Au/Ag Bimetallic Nanocomposites as a Highly Sensitive Plasmonic Material (original) (raw)
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Plasmonic properties of Au-Ag nanoparticles: Distinctiveness of metal arrangements by optical study
Journal of Applied Physics, 2014
The core-shell arrangement of binary compound plasmonic nanoparticles (NPs) is usually verified by plasmonic extinction spectra, since microscopy-based methods cannot provide analysis of many NPs. Here, we discuss possible scenarios of different metal arrangements: (i) core-shell model, (ii) bimetallic model, and (iii) mixture of pure metal NPs. The possibility of distinguishing individual cases is discussed in accordance with numerical simulations and an alternative characterization is suggested. V
Plasmonic effects of au/ag bimetallic multispiked nanoparticles for photovoltaic applications
ACS applied materials & interfaces, 2014
In recent years, there has been considerable interest in the use of plasmons, that is, free electron oscillations in conductors, to boost the performance of both organic and inorganic thin film solar cells. This has been driven by the possibility of employing thin active layers in solar cells in order to reduce materials costs, and is enabled by significant advances in fabrication technology. The ability of surface plasmons in metallic nanostructures to guide and confine light in the nanometer scale has opened up new design possibilities for solar cell devices. Here, we report the synthesis and characterization of highly monodisperse, reasonably stable, multipode Au/Ag bimetallic nanostructures using an inorganic additive as a ligand for photovoltaic applications. A promising surface enhanced Raman scattering (SERS) effect has been observed for the synthesized bimetallic Au/Ag multispiked nanoparticles, which compare favorably well with their Au and Ag spherical nanoparticle counter...
Physical Review B, 2010
The discrete dipole approximation method is used to simulate the optical response of ultrafine Au nanoparticles ͑NPs͒ with a diameter of 5 nm assembled in a planar hexagonal array. Similar calculations performed for Ag NPs arrays are also presented for comparison. For both cases, the absorption spectra are calculated for various incidence angles and interparticle distances to reveal the optical anisotropy related to the geometry of the system through the splitting of the surface-plasmon resonance ͑SPR͒ into the transverse and longitudinal modes. This effect usually results in the emergence of two SPR bands in the absorption spectrum as observed for Ag NPs arrays when the border-to-border interparticle distance becomes smaller than around one particle radius. Conversely, such a splitting is shown to be undistinguishable for Au NPs arrays whatever the interparticle distance and the incidence angle are. The different behaviors pointed out between Au and Ag NPs arrays are ascribed to the intrinsic dielectric properties of these two metals.
Unconventional Optical Response in Engineered Au-Ag Nanostructures
2019
This article describes the optical properties of nanostructures composed of silver particles embedded into a gold matrix. In previous studies these materials were shown to exhibit temperature dependent transitions to a highly conductive and strongly diamagnetic state. Here we describe the anomalous optical properties of these nanostructures. Most notably, these materials fail to obey Mie theory and exhibit an unconventional resonance with a maximum at about 4 eV, while the usual gold and silver localized surface plasmon resonances are suppressed. This effect implies a significant deviation from the bulk dielectric functions of gold and silver. We further resolved this resonance into its absorbance and scattering sub-parts. It is observed that the resonance is largely comprised of scattering, with negligible losses even at ultraviolet frequencies.
Small, 2015
Colloidal metal nanocrystals with strong, stable, and tunable localized surface plasmon resonances (SPRs) could be useful in a corrosive environment for many applications including field-enhanced spectroscopies, plasmon-mediated catalysis, etc. Here, a new synthetic strategy is reported that enables the epitaxial growth of a homogeneously alloyed AuAg shell on Au nanorod seeds, circumventing the phase segregation of Au and Ag encountered in conventional synthesis. The resulting core-shell structured bimetallic nanorods (AuNR@AuAg) have well-mixed Au and Ag atoms in their shell without discernible domains. This degree of mixing allows AuNR@AuAg to combine the high stability of Au with the superior plasmonic activity of Ag, thus outperforming seemingly similar nanostructures with monometallic shells (e.g., Ag-coated Au NRs (AuNR@Ag) and Au-coated Au NRs (AuNR@Au)). AuNR@AuAg is comparable to AuNR@Ag in plasmonic activity, but that it is markedly more stable towards oxidative treatment. Specifically, AuNR@AuAg and AuNR@Ag exhibit similarly strong signals in surface-enhanced Raman spectroscopy (SERS) that are some 30-fold higher than that of AuNR@Au. When incubated with a H2O2 solution (0.5 M), the plasmonic activity of AuNR@Ag immediately and severely decayed, whereas AuNR@AuAg retained its activity intact. Moreover, the longitudinal SPR frequency of AuNR@AuAg can be tuned throughout the red wavelengths (~620-690 nm) by controlling the thickness of the AuAg alloy shell. Our synthetic strategy is versatile to fabricate AuAg alloyed shells on different shaped Au, with prospects for new possibilities in the synthesis and application of plasmonic nanocrystals.
Hybridization of localized surface plasmon resonance-based Au–Ag nanoparticles
Biomedical Microdevices, 2008
The hybrid Au-Ag triangular nanoparticles were proposed for the purpose of biosensing. To construct the nanoparticles, an Au thin film was deposited on top of the Ag nanoparticles supported with glass substrate. The hybrid nanoparticles can prevent oxidation of the pure Ag nanoparticles due to the Au protective layer caped on the Ag nanoparticles. The hybrid nanoparticles were designed using finite-difference and time-domain algorithm. Extinction spectra of the hybrid nanoparticles excited by visible light beam with plane wave were calculated, and the corresponding electric fields at peak position of the extinction spectra were expressed also. It is clear that the hybrid nanoparticles can excite the localized surface plasmon resonance wave which can be used to detect biomolecules. As an application example, we presented relevant detection results by means of using protein A to covalently link surface of the hybrid nanoparticles. Refractive index sensitivity of the hybrid nanoparticles was derived through both computational numerical calculation and experimental detection. Both the calculated and the experimental extinction spectra show that the hybrid Au-Ag nanoparticles are useful for detecting the biomolecules.
The European Physical Journal B - Condensed Matter, 2003
Nanocrystalline Au and Ag in multilayer thin film form with Au/Ag/Au structure were prepared by high pressure (∼40 Pa) d.c. sputtering techniques. The Ag concentrations in AgxAu1−x films were changed from x = 0 to 1. These multilayer films with varying Ag concentration showed significant changes in microstructures obtained from TEM and XRD analyses. The optical absorption spectra of these multilayer films showed a single plasmon band confirming the formation of Au-Ag alloy. We ascribe this alloying to the interfacial reactions in nanophase limited at the Au-Ag interface. The red-shift and broadening of the plasmon bands with the increase in silver concentration could be associated to the increase in size of the nanoparticles and its distribution. The observed red shift in the plasmon band may be associated with the change in electronic structure at the Au-Ag interface due to configuration mixing of the atomic energy levels of Au and Ag.
Configuring Au and Ag nanorods for sensing applications
Journal of the Optical Society of America B, 2011
We have studied optimum configurations of Au and Ag nanorods for optical sensing applications. From the analysis of the resonance condition by means of the quasistatic approximation, it was found that sensitivity is controlled by two main factors: the aspect ratio of the nanorods and their composition (the metal's bulk plasma wavelength), and it depends linearly on both. The finding was confirmed quantitatively using T-matrix calculations, even for particles with a radius of 40 nm, where the quasistatic approximation is no longer valid. For ease of detection, the intensity of the surface plasmon resonance band of the nanostructures was included along with its full-width at half-maximum in the correction factor C, which on multiplying with the sensitivity (Δλ SPR =Δn m ) gives a figure of merit. It has been demonstrated that the metal nanorods, especially the larger ones, have better optical sensitivity than the nanostructures of nanobox-or nanoshell-like geometries, which have been reported to be the best optical sensors for these metals.
J. Phys. Chem. C 2020, 124, 22, 12081–12094, 2020
Bimetallic plasmonic nanoparticles enable tuning of the optical response and chemical stability by variation of the composition. The present numerical simulation study compares Ag−Au alloy, Ag@Au core−shell, and Au@Ag core−shell bimetallic plasmonic nanoparticles of both spherical and anisotropic (nanotriangle and nanorods) shapes. By studying both spherical and anisotropic (with LSPR in the near-infrared region) shapes, cases with and without interband transitions of Au can be decoupled. Explicit comparisons are facilitated by numerical models supported by careful validation and examination of optical constants of Au−Ag alloys reported in the literature. Although both Au−Ag core−shell and alloy nanoparticles exhibit an intermediary optical response between that of pure Ag and Au nanoparticles, there are noticeable differences in the spectral characteristics. Also, the effect of the bimetallic constitution in anisotropic nanoparticles is starkly different from that in spherical nanoparticles due to the absence of Au interband transitions in the former case. In general, the improved chemical stability of Ag nanoparticles by incorporation of Au comes with a cost of reduction in plasmonic enhancement, also applicable to anisotropic nanoparticles with a weaker effect. A photothermal heat transfer study confirms that increased absorption by the incorporation of Au in spherical Ag nanoparticles also results in an increased steady-state temperature. On the other hand, anisotropic nanoparticles are inherently better absorbers and hence better photothermal sources, and their photothermal properties are apparently not strongly affected by the incorporation of one metal in the other. This study of the optical/spectral and photothermal characteristics of bimetallic Au−Ag alloy versus core−shell nanoparticles provides detailed physical insight for development of new taylor-made plasmonic nanostructures.
Enhanced plasmonic behavior of bimetallic (Ag-Au) multilayered spheres
Nanoscale Research Letters, 2011
In this article we study the plasmonic behavior of some stable, highly biocompatible bimetallic metal-dielectricmetal (MDM) and double concentric nanoshell (DCN) structures. By simply switching the material of the inner structure from Au to Ag, the intensity of their surface plasmon resonance could be increased in the optical transparency region of the human tissues up to 20 and 60 percent for the MDM and DCN, respectively, while the biocompatibility is retained. The obtained results indicate that these novel structures could be highly suitable for surface enhanced Raman scattering and photothermal cancer therapy.