Surface Plasmon Resonance Frequency Research Articles

Colloidal Synthesis of Silver Nanoprisms in Aqueous Medium: Influence of Chemical Compounds in UV/Vis Absorption Spectra

In this work we explore the influence of the factors that affect the formation of silver nanoprisms (AgNPs) with distinct size and size distribution as well as the most intense absorption peak shift. Box-Behnken design analysis was applied to optimize the production of silver nanoprism via colloidal synthesis. The analysis of the responses was based on the nanoprisms plasmon peak wavelength related to in-plane dipole (tunable band) at λmax. ≥ 420 nm. The obtained results indicate that Silver ion is the main variable for the tuning of the size and the Localized Surface Plasmon Resonance (LSPR) frequency. By using the Box-Behnken design it was possible to synthesize nanoparticles with a predictable size and to establish a rigorous control of the plasmon frequency at the range of 600 up to 800 nm.

Effect of Morphology on Ultrafast Carrier Dynamics in Asymmetric Gold–Iron Oxide Plasmonic Heterodimers

Understanding how nanoscale interfaces affect electrical and optical properties of multifunctional nanocrystal heterostructures is of paramount importance for their technological application. In this context, we investigated the ultrafast carrier dynamics of rodlike gold–iron oxide nanocrystal heterodimers, in a spectral region close to the surface plasmon resonance frequency, by means of broad-band transient absorption spectroscopy. We found that the electron–phonon relaxation time is independent of the morphology of the iron oxide domain. Moreover, we revealed a transient shift in the surface plasmon resonance frequency, which can be related to charge transfer at the interface between gold and iron oxide.

Near-Field Interactions between Metal Nanoparticle Surface Plasmons and Molecular Excitons in Thin-Films. Part I: Absorption

In this and the following paper (parts I and II, respectively), we systematically study the interactions between surface plasmons of metal nanoparticles (NPs) with excitons in thin-films of organic media. In an effort to exclusively probe near-field interactions, we utilize spherical Ag NPs in a size-regime where far-field light scattering is negligibly small compared to absorption. In part I, we discuss the effect of the presence of these Ag NPs on the absorption of the embedding medium by means of experiment, numerical simulations, and analytical calculations, all shown to be in good agreement. We observe absorption enhancement in the embedding medium due to the Ag NPs with a strong dependence on the medium permittivity, the spectral position relative to the surface plasmon resonance frequency, and the thickness of the organic layer. By introducing a low-index spacer layer between the NPs and the organic medium, this absorption enhancement is experimentally confirmed to be a near-field effect. In part II, we probe the impact of the Ag NPs on the emission of organic molecules by time-resolved and steady-state photoluminescence measurements.

Surface-plasmon enhanced optical activity in two-dimensional metal chiral networks

We investigated the optical properties of a novel chiral metamaterial; two-dimensional metal chiral networks formed from metal ribbons deposited on a dielectric substrate. For zeroth-order transmitted light, sharp optical resonances were observed at spectral positions, which are determined by the surface plasmon resonance frequencies of the periodic metal structures. The experimental results are in excellent agreement with numerical calculations.

Sandwich-like Cu1.94S–ZnS–Cu1.94S nanoheterostructure: structure, formation mechanism and localized surface plasmon resonance behavior

In this communication, a thermolysis route is developed to synthesize novel Cu1.94S–ZnS–Cu1.94S nanoheterostructures with interesting sandwich-like architectures, taking Cu1.94S nanoplates as precursors. Evidently, the trimeric nanostructure is formed by a three-stage process, which includes the Zn-oleate induced assembling of Cu1.94S nanoplate couples, the heteronucleation and growth of a ZnS layer between two Cu1.94S plates dominated by interfacial diffusion, and the catalyst assisted axial growth of ZnS nanorod following the solution–liquid–solid mechanism. With epitaxial growth of ZnS nanocrystal between two Cu1.94S nanoplates, the localized surface plasmon resonance frequency of Cu1.94S shifts from 1875 to 1323 nm, indicating that this new material is potentially applicable as a light absorbing agent in laser photothermal therapy. The reported growth mechanism may provide new strategies for designing and fabricating various technologically important polymeric nanoheterostructures.

Infrared-to-visible upconversion emission in Er3+ doped TeO2-WO3-Bi2O3 glasses with silver nanoparticles

The influence of silver nanoparticles (NPs) on the frequency upconversion luminescence in Er3+ doped TeO2-WO3-Bi2O3 glasses is reported. The effect of the NPs on the Er3+ luminescence was controlled by appropriate heat-treatment of the samples. Enhancement up to 700% was obtained for the upconverted emissions at 527, 550, and 660 nm, when a laser at 980 nm is used for excitation. Since the laser frequency is far from the NPs surface plasmon resonance frequency, the luminescence enhancement is attributed to the local field increase in the proximity of the NPs and not to energy transfer from the NPs to the emitters as is usually reported. This is the first time that the effect is investigated for tellurite-tungstate-bismutate glasses and the enhancement observed is the largest reported for a tellurium oxide based glass.

Controlled Assembly and Plasmonic Properties of Asymmetric Core–Satellite Nanoassemblies

The assembly of noble metal nanoparticles offers an appealing means to control and enhance the plasmonic properties of nanostructures. However, making nanoassemblies with easily modifiable gap distances with high efficiency has been challenging. Here, we report a novel strategy to assemble gold nanoparticles (AuNPs) into Janus-type asymmetric core-satellite nanostructures. Markedly different desorption efficiency between large and small AuNPs in ethanol allows us to prepare the asymmetric core-satellite nanoassemblies in a dispersed colloidal state with near 100% purity. The resulting nanoassemblies have well-defined structures in which a core AuNP (51 nm) is covered by an average of 13 ± 3 satellite AuNPs (13 nm) with part of the core surfaces left unoccupied. Strong surface plasmon coupling is observed from these nanoassemblies as a result of the close proximity between the core and the satellites, which appears significantly red-shifted from the surface plasmon resonance frequencies of the constituting nanoparticles. The dependence of the surface plasmon coupling on a gap distance of less than 3 nm is systematically investigated by varying the length of the alkanedithiol linkers. The asymmetric core-satellite nanoassemblies also serve as an excellent surface-enhanced Raman scattering substrate with an enhancement factor of ~10(6). Finally, we demonstrate that the presented assembly method is extendible to the preparation of compositionally heterogeneous core-satellite nanoassemblies.

Influence of ion irradiation on the morphology, structure, and optical properties of gold nanoparticles synthesized in SiO2 and Al2O3 dielectric matrices

Irradiation of fused quartz (SiO2) and sapphire (Al2O3) by Ne+ and F+ ions with medium energies and their subsequent annealing enables us to control the intensity and frequency of surface plasmon resonance in Au nanoparticles (NPs) synthesized in oxide matrices. The control process can be implemented because NPs dissolve during irradiation and undergo partial reconstruction at annealing. The degree of reconstruction depends on the matrix material and the type and dose of ions. It has been found that the difference in the results obtained by means of irradiation with ions with similar masses is substantially affected by the chemical nature of the ions. The composition, morphology, and structure of the unirradiated and irradiated layers are investigated by transmission electron microscopy, X-ray photoelectron spectroscopy, and spectroscopic ellipsometry.

Investigation of surface plasmon resonance in super-period gold nanoslit arrays

Surface plasmon resonance in super-period metal nanoslits can be observed in the first order diffraction as well in the zeroth order transmission. In this paper, surface plasmon resonance modes in various super-period gold nanoslit arrays are investigated. It is found that the surface plasmon resonance frequencies are determined by the small period of the nanoslits in super-period nanoslits. The number of nanoslits in the unit cell super-period and the nanoslit width do not control the surface plasmon resonance frequencies. It is also found that the resonance wavelength observed in the first order diffraction reveals more accurate the real surface plasmon resonance wavelength in the metal super-period nanoslit array device.

Boosting the Figure-Of-Merit of LSPR-Based Refractive Index Sensing by Phase-Sensitive Measurements

Localized surface plasmon resonances possess very interesting properties for a wide variety of sensing applications. In many of the existing applications, only the intensity of the reflected or transmitted signals is taken into account, while the phase information is ignored. At the center frequency of a (localized) surface plasmon resonance, the electron cloud makes the transition between in- and out-of-phase oscillation with respect to the incident wave. Here we show that this information can experimentally be extracted by performing phase-sensitive measurements, which result in linewidths that are almost 1 order of magnitude smaller than those for intensity based measurements. As this phase change is an intrinsic property of a plasmon resonance, this opens up many possibilities for boosting the figure-of-merit (FOM) of refractive index sensing by taking into account the phase of the plasmon resonance. We experimentally investigated this for two model systems: randomly distributed gold nanodisks and gold nanorings on top of a continuous gold layer and a dielectric spacer and observed FOM values up to 8.3 and 16.5 for the respective nanoparticles.

Naturally grown Ag nanoparticles on quartz substrates as SERS substrate excited by a 488 nm diode laser system for SERDS

A silver nanoparticle ensemble was prepared under ultrahigh vacuum (UHV) conditions by Volmer–Weber growth on a quartz substrate for surface-enhanced Raman scattering (SERS) investigations of pyrene molecules. To tune the surface plasmon resonance frequency in the vicinity of the excitation wavelength of 488 nm of the diode laser, the morphology of the silver nanoparticles was optimized. The substrates were mounted in a flow-through cell as part of the optical Raman set-up. A microsystem diode laser generates two slightly different emission wavelengths (λ=487.61 nm and λ=487.91 nm) with a spectral width <10 pm and an optical power of 20 mW, i.e. SERS experiments are possible but also shifted excitation Raman difference spectroscopy (SERDS) can be carried out. For trace analysis of pyrene in water we demonstrate SERS/SERDS experiments which lead to a limit of detection of 2 nmol/l for pyrene. These results suggest that with silver nanoparticle ensembles excited at their plasmon resonance at 488 nm combined SERS/SERDS measurements can be effectively performed for in-situ trace analysis of pollutant chemicals in water.

Laser-assisted synthesis of Au-Ag alloy nanoparticles with tunable surface plasmon resonance frequency

Here we present our experimental results in synthesizing Au-Ag bimetallic nanoalloys with tunable localized surface plasmon resonance frequency through nanosecond laser-induced heating in the presence of polyvinyl alcohol as a reducing and capping agent via three different procedures: (i) Mixture of HAuCl4 and AgNO3 precursors, (ii) Mixture of Au nanoparticles (NPs) and AgNO3 precursor and (iii) Mixture of both Au and Ag NPs. Presence of single absorption band and direct dependence of the Au/Ag molar ratio to the shift of the absorption peak and lack of core-shell structure in Transmission Electron Microscope images confirms that the formed NPs are homogeneous alloys.

Electrodynamic coupling in regular arrays of gold nanocylinders

We report far-field experimental optical extinction spectra of linear chains of gold nanocylinders with interparticle separations close to the particle's surface plasmon resonance (SPR) wavelength λSPR. The spectra reveal non-monotonic shift of the SPR peak position with increase in the distance d. The non-monotonic λSPR(d) dependence is rationalized considering electromagnetic coupling between the particles in the dipole approximation. Simple expressions for the modified SPR frequencies are obtained using the dipole scattered field and taking into account both the retardation and phase lag effects.

Synthesis and Patterning of Polymer Matrix Nanocomposites Using Femtosecond Laser-assisted Processing

ABSTRACTWe describe a scalable synthesis process for the production and patterning of polymer matrix nanocomposites (PMNCs) using femtosecond laser irradiation to target specific functional behaviors. A modified, in situ chemical vapor deposition (CVD), nanoinfusion process was used to nucleate and grow nanoparticles in the bulk of an optically transparent polytetrafluoroethylene-co-hexafluoropropylene (FEP) polymer matrix. Metallic nanoparticles synthesized with this process can have a strong optical absorption at their surface plasmon resonance (SPR) frequency and we have utilized this property to selectively irradiate and pattern nanocomposites via femtosecond, photothermal heating. If the nanoparticle environment includes species used for chemical vapor deposition, the heat causes a localized decomposition of the precursor species in the immediate vicinity of the nanoparticle leading to a variety of core-shell nanostructures. Using this processing scheme, we have grown shells of tungsten oxide around silver nanoparticles within the polymer matrix resulting in a 40 nm red shift in the SPR of the silver nanoparticles in regions of the material exposed to femtosecond laser pulses. This process has also been adapted to polymers containing tungsten oxide nanoparticles so that the photocatalytic behavior of the particles could be used to the decompose precursor species in the immediate vicinity of the irradiated nanoparticles. These results demonstrate that, by using optical masks and laser processing, it is possible to synthesize nanocomposites with a high degree of control over the location, composition, size, and distribution of nanoparticles within a polymer matrix resulting in patterned materials with tailored electrical, optical, and photocatalytic properties.

Local Dipole Field Enhancement Along the Surface of Metal-Dielectric Au/Pd Core-Shell Nanostructure

The nanostructure of bimetallic Au/Pd particles was fabricated to investigate their surface plasmon (SP) dynamics and local field factor. The SP dynamics was detected according to the structure, electric dipole and multipole electrical quadrupole moment. It was found that the symmetric coupling red shifts decreased obviously with the increase of the shell thickness and the nanoparticle size, and the absorption efficiencies of the nanostructure depended on the SP resonance frequency. The waves of surface plasmon Pd/Au are achieved by gradient of electrons density between interface and shell layer. The dipole couple and electrical quadrupole moment make the plasmonic anisotropy related to transition of electron energy band. The FWHM under collective plasmonic enhancement has been found to enlarge with rise of radius ratio.Moreover, the SP resonance and the local field were measured with annular limited optical distribution in terms of dipole resonance mode and resonance frequency. The resonance scattering has been changed inspite of the Au/Pd deformation and the collective plasmon enhancement. Besides, the single particle in Z direction went up with the particle dimension. The solid structures of the Au/Pd Core/shell nanoparticles were measured by TEM and EDS

Synthesis of Monodisperse Au, Ag, and Au–Ag Alloy Nanoparticles with Tunable Size and Surface Plasmon Resonance Frequency

A facile method of preparing Au−Ag alloy nanoparticles in organic solvent, with high monodispersity and controlled size from 6 to 13 nm diameter, is described. The localized surface plasmon resonance frequency and size of alloy nanoparticles were controlled by varying both the precursor ratio and surfactant composition. Thus, the plasmon resonance frequency could be tuned by varying composition with little change in particle size.

Numerical simulations on longitudinal surface plasmons of coupled gold nanorods

We analyze numerically the localized surface plasmon resonance (LSPR) frequencies of coupled metal nanorods using discrete dipole approximation (DDA) and finite element method (FEM). The two configurations of identical nanorods are considered: end-to-end and side-by-side. Dependence of LSPR frequencies on the interparticle distance is determined by DDA. The latter for the case of large separations agrees with the result of approximate analytical method developed earlier for single metal nanorods. Distributions of electric near-fields of nanorods as well as enhancement factors at hot spots for both configurations are calculated by FEM.

Compound Hertzian chain model for copper–carbon nanocomposites' absorption spectrum

The infrared range optical absorption mechanism of carbon–copper composite thin layer coated on the diamond-like carbon buffer layer has been investigated. By consideration of weak interactions between copper nanoparticles in their network, optical absorption is modelled using their coherent dipole behaviour induced by the electromagnetic radiation. The copper nanoparticles in the bulk of carbon are assumed as a chain of plasmonic dipoles, which have coupling resonance. Considering nearest neighbour interactions for this metallic nanoparticles, surface plasmon resonance frequency (ω0) and coupled plasmon resonance frequency (ω1) have been computed. The damping rate against wavelength is derived, which leads to the derivation of the optical absorption spectrum in terms of ω0 and ω1. The dependency of the absorption peaks to the particle size and the particle mean spacing is also investigated. The absorption spectrum is measured for different Cu–C thin films with various Cu particle size and spacing. The experimental results of absorption are compared with the obtained analytical ones.

Switchable Bactericidal Effects from Novel Silica-Coated Silver Nanoparticles Mediated by Light Irradiation

Here we report on the triggering of antibacterial activity by a new type of silver nanoparticle coated with porous silica, Ag@silica, irradiated at their surface plasmon resonant frequency. The nanoparticles are able to bind readily to the surface of bacterial cells, although this does not affect bacterial growth since the silica shell largely attenuates the intrinsic toxicity of silver. However, upon simultaneous exposure to light corresponding to the absorption band of the nanoparticles, bacterial death is enhanced selectively on the irradiated zone. Because of the low power density used for the treatments, we discard thermal effects as the cause of cell killing. Instead, we propose that the increase in toxicity is due to the enhanced electromagnetic field in the proximity of the nanoparticles, which indirectly, most likely through induced photochemical reactions, is able to cause cell death.

Magnetically tunable surface plasmon resonance based on a composite consisting of noble metal nanoparticles and a ferromagnetic thin film

We demonstrate magnetically tunable surface plasmon resonance based on a composite consisting of noble metal nanoparticles and ferromagnetic thin film. We found that both the frequency and linewidth of the localized surface plasmon resonance can be manipulated by applying an external magnetic field. The underlying mechanism is attributed to the variation of the dielectric constant in the ferromagnetic thin film resulting from the change of magnetization. Our result shown here paves an alternative route for manipulation of the characteristics of the surface plasmon resonance, which may serve as a new design concept for the development of magneto-optical devices.