Polarization-dependent surface-enhanced Raman scattering from a silver-nanoparticle-decorated single silver nanowire

Single silver nanowires produced by DC electrodeposition in porous anodic alumina templates were surface-functionalized with the bifunctional molecule 4-aminobenzenthiol (ABT) then exposed to aqueous silver nanoparticles resulting in a silver nanoparticle-decorated silver nanowire. The polarization dependent surface-enhanced Raman (SERS) signal from this system showed significant intensity anisotropy when measured at a midsection of the nanowire, where the largest SERS intensities were observed when the incident light was polarized perpendicular to the nanowire's long axis but was almost isotropic near the tip of the nanowire. The observed effects were accounted for in terms of the electromagnetic fields concentrated in the collection of hot spots created through the ABT-linker-driven nanoparticle-nanowire self-assembly process.     

Plasmon-induced photochemical synthesis of silver triangular prisms and pentagonal bipyramids by illumination with light emitting diodes

We have grown silver prisms and pentagonal bipyramids, induced by plasmon excitation on a colloidal solution under the irradiation of light emitting diodes of different colors. Two methods of synthesis of the seeds were tested and their growth evolution recorded, in order to analyze the effect of the chemical synthesis and the color of the irradiation on the morphology and size of the final product. We show that the conversion rate into anisotropic nanoparticles is determined by the chemical environment and the shift of the irradiation wavelength with respect to the plasmon resonance of the seeds. The conversion rate defines the final morphology of the nanoparticles, whereas the size of the nanoparticles is univocally determined by the wavelength of irradiation, irrespective of the method to prepare the seed solution.     

Rhodium nanoparticles from cluster seeds: control of size and shape by precursor addition rate

The size-tunable synthesis of poly(vinylpyrrolidone)-stabilized cuboctahedral rhodium nanoparticles with mean diameters ranging between 3-7 nm and multipod structures was accomplished using seeded growth methods. Isotropic PVP-capped 2.9 nm seeds were prepared by ligand exchange on rhodium-triphenylphosphine metal-organic clusters. Quantitative investigation of reaction parameters in ethylene glycol revealed that size and shape could be controlled at a single reaction temperature of 120 degrees C. The rate of rhodium monomer addition was found to be critical for monodispersity and shape control, regardless of thermodynamic factors. Solvent viscosity, varied by changing the polyol solvents, indicated that autocatalytic addition kinetics are responsible for isotropic versus anisotropic growth.     

Submonolayer and single crystal film from ligand-stabilized silver nanoparticles

Ligand-stabilized silver nanoparticles were synthesized by a method of ultraviolet light irradiation reduction from a parent solution containing inorganic silver salt, then deposited on carbon coated copper microscope grid by electrophoretic technique. All samples were examined on transmission electron microscope. The results indicate that when the parent solution was irradiated for 5 min a submonolayer of silver nanoparticles was obtained; however, when the parent solution was irradiated for 10 min single crystal silver films were formed. The mechanisms about formation of the submonolayer of nanoparticles and the single crystal silver films were discussed.     

A methodology for creating a statistically derived shape grammar composed of non-obvious shape chunks

A shape grammar is a production system that can be used to create new product designs. Traditionally, a product shape grammar’s rules are created by a skilled person that understands the language of the design. In this paper the results of a principal component analysis of vehicles are used to create a vehicle shape grammar by basing the rules upon the determined shape relationships. The advantages are that: rules can be created according the results of a statistical analysis, and not according to a designer’s subjective observations; class specific vehicles can be created with fewer rule applications; and those rule applications encourage divergent designs. Using the principal component analysis based shape grammar, unique vehicles are created to demonstrate the potential of statistically based concept creation for the generation of product forms.     

A new technique for preparation of molybdenum single crystal with an optional shape

A molybdenum single crystal with an optional shape was produced by the secondary recrystallization method. First, a specimen with an optional shape was mechanically fabricated by drilling, punching or bending from a hot-rolled sheet doped with CaO and MgO. Then the specimen was isothermally annealed at 2300°C for 1 h.     

Characterization of a new mixed oxide catalyst derived from hydrogen storage alloy

A mixed oxide catalyst was prepared from a binary hydrogen storage alloy, Mg₂Cu. Oxidation of Mg₂Cu alloy gave mixed oxides of MgO and CuO, which showed high activity and high selectivity for the synthesis of alcohols from methyl linoleate. On the other hand, a catalyst prepared by the coprecipitation method deactivated with time. The nature of the catalytically active site was discussed on the basis of characterization by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and infrared analysis (I.R.). The difference between these two catalysts could be attributed to differences in the co-ordination number of copper species at the surface.     

Practical shape optimization of a levitation device for single droplets

The rigorous optimization of the geometry of a glass cell with computational fluid dynamics (CFD) is performed. The cell will be used for non-invasive nuclear magnetic resonance (NMR) measurements on a single droplet levitated in a counter current of liquid in a conical tube. The objective function of the optimization describes the stability of the droplet position required for long-period NMR measurements. The direct problem and even more the optimization problem require an efficient method to handle the high numerical complexity implied. Here, the flow equations are solved two-dimensionally and in steady state with the finite-element code SEPRAN for a spherical droplet with ideally mobile interface. The optimization is performed by embedding the CFD solver SEPRAN in the optimization environment EFCOSS. The underlying derivatives are computed using the automatic differentiation software ADIFOR. An overall concept for the optimization process is developed, requiring a robust scheme for the discretization of the geometries as well as a model for horizontal stability in the axially symmetric case. The numerical results show that the previously employed measuring cell described by Schröter is less suitable to maintain a stable droplet position than the new cell.     

Green synthesis of silver nanoparticles from purple acid phosphatase apoenzyme isolated from a new source Limonia acidissima

Green synthesis of nanoparticles is regarded as a safe and non-toxic process whereas conventional synthesis using chemical methods produces toxic substance. This study provides a novel insight for enzymatic synthesis method of silver nanoparticles using purple acid phosphatase, isolated from Limonia acidissima (wood apple) as a new source and used in the synthesis of silver nanoparticles. Stable silver nanoparticles were produced by sonochemical method using apoenzyme as a stabilising and capping agent and were characterised by various physicochemical techniques like UV–Visible spectroscopy, Fourier-transform infrared, X-ray diffraction and transmission electron microscopy. X-ray study shows that nanoparticles are composed of silver and silver oxide. The synthesised nanoparticles exhibited excellent antimicrobial activity against Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus.     

Investigation of shape effect of silver nanostructures and governing physical mechanisms on photo-activity: Zinc oxide/silver plasmonic photocatalyst

Plasmonic composites consisting of silver nanostructures and zinc oxide semiconductor have better photocatalytic performance than pure zinc oxide. To prepare the composites, nanostructures of zinc oxide particles, gold spheres, and three different silver morphology including cubes, spheres, and wires were synthesized. A detailed study of the main mechanisms governing the activity of plasmonic photocatalysts showed that the improvement of photocatalytic performance is attributed to localized surface plasmon resonance-mediated energy transfer from silver to zinc oxide. This mechanism, which is performed using non-radiative (near-field) and radiation (far-field) processes, led to an increase in the concentration of e^?/h⁺ pairs near the semiconductor. We also showed that the increase of the photocatalytic activity depends on the shape of the silver nanostructures in the composites. Our theoretical and experimental studies have shown that composites containing silver cubes have the highest increase of photocatalytic activity compared to other morphologies. The percentage of photocatalytic degradation of methylene blue solution in presence of silver cubes was about 15% higher than that of other morphologies. Therefore, by controlling the shape of noble metal nanostructures, the photocatalytic activity of a semiconductor can be maximized and adjusted.     

Surface-enhanced Raman scattering imaging of a single molecule on urchin-like silver nanowires

Urchin-like silver nanowires are prepared by reacting AgNO(3)(aq) with copper metal in the presence of cetyltrimethylammonium chloride and HNO(3)(aq) on a screen-printed carbon electrode at room temperature. The diameters of the nanowires are about 100 nm, and their lengths are up to 10 μm. Using Raman spectroscopy, the detection limit of Rhodamine 6G (R6G) on the urchin-like silver nanowire substrate can be as low as 10(-16) M, while the analytical enhancement factor is about 10(13). Raman mapping images confirm that a single R6G molecule on the substrate can be detected.     

Color-coded projection grating method for shape measurement with a single exposure

A fast and efficient technique for profilometric measurement with a color-coded grating is proposed. Eight colors are used to code the grating, and each color represents only one logical state. There are 64 stripes in one period of the color grating, which is large enough for normal measurement. Compared with the previous techniques, it has the advantages of simple hardware without moving mechanical parts, single exposure for obtaining three-dimensional information, little influence from noise and from nonlinearity of the CCD camera on the measurement accuracy, and higher anti-color-blurring capability. The suggested technique is suitable for on-line inspection and dynamic measurement of moving objects.     

Synthesis of silver nanorods by low energy excitation of spherical plasmonic seeds

Plasmon excitation of Ag seed particles with 600-750 nm light in the presence of Ag(+) and trisodium citrate was used to synthesize penta-twinned nanorods. Importantly, the excitation wavelength can be used to control the reaction rate and, consequently, the aspect ratio of the nanorods. When the excitation wavelength is red-shifted from the surface plasmon resonance of the spherical seed particles, the rate of Ag(+) reduction becomes slower and more kinetically controlled. Such conditions favor the deposition of silver onto the tips of the growing nanorods as compared to their sides, resulting in the generation of higher aspect ratio rods. However, control experiments reveal that there is only a range of low energy excitation wavelengths (between 600 and 750 nm) that yields monodisperse nanorods. This study further highlights the utility of using wavelength to control the size and shape of growing nanoparticles using plasmon-mediated methods.     

The state of strain in single GaN nanocolumns as derived from micro-photoluminescence measurements

In the present paper, studies on the state of strain in single and ensembles of nanocolumns investigated by photoluminescence spectroscopy will be presented. The GaN nanocolumns were either grown in a bottom-up approach or prepared in a top-down approach by etching compact GaN layers grown on Si(111) and sapphire (0001) substrates. Experimental evidence for strain relaxation of the nanocolumns was found. The difference and development of the strain value for different nanocolumns could be verified by spatially resolved micro-photoluminescence on single nanocolumns separated from their substrate. A common D0X spectral position at 3.473 eV was found for all separated single GaN nanocolumns independent of the substrate or processing technique used, as expected for a relaxed system.     

Preparation and analysis of a109cd gamma source implanted into a silver single crystal

Preparation of¹⁰⁹Cd gamma sources implanted by thermal diffusion into a single crystal of silver is described. The source is intended for experiments on Mössbauer excitation of the long-lived isomeric state of¹⁰⁹Ag with 88 keV energy. Two nondestructive methods are described for finding the depth of the implanted¹⁰⁹Cd atoms. One is a general-purpose method and can be used to study the diffusion of a wide class of radioactive atoms. The second method is useful only for the investigation of boundary distributions of the radioactive diffusant.Translated from Izmeritel'naya Tekhnika, No. 1, pp. 58–61, January, 1994.The authors thank V. N. Kaigorodov (Institute of Metal Physics of the Russian Academy of Sciences) whose gave us a detailed account of his studies on cadmium diffusion in silver; N. V. Lichkova and R. N. Nikolaev (Institute of Microelectronics and Extremely Pure Materials) whose prepared the silver single-crystal used in this work; to the staff of the Institute of Theoretical and Experimental Physics S. N. Zubkov, A. M. Kotov, and S. E. Starostina for their help with experiments, and to M. M. Korotkov and G. V. Gostina for a discussion of different aspects of this work.     

Fatigue behavior of Cu-Al-Be shape memory single crystals

The fatigue behavior of Cu-Al-Be shape memory single crystals is studied in cyclic loading mechanical tests. Based on literature and on tensile tests performed at various temperatures, a model is proposed to explain the mechanism of fatigue. This model is based on the idea that during cyclings, the different zones of the samples spend various lengths of time in the martensitic state. During that time, martensite evolves because of the occurrence of some reordering or other diffusional phenomena inside, and consequently, the value of the martensite start temperature for each zone changes. The kinetics of the change in mechanical behavior along with the cycles, as a function of the test temperature, are accurately described by a Johnson–Mehl relation. Relaxation tests suggest that the mechanism described not only depends on time and temperature but is also re-enforced by the movement of the martensite-matrix interface. From the kinetics of this fatigue behavior, an empirical activation energy related to the mechanism is inferred for this Cu-Al-Be alloy.     

Disorder effect in the transmission spectra of a noncompact single layer of dielectric spheres derived from microwave spectroscopy

Single layers of dielectric spheres are an interesting system to study from the fundamental and applied points of view. In this paper we present a systematic study of the influence of structural disorder on the transmission spectra of arrangements of spheres of different compactness. Glass sphere (ε=7) planes were built and their transmission spectra in the microwave range measured. Transmission behavior of this system is highly tolerant to disorder. Even in completely disordered arrangements, there is a highly rejected band with the dips of the spectrum observable. These results suggest that the collective modes of the sphere planes are formed by weakly coupled Mie modes of the individual spheres, and this coupling is governed by the average distance among the spheres. Disorder tolerance allows simpler fabrication procedures where the position of the spheres does not need to be precisely controlled.