Catalytic oxidation of carbon nanotubes with noble metal nanoparticles

Catalytic oxidation of multi-walled carbon nanotubes (MWNCTs) with some noble metal nanoparticles was observed by environmental transmission electron microscopy (E-TEM). Amoeba-like movement of the nanoparticles was observed even at a temperature of ∼400 °C, which is much lower than the melting points of any of the metals. In particular, rhodium particles reacted intensely with MWCNTs, and assumed a droplet-like shape. On the other hand, gold particles caused very little erosion of the MWCNTs under the conditions of this study.     

Photo-chemical vapor deposition of hydrogenated amorphous silicon films

A photo-chemical vapor deposition, using ultraviolet light excitation and a mercury photo-sensitization, was investigated for depositing hydrogenated amorphous silicon films from SiH₄. The photoelectric and structural properties were examined to characterize the deposited films. Those properties were depended strongly on substrate temperature, and the films which were deposited at a substrate temperature more than 200°C contained dominant SiH configurations. A relatively large single crystalline grain size of about 0.5 m was observed in a 1.0 m thick film, which was obtained at a substrate temperature as low as 200°C. Phosphorus impurity doping into the films and Pt-Schottky diode fabrication were also attempted.     

液相法制备金属纳米粒子

液相法是在均相溶液中，利用各种途径引发化学反应，通过均相或异相成核及随后的扩散生长而制备出粒径分布窄且表面功能化的纳米尺度材料．介绍了液-液两相法、反相胶束、高温液相法等制备单分散金属纳米粒子的方法和高温液相法制备金属纳米粒子的影响因素，以及近年来在金属纳米粒子的制备和性能研究上的进展，尤其是Co等多种磁性纳米粒子的制备、磁性研究．     

Expandable photo-induced synthetic route to generate highly controlled noble metal nanoparticles

A photo-stimulation strategy was applied to synthesize colloidal noble-metal nanoparticles (NPs) with a highly controlling of size and morphology with high yield at room temperature. In this controlled synthesis, photoreduction of a mixture of the noble metal precursor and a chemical reducing agent under ultraviolet (UV) illumination was used to produce electrons that reduce metal ions (Au³⁺ and Ag⁺) in toluene. Prolonged UV irradiation at 365 nm at a power of 0.14 μmol S⁻¹ m⁻² induced ripening wherein the irradiation power, exposure time, and chemical interaction of the reducing and stabilizing agents were key factors in determining the nanoscale structure of the NPs. Under optimal irradiation and chemical conditions, size and shape deviations of <6% of the Au and Ag NPs were obtained.     

Oscillatory behavior and enhancement of the surface plasmon linewidth in embedded noble metal nanoparticles

We study the Landau damping of the surface plasmon resonance of metallic nanoparticles embedded in different environments of experimental relevance. Important oscillations of the plasmon linewidth as a function of the radius of the nanoparticles are obtained from numerical calculations based on the time dependent local density approximation. These size-oscillations are understood, within a semiclassical approximation, as a consequence of correlations in the spectral density of the nanoparticles. We treat inert matrices, as well as the case with an unoccupied conduction band. In the latter case, the plasmon lifetime is greatly reduced with respect to the inert case, but the non-monotonous size-dependence persists.     

Thermalization time of noble metal nanoparticles: effects of the electron density profile

The lack of d-electron screening in the s-electron spill-out region at the surface of Ag nanoparticles increases the electron-electron interaction in this region compared to the bulk. Therefore when comparing the electron-electron interaction contribution to the thermalization time of nanoparticles of varying radius, smaller particles thermalize faster due to the increased surface to bulk ratio. One aspect which has not been addressed is the effect of the spatial distribution of charge at the surface of the nanoparticle. In this work it is shown that the size dependence of the thermalization time is very sensitive to the surface density profile. The electron thermalization time of conduction electrons in noble metal nanoparticles as a function of the radius is calculated. The sensitivity of the scattering rate to the spatial distribution of charge at the surface of the nanostructure is analyzed using several model surface profiles. The change in surface charge distribution via charging or coating of the nanospheres is shown to be a tool for control and probing of the ultra-fast electron-electron dynamics in metallic nanoparticles.     

General method of synthesis for metal nanoparticles

Sugar-assisted stable monometallic nanoparticles were synthesized by wet chemical method following a general scheme. Judicious manipulation of the reducing capabilities of different sugars has shown to have a bearing on the particle size that corroborates the shift of the absorbance peak positions and TEM analysis. Evaporation of the precursor solutions on the solid surface (strong metal--support interaction), led to the formation of smaller particles. Under the experimental condition, spherical nanoparticles of approximately 1, 3, 10 and 20 nm sizes were prepared reproducibly for gold, platinum, silver and palladium, respectively. Fructose has been found to be the best suited sugar for the synthesis of smaller particles and remained stable for months together.     

Visible fluorescence induced by the metal semiconductor transition in composites of carbon nanotubes with noble metal nanoparticles

We show that single-walled carbon nanotube (SWNT) bundles emit visible fluorescence in the presence of noble metal nanoparticles and nanorods in the solid state. Conductivity measurements with metallic nanotubes, isolated from pristine SWNTs, show that they become semiconducting in the presence of the metal nanoparticles. Nanoparticle binding increases the defects in the nanotube structures which is evident in the Raman spectra. The metal-semiconductor transition removes the nonradiative decay channels of the excited states enabling visible fluorescence. Nanotube structures are imaged using this emission with resolution below the classical limits.     

Photopolymerization in water of diacetylenes chemisorbed onto noble metal nanoparticles: a spectroscopic study

Gold and silver nanoparticles of different size, decorated by a diacetylenic monomer having a COOH anchor group, were prepared in aqueous dispersions. Topochemical polymerization of the colloidal suspensions was obtained by UV irradiation and studied by means of spectroscopic techniques (UV–visible absorption, IR and Raman spectroscopies). A variety of polymer phases were found in the case of silver nanohybrids. The main contribution for this investigation was supplied by the Raman spectra, which provide detailed information on the polymer forms and on the preferred conformation of the alkylic side chains. Copyright © 2009 John Wiley & Sons, Ltd.     

Gas-jet method for deposition of metal nanoparticles into the fluorine-polymer matrix

The work deals with the obtaining by the vacuum gas-jet technique of the metal-polymer composites consisting of silver nanoparticles introduced into a fluorocarbon polymer matrix and the investigation of their optical properties. The dependence of the optical density in the visible range of frequencies on the structure of obtained samples has been investigated. The obtained composites are found to possess the plasmon resonance effect.     

Designable formation of metal nanoparticle array with the deposition of negatively charged nanoparticles

Ultrafine gold and platinum nanoparticles (NPs) were fabricated by pulsed laser ablation in helium gas and the NPs 2-15 nm in diameter were selectively classified by an electrostatic size-selection technique employing a low-pressure differential mobility analyzer (LP-DMA). The spherical NPs obtained showed a narrower distribution of diameters of anionic NPs over cationic NPs. With this knowledge, the anionic NPs were deposited onto silicon substrates designed by electron beam lithography processing, and designable patterns of arrayed NPs were produced by removing the photoresist layer.     

The prevalent synthesis of one-dimensional noble metal nanostructures based on sulfonated polyaniline at room temperature

We describe a prevalent method of synthesizing one-dimensional (1D) noble metal nanostructures (silver nanobelts and palladium nanowires) by treatment of corresponding noble metal ions only in the presence of the conductive sulfonated polyaniline without using any other reducing agents or energies. The results show that the sulfonated polyaniline provides the dual reductant and “soft template” roles to promoting noble metal ions to form shape-controlled 1D noble metal nanostructures in high yield. The employed approach may also shed some light on the preparation of other noble metal nanostructure by using conductive polymer.     

Sonochemical immobilization of noble metal nanoparticles on the surface of maghemite: mechanism and morphological control of the products

Aqueous sample solutions containing noble metal ions (HAuCl₄, Na₂PdCl₄, H₂PtCl₆), polyethyleneglycol monostearate, and magnetic maghemite nanoparticles were irradiated with high power ultrasound. Analyses of the products showed that noble metal ions were reduced by the effects of ultrasound, and the formed noble metal nanoparticles were uniformly immobilized on the surface of the maghemite. The present “one pot process” significantly simplifies the immobilization of noble metal nanoparticles on the surface of supports, compared with the conventional impregnation method. The average diameter of immobilized Au was 7–13 nm, and the diameters of Pd and Pt were several nm. The diameters depended upon the concentration of polyethyleneglycol monostearate and the concentration of noble metal ions, but not upon the maghemite concentration, indicating the possibility of the morphological controls of the products by adjusting these preparation conditions. The measurements of the average diameters and the numbers of immobilized Au nanoparticles obtained under various conditions suggest that the nucleation of Au does not occur on the surface of maghemite, but it might occur in the homogeneous bulk solution.     

Synthesis and microstructure of metal oxide thin films containing metal nanoparticles by liquid phase deposition (LPD) method

Au nanoparticles dispersed SiO₂-TiO₂ composite films have been prepared by a novel wet process, Liquid Phase Deposition (LPD) method. The composite films were characterized by XRD, XPS, TEM, ICP, SEM and UV-VIS absorption spectroscopy. The results showed that the SiO₂-TiO₂ composite films containing Au^III and Au^I ionic species were co-deposited from a mixed solution of ammonium silicofluoride, ammonium hexafluorotitanate, boric acid and tetrachloroauric acid. The heat treatment induced the reduction of Au ions and formation of Au nanoparticles in the film. TEM observation revealed that the Au nanoparticles with 5-10 nm in diameter were found to be dispersed uniformly in the SiO₂-TiO₂ matrix. The optical absorption band due to the surface plasmon resonance of dispersed Au particles were observed at the wavelength of 550 nm and shifted toward longer wavelength with increasing heat treatment temperature. Received 28 November 2000     

Magnetically tunable surface plasmon resonance based on a composite consisting of noble metal nanoparticles and a ferromagnetic thin film

We demonstrate magnetically tunable surface plasmon resonance based on a composite consisting of noble metal nanoparticles and ferromagnetic thin film. We found that both the frequency and linewidth of the localized surface plasmon resonance can be manipulated by applying an external magnetic field. The underlying mechanism is attributed to the variation of the dielectric constant in the ferromagnetic thin film resulting from the change of magnetization. Our result shown here paves an alternative route for manipulation of the characteristics of the surface plasmon resonance, which may serve as a new design concept for the development of magneto-optical devices.     

Self-organized synthesis of silver dendritic nanostructures via an electroless metal deposition method

Unique silver dendritic nanostructures, with stems, branches, and leaves, were synthesized with self-organization via a simple electroless metal deposition method in a conventional autoclave containing aqueous HF and AgNO₃ solution. Their growth mechanisms are discussed in detail on the basis of a self-assembled localized microscopic electrochemical cell model. A process of diffusion-limited aggregation is suggested for the formation of the silver dendritic nanostructures. This nanostructured material is of great potential to be building blocks for assembling mini-functional devices of the next generation. PACS 61.46.+w; 68.70.+w; 81.65.Cf     

Multichannel Raman spectroscopy of unroughened noble metal and non-noble metal films and tunnel junctions

We demonstrate that multichannel optical detectors provide the capability of observing Raman Scattering from molecular monolayers in solid-air and solid-solid interfaces in the absence of the conditions considered essential for surface enhanced Raman scattering. We present spectra of adsorbates on smooth Ag films, air-oxidized smooth Al films and Al gratings. Finally, we demonstrate a new configuration for surface enhanced Raman scattering which need not involve noble metals. Raman scattering from a doped Al/AlOx/Sn tunnel junction provides a specific example of such a configuration.     

Polymer-supported metals and metal oxide nanoparticles: synthesis,characterization, and applications

Metal and metal oxide nanoparticles exhibit unique properties in regard to sorption behaviors, magnetic activity, chemical reduction, ligand sequestration among others. To this end, attempts are being continuously made to take advantage of them in multitude of applications including separation, catalysis, environmental remediation, sensing, biomedical applications and others. However, metal and metal oxide nanoparticles lack chemical stability and mechanical strength. They exhibit extremely high pressure drop or head loss in fixed-bed column operation and are not suitable for any flow-through systems. Also, nanoparticles tend to aggregate; this phenomenon reduces their high surface area to volume ratio and subsequently reduces effectiveness. By appropriately dispersing metal and metal oxide nanoparticles into synthetic and naturally occurring polymers, many of the shortcomings can be overcome without compromising the parent properties of the nanoparticles. Furthermore, the appropriate choice of the polymer host with specific functional groups may even lead to the enhancement of the properties of nanoparticles. The synthesis of hybrid materials involves two broad pathways: dispersing the nanoparticles (i) within pre-formed or commercially available polymers; and (ii) during the polymerization process. This review presents a broad coverage of nanoparticles and polymeric/biopolymeric host materials and the resulting properties of the hybrid composites. In addition, the review discusses the role of the Donnan membrane effect exerted by the host functionalized polymer in harnessing the desirable properties of metal and metal oxide nanoparticles for intended applications.