 28 October 2003 Paper

Synthesis and characterization of metal nanostructures with hollow interiors

Yugang Sun, Younan Xia

Proceedings Volume 5221, (2003) https://doi.org/10.1117/12.504815

KEYWORDS: Silver, Nanostructures, Gold, Metals, Nanoparticles, Crystals, Solids, Transmission electron microscopy, Particles, Nanowires

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A general approach involved template-engaged displacement reaction has been demonstrated to prepare metal nanostructures with hollow interiors by reacting solutions of appropriate salts with solid metal nanostructures. For example, silver nanostructures with various morphologies including triangular plates, cubes, spheres, rods and wires have been used as templates to react with an aqueous chloroauric acid solution. The reaction led to the formation of hollow nanostructures with shapes similar to that of silver templates. The void space, wall thickness, and crystalline structure of these hollow structures were determined with the silver templates, which were converted into soluble species during the displacement reaction. Elemental analysis and electron microscopic studies indicated that these hollow structures were made of gold/silver alloys. The capability and feasibility of this method have also been demonstrated by preparing nanotubes made of different metals (e.g., gold/silver, palladium/silver, and platinum/silver alloys). The hollow nanostructures of gold/silver alloys exhibited significantly different surface plasmonic properties from their solid counterparts. For instance, the extinction peaks of the nanoshells of gold/silver alloy with roughly spherical shape were considerably red-shifted as compared to solid colloids of silver or gold having approximately the same dimensions. The high extinction coefficient in the red and near infrared regimes should make these nanoshells particularly useful as components in fabricating plasmonic devices and labels in probing the desired biomolecules.

Proceedings Article | 15 November 2002 Paper

Synthesis and optical properties of silver bicrystalline nanowires

Yugang Sun, Younan Xia

Proceedings Volume 4807, (2002) https://doi.org/10.1117/12.451007

KEYWORDS: Silver, Nanoparticles, Gold, Nanostructures, Platinum, Scanning electron microscopy, Transmission electron microscopy, Diffraction, Nanowires, Nanorods

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This paper describes a solution-phase route to the large-scale synthesis of silver nanowires with diameters in the range of 30-40 nm, and lengths up to ~50 μm. The initial step of this synthesis involved the formation of Pt nanoparticles by reducing PtCl₂ with ethylene glycol (EG) refluxed at ~160 °C. These Pt nanoparticles could serve as seeds for the growth of silver (formed by reducing AgNO₃ with EG) through heterogeneous nucleation process because their crystal structures and lattice constants matched closely. In the presence of poly(vinyl pyrrolidone) (PVP), the growth of silver could be led to a highly anisotropic mode with formation of uniform nanowires. UV-visible spectroscopy was used to track the growth process of silver nanowires because different silver nanostructures exhibited distinctive surface plasmon resonance peaks at different frequencies. SEM, TEM, XRD, and electron diffraction were used to characterize these silver nanowires, indicating the formation of a highly pure face-centered cubic phase, as well as uniform diameter and bicrystalline structure. The morphology of these silver nanostructures could be varied from particles and rods to long wires by tuning the reaction conditions, including reaction temperature, and the ratio of PVP to silver nitrate. These silver nanowires could be used as sacrificial templates to synthesize gold nanotubes via a template-engaged replacement reaction. The dispersion of gold nanotubes exhibited a strong extinction peak in the red regime, which was around 760 nm.

Proceedings Article | 15 November 2002 Paper

Nanowires by solution-phase synthesis

Brian Mayers, Byron Gates, Yugang Sun, Yadong Yin, Yu Lu, Younan Xia

Proceedings Volume 4807, (2002) https://doi.org/10.1117/12.450993

KEYWORDS: Silver, Nanostructures, Selenium, Crystals, Tellurium, Gold, Scanning electron microscopy, Silica, Nanowires, Nanorods

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We have demonstrated a variety of solution-phase approaches for the synthesis of dimensionally confined nanostructures of a wide range of materials. These materials include metals (Ag and Au) and semiconductors (Te, Se, and Ag₂Se) with interesting properties such as high electric, thermal, and ionic conductivities, piezoelectricity, and photoconductivity. Direct and indirect routes for the solution-phase synthesis of 1-dimensional nanostructures are presented. Control over morphology, chemical purity, and crystallinity are well maintained. We show that by using solution-phase methods, it is possible to generate not only high yields of nanowires but also more complex structures such as tubes and co-axial nanocables. These nanostructures are ideal for the study of size-confinement effects on electrical and optical properties, and also as the future interconnects and active components in nanoscale electronic and electromechanical devices.

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