Optimization of ultrathin carbon film coated silver nanoshell for biomedical applications in vivo

The extinction spectroscopy and near-field enhancement of dielectric-silver nanoshell coated by tetrahedral amorphous carbon [ta-C] layer (DSC) have been calculated by using Mie theory. With decreasing the Ag layer thickness, the localized surface plasmon resonance (LSPR) of DSC nanoshell moves from the visible region into the near-infrared region and the corresponding local field factor (LFF) increases first and then decreases. In addition, the increase of ta-C shell thickness leads to red-shift of LSPR and the decrease of LFF in DSC nanoshell. We further find that the increase of the dielectric constant for the outer shell can induce a significant enhancement of near-field. Based on the simulation analysis, we show that the DSC nanoshell can provide strong near-field in near-infrared region and may be suitable for the biomedical applications in vivo.     

内嵌圆饼空心方形银纳米结构的光学性质

采用离散偶极子近似方法计算了内嵌圆饼空心方形银纳米结构的消光光谱以及其近场的电场强度分布,并进一步与空心方形纳米结构的消光光谱和表面电场做比较.结果表明,在耦合作用下内嵌圆饼空心方形银纳米结构不仅产生了新的共振模式,而且新的共振模式在传统表面增强拉曼散射的激发波长范围内,进而可以弥补由于实验上运用纳米切片法所制备的空心方形纳米结构尺寸较大导致其共振吸收峰在远红外波长范围的不足.此外,可以通过改变内嵌圆饼空心方形银纳米结构的形貌参数调节其表面等离子体共振峰的共振波长,以满足在表面增强拉曼散射、生物分子或化学分子探测上的应用.     

Numerical study of optical properties of single silver nanobowtie with anisotropic topology

Optical properties of silver nanobowtie with anisotropic topology, which is separated with nanogap that is horizontal (Y direction) and vertical (Z direction) to the line between the two constituent triangles (i.e., the bowtie axis), are studied. A discrete dipole approximation (DDA) method is used to determine the extinction efficiency and the electric field (E-field) distribution, then the corresponding enhancement factor (EF) and the full width half maximum (FWHM) of the E-field are obtained and analyzed. Our results show that the wavelength of localized surface plasmon resonance (LSPR)-induced blue-shifts and the maximum EF decrease were observed with increasing gap size for the parallel polarized (Z-polarized) excitation. It is also found that the light spot at the “hot spot” in the gap becomes larger and deviates from the rectangular pattern with the increase of the gap in the Z direction (Z-gap), and the FWHM in the Z direction of the localized E-field in the gap broadens with either an increase in the gap in the Y direction (Y-gap) or the Z-gap. These behaviors are due to the decrease of the coupling efficiency of near-field plasmon coupling. In contrast, the wavelength of the LSPR and the maximum EF excited by the perpendicularly polarized (Y-polarized) light show less dependence on the gap size than that of the Y-polarized light. PACS  73.20.Mf; 78.67.-n     

Local field enhancement of pair arrays of silver nanospheres

Local field surface plasmon excitation of pair arrays of silver nanospheres was studied using three-dimensional finite-difference time-domain method. The near-field enhancement was associated with the radius of nanosphere and the incident wavelength, the highest of which always appeared in the penultimate gaps, regardless of the number of the pairs. The surface plasmon resonance could be controlled and tuned by radius of nanosphere and incident wavelength.     

Comparison investigation of near- and far-field properties for plasmon resonance of silver nanosphere dimers

Near- and far-field plasmon resonance properties of silver nanospheres dimers are calculated and compared based on the Generalized Multiparticle Mie-solution method. Greater differences between near- and far-field plasmon resonances are found than those of silver single nanoparticle, while the dimer of strongest near-field electric field amplitude and the dimer of highest far-field extinction coefficient almost have the same geometry parameter value under the illumination with fixed wavelength and polarization.     

数值模拟探针诱导表面等离子体共振耦合纳米光刻

采用有损耗介质和色散介质的二维时域有限差分方法,数值模拟了以光波长514.5nm的p偏振基模高斯光束为入射光源,激发Kretschmann型表面等离子体共振,并通过探针的局域场增强效应实现纳米光刻的新方法——探针诱导表面等离子体共振耦合纳米光刻.分别就探针与记录层的间距以及探针针尖大小,模拟分析了不同情况下探针的局域场增强效应和记录层表面的相对电场强度振幅分布.结果表明,探针工作在接触模式时,探针的局域场增强效应最明显,记录层表面的相对电场强度振幅的对比度最大;当探针针尖距记录层5nm时,针尖下方记录层表面的相对电场强度振幅大于光刻临界值的分布宽度与针尖尺寸相近. 关键词： 纳米光刻 表面等离子体共振 时域有限差分方法     

Three-dimensional analysis of silver nano-particles doping effects on super resolution near-field structure

The super resolution near-field structure which incorporates a AgOx thin film was studied through the calculation using three-dimensional (3D) finite-difference time-domain method. The influences of the optical field distribution generate by some factors, e.g., the polarization direction, the wavelength of incident light and the size of silver nano-particles, which are sensitive to the surface plasmon resonance are discussed in detail. The goal of this study is to explain the physical mechanisms responsible for the super-resolution near-field structure phenomena in 3D model and give a better understanding of the optical properties between AgOx layer and incident light.     

Optical properties of the Au–Ag alloy nanowire coated with an anisotropic shell

The optical properties of the Au–Ag alloy nanowire coated with a cylindrical shell with radial dielectric anisotropy are investigated based on quasistatic theory. Numerical results show that the surface plasmon resonance (SPR) peak is redshifted with increasing the component ratio of Au in the alloy, while the intensity of extinction section at the SPR increases with increasing the component ratio of Ag in the alloy. In addition, as the extent of anisotropy of the shell increases, the extinction section at SPR wavelength decreases and the SPR wavelength is redshifted, but compared with the isotropic shell consisting of comparable dielectric constant materials, the SPR has a distinct blueshift for anisotropic shell. We also find that the field enhancement can be completely concentrated inside the anisotropic shell and the electromagnetic transparency can be exhibited.     

Comparing the interparticle coupling effect on sensitivities of silver and gold nanoparticles

The wavelength shift of surface plasmon resonance peak resulting from the electromagnetic coupling noble metal nanoparticle increases with the increase in the dielectric constant of the medium and the decrease in the interparticle separation distance. In this work, the discrete dipole approximation method was used to calculate the extinction efficiency spectra of the silver–silver and gold–gold nanoparticle pairs. This work shows that the silver coupled-particle system has higher plasmon resonance sensitivity as compared to the gold coupled-particle system. However, the silver coupled-particle system has lower and a faster near-exponential decay of sensitivity enhancement factor than the gold coupled-particle system. Thus, the silver coupled-particle may be more suited for sensing applications as compared to the gold coupled-particle, but the interparticle coupling effect displays more pronounced effect on the gold coupled-particle system as compared to the silver coupled-particle system.     

Nanosphere Templated Metallic Grating Assisted Enhanced Fluorescence

In this paper, enhanced fluorescence from a silver film coated nanosphere templated grating is presented. Initially, numerical simulation was performed to determine the plasmon resonance wavelength by varying the thickness of the silver film on top of a monolayer of 400 nm nanospheres. The simulation results are verified experimentally and tested for enhancing fluorescence from fluorescein isothiocyanate whose excitation wavelength closely matches with the plasmon resonance wavelength of the substrate with 100 nm silver film over nanosphere. The 12 times enhancement in the intensity is attributed to the local field enhancement in addition to the excitation of surface plasmon polaritons along the surface.     

Plasmonic-enhanced two-photon fluorescence with single gold nanoshell

Single gold nanoshell with mutilpolar plasmon resonances is proposed to enhance two-photon fluorescence efficiently.The single emitter single nanoshell configuration is studied systematically by employing the finite-difference time-domain method.The emitter located inside or outside the nanoshell at various positions leads to a significantly different enhancement effect.The fluorescent emitter placed outside the nanoshell can achieve large fluorescence intensity given that both the position and orientation of the emission dipole are optimally controlled.In contrast,for the case of the emitter placed inside the nanoshell,it can experience substantial two-photon fluorescence enhancement without strict requirements upon the position and dipole orientations.Metallic nanoshell encapsulating many fluorescent emitters should be a promising nanocomposite configuration for bright two-photon fluorescence label.The results provide a comprehensive understanding about the plasmonic-enhanced two-photon fluorescence behaviors,and the nanocomposite configuration has great potential for optical detecting,imaging and sensing in biological applications.     

Electromagnetic energy transport in a chain waveguide of silver nanoshell cylinder array

Abstract

Plasmonic wave propagation in a chain waveguide created by a triangular array of silver nanoshell cylinder was investigated using finite element method and Finite Difference Time Domain Method. It is observed that the trimer nanoshell cylinder array provides better field propagation compared to single-chain and pair-chain nanoshell cylinder arrays. Results show that the resonant wavelength of the structure is highly sensitive to the permittivity of either the core or the surrounding medium. It is also observed that as the core thickness of the waveguide is increased surface plasmon resonance shows a red shift.     

Tunable local surface plasmon resonance in liquid-crystal-coated Ag nanoparticles

The far-field and near-field properties of a spherical nematic liquid crystal (NLC) coated metal nanoparticle (NPs) have been investigated in an external field, basing on the quasistatic theory. The resonant wavelength is tunable by varying metallic material of core, anisotropy extent and thickness of liquid crystals (LCs). The field enhancement is along the incident polarization near the outer surface of the shell. The direction of field is reverse in the inner surface comparing with the one if outer shell. In contrast to isotropy shell, the surface plasmon resonance (SPR) shows an obvious red shift and field enhancement near outer surface of the shell always is stronger.     

基于银纳米线的类熊猫型微结构光纤传感器

设计了基于银纳米线等离子体共振效应的大孔径微流通道的类熊猫型微结构光纤传感器,采用全矢量有限元法对该传感器进行了数值研究,讨论了待测液折射率等参数对光纤传感器的损耗和灵敏度的影响。结果表明:随着待测液折射率和银纳米线直径的增大,损耗和光谱峰值λpeak都将增大;并且当银纳米线的直径增加到一定程度时,损耗和灵敏度都会呈现多峰值现象。最后取银纳米线直径d=150 nm,得到最大幅度灵敏度为910 dB/RIU,最大光谱灵敏度为1 400 nm/RIU。     

Goldstone mode of a magnon Bose−Einstein condensate in MnCO<Subscript>3</Subscript>

The dependence of the enhancement of the Raman scattering on the size of a dielectric column is measured in structures with the spatial modulation of the height and lateral sizes of the dielectric coated with a thick metal layer (10–80 nm). It is established that, in the case of a thick metal coating (silver, gold, and copper coatings are used) at dimensions of the dielectric column close to the laser pump wavelength, considerable enhancement of the Raman signal oscillating upon the variation of the geometrical dimensions of the structure is observed. It is shown that the observed resonance enhancement of the Raman signal is associated with the transformation of the electromagnetic radiation into localized plasmon–polariton modes, and the efficiency of such transformation is determined by the commensurability of the wavelength of the plasmon–polariton mode and the planar size of the metal film. For different metal coatings, the dependence of the enhancement of the Raman scattering on the laser wavelength is measured.     

Modulation of Fano resonances in symmetry-broken gold-SiO2-gold nanotube dimers

Fano resonances in the symmetry-broken gold-SiO2-gold(BGSG)nanotubes and the associated dimers have been investigated based on the finite element method.In the BGSG nanotube,the symmetry breaking induced the interactions of the inner gold core and outer gold nanoshell plasmons of all multipolar orders and hence the red-shifts of the plasmon resonance modes and the enhanced quadrupole mode peaks were observed.The interference of the quadrupole mode peak with the subradiant dipole mode caused a Fano-dip in the scattering spectrum.By increasing the core offset-value in the BGSG nanotube,the Fano dip with low energy showed a red-shift and became deeper.Unexpectedly the plasmon coupling between a GSG nanotube and a BGSG nanotube can lead to two strong Fano dips in the scattering spectra of the dimer.It was further noted that the thin side of the BGSG nanotube located at two sides of the dimer gap can lead to the strong near-field coupling between two BGSG nanotubes and hence a deeper and broader Fano dip.     

Internal quantum efficiency enhancement of silicon nanocrystals using double layer Au-rich cermet films

To improve the internal quantum efficiency of silicon nanocrystals, a double layer structure with Au-rich cermet is proposed. In the region far below surface plasmon resonance energy, effective enhancement can be still obtained, which indicates means to make surface plasmon mediated enhancement efficient in a wide wavelength region especially for long wavelength.     

Synthesis and Optical Properties of Anisotropic Metal Nanoparticles

In this paper we overview our recent studies of anisotropic noble metal (e.g. gold and silver) nanoparticles, in which a combination of theory and experiment has been used to elucidate the extinction spectra of the particles, as well as information related to their surface enhanced Raman spectroscopy. We used wet-chemical methods to generate several structurally well-defined nanostructures other than solid spheres, including silver nanodisks and triangular nanoprisms, and gold nanoshells and multipods. When solid spheres are transformed into one of these shapes, the surface plasmon resonances in these particles are strongly affected, typically red-shifting and even splitting into distinctive dipole and quadrupole plasmon modes. In parallel, we have developed computational electrodynamics methods based on the discrete dipole approximation (DDA) method to determine the origins of these intriguing optical features. This has resulted in considerable insight concerning the variation of plasmon wavelength with nanoparticle size, shape and dielectric environment, as well as the use of these particles for optical sensing applications.     

Numerical synthesis of metallic nanostructures for enhancing the emission of a dipole through surface plasmon coupling

In this study, we numerically synthesize a two-dimensional metallic nanostructure consisting of a Au half-space and two separate Ag elliptical cylinders by the simulated annealing (SA) method. The simulated nanostructure is so designed that the surface plasmon polariton (SPP) and the localized surface plasmon (LSP) are simultaneously excited at their common resonant wavelength (535 nm), leading to the enhancement of emission of a nearby dipole source. This enhancement effect is more significant than that of the case where only one of the SPP and LSP is excited. In numerically synthesizing a metallic nanostructure, we try to maximize both the downward emission (in the direction away from the metallic structure) and the emission efficiency. A cost function is defined as some combination of the downward emission and the emission efficiency. We adjust the simulated structure by SA to minimize the cost function at a designated resonant wavelength, and calculate and analyze the spectra of downward emission and emission efficiency for the optimal structure. Other structures are also investigated for comparison. From numerical simulations, it is demonstrated that the enhancement of dipole emission is better for optimization at wavelength 535 nm than at other wavelengths. Note that the downward emission and the emission efficiency can reach maxima almost simultaneously when the SPP and the LSP couple effectively at a common resonant wavelength. This implies that the lighting efficiency of green light-emitting diodes (LEDs) can be increased by the coupling effect at a common resonant wavelength of SPP and LSP.     

Influence of spherical anisotropy on the optical properties of?plasmon resonant metallic nanoparticles

We demonstrate the features of the dipole and quadrupole resonant modes in extinction spectra of spherically anisotropic nanoparticles based on full-wave scattering theory. It is found that in a core–shell nanosphere, the introduction of spherical anisotropy in the core leads to a blue shift in resonant wavelengths for small nanoparticles, while, for large nanoparticles (core radius larger than 90 nm), the dipole resonant wavelength remains unchanged with the variation of spherical anisotropy. In addition, the peak strengths for the dipole and quadrupole modes are also studied. Numerical simulations show that the strong localization of electric fields can be further enhanced and tuned by adjusting the spherical anisotropy in the core. In contrast, the anisotropy introduced in the shell results in a blue shift for small nanoparticles but a red shift for nanoparticles with larger size. The tunability of plasmon resonant shifts in extinction spectra and tailored localization of enhanced fields are revealed.