The silica@Ag-Cu alloy core-shell composite colloids have been successfully synthesized by an electroless plating approach to explore the possibility of modifying the plasmon resonance at the nanoshell surface by varying the metal nanoshell composition for the first time. The surface plasmon resonance of the composite colloids increases in intensity and shifts towards longer, then shorter wavelengths as the Cu/Ag ratio in the alloy shell is increased. The variations in intensity of the surface plasmon resonance with the Cu/Ag ratio obviously affect the Raman bands of the silica colloid core. The report here may supply a new technique to effectively modify the surface plasmon resonance. 相似文献
In this study, we first numerically investigate the appearance and properties of multiple Fano resonances in two-dimensional hexagonal non-close-packed arrays of symmetric metallic shells. The coexistence of broad sphere-like plasmon modes formed from the near-field interaction between the individual sphere plasmons and substantially narrower void plasmon modes supported by the inner surface of the individual shell resonant over the same range of energies can produce such Fano resonances. In particular, void and sphere-like plasmon modes of different angular momentum could directly interact without the need of symmetry breaking in the structure. A cost-effective colloidal crystal templating method is utilized to prepare the arrays of the metallic shells with small openings. The effect of the symmetry breaking on the Fano resonances in metallic cup arrays is experimentally and numerically investigated. Further tunability on the Fano resonances is gained by changing the size of the inner dielectric core, hence changing the moment of the void plasmon modes and consequently the resonance frequency. By adopting the polymer dielectric core with gain materials, our study may offer realizable experimental opportunities towards subwavelength low threshold plasmonic lasing. 相似文献
Frequency shifts, radiative decay rates, the Ohmic loss contribution to the nonradiative decay rates, fluorescence yield, and photobleaching of a two-level atom radiating anywhere inside or outside a complex spherical nanoshell, i.e., a stratified sphere consisting of alternating silica and gold concentric spherical shells, are studied. The changes in the spectroscopic properties of an atom interacting with complex nanoshells are significantly enhanced, often more than two orders of magnitude, compared to the same atom interacting with a homogeneous dielectric sphere. The detected fluorescence intensity can be enhanced by 5 or more orders of magnitude. The changes strongly depend on the nanoshell parameters and the atom position. When an atom approaches a metal shell, decay rates are strongly enhanced yet fluorescence yield exhibits a well-known quenching. Rather contra-intuitively, the Ohmic loss contribution to the nonradiative decay rates for an atomic dipole within the silica core of larger nanoshells may be decreasing when the silica core–inner gold shell interface is approached. The quasi-static result that the radial frequency shift in a close proximity of a spherical shell interface is approximately twice as large as the tangential frequency shift appears to apply also for complex nanoshells. Significantly modified spectroscopic properties (see computer program available at http://www.wave-scattering.com) can be observed in a broad band comprising all (nonresonant) optical and near-infrared wavelengths. 相似文献
In this paper, an improved surface seeding and shell growth technique was developed to prepare Ag-polystyrene core shell composite. Polyethyleneimine (PEI) could act as the linker between Ag ions (Ag nanoparticles) and polystyrene (PS) colloids and the reducing agent in the formation of Ag nanoparticles. Due to the multi-functional characteristic of PEI, Ag seeds formed in-situ and were immobilized on the surface of PEI-modified PS colloids and no free Ag clusters coexist with the Ag “seeding” PS colloids in the system. Then, the additional agents could be added into the resulting dispersions straightly to produce a thick Ag nanoshell. The Ag nanoshell with controllable thickness was formed on the surface of PS by the “one-pot” surface seeding and shell growth method. The Ag-coverage increased gradually with the increasing of mass ratio of AgNO3/PS. The optical properties of the Ag-PS colloids could be tailored by changing the coverage of Ag. 相似文献
We apply the plasmon hybridization method to a nanoshell with a nonconcentric (offset) core and investigate how the energy and excitation cross section of the plasmon modes depend on the offset distance D of the inner core from the nanoshell center. A two-center spherical coordinate system is used for mathematical convenience. It is shown that the presence of an offset core shifts the plasmon energies and makes higher multipolar nanoshell plasmons dipole active and visible in the optical spectrum. The dependence of the plasmon shifts on D is weak for small offsets but strong for large offsets. The polarization dependence of the optical absorption spectra is found to be relatively weak. The electromagnetic field enhancements are shown to be much larger than on a concentric nanoshell. The results agree very well with results from finite difference time domain simulations. 相似文献
The replacement reaction between hydrophobized Ag nanoparticles and hydrophobized AuCl4- in toluene has been examined in detail. The conclusions obtained under our experimental conditions are different from those reported in the literature in three aspects: (1) a detectable contraction of the Ag nanoparticle sacrificial templates during the course of the reaction is shown; (2) the deposition of Au on the shrunken Ag templates inhibits further Ag oxidation, resulting in the formation of core-shell Ag-Au nanoparticles instead of Au nanoshells; and (3) the significant red-shift in the surface plasmon resonance (SPR) band is more of a consequence of shape and chemical composition changes rather than as an indication of Au nanoshell formation. Solvent and temperature are influential environmental factors that determine the structure and composition of nanoparticles formed by the replacement reaction. 相似文献
We report the plasmonic enhancement of the photocatalytic properties of Pt/n-Si/Ag photodiode photocatalysts using Au/Ag core/shell nanorods. We show that Au/Ag core/shell nanorods can be synthesized with tunable plasmon resonance frequencies and then conjugated onto Pt/n-Si/Ag photodiodes using well-defined chemistry. Photocatalytic studies showed that the conjugation with Au/Ag core/shell nanorods can significantly enhance the photocatalytic activity by more than a factor of 3. Spectral dependence studies further revealed that the photocatalytic enhancement is strongly correlated with the plasmonic absorption spectra of the Au/Ag core/shell nanorods, unambiguously demonstrating the plasmonic enhancement effect. 相似文献
Ag-TiO(2) films exhibiting multicolor photochromism were prepared by photoelectrochemical reduction of Ag(+) to Ag nanoparticles in nanoporous TiO(2) films under UV light. Color of the Ag-TiO(2) film, initially brownish-gray, changes under a colored visible light to the color of the light and reverts to brownish-gray under UV light. Their chromogenic properties were improved by simultaneous irradiation for Ag deposition with UV and blue lights to suppress the formation of anisotropic Ag particles. Nonvolatilization of a color image was also achieved by removing Ag(+) that was generated during the irradiation with a colored light. Once nonvolatilized, the image can be reproduced by UV light, even after the image is discolored under white light. This new effect evidenced that nanopores in the TiO(2) film determine the resonance wavelengths of the Ag particles, as their molds. In addition, solvatochromic behavior of the Ag-TiO(2) film proved that nanospaces left around the Ag nanoparticles affect the resonance wavelengths of the Ag particles. 相似文献
The Fano-Anderson model for a discrete state embedded within a continuum is revisited within the context of excitation and decay processes which lead to some manifestations of Fano lineshape profiles. The phenomenon of resonance tunneling between an STM tip and a metal surface upon which there are isolated adsorbed atoms is discussed and the relationship between the spectroscopic signature of such systems and that of the Fano profile is taken up. Recent experimental studies of Kondo systems of magnetic adsorbates such as Co and Ce adsorbed on noble metal (111) surfaces have motivated this work. 相似文献
The effects of permeability and permittivity of the magnetic nanorods filled in composite films have been studied in the broadband radio-frequency range from 0.5 to 10 GHz on a microstrip line. The transmission power absorption of the composite film on a microstrip line was simulated using 3D FEM HFSS program. The model of microstrip line was designed based on IEC standard (IEC 62333-2). The permeability of composite film with magnetic nanorods could be controlled by the aspect ratio of nanorods. The ferromagnetic resonance frequency and the relative complex permeability with the change of aspect ratio were calculated by the Landau–Lifshitz–Gilbert equation. Given the bulk magnetization of 5 kG, the power loss frequency region has exhibited the 2.5–7 GHz broadband frequency by mixing of nanorods with various aspect ratios from 2 to 10. The permittivity effects have been evaluated by changing the real part of permittivity with a fixed imaginary part value and vice versa. The power losses were increased with the proportional to the imaginary part of permittivity and did not show any significant change with the increment of the real part of permittivity. The conduction electromagnetic noise in near field can be suppressed by controlling complex permeability with various aspect ratios of the magnetic nanorods in the composite.
Noble metal nanostructures have been the research focus for many decades because of their real or poten-tial applications, such as catalysis, photography, optics, electronics, optoelectronics, information storage, bio-logical and chemical sensing, surface… 相似文献
The in vitro uptake of core-shell nanoparticles encapsulated in a bio-macromolecular nanoshell assembled from multilayered polyelectrolytes was studied. Sulfate modified fluorescent polystyrene nanobeads (diameter 200 nm) were used as a solid core upon which charged multilayers of poly-l-lysine, chitosan, and heparin sulfate are electrostatically deposited utilizing a layer-by-layer (LbL) self-assembly process. The nanoshell composed of the multilayered polyelectrolytes was modified with poly(ethylene glycol) (PEG) of varying molecular weights (either MW 2000, 5000, or 20 000 Da) to form a hydrophilic and long-circulating nanoparticle. The assembly of the nanoshell was confirmed by zeta potential, transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). The reversal in charge upon the deposition of alternating polyelectrolytes was observed by zeta potential measurements. The nanometer thickness of the nanoshell was confirmed by TEM. The presence of the (C-C-O)(n)() backbone in PEG at the surface of the nanoshell was confirmed by the increase in (C-O,N) peak area concentrations compared to (C-C) peak area, and these results were gathered from XPS. In vitro studies between suspension macrophages and core-shell nanoparticles were performed to determine how the hydrophilicity and the charge on the nanoshell can promote or reduce uptake. Results showed that after 24 h uptake was decreased 3-fold when PEGs of 2000 and 20 000 Da were chemisorbed to the nanoshell, as opposed to a nanoshell with either a positive or highly negative charge. Confocal microscopy aided in verifying that core-shell nanoparticles were internalized within the cell cytoplasm and were not attached to the cell surface. Protein adhesion studies with bovine serum albumin were performed to determine the relationship between surface charge and opsonization of core-shell nanoparticles. It was found that a hydrophilic surface with a low negative charge reduced protein adsorption and uptake. The in vitro uptake of macrophages and protein adsorption onto core-shell nanoparticles formed using layer-by-layer assembly has not been previously studied. 相似文献
This paper explores Fano resonances due to non-adiabatic coupling of vibrational modes and the electron continuum in dipole-bound anions. We adopt a simple one-electron model consisting of a point dipole and an auxiliary potential to represent the electron interaction with the neutral core. Nuclear motion is added by assuming that harmonic vibrations modulate the dipole moment. When the model is parameterized to simulate key features of the water tetramer anion, the resultant photodetachment lineshape closely resembles that observed experimentally and analyzed as a Fano resonance with a parameter q close to -1. Other parameterizations are explored for the model and it is found that large changes in the auxiliary potential are required to change the sign of q. This is consistent with the experimental finding that q is negative for all water cluster sizes studied. 相似文献