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At least 19 recordsLinked to original sources
PubMed2006

Tailoring surface plasmons through the morphology and assembly of metal nanoparticles.

Metal nanoparticles can be used as building blocks for the formation of nanostructured materials. For the design of materials with specific (optical) properties, several approaches can be followed, even when starting from the very same basic units. In this article, a survey is provided of the optical properties of noble metal nanoparticles, specifically gold, silver, and their combinations, prepared in solution through colloid chemical methods. The optical properties are shown to be mainly influenced by the surface plasmon resonance of conduction electrons, the frequency of which is not only determined by the nature of the metal but also by a number of other parameters, such as particle size and shape, the presence of a capping shell on the particle surface, or the dielectric properties of the surrounding medium. Recent results showing how these various parameters affect the optical properties are reviewed. The results highlight the high degree of control that can now be achieved through colloid chemical synthesis.

Journal Article↗
PubMed2004

Acetate stabilization of metal nanoparticles and its role in the preparation of metal nanoparticles in ethylene glycol.

Acetate-stabilized ruthenium nanoparticles were prepared by the NaBH4 reduction of the metal precursor salt at room temperature. Nanoparticles with a mean diameter of 2.20 nm and a standard deviation of 1.03 nm could be obtained under experimental conditions. The Ru nanoparticles so obtained could be easily extracted to a toluene solution of alkylamine, giving rise to alkylamine-stabilized Ru nanoparticles with a mean diameter of 2.96 nm and a standard deviation of 0.92 nm. The new found role of acetate stabilization was used to formulate a mechanism for the formation of metal (Pt, Ru) nanoparticles in ethylene glycol. In this mechanism metal nanoparticles are stabilized in ethylene glycol by adsorbed acetate ions, which are produced as a product of the OH- catalyzed reaction between the metal precursor salt and ethylene glycol.

Acetates↗
PubMed2005

Controlling interparticle spacing among metal nanoparticles through metal-catalyzed decomposition of surrounding polymer matrix.

Systematic and reproducible control over average interparticle spacing of Pt, Ni, and Cu nanoparticles embedded in polyimide thin layers was achieved. The metal-catalyzed decomposition of polyimide matrixes surrounding metal nanoparticles causes a decrease in the composite layer thickness, while maintaining the size of nanoparticles. This ability provides an effective methodology for the preparation of metal/polymer nanocomposites with tailored microstructures and holds great promise toward the fundamental understanding of the physical interactions among metal nanoparticles.

Journal Article↗
PubMed2006

Synthesis of metal nanoparticles stabilized by metal-carbon bonds.

A new method for the preparation of metal nanoparticles in organic media is proposed. This is based on the formation of metal-carbon bonds after reduction of the corresponding diazonium derivative of the capping ligand. The particles are very stable due to the strong metal-ligand covalent bond, and the proposed method appears to be an alternative for the preparation of monolayer-protected metal nanoparticles when the formation of metal-sulfur or metal-nitrogen bonds needs to be avoided.

Journal Article↗
PubMed2006

Coherent excitation of vibrational modes in metallic nanoparticles.

Excitation of metal nanoparticles with subpicosecond laser pulses causes a rapid increase in the lattice temperature, which can impulsively excite the phonon modes of the particle that correlate with the expansion coordinates. The vibrational periods depend on the size, shape, and elastic constants of the particles. Thus, time-resolved spectroscopy can be used to examine the material properties of nanometer-sized objects. This review provides a brief overview of the steady-state and time-resolved electronic spectroscopy of metal particles, which is important for understanding why vibrational motion appears in transient absorption traces. I also describe how the vibrational modes observed in the experiments are assigned, and what information can be obtained from the measurements. Our work has been mainly concerned with noble metal particles (gold and silver) in aqueous solution. The different shapes that have been examined to date include spheres, rods, and triangles, all with different sizes.

Lasers↗
PubMed2005

Electromagnetic coupling between a metal nanoparticle grating and a metallic surface.

The electromagnetic coupling between a two-dimensional grating of resonant gold nanoparticles and a gold metallic film is investigated. We report on the observation of multipeaks in the extinction spectra attributed to resonant modes of the hybrid system, resulting from the coupling between the localized plasmon of the nanoparticles with the underlying surface plasmon mode. Simulations based on the Fourier modal method give good agreement with the experimental measurements and allow for the identification of the respective contributions.

Journal Article↗
PubMed2005

Synthesis of amorphous carbon nanoparticles and carbon encapsulated metal nanoparticles in liquid benzene by an electric plasma discharge in ultrasonic cavitation field.

A newly-developed method permits an electric plasma discharge to occur with relatively low electric power in insulating organic solutions due to the presence of an ultrasonic cavitation. A stable electric plasma could be generated in an ultrasonic cavitation field containing a thousand tiny activated bubbles, in which the electric conductivity could be improved due to formed radicals and free electrons, using copper electrodes and a titanium ultrasonic horn. This method allowed us to synthesize pyrolytic amorphous carbon nanoparticles smaller than about 30 nm in diameter from benzene liquid. In addition, we synthesized TiC nanoparticles about 50-150 nm in size, and copper nanoparticles smaller than 10 nm, which were encapsulated in multilayered graphite cages. Finally, we used GC-MS and MALDI-TOF-MS to observe and analyze the polymerized compounds and the degree of polymerization of the benzene liquid after the plasma treatment.

Benzene↗
PubMed2005

Inhibition of DNA hybridization by small metal nanoparticles.

The inhibition of DNA hybridization by small metal nanoparticles has been examined in detail. DNA melting point analysis showed that the oligonucleotides adsorb strongly and nonspecifically on small metal nanoparticles, inhibiting the hybridization of complementary DNA sequences in common buffered solutions. The nonspecific interaction is even strong enough to disrupt pre-existing hydrogen bonds in short double-stranded DNA. The nonspecific interaction could be weakened by increasing the particle size. As an example, a core-shell assisted method was used to successfully assemble Pt nanoparticles by DNA hybridization that could not be done otherwise.

DNA, Single-Stranded↗
PubMed2007

Catalytic applications of metal nanoparticles in imidazolium ionic liquids.

Metal nanoparticles (MNPs) with a small diameter and narrow size distribution can be prepared by H(2) reduction of metal compounds or decomposition of organometallic species dissolved in ionic liquids (ILs). MNPs dispersed in ILs are catalysts for reactions under multiphase conditions. These soluble MNPs possess a pronounced surfacelike rather than single-site like catalytic properties. In other cases the MNPs are not stable and tend to aggregate or serve as reservoirs of mononuclear catalytically active species.

Journal Article↗
PubMed2006

Single-walled carbon nanotube growth from highly activated metal nanoparticles.

We demonstrate that any metal, even gold, silver, and copper, can act as a catalyst for SWCNT synthesis in chemical vapor deposition (CVD). Metal nanoparticles 3 nm or less in diameter, introduced into CVD ambience immediately after heat treatment at 800-950 degrees C in air, produce SWCNTs. The activation method is effective for copper and various noble metals as well as for iron-family elements. This implies that any metal particle may produce SWCNTs when its size becomes 1-3 nm. In other words, carbon atoms can form SWCNTs in a self-assembling fashion on nanoparticles without the specific functions of iron-family elements.

Journal Article↗
PubMed2006

One-step one-phase synthesis of monodisperse noble-metallic nanoparticles and their colloidal crystals.

A variety of metallic nanoparticles with a narrow size distribution have been synthesized in a facile one-phase method in which amine-borane complexes are applied as reducing agents. It is particularly striking that large colloidal crystals with sizes up to tens of micrometers can directly form from the reaction mixtures without any further treatment. By using the synthetic route described, large-scale syntheses of both mono- and alloyed metallic nanoparticles with a narrow size distribution can be easily achieved.

Journal Article↗
PubMed2005

Catalysis with transition metal nanoparticles in colloidal solution: nanoparticle shape dependence and stability.

While the nanocatalysis field has undergone an explosive growth during the past decade, there have been very few studies in the area of shape-dependent catalysis and the effect of the catalytic process on the shape and size of transition metal nanoparticles as well as their recycling potential. Metal nanoparticles of different shapes have different crystallographic facets and have different fraction of surface atoms on their corners and edges, which makes it interesting to study the effect of metal nanoparticle shape on the catalytic activity of various organic and inorganic reactions. Transition metal nanoparticles are attractive to use as catalysts due to their high surface-to-volume ratio compared to bulk catalytic materials, but their surface atoms could be so active that changes in the size and shape of the nanoparticles could occur during the course of their catalytic function, which could also affect their recycling potential. In this Feature Article, we review our work on the effect of the shape of the colloidal nanocatalyst on the catalytic activity as well as the effect of the catalytic process on the shape and size of the colloidal transition metal nanocatalysts and their recycling potential. These studies provide important clues on the mechanism of the reactions we studied and also can be very useful in the process of designing better catalysts in the future.

Journal Article↗
PubMed2006

Deposition of metal nanoparticles on carbon nanotubes via hexane modified water-in-CO2 microemulsion at room temperature.

Carbon nanotube-supported metallic nanoparticles (Pd, Rh, and bimetallic Pd-Rh) with diameters in the range 2-10 nm can be synthesized by hydrogen reduction of metal ions dissolved in the water core of a CO2 microemulsion in liquid CO2 at room temperature. The microemulsion is stabilized by sodium bis(2-ethylhexyl)sulfosuccinate (AOT) and dissolved in liquid CO2 with the aid of hexane as a modifier. The metal nanoparticles synthesized in the microemulsion can be deposited on surfaces of multi-walled carbon nanotubes (MWCNTs) by stirring in the liquid CO2 phase. This simple method produces uniformly distributed metal nanoparticles on surfaces of the MWCNTs with high yields. The carbon nanotube-supported Pd/Rh bimetallic nanoparticles exhibit high catalytic activities for hydrogenation of aromatic compounds and can be reused without losing catalytic activity.

Adsorption↗
PubMed2006

Absorption and scattering microscopy of single metal nanoparticles.

Several recently developed detection techniques opened studies of individual metal nanoparticles (1-100 nm in diameter) in the optical far field. Eliminating averaging over the broad size and shape distributions produced by even the best of current synthesis methods, these studies hold great promise for gaining a deeper insight into many of the properties of metal nanoparticles, notably electronic and vibrational relaxation. All methods are based on detection of a scattered wave emitted either by the particle itself, or by its close environment. Direct absorption and interference techniques rely on the particle's scattering and have similar limits in signal-to-noise ratio. The photothermal method uses a photo-induced change in the refractive index of the environment as an additional step to scatter a wave with a different wavelength. This leads to a considerable improvement in signal-to-background ratio, and thus to a much higher sensitivity. We briefly discuss and compare these various techniques, review the new results they generated so far, and conclude on their great potential for nanoscience and for single-molecule labelling in biological assays and live cells.

Absorption↗
PubMed2006

Shape/size-controlled syntheses of metal nanoparticles for site-selective modification of carbon nanotubes.

Shape- and size-controlled syntheses of metal nanoparticles have been achieved by galvanic displacement reaction between an aqueous solution of metal salt and Cu foil substrate. In particular, cubic and spheric nanoparticles of Pt (Au) with a fairly narrow size distribution were produced by reacting K(2)PtCl(4) (HAuCl(4)) with a Cu foil in an aqueous medium with and without CuCl(2) under different reaction conditions (e.g., different concentrations and reaction times). In conjunction with the substrate-enhanced electroless deposition (SEED) technique (Qu, L.; Dai, L. J. Am. Chem. Soc. 2005, 127, 10806), the shape/size-controlled syntheses have been successfully exploited to site-selectively deposit these metal nanoparticles onto the outerwall, innerwall, or end-tip of carbon nanotubes (CNTs). Asymmetric sidewall modification by attaching the innerwall and outerwall of CNTs with metal nanoparticles of different shapes was also achieved. Furthermore, it was demonstrated that the nanotube-supported Pt nanoparticles could be converted into hollow Au nanoboxes by galvanic displacement of Pt with Au. These CNT-supported metal nanoparticles were shown to possess interesting optical and electrocatalytic properties.

Journal Article↗
PubMedDate not supplied

J-aggregates on metal nanoparticles characterized through ultrafast spectroscopy and near-field optics.

Illumination of metal nanoparticles at the plasmon resonance produces enhanced evanescent fields on the nanoparticles' surfaces. The unusual strength of the field makes it a target for exploring photoinduced phenomena at the nanoscale, if efficient functionalization or coating of the nanoparticle surface with appropriate chromophores is possible. One direction is to use cyanine dyes that form monolayers of J-aggregates on the surface of noble metal nanoparticle colloids. The unique, collective electronic properties of J-aggregates produce excitons with enormous extinction coefficients that are of interest for their efficient energy transfer, electron transfer, and nonlinear optical properties. In that vein, we report our results on time-resolved spectroscopy and near-field scanning optical microscopy (NSOM) of J-aggregate exciton dynamics on Ag and Au nanoparticle colloids. Ultrafast transient absorption studies show that J-aggregate exciton lifetimes on Ag nanoparticles are much longer than on Au nanoparticles, with a 300 ps lifetime that is two orders of magnitude longer than the electronic processes in the nanoparticles themselves. Complementary NSOM studies of the colloids show that fluorescence from the J-aggregates on the Ag nanoparticles is induced by the scanning probe. These results may be significant for improving the nanophotonic performance of hybrid materials for nanoscale applications.

Journal Article↗
PubMed2005

Surface diffusion and coalescence of mobile metal nanoparticles.

The diffusion and coalescence of metal nanoparticles play important roles in many phenomena. Here, we offer a new integrated overview of the main factors that control the nanoparticle coalescence process. Three factors are considered in our description of the coalescence process: nanoparticle diffusion across the surface, their physical and thermodynamic properties, and the mechanism of coalescence. We demonstrate that the liquid-like properties of the surface layers of the nanoparticles play an essential role in this process. We present experimental evidence for our opinion, based on the high-resolution electron microscopic analysis of several different types of nanoparticles.

Journal Article↗