Multilayer Nanoshells Research Articles

Magnetic-Based Double Fano Resonances in Au-SiO2-Si Multilayer Nanoshells

Compared to metallic nanostructures employed in plasmonics, dielectric materials with high refractive index can directly engineer magnetic responses in addition to the electric responses in plasmonic structures. In this work, we have demonstrated that the magnetic-based double Fano resonances can be achieved in the Au-SiO2-Si multilayer nanoshells due to the strong interaction between electric resonances and magnetic resonances. The observed double Fano resonances arise from two distinct origins: (1) the interference of magnetic dipole resonance of Si core and electric dipole resonance of Au shell, which excites a Fano resonance even in a symmetric nanoshell, and (2) the interference between magnetic quadrupole resonance of Si core and electric quadrupole resonance of Au shell, introduced by symmetry breaking of Si core. Dipole radiative enhancement spectra are used to analyze electric and magnetic responses of Au-SiO2-Si multilayer nanoshells, and the asymmetric Fano line shape is fitted by a coupled oscillator model. Also, magnetic-based Fano resonances can be adjusted easily by means of varying the geometrical parameters. The spectral sensitivity of Au-SiO2-Si multilayer nanoshells is also investigated, and the Fano resonance modulated from scratch can be found when the intermediate dielectric layer between Au shell and Si core is altered. The Au-SiO2-Si multilayer nanoshells that show better tunability of magnetic-based Fano resonances may provide the various applications ranging from novel optical devices to biological sensors.

An Analytical Formulation Enabling Analysis of Resonance Eigenmodes and Their Interferences in Scattering From Plasmonic Nanostructures, Applications in Engineering the Radiation Loss

An analytic formulation revealing exact contribution of different factors affecting the interference interaction between eigenmodes of a scatterer is presented by utilizing our previously reported modal scattering power formula. For special case of arbitrary multilayer concentric and nonconcentric nanoshells, a recursive method for analytically calculating the T-matrix, and each of these factors is derived. Results for a three layer structure showing the conditions for constructive and destructive interference interactions are discussed in details. It is shown that the interference interaction can occur in the vicinity of the overlapping resonance frequencies of the two spatially overlapping eigenmodes. The role of the phase characteristic of the eigenmodes at the resonance points in the interference phenomena is discussed. Different factors determining the phase behavior originating from either the incidence, or the characteristics of the scatterer itself are studied. These provide the ability to engineer the incidence, and the scatterer properties for achieving desired interference behavior. As a practical example for the application of this approach, reducing radiation loss of a plasmonic nanostructure through tailoring of structural parameters, and synthesis of proper incidence is presented.

Theoretical Studies of Tunable Localized Surface Plasmon Resonance of Gold-Dielectric Multilayered Nanoshells

Tunable properties of localized surface plasmon resonances (LSPR) of gold-dielectric multilayered nanoshells are studied by quasi-static theory and plasmon hybridization theory. Multilayered nanoshells with the gold core and nanoshell separated by a spacer layer exhibit strong coupling between the core and nanoshell plasmon resonance modes. It is found that the absorption spectra characteristics of LSPR are sensitive to multiple parameters including the surrounding medium refractive index, the dielectric constant of spacer layer, the radius of inner core gold sphere, outer shell layer thickness, and their coupling strength. The results show that LSPR is mainly influenced by the ratio of spacer layer dielectric constant e 2 to surrounding medium dielectric constant e 4. Absorption spectrum of $\left |\omega _{-}^{+}\right \rangle $ mode is red-shifted with increasing core radius when e 2 > e 4. It is surprising to find that LSPR is blue-shifted with increasing core radius when e 2 < e 4, and no shift when e 2 = e 4. These interesting contrary shifts of $\left |\omega _{-}^{+}\right \rangle $ mode with different ratios e 2/e 4 are well analysed with plasmon hybridization theory and the distributions of induced charges interaction between the inner core and outer shell. In addition, for the sake of clarity, the distributions of electric filed intensity at their plasmon resonance wavelengths are also calculated. This work may provide an alternative approach to analyse property of the core-shell nanoshell particles based on plasmon hybridization theory and the induced charge interaction.

Resonance coupling in plasmonic nanomatryoshka homo- and heterodimers

Here, we examine the electromagnetic (EM) energy coupling and hybridization of plasmon resonances between closely spaced concentric nanoshells known as “nanomatryoshka” (NM) units in symmetric and antisymmetric compositions using the Finite Difference Time Domain (FDTD) analysis. Utilizing plasmon hybridization model, we calculated the energy level diagrams and verified that, in the symmetric dimer (in-phase mode in a homodimer), plasmonic bonding modes are dominant and tunable within the considered bandwidth. In contrast, in the antisymmetric dimer (out-of-phase mode in a heterodimer), due to the lack of the geometrical symmetry, new antibonding modes appear in the extinction profile, and this condition gives rise to repeal of dipolar field coupling. We also studied the extinction spectra and positions of the antibonding and bonding modes excited due to the energy coupling between silver and gold NM units in a heterodimer structure. Our analysis suggest abnormal shifts in the higher energy modes. We propose a method to analyze the behavior of multilayer concentric nanoshell particles in an antisymmetric orientation employing full dielectric function calculations and the Drude model based on interband transitions in metallic components. This study provides a method to predict the behavior of the higher energy plasmon resonant modes in entirely antisymmetric structures such as compositional heterodimers.

Theoretical Assessment of Localized Surface Plasmon Resonance Properties of Au-Interlayer-Ag Multilayered Nanoshells

The localized surface plasmon resonance (LSPR) properties of Au-interlayer-Ag multilayered nanoshells are studied by discrete dipole approximation (DDA) and plasmon hybridization theory. Concentric nanoshells with the metal core and nanoshell separated by an interlayer exhibit strong coupling between the core and nanoshell plasmon resonance modes. The coupled resonance mode wavelengths show a remarkable dependence on the Au core radius, refractive index of the surrounding medium, and different kinds of interlayer materials. If the interlayer is metallic, the contribution of the Au core to LSPR is suppressed, but a semiconducting interlayer can enhance the contribution. Calculation of the electric field enhancement shows that the location of the field enhancement is specified by different resonance patterns. The Au-ITO-Ag nanoshell shows strong near-field enhancement in several regions, especially in the infrared region, which have potential applications in surface-enhanced spectroscopy.

Analysis of Localized Surface Plasmon Resonance in Ag/ITO/CdS/SiO2 Multilayered Nanostructured Composite

Multilayered nanoshells have attracted much attention due to their unique optical, electronic and magnetic properties. In this work, numerical calculation using discrete dipole approximation (DDA) is conducted to investigate the quad-layered metal nanoshell consisting of a particle with a dielectric silica (SiO2) core, inner cadium sulfide (CdS) shell, middle indium tin oxide (ITO) shell and outer metal silver (Ag) shell. The phenomenon is interpreted by plasmon hybridization theory and the Ag–ITO–CdS–SiO2 multilayered nanoshells are studied by extinction spectra of localized surface plasmon resonance. The variation in the spectrum peak with nanoparticle thickness and refractive index of the surrounding medium is derived. The electric field enhancement contour around the nanoparticles under illumination is analyzed at the plasmon resonance wavelength. The [Formula: see text], [Formula: see text], and [Formula: see text] modes red-shift with the refractive index of the surrounding medium and increase in the layer thickness causes either blue-shift or red-shift as shown by the extinction spectra. The mechanism of the red-shift or blue-shift is discussed. The [Formula: see text] mode blue-shifts and furthermore, the [Formula: see text] and [Formula: see text] modes of the Ag coated multilayered nanostructure are noticeable by comparing the extinction efficiency spectra of the Au–ITO–CdS–SiO2 and Ag–ITO–CdS–SiO2 multilayered nanoshells.

Optical coherent thermal emission by excitation of magnetic polariton in multilayer nanoshell trimer.

A theoretical demonstration is given of coherent thermal emission via the visible region by exciting magnetic polaritons in isolated metal-dielectric-metal multilayer nanoshells and the collective behavior in a trimer comprising multilayer nanoshells. The dipolar metallic core induces magnetic polaritons in the dielectric shell creating a large enhancement of the emissivity, whose mechanism is different from that of film-coupled metamaterials. The coupling effect of the magnetic polaritons and the electric/magnetic modes of symmetric nanoparticle trimers is discussed to understand the collective behavior in self-assembled nanoparticle clusters with potential solar energy utilizations. The concept of hybridization is employed to understand the collective magnetic polaritons of a multilayer nanoshell trimer. The fundamental understanding gained herein opens up new ways to explore, control, and tailor spectral absorptance, thus facilitating rational design of novel self-assembled nanoclusters for energy harvesting.

Double-band enhancement of effective third-order nonlinear susceptibility in gold-dielectric-gold multilayer nanoshells

The effective third-order nonlinear susceptibility χ eff (3) of gold-dielectric-gold three-layer nanoshells was theoretically studied using the quasi-static approximation. Because of the physical origin from the SPR-induced local field enhancement, both the real and imaginary parts of the enhancement factor of χ eff (3) present maximum responses near the plasmon wavelengths. By altering the geometry parameters and local dielectric environment of the nanoshells, the intensity, wavelength position, and band number of the χ eff (3) could be fine tuned. The mode transformation of the χ eff (3) from single band to double band has been observed as the separate layer dielectric constant is increased or the inner gold sphere radius is increased. The band number of χ eff (3) also depends on the thickness of the outer gold shell. However, only single maximum response band of χ eff (3) could be observed when the shell thickness is too small or too large.

Nanosphere-in-a-nanoegg: damping the high-order modes induced by symmetry breaking.

We study the optical properties of the nanosphere-in-a-nanoegg structure (NSNE) by the three-dimensional finite difference time domain method. We demonstrate the suppression of the high-order plasmon modes in NSNE, which is induced by the plasmon interaction between the inner nanosphere and the outer nanoegg shell. A two-layer plasmon hybridization model is presented to explain this mechanism. The results we showed for plasmon mode suppression would be important to the design of the metal plasmonic devices. In addition, due to high tunable plasmon resonances in the near-infrared region (700 to 1,300 nm) with sub-100-nm size, NSNE can serve as a good substitute for the Au-silica-Au multilayer nanoshells in biological applications. Furthermore, compared with the Au-silica-Au nanoshells, NSNE has the advantage that the strong field enhancement can be achieved at the outer surface of the Au shell.

Multilayered Nanoshells: Controlled Synthesis of Multilayered Gold Nanoshells for Enhanced Photothermal Therapy and SERS Detection (Small 1/2015)

A facile and controlled route to fabricate multilayered gold nanoshells (MLGSs) with tunable dimensions, excellent uniformity, and well-defined core-shell nanostructures is reported by Y. Li, J. Shi, and co-workers on page 77. It is demonstrated experimentally that MLGSs possess higher photothermal efficiency than conventional gold nanoshells, and significantly improved Raman stability as SERS substrates under photothermal conditions.

Superparamagnetic plasmonic nanocomposites: Synthesis and characterization studies

Bifunctional magneto-optical nanocomposites have recently received significant attention because of their simultaneous magnetic and optical properties, and they can be considered as one of the most promising candidates for future medical diagnosis and therapy. In this paper, multilayer magnetic gold nanoshells were prepared by coating a magnetic shell around outer surface of silica-gold nanoshells (GNs) via using three procedures based on surface modification of gold nanoshells or magnetite nanoparticles (MNs) in order to increase the affinity between these nanostructures. The procedures used in this work include attachment of MNs onto the surface of 3-aminopropyltriethoxysilane (APTES) modified GNs (P1), attachment of APTES-modified MNs onto the surface of GNs (P2) and attachment of APTES-modified MNs onto the surface of 3-mercaptopropionic acid (MPA) modified GNs (P3). From the microscopic characterizations, it is inferred that the surface of the nanocomposites obtained from P1 is smooth. So, P1 is more preferable to produce spherical smooth SiO2@Au@Fe3O4 nanostructures. Besides, the spectroscopic and magnetization data of obtained nanocomposites reveal that all the synthesized nanocomposites have superparamagnetic plasmonic nature. Therefore, they can be considered as possible options for multimodal applications requiring bifunctional magnetic plasmonic structures such as simultaneous MRI imaging and photothermal therapy.

The Effect of Metal Type on the Separate Dielectric Layer-Dependent Plasmon Coupling in Al–Au Bimetallic Metal-Dielectric-Metal Nanoshells

Metal type-dependent plasmonic absorption properties of Al–Au bimetallic metal-dielectric-metal nanoshells have been investigated theoretically by using the quasi-static theory of classical electrodynamics. It has been found that the three-layered nanoshells present different surface plasmon resonance (SPR) properties when the metal type of the inner core and outer shell is exchanged. For Al-dielectric-Au nanoshell, the |ω−−〉 band takes the major role of the absorption spectrum. Whereas for Au-dielectric-Al nanoshell, the |ω−+〉 mode has the highest intensity. The corresponding physical origin has been attributed to the different optical parameters of Au and Al, which results in different local field enhancement and plasmon energy at each plasmon hybridization mode. The plasmonic absorption properties also depend on the thickness of the separate layer and are further affected by the metal type of the inner core and outer shell. For Al-dielectric-Au nanoshell, the increasing separate layer thickness results in distinct red shift of |ω−+〉 peak but slight blue shift of the |ω+−〉 peak. For Au-dielectric-Al nanoshell, the |ω+−〉 and |ω−+〉 modes fade down and blue shifts, whereas the major peak corresponding to the |ω−−〉 mode blue shifts and gets intense firstly and then red shifts and decreases as the thickness is increased. These results indicate that different plasmon hybridization modes of the multilayered nanoshell could be enhanced selectively by choosing different type of metal as the outer shell.

Controlled synthesis of multilayered gold nanoshells for enhanced photothermal therapy and SERS detection.

It can be streamlined: A facile and controllable approach for the fabrication of core/shell-structured multilayer gold nanoshells with uniform nanosize, monodispersity, and tunable plasmonic properties has been successfully developed by utilizing an organosilica layer as the dielectric spacer layer.

Triple plasmon resonance of bimetal nanoshell

In this paper, light absorption spectra properties of a bimetal multilayer nanoshell based on quasi-static approach are investigated. Comparing with silver-dielectric-silver and silver-dielectric-gold nanoshells, gold-dielectric-silver nanoshells have three intense and separated plasmon peaks which are more suitable for multiplex biosensing. Calculations show that relatively small thickness of outer silver shell and large dielectric constant of middle dielectric layer of gold-dielectric-silver nanoshell are suitable to obtain the triple plasmon resonance.

Localized Hybrid Plasmon Modes Reversion in Gold–Silica–Gold Multilayer Nanoshells

The plasmon hybridization theory is widely used to study the plasmon response of metallic nanostructures. In this work, we study the plasmon hybridization picture of the gold–silica–gold multilayer nanoshells from the viewpoint of the optical extinction spectrum and the charge density distribution. We find that reducing the distance between the Au core and the Au shell causes the conversion from |ω–+⟩ to |ω+–⟩ modes of the high energy extinction peak. According to our opinion, it is because the increased plasmon interaction between the Au core and the Au shell induces the energy reversion of the |ω–+⟩ and |ω+–⟩ plasmon modes. The interesting contrary shift effect of the high energy extinction peaks with different dielectric constants of the middle silica shell and outer surrounding is well-explained by the |ω+–⟩ modes. The energy reversion of hybrid plasmon modes we reported would give new insight into the plasmon hybridization theory. Moreover, our study could offer a modified way based on the charge interaction analysis, which is a necessary supplement to the plasmon hybridization theory, for studying plasmon responses in the optical spectrum of metal nanostructures.

Degenerate four waves mixing in multilayer nanoshell

We will present a detailed investigation of intersubband transitions process in core-multi shells quantum dots. The confined wave functions and eigenenergies of electrons in quantum dots have been calculated under the effective-mass approximation by solving a three-dimensional Schrodinger equation. Excellent dependence is found between size effects, time relaxation and degenerate four wave mixing (DFWM). We found that the enhancement of the thickness layers lead to strongly enhancement in peak value of DFWM.

Optical and spectral tunability of multilayer spherical and cylindrical nanoshells

This theoretical work presents a comparative study of the optical properties and spectral tunability of hybrid multilayer spherical and cylindrical nanoshells based on the quasi-static approximation of classical electrodynamics. The interband transitions have been considered using the Drude–Lorentz model for the complex dielectric function of metallic layers because the optical properties of metals arise from both the optical excitation of interband transitions and the free-electron response. A general formula for N-ayer concentric nanoshells is arranged, and numerical calculations are performed for the four-layer nanoshells as an example. We have analyzed in detail different configurations of nanoshells such as dielectric-metal-dielectric-metal with dielectric core, metal-dielectric-metal-dielectric with metal core and semiconductor-metal-dielectric-metal with semiconductor core because composition of nanoshells have dramatic influence on their optical properties. The absorbance spectrum behavior of the shell thicknesses, surrounding medium, shape and composition of each layer of the nanoshell is numerically investigated.

The Study of Surface Plasmon Resonance in Au-Ag-Au Three-Layered Bimetallic Nanoshell: The Effect of Separate Ag Layer

Localized surface plasmon resonance (LSPR) properties of Au-Ag-Au three-layered nanoshell are investigated theoretically using the quasi-static electricity. Triple-bands LSPRs have been observed in the absorption spectrum. Both the peak wavelength and intensity could be fine tuned by altering the thickness and radius of the separate Ag layer. The properties and physical origin of the LSPR in the Au-Ag-Au three-layered nanoshell is much different from that of Au-dielectric-Au three-layered nanoshell. The corresponding physical mechanism has been illustrated by plotting the local electric field patterns and analyzing the interaction of the surface charges from different metal interfaces. Although the LSPR of Au-Ag-Au three-layered nanoshell is affected by the plasmon hybridization from all metal surfaces, it has been found that the plasmon coupling in different metallic layer takes main effect on the LSPR properties of different absorption peaks. These results indicate that the different type of metallic layers appearing alternately in the multilayered nanoshells could create abundant tunable LSPR modes, which provides potential for multiplex biosensing based on LSPR.

Energy Absorption in Gold Nanoshells

A modeling study on energy absorption and transport in an isolated nanoshell and aggregates of nanoshells under localized surface plasma resonance (SPR) conditions is presented. A comprehensive model for multi-scattering of electromagnetic waves by a cluster of multilayered nanoshells is developed, which applies the Wigner-Eckart theorem for the calculation of the total scattering cross sessions of nanoshell aggregates. Absorption by an isolated nanoshell and by nanoshell clusters is studied using the model. Results show that the inter-nanoshell coupling results in strong field enhancement near the particle surface. Energy absorption in a nanoshell can be tuned by varying the structural parameters of the nanoshell. Smaller particles are more absorbing than the large ones, other conditions being equal. Because of the presence of a dielectric cavity, the radial distribution of the absorbed power in the metal shell may differ from the classical skin depth phenomena. The interaction among particles in close proximity causes the energy absorption efficiency and the resonance position of a nanoshell cluster to differ from those of an isolated nanoshell.

Obtain Quadruple Intense Plasmonic Resonances from Multilayered Gold Nanoshells by Silver Coating: Application in Multiplex Sensing

Four intense and separate localized surface plasmon resonance (LSPR) absorption peaks have been obtained in the gold-dielectric–gold–silver multilayer nanoshells. The silver coating on the gold shell results in a new LSPR peak at about 400 nm corresponding to the $$ {{\left| {\omega_{+}^{-}} \right\rangle}_{Ag }} $$ mode. The intense local electric field concentrated in the silver shell at the wavelength of 400 nm indicates that this new plasmonic band is coming from the symmetric coupling between the antibonding silver shell plasmon mode and the inner sphere plasmon. Increasing the silver shell thickness also leads to the intensity increasing of the $$ {{\left| {\omega_{+}^{-}} \right\rangle}_{Au }} $$ mode and blue shift of $$ \left| {\omega_{-}^{+}} \right\rangle $$ and $$ \left| {\omega_{-}^{-}} \right\rangle $$ modes. Therefore, quadruple intense plasmonic resonances in the visible region could be achieved in gold-dielectric–gold–silver multilayer nanoshells by tuning the geometrical parameters. And the quadruple intense plasmonic resonances in the visible region provide well potential for multiplex biosensing based on LSPR.