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Biomedical subjects

Peidong Yang

Publications and source records attributed to Peidong Yang.

At least 37 records · Page 2Linked to original sources
PubMed2005

Optical routing and sensing with nanowire assemblies.

The manipulation of photons in structures smaller than the wavelength of light is central to the development of nanoscale integrated photonic systems for computing, communications, and sensing. We assemble small groups of freestanding, chemically synthesized nanoribbons and nanowires into model structures that illustrate how light is exchanged between subwavelength cavities made of three different semiconductors. The coupling strength of the optical linkages formed when nanowires are brought into contact depends both on their volume of interaction and angle of intersection. With simple coupling schemes, lasing nanowires can launch coherent pulses of light through ribbon waveguides that are up to a millimeter in length. Also, interwire coupling losses are low enough to allow light to propagate across several right-angle bends in a grid of crossed ribbons. The fraction of the guided wave traveling outside the wire/ribbon cavities is used to link nanowires through space and to separate colors within multiribbon networks. In addition, we find that nanoribbons function efficiently as waveguides in liquid media and provide a unique means for probing molecules in solution or in proximity to the waveguide surface. Our results lay the spadework for photonic devices based on assemblies of active and passive nanowire elements and presage the use of nanowire waveguides in microfluidics and biology.

Journal Article↗
PubMed2005

Nanowire dye-sensitized solar cells.

Excitonic solar cells-including organic, hybrid organic-inorganic and dye-sensitized cells (DSCs)-are promising devices for inexpensive, large-scale solar energy conversion. The DSC is currently the most efficient and stable excitonic photocell. Central to this device is a thick nanoparticle film that provides a large surface area for the adsorption of light-harvesting molecules. However, nanoparticle DSCs rely on trap-limited diffusion for electron transport, a slow mechanism that can limit device efficiency, especially at longer wavelengths. Here we introduce a version of the dye-sensitized cell in which the traditional nanoparticle film is replaced by a dense array of oriented, crystalline ZnO nanowires. The nanowire anode is synthesized by mild aqueous chemistry and features a surface area up to one-fifth as large as a nanoparticle cell. The direct electrical pathways provided by the nanowires ensure the rapid collection of carriers generated throughout the device, and a full Sun efficiency of 1.5% is demonstrated, limited primarily by the surface area of the nanowire array.

Coloring Agents↗
PubMed2005

Thermal wetting of platinum nanocrystals on silica surface.

Thermal stability of facetted Pt nanocrystals on amorphous silica support films was investigated using in situ transmission electron microscopy in a temperature range between 25 and 800 degrees C. The particles started to change their shapes at approximately 350 degrees C. Above 500 degrees C, the particles spread on the support film with increasing temperature, rather than becoming more spherical. Such temperature-induced wetting of Pt nanoparticles on silica surface can be attributed to the interfacial mixing of Pt and SiO(2) and the resulting negative interface energy.

Journal Article↗
PubMed2005

Selective growth of Si nanowire arrays via galvanic displacement processes in water-in-oil microemulsions.

Galvanic displacement processes are employed in water-in-oil microemulsions to deposit gold nanoclusters selectively on Si surfaces and sidewalls. The gold clusters then serve as catalysts to achieve selective growth of vertically and laterally aligned Si nanowire arrays by chemical vapor deposition via the vapor-liquid-solid growth mechanism. The size of the gold clusters is shown to have a good correlation with the microemulsion parameters, which in turn controls the size of the synthesized nanowires.

Journal Article↗
PubMed2005

Crystal overgrowth on gold nanorods: tuning the shape, facet, aspect ratio, and composition of the nanorods.

Electrochemically prepared Au nanorods were used as seeds for the overgrowth of thin shells of gold, silver, and palladium by using a mild reducing agent, ascorbic acid, in the presence of surfactants at ambient condition. The unique crystal facets of the starting nanorods results in anisotropic crystal overgrowth. The overgrowth rates along different crystallographical directions can be further regulated by adding foreign ions or by using different metal reduction methods. This overgrowth study provides insights on how different metal ions could be reduced preferentially on different Au nanorod surfaces, so that the composition, aspect ratio, shape, and facet of the resulting nanostructures can be rationally tuned. These surfactant-stabilized bimetallic Au(core)M(shell) (M=Au, Ag, Pd) nanorod colloids might serve as better substrates in surface-enhanced Raman spectroscopy as well as exhibiting enhanced catalytic properties.

Crystallization↗
PubMed2005

ZnO nanowire transistors.

ZnO nanowire field-effect transistors (FETs) were fabricated and studied in vacuum and a variety of ambient gases from 5 to 300 K. In air, these n-type nanowire transistors have among the highest mobilities yet reported for ZnO FETs (mu(e) = 13 +/- 5 cm(2) V(-1) s(-1)), with carrier concentrations averaging 5.2 +/- 2.5 x 10(17) cm(-3) and on-off current ratios ranging from 10(5) to 10(7). Four probe measurements show that the resistivity of the Ti/Au-ZnO contacts is 0.002-0.02 Omega.cm. The performance characteristics of the nanowire transistors are intimately tied to the presence and nature of adsorbed surface species. In addition, we describe a dynamic gate effect that seems to involve mobile surface charges and causes hysteresis in the transconductance, among other effects.

Nanowires↗
PubMed2005

Pt nanocrystals: shape control and Langmuir-Blodgett monolayer formation.

We report the synthesis of monodisperse Pt nanocrystals with three different shapes-cubes, cuboctahedra, and octahedra, selectively, with similar sizes of 9-10 nm by a modified polyol process. We found that addition of silver ion enhances the crystal growth rate along 100, and essentially determines the shape and surface structure of the Pt nanocrystals. After the reaction, the silver species can be easily removed by repetitive precipitation giving pure Pt nanoparticles. Two-dimensional arrays of the Pt nanocrystals were assembled by using the Langmuir-Blodgett (LB) method. The particles were evenly distributed on the entire substrate, and their surface coverage and density can be precisely controlled by tuning the surface pressure. The resulting Pt LB layers are potential candidates for 2-D model catalysts as a result of their high surface area and the structural uniformity of the metal nanocrystals.

Crystallization↗
PubMed2005

Thermally driven interfacial dynamics of metal/oxide bilayer nanoribbons.

Solid-solid interfacial processes greatly affect the performance of electronic and composite materials, but probing the dynamics of buried interfaces is challenging and often involves lengthy or invasive sample preparation. We show that bilayer nanoribbons-made here of tin dioxide and copper-are convenient structures for observing as-made interfaces as they respond to changing temperature in a transmission electron microscope (TEM). At low temperatures (<200 degrees C), differential thermal expansion causes the bilayers to bend when heated or cooled, with the motion determined by the extent of Cu-SnO(2) epitaxy. At higher temperatures, we are able to watch-in real time and with nanometer resolution-a progression of grain growth, interdiffusion, island formation, solid-state chemical reactions, and melting. This novel TEM geometry is readily applicable to other nanoribbon/coating combinations and is well suited to observing interfacial phenomena driven thermally or by the application of mechanical, electrical, or magnetic forces.

Alloys↗
PubMed2005

Controlled growth of Si nanowire arrays for device integration.

Silicon nanowires were synthesized, in a controlled manner, for their practical integration into devices. Gold colloids were used for nanowire synthesis by the vapor-liquid-solid growth mechanism. Using SiCl4 as the precursor gas in a chemical vapor deposition system, nanowire arrays were grown vertically aligned with respect to the substrate. By manipulating the colloid deposition on the substrate, highly controlled growth of aligned silicon nanowires was achieved. Nanowire arrays were synthesized with narrow size distributions dictated by the seeding colloids and with average diameters down to 39 nm. The density of wire growth was successfully varied from approximately 0.1-1.8 wires/microm2. Patterned deposition of the colloids led to confinement of the vertical nanowire growth to selected regions. In addition, Si nanowires were grown directly into microchannels to demonstrate the flexibility of the deposition technique. By controlling various aspects of nanowire growth, these methods will enable their efficient and economical incorporation into devices.

Colloids↗
PubMed2005

Electrostatic control of ions and molecules in nanofluidic transistors.

We report a nanofluidic transistor based on a metal-oxide-solution (MOSol) system that is similar to a metal-oxide-semiconductor field-effect transistor (MOSFET). Using a combination of fluorescence and electrical measurements, we demonstrate that gate voltage modulates the concentration of ions and molecules in the channel and controls the ionic conductance. Our results illustrate the efficacy of field-effect control in nanofluidics, which could have broad implications on integrated nanofluidic circuits for manipulation of ions and biomolecules in sub-femtoliter volumes.

Electrochemistry↗
PubMed2005

General route to vertical ZnO nanowire arrays using textured ZnO seeds.

A method for growing vertical ZnO nanowire arrays on arbitrary substrates using either gas-phase or solution-phase approaches is presented. A approximately 10 nm-thick layer of textured ZnO nanocrystals with their c axes normal to the substrate is formed by the decomposition of zinc acetate at 200-350 degrees C to provide nucleation sites for vertical nanowire growth. The nanorod arrays made in solution have a rod diameter, length, density, and orientation desirable for use in ordered nanorod-polymer solar cells.

Anisotropy↗
PubMed2005

Effects of biological reactions and modifications on conductance of nanofluidic channels.

Conductance characteristics of nanofluidic channels (nanochannels) fall into two regimes: at low ionic concentrations, conductance is governed by surface charge while at high ionic concentrations it is determined by nanochannel geometry and bulk ionic concentration. We used aminosilane chemistry and streptavidin-biotin binding to study the effects of surface reactions on nanochannel conductance at different ionic concentrations. Immobilization of small molecules such as aminosilane or biotin mainly changes surface charge, affecting conductance only in the low concentration regime. However, streptavidin not only modifies surface charge but also occludes part of the channel, resulting in observable conductance changes in both regimes. Our observations reflect the interplay between the competing effects of charge and size of streptavidin on nanochannel conductance.

Biotin↗
PubMed2005

DNA translocation in inorganic nanotubes.

Inorganic nanotubes were successfully integrated with microfluidic systems to create nanofluidic devices for single DNA molecule sensing. Inorganic nanotubes are unique in their high aspect ratio and exhibit translocation characteristics in which the DNA is fully stretched. Transient changes of ionic current indicate DNA translocation events. A transition from current decrease to current enhancement during translocation was observed on changing the buffer concentration, suggesting interplay between electrostatic charge and geometric blockage effects. These inorganic nanotube nanofluidic devices represent a new platform for the study of single biomolecule translocation with the potential for integration into nanofluidic circuits.

DNA↗
PubMed2004

Nanoribbon waveguides for subwavelength photonics integration.

Although the electrical integration of chemically synthesized nanowires has been achieved with lithography, optical integration, which promises high speeds and greater device versatility, remains unexplored. We describe the properties and functions of individual crystalline oxide nanoribbons that act as subwavelength optical waveguides and assess their applicability as nanoscale photonic elements. The length, flexibility, and strength of these structures enable their manipulation on surfaces, including the optical linking of nanoribbon waveguides and other nanowire elements to form networks and device components. We demonstrate the assembly of ribbon waveguides with nanowire light sources and detectors as a first step toward building nanowire photonic circuitry.

Journal Article↗
PubMed2004

Crystallographic alignment of high-density gallium nitride nanowire arrays.

Single-crystalline, one-dimensional semiconductor nanostructures are considered to be one of the critical building blocks for nanoscale optoelectronics. Elucidation of the vapour-liquid-solid growth mechanism has already enabled precise control over nanowire position and size, yet to date, no reports have demonstrated the ability to choose from different crystallographic growth directions of a nanowire array. Control over the nanowire growth direction is extremely desirable, in that anisotropic parameters such as thermal and electrical conductivity, index of refraction, piezoelectric polarization, and bandgap may be used to tune the physical properties of nanowires made from a given material. Here we demonstrate the use of metal-organic chemical vapour deposition (MOCVD) and appropriate substrate selection to control the crystallographic growth directions of high-density arrays of gallium nitride nanowires with distinct geometric and physical properties. Epitaxial growth of wurtzite gallium nitride on (100) gamma-LiAlO(2) and (111) MgO single-crystal substrates resulted in the selective growth of nanowires in the orthogonal [1\[Evec]0] and [001] directions, exhibiting triangular and hexagonal cross-sections and drastically different optical emission. The MOCVD process is entirely compatible with the current GaN thin-film technology, which would lead to easy scale-up and device integration.

Crystallization↗
PubMed2004

Solution-phase synthesis of single-crystalline iron phosphide nanorods/nanowires.

A solution-phase route for the preparation of single-crystalline iron phosphide nanorods and nanowires is reported. We have shown that the mixture of trioctylphosphine oxide (TOPO) and trioctylphosphine (TOP), which are commonly used as the solvents for semiconductor nanocrystal synthesis, is not entirely inert. In the current process, TOP, serving as phosphor source, reacts with Fe precursors to form FeP nanostructures with large aspect ratios. In addition, the experimental results show that both TOP and TOPO are necessary for the formation of FeP nanowires and their ratio appears to control the morphology of the produced FeP structures. A possible growth mechanism is discussed.

Journal Article↗