Study of the Plasmon Talbot Effect of Metallic Nanolenses Induced by Linearly Polarized Illumination

The plasmon Talbot effect of metallic nanolenses was studied theoretically and experimentally for the linearly polarized incident beam case. To demonstrate this self-imaging-based focusing property of the metallic nanolenses, a plasmonic nanolens with five periodic concentric through rings on Al film supported on quartz substrate was numerically studied firstly by the use of rigorous finite-difference and time-domain algorithm. To further demonstrate its working performance experimentally, it was fabricated by means of a focused ion beam direct milling technique. A near-field scanning optical microscope (NSOM) was then employed for the optical characterization of its focusing property. The experimental results indicate that the NSOM probing-based results are in agreement with the theoretical calculation results in general.     

Near-Infrared Super Resolution Imaging with Metallic Nanoshell Particle Chain Array

We propose a near-infrared super resolution near field imaging system with an array of metallic nanoshell particle chain. The imaging array can plasmonically transfer the near field components of dipole sources and the super resolution images can be reconstructed in the output plane. By decreasing the metallic nanoshell’s thickness of the fixed size nanoparticle, the plasmon resonance wavelength of the isolate nanoshell particle is red-shifted to the near-infrared region. The operation wavelength of the imaging array is correspondingly red-shifted to the near-infrared region. In this paper, we study the incoherent and coherent super resolution imaging. The field intensity distributions at the different planes of imaging process are calculated using the finite element method. The simulation results demonstrate that the array has super resolution imaging capability at near-infrared wavelengths in the incoherent and coherent manners. The results also show that the image formation highly depends on the source coherence. In the same structural parameters, the reconstructed images under the illumination of incoherent light source reach to the higher image quality and spatial resolution than the images under the illumination of coherent light source of in phase. By reasonably designing parameters of the imaging array, the approximate spatial resolutions of λ/13 in incoherent case and λ/10 in coherent case are obtained at the near-infrared wavelength of 764 nm. Furthermore, the image–array distance and the chains’ spacing also affect the image reconstruction.     

Optical Absorption Modeling of Plasmonic Organic Solar Cells Embedding Silica-Coated Silver Nanospheres

We numerically study plasmonic solar cells in which a square periodic array of core–shell Ag@SiO₂ nanospheres (NSs) are placed on top of the indium tin oxide (ITO) layer using a 3D finite-difference time-domain (FDTD) method. We investigate the influence of various parameters such as the periodicity of the array, the Ag core diameter, the active layer thickness, the shell thickness, and the refractive index of the shell materials on the optical performance of the organic solar cells (OSC). Our results show that the optimal periodicity of the array of NSs is dependent on the size of Ag core NSs in order to maximize optical absorption in the active layer. A very thin active layer (<70 nm) and an ultrathin (<5 nm) SiO₂ shell are needed in order to obtain the highest optical absorption enhancement. Strong electric field localization is observed around the plasmonic core–shell nanoparticles as a result of localized surface plasmon resonance (LSPR) excited by Ag NSs with and without silica shell. Embedding 50 nm Ag NSs with 1-nm-thick SiO₂ shell thickness on top of ITO leads to an enhanced intrinsic optical absorption in a 40-nm-thick poly(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) active layer by 24.7% relative to that without the NSs. The use of 1-nm-thick ZnO shell instead of SiO₂ leads to an enhanced intrinsic absorption in a 40-nm-thick P3HT:PCBM active layer by 27%.

     

Spatial Distribution of Optical Near-Fields in Plasmonic Gold Sphere Segment Voids

We present a comprehensive experimental and computational study on the electromagnetic field distribution in sphere segment void arrays. Surface plasmon polaritons can be excited in these void arrays, resulting in greatly enhanced electromagnetic fields. With the scanning near-field optical microscope (SNOM) we are able to measure the electromagnetic field distribution at the sample surface. For this purpose, an array of relatively large voids with a sphere diameter of 900 nm was fabricated, allowing for an easy access of the scanning glass-fibre tip and yielding very detailed scans. Complementary, finite-difference time-domain (FDTD) calculations on a complete void array have been performed and compared with the SNOM intensity maps and experimental reflectivity data. We show in a direct way both the existence of extended and localised modes in the Au void array for three different void depths. We also show and discuss the changes that the modes undergo for the different void depths and excitation wavelengths. Moreover, since the simulations were performed for two different void geometries, one containing perfectly spherical void surfaces and another more realistic one, which considers the presence of interstitial wall holes and other imperfections, as observed in scanning electron micrographs, we were able to determine by comparison with the experiment under which conditions an array of idealised sphere segment voids is a meaningful model. This demonstrates that both SNOM and FDTD simulations are powerful tools for understanding the plasmonic response of metallic nanostructures, thus enabling, for instance, a design for applications in ultra-sensitive optical detection.     

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 ε ₂ to surrounding medium dielectric constant ε ₄. Absorption spectrum of \(\left |\omega _{-}^{+}\right \rangle \) mode is red-shifted with increasing core radius when ε ₂ > ε ₄. It is surprising to find that LSPR is blue-shifted with increasing core radius when ε ₂ < ε ₄, and no shift when ε ₂ = ε ₄. These interesting contrary shifts of \(\left |\omega _{-}^{+}\right \rangle \) mode with different ratios ε ₂/ε 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.     

Highly Sensitive Refractive Index Sensing with Surface Plasmon Polariton Waveguides

Two prototypical transducer structures are proposed, including a single-waveguide (SW) and Mach–Zehnder interferometer (MZI), implemented with surface plasmon polariton waveguides. Formulas of the output power with structural parameters are deduced respectively. The sensitivities are found to be proportional to S ₁ for SW and S ₂ for MZI, which are dependent on waveguide parameters. Maximizing S ₁ or S ₂ maximizes the corresponding sensitivity, leading to optimized waveguide designs and preferred operating wavelengths. Sensitivity parameters S ₁ and S ₂ are calculated for fundamental modes of V grooves, triangular wedges, and dielectric-loaded surface plasmon polariton waveguides (DLSPPWs), as a function of measured material refractive index n _c (n _c ?=?1.3～1.6, representative refractive index of biochemical matter), at wavelength λ?=?1.55 μm. Finally, the sensitivity S ₂ is analyzed as a function of work wavelength for DLSPPWs with different ridge thickness and specific fluidic SPP waveguide for biochemical sensing is presented. The results offer foundations for application of surface plasmon polariton waveguides in biochemical sensing.     

Buried Effects of Surface Plasmon Resonance Modes for Periodic Metal–Dielectric Nanostructures Consisting of Coupled Spherical Metal Nanoparticles with Cylindrical Pore Filled with a Dielectric

We numerically investigate the buried effects of surface plasmon resonance (SPR) modes for the periodic silver-shell nanopearl dimer (PSSND) array and their solid counterparts with different buried depths in a silica substrate by means of finite element method with three-dimensional calculations. The investigated PSSND array is an important novel geometry for plasmonic metal nanoparticles (MNPs), combining the highly attractive nanoscale optical properties of both metallic nanoshell and cylindrical pore filled with a dielectric. Numerical results for SPR modes corresponding to the effects of different illumination wavelengths, absorption spectra, pore–dielectric, electric field components and total field distribution, charge density distribution, and the model of the induced local field or an applied field of the PSSND array are reported as well. It can be found that the buried MNPs with cylindrical pore filled with a dielectric in a substrate exhibit tunable SPR modes corresponding to the bonding and antibonding modes that are not observed for their solid counterparts.     

Scattering Efficiency and LSPR Tunability of Bimetallic Ag,Au, and Cu Nanoparticles

Scattering efficiencies of Ag–Cu, Ag–Au, and Au–Cu alloy nanoparticles are studied based on Mie theory for their possible applications in solar cells. The effect of size (radius), surrounding medium, and alloy composition on the scattering efficiency at the localized surface plasmon resonance (LSPR) wavelengths has been reported. In the alloy nanoparticles of Ag_1?x Cu _x , Au_1?x Cu _x and Ag_1?x Au _x ; the scattering efficiency gets red-shifted with increase in x. Moreover, the scattering efficiency enhancement can be tuned and controlled with both the alloy composition and the surrounding medium refractive index. A linear relationship which is in good agreement to the experimental observations between the scattering efficiency and metal composition in the alloys are found. The effect of nanoparticle size and LSPR wavelength (scattering peak position) on the full width half maxima and scattering efficiency has also been studied. Comparison of Au–Ag, Au–Cu, and Ag–Cu alloy nanoparticles with 50-nm radii shows the optical response of Ag–Cu alloy nanoparticle with wide bandwidth in the visible region of the electromagnetic spectrum making them suitable for plasmonic solar cells. Further, the comparison of Ag–Cu alloy and core@shell nanoparticles of similar size and surrounding medium shows that Cu@Ag nanoparticle exhibits high scattering efficiency with nearly the same bandwidth.     

Comparisons of Surface Plasmon Sensitivities in Periodic Gold Nanostructures

The wavelength sensitivities of three kinds of nanostructures (nanoslits, nanoholes, and concentric circles) with various aperture sizes were compared in water environment. These nanostructures were made on a 110-nm-thick gold film with a period of 600 nm. Surface plasmon resonances in these nanostructures produce transmission dips near the phase-matching conditions while peaks at longer wavelengths. The wavelength sensitivities measured at dips are close to theoretical predictions and about 1.5 times larger than those measured at peaks. Such sensitivity difference is attributed to various surface plasmon distributions, as illustrated by the finite-difference time-domain calculations. In addition, the sensitivity decreases with the increase of aperture size. The nanoslit array and concentric circles have better sensitivities than the nanohole array due to the no cut-off transmission.     

Tunable Extraordinary Optical Transmission in a Metal Film Perforated with Two-Level Subwavelength Cylindrical Holes

We propose a novel plasmonic metal structure composed of a silver film perforated with a two-dimensional square array of two-level cylindrical holes on a silica substrate. The transmission properties of this structure are theoretically calculated by the finite-difference time-domain (FDTD) method. Double-enhanced transmission peaks are achieved in the visible and infrared regions, which mainly originate from the excitation of localized surface plasmon resonances (LSPRs), the hybridization of plasmon modes, and the optical cavity mode formed in the holes. The enhanced transmission behaviors can be effectively tailored by changing the geometrical parameters and dielectric materials filled in the holes. These findings indicate that our proposed structure has potential applications in highly integrated optoelectronic devices.     

Plasmonic Properties of Gold Nanostructures on Gold Film

This paper reports on a systematic study of the plasmonic properties of periodic arrays of gold cylindrical nanoparticles in contact with a gold thin film. Depending on the gold film thickness, it observes several plasmon bands. Using a simple analytical model, it is able to assign all these modes and determine that they are due to the coupling of the grating diffraction orders with the propagating surface plasmons travelling along the film. With finite difference time domain (FDTD) simulations, it demonstrates that large field enhancement occurs at the surface of the nanocylinders due to the resonant excitation of these modes. By tilting the sample, it also observes the evolution of the spectral position of these modes and their tuning through nearly the whole visible range is possible. Such plasmonic substrates combining both advantages of the propagative and localised surface plasmons could have large applications in enhanced spectroscopies.

     

Field distribution and quality factor of surface plasmon resonances of metal meshes for mid-infrared sensing

We studied surface plasmon sensors based on micrometric metal meshes by optical transmission spectroscopy as a function of the angle of incidence. The mesh period was set to 2 μm for operation at mid-infrared wavelengths. Metal meshes on dielectric substrates were compared to suspended meshes obtained with a lift-off-free fabrication process, which reduces plasmon damping and increases the quality factor up to 25. We have numerically calculated the electric field distribution of “dark” quadrupole-like modes and found that the suspended mesh provides an enhanced interaction volume extending up to hundreds of nanometers in free space. Our sensors have been experimentally tested and they exhibited a sensitivity up to 1.4?·?10^?3?nm^?1, at least 1 order of magnitude better than standard mid-infrared absorption spectroscopy.     

Emission and Transmission Properties of a Doubly Resonant 3D Nanodisk Yagi–Uda Antenna for Wireless Optical Communications

In this paper, a novel doubly resonant three-dimensional (3D) nanodisk Yagi–Uda antenna, conceived for realizing wireless optical links within electronic circuits, is proposed. The prominent emitting properties of this nanoantenna have been deeply investigated both in the near and far field through a useful comparison with a more traditional 3D nanorod Yagi–Uda antenna. The behavior of the nanodisk antenna, both configured as a single nanoantenna and arranged in planar arrays, have been illustrated, emphasizing its improved performances with relation to crucial aspects as directional features, wavelength bands of operation, frequency tuning, and polarization influence on radiation. In particular, the single nanodisk antenna has been accurately designed to enhance the transmission feature in the near field at the wavelengths λ?=?1.3 and λ?=?1.55 μm. Also, the emission pattern of the array of nanodisk antennas has been properly tailored to ensure high peaks of directivity and narrow beam width in those ranges. Hence, efficient unidirectional angle patterns have been shaped for any operation wavelength and dimensions of the array, reaching extremely effective outcomes for a 3?×?3 array, which exhibits a maximum of directivity of 19 and 17.6 and ?3 dB points at 18° and 21° for λ?=?1.3 and λ?=?1.55 μm, respectively.     

Plasmonic Focusing in Nanostructures

In this review, we show that by designing the metallic nanostructures, the surface plasmon (SP) focusing has been achieved, with the focusing spot at a subwavelength scale. The central idea is based on the principle of optical interference that the constructive superposition of SPs with phase matching can result in a considerable electric-field enhancement of SPs in the near field, exhibiting a pronounced focusing spot. We first reviewed several new designs for surface plasmon focusing by controlling the metallic geometry or incident light polarization: We made an in-plane plasmonic Fresnel zone plates, a counterpart in optics, which produces an obvious SP focusing effect; We also fabricated the symmetry broken nanocorrals which can provide the spatial phase difference for SPs, and then we propose another plasmon focusing approach by using semicircular nanoslits, which gives rise to the phase difference through changing refractive index of the medium in the nanoslits. Further, we showed that the spiral metallic nanostructure can be severed as plasmonic lens to control the plasmon focusing under a linearly polarized light with different angles.

     

Hydrodynamic Analysis and Responsivity Improvement of a Metal/Semiconductor/Metal Plasmonic Detector

Characteristic improvements of photon/plasmon detectors have been the subject of several investigations in the area of plasmonic integrated circuits. Among different suggestions, silicon-based metal-semiconductor-metal (MSM) waveguides are one of the most popular structures for the implementation of high-quality photon/plasmon detectors in infrared wavelengths. In this paper, an integrated silicon-germanium (SiGe) core MSM plasmon detector is proposed to detect λ = 1550 nm with internal photoemission mechanism. Performance characteristics of the new sub-micron device are simulated with a simplified hydrodynamic model. In a specific bias point (V = 3 V and the incident optical power of 0.31 mW), the output current is 404.3 μA (276 μA detection current and 128.3 μA dark current), responsivity is 0.89 A/W, and the 3-dB electrical bandwidth is 120 GHz. Simulation results for the proposed plasmon detector, in comparison with the empirical results of a reported Si-based MSM device, demonstrate considerable responsivity enhancement.

     

Tuning the Fano Resonance Between Localized and Propagating Surface Plasmon Resonances for Refractive Index Sensing Applications

Localized and propagating surface plasmon resonances are known to show very pronounced interactions if they are simultaneously excited in the same nanostructure. Here, we study the Fano interference that occurs between localized surface plasmon resonance (LSPR) and propagating surface plasmon polariton (SPP) modes by means of phase-sensitive spectroscopic ellipsometry. The sample structures consist of periodic gratings of gold nanodisks on top of a continuous gold layer and a thin dielectric spacer, in which the structural dimensions were tuned in such a way that the dipolar LSPR mode and the propagating SPP modes are excited in the same spectral region. We observe pronounced anti-crossing and strongly asymmetric line shapes when both modes move to each other’s vicinity, accompanied of largely increased phase differences between the respective plasmon resonances. Moreover, we show that the anti-crossing can be exploited to increase the refractive index sensitivity of the localized modes dramatically, which result in largely increased values for the figure-of-merit which reaches values between 24 and 58 for the respective plasmon modes.     

中国斑粉蝶属分类研究（鳞翅目：粉蝶科）

系统地整理了中国斑粉蝶属DeliasHübner,1819的全部种类,共11种31亚种,包括3个中国 新记录亚种：倍林斑粉蝶指名亚种D. berinda berinda Moore、洒青斑粉蝶不丹亚种D.Sanaca bhutya Talbot和侧条斑粉蝶帕瓦亚种D. lativitta parva Talbot。提出将D.Lativitta tai Yoshino作为侧条斑粉蝶云南亚种D. lativitta yunnana Talbot的同物 异名,D. patrua guiyangensis Zhou et Zhang作为Delias berinda adelma Mitis的同物异名。阐述了各亚种的主要识别特征及其地理分布,分析了区系成分,并提供了分 种检索表及全部种类的雄外生殖器和大部分种类的雌性外生殖器特征图。附有3新记录亚种和国 内未见标本记载的2种的成虫彩色照片     

Visualization of Near-Field Enhancements of Gold Triangles by Nonlinear Photopolymerization

We report in this paper the near-field distribution in the case of gold triangle arrays by means of two-photon polymerization for a dipole and a quadrupole plasmon mode. In order to link the finite difference in the time domain (FDTD) simulations of the triangle array and the experimental results, extinction spectra for both cases in air and SU-8 environments are shown. In case of the 40-nm thick gold triangles with 85-nm side-length, we show that the calculated and experimentally obtained near-field for the excited dipole mode has the same distribution along the polarization of the exciting laser beam. In case of bigger triangles of 540-nm side-length a quadrupole mode is excited, which leads to a rotation of the near-field distribution by 90° referred to the polarization of the beam. This effect is also shown in the FDTD simulations.     

Rhodium Plasmonics for Deep-Ultraviolet Bio-Chemical Sensing

Rhodium (Rh) has been recently introduced as a perfect metal for ultraviolet (UV) applications with the advantages of its oxide-free nature and support of strong plasmon resonant modes at very short wavelengths. We report on a simple platform of nanoplasmonic structures to support strong plasmonic Fano resonances across the deep-UV spectrum for biochemical sensing applications. We investigate the plasmonic response of several types of Rh nanoparticles and designed dimer-type antennas using nanorings with geometrical tunability in both symmetric and antisymmetric assemblies. Using numerical and theoretical methods, it is shown that Rh-based dimer antennas with broken symmetry can be tailored to support strong plasmon resonant modes at the deep-UV region (\( E>6\; eV \)). We also propose a complex infinity-shaped structure composed of a pair of split rings with a nanodisk in between with extra degree of tunability to push the plasmon resonant modes further in deep-UV spectrum. Plasmon hybridization theory is used to describe formation of plasmonic Fano-resonant dips in simple nanoscale assemblies. We calculate the corresponding figure of merit for the Rh-based nanostructure around 11.5 which shows an excellent sensitivity to the refractive index perturbations of the surrounding medium at very short wavelengths for sensing applications.