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Yadong Yin

Publications and source records attributed to Yadong Yin.

15 recordsLinked to original sources
PubMed2006

Faceting of nanocrystals during chemical transformation: from solid silver spheres to hollow gold octahedra.

We demonstrate that performing a replacement reaction on single crystalline Ag nanospheres of approximately 10 nm in diameter in an organic solvent produces hollow Au nanocrystals with an octahedral shape. Different from those Au shells made by starting with Ag particles about 1 order of magnitude larger, which largely reproduce that of the sacrificial Ag counterparts, the hollow nanocrystals obtained in this work show significant changes in the external morphology from the spherical Ag precursors. This evolution of a faceted external morphology during chemical transformation is made possible by the enhanced role of surface effects in our smaller nanocrystals. The competition between the Au atom deposition and Ag atom dissolution on various nanocrystal surfaces is believed to determine the final octahedral shape of the hollow Au nanocrystals. Simultaneous achievement of surface-mediated shape control and a hollow morphology in a one-pot, single-step synthetic procedure in this study promises an avenue to finer tuning of particle morphology, and thus physical properties such as surface plasmon resonance.

Journal Article↗
PubMed2006

Right bipyramids of silver: a new shape derived from single twinned seeds.

Silver nanoparticles with a single (111) twin were selectively nucleated and grown for the first time to produce right bipyramids 75-150 nm in edge length. Key to the production of single twinned seeds was the addition of NaBr to a polyol synthesis in which AgNO3 is reduced by ethylene glycol in the presence of poly(vinyl pyrrolidone). Examination of nanoparticles at different stages of the reaction with electron microscopy revealed that the spherical, single twinned seeds grew to become right bipyramids through enlargement of their (100) facets. The UV-vis-NIR spectrum exhibited by right bipyramids is distinct from that of any other silver nanostructure, and their sharp corners make these new nanoparticles especially promising for enhancement of Raman scattering.

Crystallization↗
PubMed2006

V2O5 nanorods on TiO2 nanofibers: a new class of hierarchical nanostructures enabled by electrospinning and calcination.

Electrospinning provides a simple approach to fabricating nanofibers and assemblies with controllable hierarchical structures. In this communication, we demonstrate that electrospinning can be combined with calcination to further maneuver the morphology and phase structure of nanofibers. More specifically, single-crystal V2O5 nanorods could be grown on rutile nanofibers by carefully calcining composite nanofibers consisting of amorphous V2O5, amorphous TiO2, and poly(vinylpyrrolidone). The size of the resulting V2O5 nanorods could be conveniently controlled by varying the composition of the nanofibers and/or the calcination temperature. In addition to the nanorod-on-nanofiber hierarchical structure, we believe this approach can also be extended to fabricate other more complex architectures.

Crystallization↗
PubMed2006

Synthesis and electrical characterization of silver nanobeams.

By slowing the rate of atomic addition to singly twinned seeds, we have grown silver nanobeams with lengths of 3-30 mum, widths ranging from 17 to 70 nm, and a width to thickness ratio of 1.4. The well-defined dimensions, smooth surface, and crystallinity of nanobeams make them promising candidates for studying the effects of size on electron transport. With a simple method that allows rapid characterization of single nanobeams, we find that even the thinnest nanobeams largely retain the low resistivity of bulk silver. Nanobeams can support remarkably high current densities of up to 2.6 x 10(8) A cm(-2) before the conduction path is broken by the formation of a nanogap.

Crystallization↗
PubMed2005

Kinetically controlled synthesis of triangular and hexagonal nanoplates of palladium and their SPR/SERS properties.

The rapid reduction of Na(2)PdCl(4) by ethylene glycol in the presence of poly(vinyl pyrrolidone) (PVP) has recently been demonstrated as a convenient method of generating Pd cubooctahedra and twinned nanoparticles. Here we describe a new procedure where Pd triangular or hexagonal nanoplates could be selectively synthesized by manipulating the reduction kinetics of the polyol process. More specifically, the reduction rate was substantially reduced through the introduction of Fe(III) species and the O(2)/Cl(-) pair, two wet etchants for Pd(0). The etching power of the O(2)/Cl(-) pair could be further enhanced by adding an acid to lower the pH of the reaction solution. Unlike the previously reported synthesis of Ag and Au nanoplates, light was found to have no indispensable role in the formation of Pd nanoplates. Both triangular and hexagonal nanoplates of Pd exhibited surface plasmon resonance (SPR) peaks in the visible region, and their positions matched with the results of discrete dipole approximation (DDA) calculation. Thanks to their sharp corners and edges, these Pd nanoplates could serve as active substrates for surface-enhanced Raman scattering (SERS).

Journal Article↗
PubMed2005

Colloidal nanocrystal synthesis and the organic-inorganic interface.

Colloidal nanocrystals are solution-grown, nanometre-sized, inorganic particles that are stabilized by a layer of surfactants attached to their surface. The inorganic cores possess useful properties that are controlled by their composition, size and shape, and the surfactant coating ensures that these structures are easy to fabricate and process further into more complex structures. This combination of features makes colloidal nanocrystals attractive and promising building blocks for advanced materials and devices. Chemists are achieving ever more exquisite control over the composition, size, shape, crystal structure and surface properties of nanocrystals, thus setting the stage for fully exploiting the potential of these remarkable materials.

Journal Article↗
PubMed2005

Understanding the role of oxidative etching in the polyol synthesis of Pd nanoparticles with uniform shape and size.

Uniform cubooctahedral nanoparticles of Pd were synthesized using a modified polyol process. Like the silver system, the Pd nanoparticles underwent dissolution due to oxidative etching by Cl-/O2. In the early stage of etching, the twinned particles in a sample were selectively removed to leave behind uniform, single-crystal cubooctahedra. If the etching was allowed to continue, the single-crystal cubooctahedra were also attacked and partially dissolved. Understanding the role of oxidative etching is critical to the achievement of both uniform shape and size.

Ethylene Glycol↗
PubMed2005

Size-dependence of surface plasmon resonance and oxidation for Pd nanocubes synthesized via a seed etching process.

Pd nanocubes between 8 and 50 nm in size were synthesized at the same concentration of Na2PdCl4 precursor by controlling the number of seeds formed in the nucleation stage. Increasing the concentration of FeCl3, an oxidative etchant for Pd, reduced the number of seeds and led to formation of larger Pd nanocubes. The larger nanocubes exhibited surface plasmon resonance peaks in the visible region, the locations of which matched with the results of the discrete dipole approximation calculation. While the nanocubes of 25 and 50 nm in size oxidized in air to form Pd@PdO core-shell structures, the 8-nm nanocubes were stable in air for over 90 days.

Crystallization↗
PubMed2004

Cation exchange reactions in ionic nanocrystals.

Cation exchange has been investigated in a wide range of nanocrystals of varying composition, size, and shape. Complete and fully reversible exchange occurs, and the rates of the reactions are much faster than in bulk cation exchange processes. A critical size has been identified below which the shapes of complex nanocrystals evolve toward the equilibrium shape with lowest energy during the exchange reaction. Above the critical size, the anion sublattice remains intact and the basic shapes of the initial nanocrystals are retained throughout the cation exchange. The size-dependent shape change can also be used to infer features of the microscopic mechanism.

Journal Article↗
PubMed2004

Formation of hollow nanocrystals through the nanoscale Kirkendall effect.

Hollow nanocrystals can be synthesized through a mechanism analogous to the Kirkendall Effect, in which pores form because of the difference in diffusion rates between two components in a diffusion couple. Starting with cobalt nanocrystals, we show that their reaction in solution with oxygen and either sulfur or selenium leads to the formation of hollow nanocrystals of the resulting oxide and chalcogenides. This process provides a general route to the synthesis of hollow nanostructures of a large number of compounds. A simple extension of the process yielded platinum-cobalt oxide yolk-shell nanostructures, which may serve as nanoscale reactors in catalytic applications.

Journal Article↗
PubMed2003

Self-assembly of spherical colloids into helical chains with well-controlled handedness.

Physical constraint and capillary force have been combined to provide a generic approach to assemble achiral building blocks such as monodisperse spherical colloids into helical mesostructures. The key component of this process is an array of V-shaped grooves anisotropically etched in the surface of a Si(100) wafer. The structural arrangement among the spherical colloids is determined by the ratio between the width of the V-grooves and the diameter of the colloids. Double-layered structures with a helical morphology will be formed when this ratio falls between 2.70 and 2.85. The exact handedness of these helical structures could be controlled by varying the relative orientation of capillary force with respect to the longitudinal axis of the spirals. The processing of an achiral material into helical mesostructures having well-controlled handedness should allow us to explore new properties that this material otherwise does not exhibit. The self-assembly process may also provide valuable insights to improve our understanding on the mechanism(s) by which pure enantiomers with a particular sense of rotation evolved in nature.

Colloids↗