Nanoshell Arrays Research Articles

Influence of structural defects on the optical properties of strongly coupled Au nanoshell arrays

The effects of different defects on optical properties and plasmon resonances properties of Au nanoshell arrays were investigated by using the finite-difference time-domain (FDTD) theory. It is found that the optical properties of the nanoshell arrays are strongly influenced by different defects. We show that when the hollow Au nanoshell arrays are placed in air, there is a wide photonic band gap (PBG) in the infrared region, but the band gap becomes narrower as we introduced different defects. Based on the distributions of electric field component Ez and the total energy distribution of the electric and the magnetic field, we show that there exhibit dipoles field distributions for the plasmon mode at the long-wavelength edge of the band gap, but composite higher order modes are excited at the short-wavelength edge of the band gap. The plasmon resonant modes also can be controlled by introducing defects.

Fundamental research on the label-free detection of protein adsorption using near-infrared light-responsive plasmonic metal nanoshell arrays with controlled nanogap

In this work, we focused on the label-free detection of simple protein binding using near-infrared light-responsive plasmonic nanoshell arrays with a controlled interparticle distance. The nanoshell arrays were fabricated by a combination of colloidal self-assembly and subsequent isotropic helium plasma etching under atmospheric pressure. The diameter, interparticle distance, and shape of nanoshells can be tuned with nanometric accuracy by changing the experimental conditions. The Au, Ag, and Cu nanoshell arrays, having a 240-nm diameter (inner, 200-nm polystyrene (PS) core; outer, 20-nm metal shell) and an 80-nm gap distance, exhibited a well-defined localized surface plasmon resonance (LSPR) peak at the near-infrared region. PS@Au nanoshell arrays showed a 55-nm red shift of the maximum LSPR wavelength of 885 nm after being exposed to a solution of bovine serum albumin (BSA) proteins for 18 h. On the other hand, in the case of Cu nanoshell arrays before/after incubation to the BSA solution, we found a 30-nm peak shifting. We could evaluate the difference in LSPR sensing performance by changing the metal materials.

Synthesis and magnetic properties of large-area ferromagnetic cylindrical nanoshell and nanocup arrays

Large-area arrays of magnetic Ni80Fe20 cylindrical nanoshells, nanocups, and perforated nanocups were synthesized using oblique deposition into topographical templates patterned using laser interference lithography. The geometry of the template and the tilt angle of the sample during deposition provide versatile control over the final geometry and dimension of nanostructures with thickness below 10 nm. Decreasing shell thickness led to a magnetization switching path between onion (bidomain) and reverse onion states, bypassing the vortex (flux-closed) state. The variation of magnetization reversal processes with geometry was characterized using vibrating sample magnetometry, and the results were in good agreement with micromagnetic simulations.

Fabrication and infrared-transmission properties of monolayer hexagonal-close-packed metallic nanoshells

This paper presents a novel method for fabricating a monolayer of hexagonal-close-packed metallic nanoshells with a small opening, based on a combination of a porous polymer template and a nanocrystal-seeded electroless plating technique. Light transmission spectra of the metallic nanoshell arrays are measured, which show that light can transmit through the dense particle assemblies via excitations of a variety of surface-plasmons (SPs). Further numerical simulations confirm these transmission resonances and reveal that they are attributed to the excitations of localized quadrupolar spherelike and Fano-type hybridized SP modes supported by the specific structure. The present metallic microstructure could find applications in plasmonics.

Confined Mie Plasmons in Monolayer Hexagonal-Close-Packed Metallic Nanoshells

Using a double templating method by electroless deposition within a templating organic porous mold, we fabricate a monolayer of hexagonal-close-packed metallic nanoshells, each with a small opening. Light transmission spectra of the metallic nanoshell arrays are measured, which show transmission resonances at specific wavelengths whose positions are observed to be independent of the incident angle as well as light polarizations. More interestingly, the resonance wavelengths of Mie plasmon modes are also independent of the surrounding medium. Further numerical simulations confirm these transmission resonances and reveal that they are attributed to the excitations of highly localized dipolar, quadrupolar and hexapolar Mie plasmon modes, which are highly confined within metallic nanoshells.

Effect of symmetry breaking on localized and delocalized surface plasmons in monolayer hexagonal-close-packed metallic truncated nanoshells

We numerically study the effect of the symmetry breaking on surface plasmon (SP) modes in two-dimensional dense arrays of truncated metal nanoshells (nanocups), by investigating light transmission through the arrays. We show that localized spherelike and voidlike Mie SP modes, and delocalized Bragg-type SP modes in complete nanoshell arrays become progressively weak and finally disappear when the opening angle of nanocups is increased to tens of degrees. Under higher degree of symmetry breaking, however, the coupling between spherelike and voidlike SP modes leads to an enhancement of SP resonances even though these modes are weakly excited, due to the large optical cross section of voidlike modes. Energy variations of the hybridized mode versus the opening angle are well predicted using a plasmon standing wave model. Furthermore, disappeared Bragg-type SP modes could be re as a result of near-field coupling via hot spots around the rims of nanocups.

Novel and Simple Route to Fabricate 2D Ordered Gold Nanobowl Arrays Based on 3D Colloidal Crystals

In this study, we present a new method to fabricate large-area two-dimensionally (2D) ordered gold nanobowl arrays based on 3D colloidal crystals by wet chemosynthesis, which combines the advantages of a very simple preparation and an applicability to "real" nanomaterials. By combination of in situ growth of gold nanoshell (GNSs) arrays based on three-dimensional (3D) colloidal silica crystals, a monolayer ordered reversed GNS array (2D ordered GNS array) was conveniently manufactured by an acrylic ester modified biaxial oriented polypropylene (BOPP). 2D ordered gold nanobowl array with adjustable periodic holes, good stability, reproducibility, and repeatability could be obtained when the silica core was etched by HF solution. The surface-enhanced Raman scattering (SERS) enhancement factor (EF) of this 2D ordered gold nanobowl array could reach 1.27 × 10(7), which shows high SERS enhancing activity and can be used as a universal SERS substrate.

Complex modes and near-zero permittivity in 3D arrays of plasmonic nanoshells: loss compensation using gain [Invited

We report on the possibility of adopting active gain materials (specifically, made of fluorescent dyes) to mitigate the losses in a 3D periodic array of dielectric-core metallic-shell nanospheres. We find the modes with complex wavenumber in the structure, and describe the composite material in terms of homogenized effective permittivity, comparing results from modal analysis and Maxwell Garnett theory. We then design two metamaterials in which the epsilon-near-zero frequency region overlaps with the emission band of the adopted gain media, and we show that metamaterials with effective parameters with low losses are feasible, thanks to the gain materials. Even though fluorescent dyes embedded in the nanoshells’ dielectric cores are employed in this study, the formulation provided is general, and could account for the usage of other active materials, such as semiconductors and quantum dots.

Effects of dielectric core and embedding medium on plasmonic coupling of gold nanoshell arrays

The effects of the dielectric core and the dielectric embedding medium separately on transmission spectra and plasmon resonance properties of gold nanoshell arrays were investigated by using the finite-difference time-domain (FDTD) theory. It is found that when the hollow nanoshell arrays are placed in air, the wide photonic band gap becomes narrower as the core dielectric constant increases. On the contrary, when the nanoshell arrays with dielectric core are placed in the dielectric medium, the photonic band gap becomes wider. Furthermore, increasing core or medium dielectric constant leads to a redshift of the transmission spectra due to the polarization of the dielectric. Based on the electric field distributions, we also clearly show that the plasmon properties of the nanoshell arrays are strongly influenced by the presence of the dielectric.

OPTICAL PROPERTIES AND PLASMON RESONANCE OF COUPLED GOLD NANOSHELL ARRAYS

The optical properties and plasmon resonances coupling of ordered gold nanoshell arrays are investigated theoretically by means of finite-difference time-domain (FDTD) theory. We showed that the thickness, size and inter-shell distance of the nanoshells can tune the optical transmission of the system and the highly geometry-dependent plasmon response can be seen as an interaction between the essentially fixed-frequency plasmon response of a nanosphere and that of a nanocavity for the nanoshells. We also revealed the two different resonance modes by analyzing the spatial distributions of electric field component Ez. We proposed that the peaks of the lower energy mainly originate from the sphere plasmons coupling and the peaks of the higher energy are mainly attributed to the coupling between the sphere plasmons and the cavity plasmons.

Surface Nanometer‐Scale Patterning in Realizing Large‐Scale Ordered Arrays of Metallic Nanoshells with Well‐Defined Structures and Controllable Properties

AbstractSurface patterns of nanoshell arrays play an important role in diverse applications including surface‐enhanced Raman scattering (SERS) sensors, lithium‐ion batteries, solar cells, and optical devices. This paper describes an innovative surface nanopatterning technique for realizing large‐scale ordered arrays of metallic spherical nanoshells with well‐defined structures. Ag nanoshell arrays are prepared using polystyrene sphere templates by an electrophoretic process in Ag colloidal solutions. The fabricated Ag nanoshell arrays have a high controllability of the structural parameters, including the diameter, the surface roughness, and the intershell spacing, giving rise to the tunable properties of nanoshell arrays. As an example, tunable SERS and localized surface plasmon resonance of the nanoshell arrays are demonstrated by controlling the structural parameters. The surface nanopatterning technique shown in this paper is a general fabrication process in achieving not only metallic nanoshell arrays, but also nanoshell arrays of semiconductors and metallic oxides.

Superhydrophobic Cylindrical Nanoshell Array

A superhydrophobic property was demonstrated on a cylindrical poly crystalline silicon nanoshell array due to its geometrical properties, even without a hydrophobic coating. The proposed structure showed superior water-repellency compared to a conventional pillar structure with an identical structural dimension. This superhydrophobic property is attributed to an air pillar that exists in the nanoshell. Through the calculation of capillary pressure, the stability of the air pillar was confirmed. Furthermore, a droplet impinging test was conducted on the fabricated cylindrical nanoshell array to verify the robust Cassie state of the proposed structure under a dynamic condition.

Fabrication of Nanoshell Arrays Using Directed Assembly of Nanospheres

Extraordinary transmission of light has been observed when light is incident on periodic nanostructures patterned metal films, which results from the interaction between the incident photons and the excited surface plasmon polaritons with wavenumbers constrained by the geometry and periodicity of the surface structure. Usually, the surface patterns are fabricated by Focused Ion Beam (FIB) milling, which is expensive and has low throughput. We employ the nanosphere lithography method to fabricate periodic nanoshell arrays on a gold film as an alternative to FIB milling. In this process, polystyrene nanospheres are deposited on glass substrates as a template for subsequent gold deposition. This results in the close-packed hexagonal nanoshell arrays patterned gold surface. The transmission spectra of the patterned surfaces show strong enhanced transmission in the red and IR wavelength regions, and the peak enhanced transmission wavelengths vary with the chemical environments above the surface.

Enhanced surface plasmon resonance based on the silver nanoshells connected by the nanobars

Enhanced surface plasmon resonances in a silvershell nanocylindrical pair connected by a different type of nanobar that interacts with incident plane wave of transverse magnetic polarization are simulated by use of the finite element method. Arrays of silver nanoshells connected by silver nanobars are also investigated. The proposed structure exhibits a red-shifted localized surface plasmon that can be tuned over an extended wavelength range by varying the width of the nanobar and the dielectric constant in dielectric holes (DHs). The increase in the scattering cross sections is attributed to the effects of surface plasmon on the nanobar surface and a larger effective size of DH that is filled with a higher refractive medium. The predictive character of these calculations allows one to tailor the shape of the nanoparticle to achieve excitation spectra on demand with a controlled field enhancement.

Fabrication of discrete array of metallodielectric nanoshells and their surface plasmonic properties

In this paper we describe the fabrication of two-dimensionally periodic non-close-packed nanoshell arrays, consisting of a spherical polystyrene core coated with a thin gold shell, as well as their surface plasmonic properties. The principle of this procedure relies on stepwise integration of spin-coat-assisted colloidal self-assembly of the single layer of close-packed polystyrene nanoparticle, atmospheric pressure plasma-induced isotropic etching, and deposition of gold thin film by thermal evaporation. The plasma process converted the close-packed nanoparticle array into non-close-packed arrangement without changing their original spherical shape and periodicity. Both experimental and theoretical studies revealed that the densely packed nanoshell array with a 160 nm inner core diameter and a 20 nm thick shell strongly scattered and absorbed near infrared light, due to the interaction between primitive plasmon modes associated with the surface of the nanoparticle. Furthermore, the resultant nanoshell array was utilized for near infrared light responsible localized surface plasmon resonance based sensor. The bulk refractive index sensitivity was 220 nm RIU − 1 .

Collective surface plasmon resonance coupling in silver nanoshell arrays

Collective surface plasmon resonance (SPR) excitations in an ordered array of silver nanoshells have been theoretically studied using generalized Mie theory. Near- and far-field radiative coupling between the nanoshells in the array result in a non-monotonic shift of the collective SPR band. When the distance between the shells in the array approaches that of the collective SPR wavelength, we observe narrowing of the collective SPR band due to constructive interference between the scattered electric field from the particles in the array. Further increase of the distance between the nanoshells in the array leads to destructive interference and broadening of the collective SPR band.

Metallic Nanoparticle Arrays: A Common Substrate for Both Surface-Enhanced Raman Scattering and Surface-Enhanced Infrared Absorption

Nanoshell arrays have recently been found to possess ideal properties as a substrate for combining surface enhanced raman scattering (SERS) and surface enhanced infrared absorption (SEIRA) spectroscopies, with large field enhancements at the same spatial locations on the structure. For small interparticle distances, the multipolar plasmon resonances of individual nanoshells hybridize and form red-shifted bands, a relatively narrow band in the near-infrared (NIR) originating from quadrupolar nanoshell resonances enhancing SERS, and a very broadband in the mid-infrared (MIR) arising from dipolar resonances enhancing SEIRA. The large field enhancements in the MIR and at longer wavelengths are due to the lightning-rod effect and are well described with an electrostatic model.

Plasmonic Nanoshell Arrays Combine Surface‐Enhanced Vibrational Spectroscopies on a Single Substrate

Sensitive support: Assembling plasmonic nanoshells into periodic arrays with nanoscale interparticle gaps gave a substrate on which surface-enhanced (SE) Raman spectroscopy (RS) and infrared absorption (IRA) spectroscopy can be performed simultaneously to enable molecular detection and characterization with high precision and sensitivity. The picture shows an SEM image of the Au nanoshell array and SERS and SEIRA spectra of a p-mercaptoaniline monolayer on the array.

Realization of periodic and quasiperiodic microstructures with sub-diffraction-limit feature sizes by far-field holographic lithography

The authors experimentally demonstrate a far-field holography for the realization of Ag nanoparticles-embedded periodic and quasiperiodic microstructures with feature sizes beyond the diffraction limit. Periodic cylindrical nanoshell arrays with about 240nm hole diameter and 12-fold symmetry quasiperiodic structures with 220nm feature sizes are achieved, respectively, by using a 632.8nm laser beam. Our results imply that conventional far-field optical technology is capable of fabricating nanostructures in modern micromanufacture.

Ordered Array of Gold Nanoshells Interconnected with Gold Nanotubes Fabricated by Double Templating

Ordered interconnected gold nanoshells and nanotubes (see figure) are made by electroless plating in a macroporous polymer replicated from a non-close-packed silica colloidal crystal. The size of the gold nanoshells and nanotubes can be altered by varying the sintering and etching conditions for the silica template. A remarkable modulation in optical reflectivity resulting from surface plasmon excitation has been observed in the microstructure.