Triangular Ag Research Articles

Optical Properties of Nanowire Dimers with a Spatially Nonlocal Dielectric Function

We study the optical spectra and electromagnetic field enhancements around cylindrical and triangular Ag nanowire dimers, allowing for a spatially nonlocal dielectric function that partially accounts for quantum mechanical effects. For the triangular structures, we pay particular attention to how these properties depend on the sharpness of the nanowire's tips. We demonstrate that significant differences exist from classical electrodynamics that employs a more common, spatially local dielectric function. These differences are shown to arise from the optical excitation of volume plasmons inside of the structures, analogous to one-particle quantum mechanical states, which lead to complex and striking patterns of material polarization. These results are important for further understanding the optical properties of structures at the nanoscale and have implications for numerous physical processes, such as surface-enhanced Raman scattering.

Porous Ag–Pd triangle nanoplates with tunable alloy ratio for catalyzing electroless copper deposition

Porous triangular Ag–Pd nanoplates of various bimetallic ratios were prepared by a galvanic displacement reaction in which Pd(OAc) 2 reacted with Ag nanoplates. In order to reduce the interaction of free hexadecyltrimethylammonium bromide (CTAB) with the synthesized Ag–Pd nanoplates during this reaction, Ag nanoplate/CTAB solution was precipitated by high-speed centrifugation before synthesizing the porous bimetallic nanotemplates. The kinetics of electroless copper deposition (ECD) catalyzed by these bimetallic nanoplates are analyzed by using a quartz crystal microbalance (QCM). The results reveal that Ag 18Pd 1 nanoplates show better catalytic activity than Ag 18Pd 1.5 and Ag 18Pd 2 nanoplates. Further, the catalytic activity of the porous nanoplates in the ECD bath can be controlled by varying their alloy ratios.

Fabrication of Hierarchical Nanostructure of Silver via a Surfactant-Free Mixed Solvents Route

The dendritic Ag nanostructure with ordered branches and a “clean” surface has been successfully prepared via a facile surfactant-free and acetone-based mixed solvents route at room temperature. Experiments and structural characterizations reveal that the dendritic Ag nanostructure is evolved from the initially generated triangular nanoplates by the reaction of AgNO3 with l-ascorbic acid to the dendrites through both the Ostwald ripening and the oriented attachment growth processes. The acetone plays the key role in controlling the nucleation, growth, conversion, and assembly of the Ag nanoparticles. In the absence of acetone, only the polyhedral particles can be obtained. The yield of the dendrites is dependent on the volume ratio of acetone to water. The present work provides an example for the synthesis of a novel metal nanostructure by simply adjusting the solvent components, which is important for the qualitative understanding of the solvent effect on the morphology of nanostructures and the controllable synthesis of desired nanostructures. The dendritic Ag nanostructure possesses surface-enhanced Raman scattering (SERS) performance similar to that from triangular Ag nanoplates, and they both show much better SERS enhancement ability than that of polyhedral Ag particles which might be relative to their different geometric shapes and microstructures. It is expected that the dendritic Ag nanostructure may find potential applications such as in catalysis, molecular probe, and biological sensing.

Simulating Synthesis of Metal Nanorods, Nanoplates, and Nanoframes by Self-Assembly of Nanoparticle Building Blocks

A general synthesis strategy to prepare metal nanostructures by self-assembly was proposed by molecular dynamics (MD) simulation. In this simulating synthesis strategy, the metal nanostructures were generated by the self-assembly of the amorphous nanoparticles with the attractive forces of the nanoparticle−nanoparticle interactions by the annealing MD method at high temperatures, and finally, the resulting amorphous metal nanostructures were cooled to 10 K, which could resemble the nanoparticle self-assembly in experiment. By using the simulating synthesis, we obtained the full atomistic models of the shape-controlled metal nanostructures, including Au, Ag−Au, and beaded Ag−Cu nanorods, triangular and hexagonal Ag nanoplates, triangular Ag−Au and hexagonal Au, cubic hollow Fe, and Ag−Au nanoframes. It is found that these models are in good agreement with the experimental results. Moreover, we predicted a new metal nanostructure, Au nanoporous framework architecture, which has not been reported in experime...

Photocatalytic growth and plasmon resonance-assisted photoelectrochemical toppling of upright Ag nanoplates on a nanoparticulate TiO2 film

Triangular and hexagonal Ag nanoplates deposited on a TiO(2) film in a mostly vertical orientation topple under visible light, resulting in a decrease of extinction at the excitation wavelength and increase at longer wavelengths.

Wavelength-Scanned Surface-Enhanced Resonance Raman Excitation Spectroscopy

We explore the correlation between localized surface plasmon resonance (LSPR) of triangular Ag nanoparticles, molecular resonance, and the surface-enhanced resonance Raman excitation profile of molecules adsorbed on these nanostructures. Ag nanoparticles with various LSPRs were fabricated with nanosphere lithography (NSL). A monolayer of tris(2,2′-bipyridine)-ruthenium(II) (Ru(bpy)32+) was introduced to the NSL Ag nanoparticles, and its effect on the LSPR was monitored by UV−vis spectroscopy. Wavelength-scanned surface-enhanced resonance Raman excitation spectroscopy (WS SERRES) profiles of Ru(bpy)32+ adsorbed on Ag nanoparticle arrays were measured for excitation wavelengths in the range of 400−500 nm. The WS SERRES profiles are correlated, both spatially and spectrally, with the corresponding LSPR spectra of the nanoparticle arrays and with the solution absorption spectrum of Ru(bpy)32+. The WS SERRES profile peak position depends on the relative spectral position of LSPR and the molecular resonance. Quasi-static electrodynamics modeling was applied to simulate the WS SERRES profiles, and the calculations are in agreement with the experimental results, demonstrating that the WS SERRES profiles involve multiplicative electromagnetic and resonance Raman enhancements.

Ag−Pt Nanoplates: Galvanic Displacement Preparation and Their Applications As Electrocatalysts

Ag−Pt circular, hexagonal, and triangular nanoplates are successfully prepared by the galvanic displacement reaction and used as electrocatalysts for hydrogen evolution reaction. As an electrochemical analyses, fair comparison regarding the activity can be thus made among these newly electrocatalysts. The triangular Ag−Pt nanoplates are measured to have maximum electrochemical activity.

Activator for Electrolessly Depositing Copper from Triangular Ag∕Pd Nanoshells

This article reports that triangular nanoshells are synthesized via the galvanic displacement reaction and further applied as activators for electroless copper deposition. Information as revealed by electrochemical quartz crystal microbalance, deposition rate catalyzed by the triangular nanoshells is and exhibit different electrochemical activity in the electroless deposition of copper.

Linear and Nonlinear Optical Phenomena of Metallic Nanoparticles

We have numerically characterized localized surface plasmons (LSPs) of triangular and cubic Ag particles on a substrate using the so-called finite-difference time-domain (FDTD) method. Especially, we have evaluated the effect of roundness around the prism corners on the characteristics of LSPs and, in addition to that, have focused onto a change in the characteristics of LSPs caused by an interaction between a particle and a substrate. Introduction of roundness decreases the field enhancement and existence of the substrate has made characteristics of LSP modes change. We have also simulated nonlinear optical response of an Ag nanosphere coated with a CdS film, being a Kerr material, by using a nonlinear 3-D FDTD method for spherical coordinates. We have presented extinction spectra of a triangle Ag particle that was processed by using a focused ion beam (FIB) lithography. The experimental spectrum has been well interpreted by introducing roundness around the triangle corners. Ag particles coated with a CdS film have been synthesized by employing the reversed micelle method. We have shown the first experimental observation of the optical nonlinear response for the single Ag nanoparticle coated with a CdS material, based on the optical Kerr effect due to an electronic nonlinearity, at room temperature.

ARPES and STS investigation of noble metal Shockley states: Confinement in vicinal Au(1 1 1) surfaces and self-organized nanostructures

Spectroscopic effects associated with the superperiodic surface structure have been observed in Au(1 1 1) vicinal surfaces and nanostructured systems. In the vicinal Au(23 23 21) surface, high resolution angle resolved photoemission spectroscopy shows the opening of several gaps in the surface band structure, whereas scanning tunneling spectroscopy reveals the energy dependence of the electronic density. These combined spectroscopic data allow to determine the reconstruction potential by deducing their first Fourier components. We also demonstrate that due to the peculiar growth on this Au vicinal surface, we can obtain a self-assembled superlattice of triangular Ag islands. The high ordering of the nanostructures leads to homogenous electronic properties.

Dissolution–recrystallization mechanism for the conversion of silver nanospheres to triangular nanoplates

A solution chemistry method for transforming polycrystalline Ag spherical particles into single crystalline triangular Ag nanoplates has been developed. The synthesis consists of three consecutive steps: (1) the synthesis of Ag nanospheres by NaBH 4 reduction of AgNO 3 in the presence of sodium citrate; (2) the conversion of citrate-stabilized Ag nanospheres into SDS (sodium dodecyl sulfate)-stabilized Ag nanospheres, and (3) the aging of the SDS-stabilized Ag nanospheres in 0.01 M NaCl solution. Our study indicates that the shape evolved through a Ag nanoparticle dissolution- and re-deposition process; and demonstrated the critical role of SDS in the process: SDS regulates the dynamics in the dissolved O 2/Cl − etching of the Ag nanospheres and the reduction of the released Ag + by citrate ions in the same solution. SDS also functions as a shape-directing agent to assimilate the Ag 0 atoms into single crystalline triangular Ag nanoplates. A model for the shape conversion is also proposed which provides the clue for the synthesis of anisotropic Ag nanoparticles with other shapes (rods, wires, cubes, etc.).

Tracking Single Molecular Diffusion on Glass Substrate Modified with Periodic Ag Nano-architecture

Diffusion of individual dye-labeled molecules in self-spreading lipid bilayer on glass substrate in aqueous solution was observed directly using total internal reflection fluorescence microscopy (TIRFM). The molecular diffusion was evaluated quantitatively by the mean square displacement (MSD) analysis for the trajectories of individual molecules. The mode of normal Brownian diffusion in lipid bilayer was changed in the presence of the periodic triangular Ag nanoparticles on the surface of the substrate. Suppressed diffusivity observed at the system with the triangular Ag nanoparticles was attributed to the confinement of the molecular motion in the micro-compartment surrounded by the Ag triangles.

Solution-Phase, Triangular Ag Nanotriangles Fabricated by Nanosphere Lithography

A novel method to produce solution-phase triangular silver nanoparticles is presented. Ag nanoparticles are prepared by nanosphere lithography and are subsequently released into solution. The resulting nanoparticles are asymmetrically functionalized to produce either single isolated nanoparticles or dimer pairs. The structural and optical properties of Ag nanoparticles have been characterized. Mie theory and the Discrete Dipole Approximation method (DDA) have been used to model and interpret the optical properties of the released Ag nanoparticles.

A Nanoscale Optical Biosensor: Real-Time Immunoassay in Physiological Buffer Enabled by Improved Nanoparticle Adhesion

The shift in the extinction maximum, λmax, of the localized surface plasmon resonance (LSPR) spectrum of triangular Ag nanoparticles (∼90 nm wide and 50 nm high) is used to probe the interaction between a surface-confined antigen, biotin (B), and a solution-phase antibody, anti-biotin (AB). Exposure of biotin-functionalized Ag nanotriangles to 7 × 10-7 M < [AB] < 7 × 10-6 M caused a ∼38 nm red-shift in the LSPR λmax. The experimental normalized response of the LSPR λmax shift, (ΔR/ΔRmax), versus [AB] was measured over the concentration range 7 × 10-10 M < [AB] < 7 × 10-6 M. Comparison of the experimental data with the theoretical normalized response for a 1:1 binding model yielded values for the saturation response, ΔRmax = 38.0 nm, the surface-confined thermodynamic binding constant, Ka,surf = 4.5 × 107 M-1, and the limit of detection (LOD) < 7 × 10-10 M. The experimental saturation response was interpreted in terms of a closest-packed structural model for the surface B−AB complex in which the long axis of AB, lAB = 15 nm, is oriented horizontally and the short axis, hAB = 4 nm is oriented vertically to the nanoparticle surface. This model yields a quantitative response for the saturation response, ΔRmax = 40.6 nm, in good agreement with experiment, ΔRmax = 38.0 nm. An atomic force microscopy (AFM) study supports this interpretation. In addition, major improvements in the LSPR nanobiosensor are reported. The LSPR nanobiosensor substrate was changed from glass to mica, and a surfactant, Triton X-100, was used in the nanosphere lithography fabrication procedure. These changes increased the adhesion of the Ag nanotriangles by a factor of 9 as determined by AFM normal force studies. The improved adhesion of Ag nanotriangles now enables the study of the B−AB immunoassay in a physiologically relevant fluid environment as well as in real-time. These results represent important new steps in the development of the LSPR nanosensor for applications in medical diagnostics, biomedical research, and environmental science.

A Highly Sensitive and Selective Surface-Enhanced Nanobiosensor

AbstractNanosphere lithography (NSL) derived triangular Ag nanoparticles were used to create an extremely sensitive and specific optical biological and chemical nanosensor. Using simple UV-vis spectroscopy, biotinylated surface-confined Ag nanoparticles were used to detect streptavidin down to one picomolar concentrations. The system was tested for nonspecific binding interactions with bovine serum albumin and was found to display virtually no adverse results. The extremely sensitive and selective response of the Ag nanoparticle sensor indicates an exciting use for biological and chemical sensing.