Individual Metal Particles Research Articles

Align Ag Nanorods via Oxidation Reduction Growth Using RF‐Sputtering

Silver nanorod arrays grew on the individual metallic silver particles after the thermal decomposition of the silver oxides. The formation of silver oxide came from the input of oxygen during sputtering. The subsequent growth of the Ag nanorods started from the single silver grain that originated from the decomposition caused by thermal reduction. This method for oxidation reduction growth used no catalysts and improved the interface effect for the lattice match. Photoluminescence of Ag nanorods was detected at 2.17 eV.

Spatial Nonlocality in the Optical Response of Metal Nanoparticles

Spatial nonlocality is known to play an important role in nano-optics when small nanometer-sized structures are involved, but few efforts have been made to assess nonlocal effects in a rigorous way. We present two different approaches to account for nonlocality in metal nanoparticles: (i) the nonretarded specular reflection model and (ii) the retarded hydrodynamical model. Excellent agreement with available experiments is obtained from our parameter-free simulations, which lead to dramatic differences with respect to local theory. Both models predict sizable plasmon blue shifts and broadenings in individual metal nanoparticles, nanoshells, particle dimers, and Yagi–Uda antennas. An analysis of plasmon resonances for varying particle size and spacing allows us to separate nonlocal and retardation effects within the hydrodynamical model. We find a wide range of geometrical parameters for which nonlocal effects coexist with significant retardation. This study is particularly relevant for broad, active areas involving applications of local field enhancement to biosensing and nonlinear optics in plasmonics.

Photoabsorption ofAgN(N∼6–6000)Nanoclusters Formed in Helium Droplets: Transition from Compact to Multicenter Aggregation

Ag(N) clusters with up to thousands of atoms were grown in large He droplets and studied by optical spectroscopy. For N≲10(3) the spectra are dominated by a surface plasmon resonance near 3.8 eV and a broad feature in the UV, consistent with absorption by individual metallic particles. Larger clusters reveal unexpectedly strong broad absorption at low frequencies, extending down to ≈0.5 eV. This suggests a transition from single-center to multicenter formation, in agreement with estimates of cluster growth kinetics in He droplets. Moreover, the spectra of large clusters develop a characteristic dispersion profile at 3.5-4.5 eV, indicative of the coexistence of localized and delocalized electronic excitations in composite clusters, as predicted theoretically.

Metals and metal oxides particles produced by pulsed laser ablation under high vacuum

A pulsed KrF Excimer laser (248 nm, 15 mJ) was utilized to synthesize different particles on (111) Si substrate under vacuum \sim 10^{-6} torr using Aluminum (Al), Platinum (Pt), Tungsten (W), Molybdenum (Mo), Cadmium Oxide (CdO), and Yttrium Oxide (Y_2O_3) targets. Scanning electron microscope (SEM) was used to study particle size distribution on silicon substrate. The size of individual metal particles was found to be ranging from 71 nm to 2 \mu m whereas metal oxides particles were found in the range of 71 nm to 1.1 \mu m. The particles below 100 nm are formed by gas phase condensation of ions, atoms and molecules whereas particles greater than 100 nm size results either from the ejection of liquid droplets from the melt surface or stresses induced by laser on target surface. The advantage of particle formation due to laser ablation in high vacuum is pure particles production.

An analytical method to study the effects of a substrate in surface-enhanced Raman scattering

In studies of surface-enhanced Raman scattering (SERS), individual metal nanoparticle and particle assemblies introduce enhancement of electromagnetic fields. However, the contributions to enhancement due to the substrate supporting the particles are yet to be studied analytically. In this communication, we present an analytical method to investigate the effect of a substrate with realistic layers in SERS. The proposed method quantifies the effect of a substrate on the electric field on the nanoparticles surface in SERS experiments. By applying the proposed method, optimal constructions of a substrate can be obtained to maximize the surface electric field while a poorly constructed one can be avoided. The maximization can lead to a high Raman enhancement factor. The method is verified using numerical simulations.

On possibility of vapor-phase combustion for fine aluminum particles

A simplified heat transfer model applicable for vapor-phase combustion of individual fine metal particles predicts existence of a critical particle diameter, below which the vapor-phase flame alone cannot be self-sustaining. Other heat generation mechanisms (i.e. surface oxidation) should complement the vapor-phase flame. The predicted critical particle diameter is a function of the flame temperature and pressure. For single aluminum particles burning in atmospheric pressure air, CO 2 and H 2O, the predicted critical particle diameters are close to 6, 7, and 15 μm, respectively.

Morphological study of metal/dielectric composite films with various spatial distributions of metal particles

Morphological properties of metal/dielectric composite films consisting of individual metal particles in a dielectric matrix were studied by methods of computational physics. The simulated composite structures were prepared by hard-sphere and soft-sphere models with given spatial distribution of objects ranging from totally random, through various degrees of order up to anisotropic in certain directions. The images of sections of generated composite films were processed using the two strongest morphological methods – of “Voronoi tessellation” and “covariance function” with the aim to analyse the spatial distribution of particles in the composite film and to reveal the possible irregularities in this distribution. The results show that both the methods can effectively help to quantify the degree of particles arrangement as well as the anisotropy of structures studied.

Improvement of thermal stability of NO oxidation Pt/Al2O3 catalyst by addition of Pd

The present work has been undertaken to tailor Pt/Al2O3 catalysts active for NO oxidation even after severe heat treatments in air. For this purpose, the addition of Pd has been attempted, which is less active for this reaction but can effectively suppress thermal sintering of the active metal Pt. Various Pd-modified Pt/Al2O3 catalysts were prepared, subjected to heat treatments in air at 800 and 830°C, and then applied for NO oxidation at 300°C. The total NO oxidation activity was shown to be significantly enhanced by the addition of Pd, depending on the amount of Pd added. The Pd-modified catalysts are active even after the severe heat treatment at 830°C for a long time of 60h. The optimized Pd-modified Pt/Al2O3 catalyst can show a maximum activity limited by chemical equilibrium under the conditions used. The bulk structures of supported noble metal particles were examined by XRD and their surface properties by CO chemisorption and EDX-TEM. From these characterization results as well as the reaction ones, the size of individual metal particles, the chemical composition of their surfaces, and the overall TOF value were determined for discussing possible reasons for the improvement of the thermal stability and the enhanced catalytic activity of Pt/Al2O3 catalysts by the Pd addition. The Pd-modified Pt/Al2O3 catalysts should be a promising one for NO oxidation of practical interest.

Full field imaging and spectroscopy of individual gold nanoparticles

Most applications involving metallic nanoparticle labelling necessitate both fast imaging and local spectroscopy of individual beads. We present an imaging method based on a guided laser illumination associated to spatial modulation which allows the detection of gold particles down to 10 nm. Using an imaging spectrometer and white incoherent illumination, the same system delivers individual spectroscopy of several gold beads simultaneously, allowing a fast and selective discrimination between individual metal particles and aggregates or dust.

A novel approach to detect and characterize the scattering patterns of single Au nanoparticles using confocal microscopy

We demonstrate a novel optical method for characterizing single Au nanoparticles by acquiring their scattering patterns. This technique combines confocal microscopy and higher-order laser modes for detecting the light scattered by sub-wavelength-sized nanoobjects. The optical patterns are generated by the coherent superposition of the field scattered by individual metallic particles and the excitation field reflected at the cover slide-air interface and provide information about the particles' position, orientation, size and shape. Detectable changes in the full width at half maximum (FWHM) of the signal intensity permit to distinguish between 20- and 60-nm diameter Au spheres. The confocal images are also very sensitive to the particle's geometry and polarizability, that is, Au nanospheres, Au nanorods and triangular Au nanoplates give different characteristic patterns if the excitation wavelength is varied.

Effect of Substrate Temperature on Deposition Behavior of Copper Particles on Substrate Surfaces in the Cold Spray Process

The deposition behavior of sprayed individual metallic particles on the substrate surface in the cold spray process was fundamentally investigated. As a preliminary experiment, pure copper (Cu) particles were sprayed on mirror-polished stainless steel and aluminum (Al) alloy substrate surfaces. Process parameters that changed systematically were particle diameter, working gas, gas pressure, gas temperature, and substrate temperature, and the effect of these parameters on the flattening or adhesive behavior of an individual particle was precisely investigated. Deposition ratio on the substrate surface was also evaluated using these parameters. From the results obtained, it was quite noticeable that the higher substrate temperature brought about a higher deposition rate of Cu particles, even under the condition where particles were kept at room temperature. This tendency was promoted more effectively using helium instead of air or nitrogen as a working gas. Both higher velocity and temperature of the particles sprayed are the necessary conditions for the higher deposition ratio in the cold spraying. However, instead of particle heating, substrate heating may bring about the equivalent effect for particle deposition.

320 コールドスプレーしたCu粒子の付着におよぼす基材温度の影響(OS13-1 コールドスプレー皮膜の付着メカニズムとその皮膜特性,OS13 コールドスプレー皮膜の付着メカニズムとその皮膜特性)

Self designed cold spray equipment was installed in the laboratory and deposition behavior of sprayed individual metallic particles on the substrate surface was fundamentally investigated. As a preliminary experiment, pure Cu particles were sprayed on mirror polished stainless steel substrate surface. Particles diameter, process gas, gas pressure, gas temperature and substrate temperature were systematically changed as the process parameters, and effect of these parameters on the flattening or deposition behavior of an individual particle was investigated. From the results obtained, it was found that the deposition temperature is a possible domination on the deposition behavior in cold spray process.

コールドスプレー法における銅粒子堆積機構の解明

Application of cold spray process is expected in the various industrial fields such as automobile, aircraft and electronics. So many investigations for practical application have been actively performed in many research organizations. However, as the process has just started in these days, fundamental aspect like deposition mechanism itself has not been well understood up to today. To establish the higher reliability or controllability of the cold spray process, fundamental research, especially on the deposition mechanism, may become a key for the process development. We tried the clarification of particle deposition mechanism in cold spray process by experimental approach. In this study, deposition behavior of sprayed individual particle onto substrate surface was investigated precisely.Self designed cold spray equipment was installed in the laboratory and deposition behavior of sprayed individual metallic particles on the substrate surface was fundamentally investigated. As a preliminary experiment, pure Cu particles were sprayed on mirror polished stainless steel substrate surface. Particles diameter, process gas, gas pressure, gas temperature and substrate temperature were systematically changed as the process parameters, and effect of these parameters on the flattening or deposition behavior of an individual particle was investigated.

Single-walled carbon nanotube synthesis using ferrocene and iron pentacarbonyl in a laminar flow reactor

A gas-phase process of single-walled carbon nanotube (SWCNT) formation, based on thermal decomposition of iron pentacarbonyl or ferrocene in the presence of carbon monoxide (CO), was investigated in ambient pressure laminar flow reactors in the temperature range of 600–1300 °C. Ferrocene was found to be a better catalyst precursor in the studied conditions since iron pentacarbonyl decomposes at lower temperatures resulting in the excessive growth of catalyst particles. In situ sampling carried out at 1000 °C showed that the SWCNT growth occurred from individual metal particles in the heating section of the furnace in the temperature range of 891–928 °C, in which the growth rate was estimated to exceed 2 μ m / s . FT-IR measurements of gaseous products revealed that the majority of the CO disproportionation took place on the reactor walls. Raman measurements confirmed the results of TEM observations, namely, the formation of very high purity SWCNT product. On-line aerosol number size distributions were measured to detect the conditions of SWCNT formation and the product morphology changes. Mechanism of SWCNT formation in the gas phase from ferrocene and CO is discussed.

Characterization of atmospheric dry deposition particulates in Kobe, Japan

The sources and character of individual metal and metalloid particles from atmospheric dry depositions in Kobe, Japan were investigated. Japan faces long-range pollutant transportation from northeastern Asia during winter and spring. Information regarding their properties and sources is useful for evaluating their affects on the environment and human health. Individual metal and metalloid particles that were collected for every 24 h on the plate, which was designed to reduce a local turbulence, were characterized for their composition, diameter, and deposition fluxes using a field emission scanning electron microscope with an energy dispersive X-ray spectrometer. Approximately 3000 metal and metalloid particles were classified into 14 types based on their composition and further classified into four groups based on their distribution patterns. They are (A) Fe–O, Fe–Ba–Sb–Cu–S–Ti–O, Fe–Zn–O, Zn–O, Ni–O, and Mn–Fe–O; (B) Cu–Zn–O and Cu–Sn–O; (C) Pb–O, Sn–Sb–O, and Ag–O; (D) Pb–Zn–Cl–Si–S–O and Bi–Cl–O. From these data, this study suggests their sources as the Asian continent (Group A), local source (Group B), multiple sources (Group C), and incineration process (Group D). This study shows (1) the sources and character of individual metal and metalloid particles from short-term atmospheric depositions in Kobe, Japan and (2) application of individual particle analysis for atmospheric depositions.

Bulk and surface characterisation of metal powders for direct laser sintering

Two different metal powder mixtures usable for direct metal laser sintering were analysed. Bulk chemical compositions were determined with ion-coupled plasma–atomic emission spectroscopy. Morphological, as well as microstructural properties of individual metal particles were determined with a light microscope and high-resolution field-emission scanning electron microscope (SEM). Additionally, SEM/EDS analysis has been performed for microanalyses of powder particles.

Surface chemical analysis of prealloyed water atomised steel powder

Prealloyed water atomised steel powder was investigated regarding composition, morphology and thickness of the surface oxide. The materials were two varieties of Cr alloyed and one Mo alloyed. The oxides formed on powder surfaces were studied by means of the surface analytical techniques X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy, in combination with high resolution electron microscopy and X-ray microanalysis.On all powder surfaces, the oxide formed contained strong oxide forming elements such as Cr, Mn and Si. Still, the dominant oxide on the powder surface was Fe oxide, the relative cation concentration in the surface being about 80%. The surface morphology showed a heterogeneous structure with particulate compounds supposed to be rich in strong oxide formers and an Fe rich thin oxide layer. This heterogeneous surface oxide morphology was more pronounced for the Mo alloyed powder compared with the Cr alloyed varieties. For this alloy, the average thickness of the oxide layer was somewhat larger (7–87·5 nm for fraction , <63 μm and 63–106 μm) compared with that of Cr alloyed powder (6–7 nm in all cases for fraction , <63 μm and 63–106 μm). An interesting observation was that Cr oxide also appeared on the nominally Cr free Mo alloyed powder, which indicates selective oxidation of Cr also when this element is present in low quantities. Although the alloying elements are enriched by a factor of 40–50 in the surface oxide, there is little effect on depletion of them from the steel matrix.From a sintering point of view, the particulate oxide compounds should play a minor role, since the most probable contacts between individual metal particles are Fe oxide/Fe oxide.

Modeling of Surface Structure of Supported Catalysts. Application to Deactivation of FT Reactors

Water in Fischer−Tropsch synthesis (FTS) on supported cobalt catalysts is known to deactivate the catalysts. The deactivation involves the reoxidation of highly dispersed cobalt phase by water and water-induced sintering. In both cases, the dispersion state of the cobalt phase in the supported catalyst plays an important role. Therefore, the deactivation kinetics depends on the surface structure of the catalyst. Mathematical models are formulated to describe the deactivation behavior of cobalt catalyst pellets with the dependence on catalyst structure and reaction conditions. On the crystallite scale, a size-dependent deactivation model for individual metal particles is built; on the catalyst scale, the deactivation and growth (shrinking) of each individual metal crystallite in the pellet as well as the radial distribution for temperature and concentrations are accounted for using a population balance equation (PBE) coupled with intraparticle diffusion-reaction equations. The model is used for optimizatio...

In vitro genotoxic effects of different combinations of cobalt and metallic carbide particles.

Occupational exposure to hard metal dust, consisting of tungsten carbide (WC) and metallic cobalt particles (Co), is associated with an increased risk of lung cancer, while no increased risk was observed in workers exposed to Co alone. In vitro, in human peripheral blood mononucleated cells (PBMC), we previously demonstrated that WC-Co is more genotoxic than Co and WC alone. A possible mechanism underlying this higher genotoxicity is a specific physicochemical interaction between Co and WC particles leading to the enhanced short-term formation of active oxygen species. The aim of this study was to evaluate the in vitro genotoxicity of other combinations of Co with metal carbide particles in comparison with WC-Co. The ability of Cr(3)C(2), Mo(2)C and NbC and of their powder mixtures with Co to induce DNA strand breaks and alkali-labile sites was assessed by the alkaline Comet assay and their potential to induce chromosome(/genome) mutations by the cytokinesis-block micronucleus test on human PBMC from two donors. PBMC were treated in vitro for 15 min, 24 h after the onset of PHA stimulation. In the micronucleus test, while the metal carbides alone did not increase the micronucleus frequency, Co alone and the four tested carbide-Co mixtures induced a statistically significant concentration-dependent increase in micronucleated binucleates. In addition to WC, NbC and Cr(3)C(2) particles were able to interact with Co, producing a higher mutagenic effect than the individual metal particles. Mo(2)C particles did not display interactive mutagenicity with Co in the micronucleus test, possibly related to their small specific surface area, compactness and/or spherical shape. With the Comet assay, applied directly at the end of the treatment, less clear results, due to inter-experimental and inter-donor variation, were obtained. These data indicate that particular interaction of a metal carbide with Co leading to enhanced mutagenicity is not specific for WC.

Arabinogalactan from the Western larch tree: A new, purified and highly water-soluble polysaccharide-based protecting agent for maintaining precious metal nanoparticles in colloidal suspension

TEM and non-contact atomic force microscopy studies conducted on unprotected and protected platinum, palladium and silver nanoparticle suspensions provide evidence for the protective ability of a newly available polysaccharide known as arabinogalactan. The arabinogalactan offers advantages over conventionally used gum arabic in being highly water soluble, capable of being prepared in higher purity and not settling out insoluble material over time. Nanoparticle suspensions prepared in the presence of this protecting agent show a change in overall particle morphology and reduction in the necklace like aggregation typical of unprotected particles on the TEM grids. It is believed that the protective action exerted by the arabinogalactan on the metal nanoparticles arises out of its unique spheroidal structure adopted in aqueous solution which is thought to sequester individual metal particles by virtue of surface interactions between oxide functionalities on the colloid and hydroxyl groups on the arabinogalactan.