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1.
A novel method is presented for complex structure fabrication, which is capable of breaking the hexagonal symmetry of the conventional colloid sphere lithography via the interferometric illumination of colloid sphere monolayers (IICSM). It is demonstrated that the perfect lateral synchronization of a linear intensity modulation originating from two-beam interference with respect to a hexagonal colloid sphere monolayer makes it possible to tune four complex structure parameters independently. Based on comparative study of hexagonal and rectangular hole doublet-arrays, which can be generated by linearly polarized light via homogeneous illumination and via IICSM, it is shown that the novel IICSM method enables plasmonic spectral engineering with higher degrees of freedom. The unique spectral properties of the complex patterns attainable via IICSM are more precisely tunable by properly selected azimuthal orientation during illumination and by the surrounding medium. It is shown that coupling phenomena between propagating and localized plasmonic modes on appropriately designed complex structures result in unique charge and near-field distribution accompanied by narrow Fano lines. Optimal configurations of complex plasmonic structures consisting of a rectangular array of hole doublets with different geometrical size parameters are presented, which ensure enhanced sensitivity in bio-detection. 相似文献
2.
A facile procedure to fabricate large arrays of highly ordered metal nanocups, 250 nm in diameter, is reported. The nanostructure
is generated from periodic photoresist templates created by holographic laser interference lithography. A subsequent gold
deposition and a peeling-off step respectively results in a large area of hemispherical nano-indentations or nanocups. A wide
range of coating materials can be used, and the dimensions and periodicity of the structure are easily controlled. The structure’s
ability to support localized surface plasmon polaritons was manifested by reflectance spectroscopy. A good correlation between
experimental data and calculated data was observed. 相似文献
3.
We present a quantum mechanical approach to calculate broadening of plasmonic resonances in metallic nanostructures due to collisions of electrons with the surface of the structure. The approach is applicable if the characteristic size of the structure is much larger than the de Broglie electron wavelength in the metal. The approach can be used in studies of plasmonic properties of both single nanoparticles and arrays of nanoparticles. Energy conservation is insured by a self-consistent solution of Maxwell's equations and our model for the photon absorption at the metal boundaries. Consequences of the model are illustrated for the case of spheroid nanoparticles, and results are in good agreement with earlier theories. In particular, we show that the boundary-collision broadening of the plasmonic resonance in spheroid nanoparticles can depend strongly on the polarization of the impinging light. 相似文献
4.
The ability to precisely tailor lineshapes, operational bandwidth, and localized electromagnetic field enhancements (“hot spots”) in nanostructures is currently of interest in advancing the performance of plasmonics-based chemical and biological sensing techniques. Fractal geometries are an intriguing alternative in the design of plasmonic nanostructures as they offer tunable multiband response spanning the visible and infrared spectral regions. A numerical study of the optical behavior of ternary tree fractal plasmonic nanoantenna is presented. Self-similar features are seen to emerge in the extinction spectra with the increase in fractal order N of the tree structure. Plasmon oscillations occurring at different length scales are shown to correspond to the multiple peaks and are compared with the spatial maps of electric field enhancement at the surface of the nanoantenna. The multiple peaks are shown to be independently tunable by structural variation. The robustness of the spectral response and polarization dependence arising due to various asymmetries is discussed. 相似文献
5.
We report a simple method for preparation of plasmonic nanostructures containing two, three, four, and five closely spaced 15-nm gold particles. The structures were separated from each other and purified to greater than 90 % by electrophoresis. The plasmon absorption spectra of the structures are redshifted with respect to the spectrum of gold nanoparticles not connected to each other. The magnitude of the redshift is directly proportional to the number of nanoparticles in the structure. 相似文献
6.
A set of periodic plasmonic nanostructures is designed and fabricated as a means to investigate light absorption in single-crystal silicon thin-film structures with silicon-on-insulator (SOI) wafers as a model system. It is shown both computationally and experimentally that plasmon-induced absorption enhancement is remarkably higher for such devices than for thick or semi-infinite structures or for the thin-film amorphous silicon solar cells reported in the literature. Experimental photocurrent enhancements of the orders of 12 and 20 are demonstrated for non-optimized 2200-nm-thick photoconductive and 300-nm-thick photovoltaic test structures, respectively. Theoretical absorption enhancements as high as 80 are predicted to be achievable for the similar structures. The features of the spectral enhancements observed are attributed to several interacting resonance phenomena: not just to the favourable scattering of light by the periodic plasmonic nanoparticle arrays into the SOI device layer and coupling to the waveguide modes interacting with the plasmonic array but also to the Fabry-Pérot type interferences in the layered structure. We show that the latter effect gives a significant contribution to the spectral features of the enhancements, although frequently ignored in the discussions of previous reports. 相似文献
7.
We present a computational study of the plasmonic response of a gold–silica–gold multilayered nanostructure based on truncated nanocones. Symmetry breaking is introduced by rotating the nanostructure and by offsetting the layers. Nanocones with coaxial multilayers show dipole–dipole Fano resonances with resonance frequencies depending on the polarization of the incident light, which can be changed by rotating the nanostructure. By breaking the axial symmetry, plasmonic modes of distinct angular momenta are strongly mixed, which provide a set of unique and higher order tunable Fano resonances. The plasmonic response of the multilayered nanocones is compared to that of multishell nanostructures with the same volume and the former are discovered to render visible high-order dark modes and to provide sharp tunable Fano resonances. In particular, higher order tunable Fano resonances arising in non-coaxial multilayer nanocones can vary the plasmon lines at various spectral regions simultaneously, which makes these nanostructures greatly suitable for plasmon line shaping both in the extinction and near field spectra. 相似文献
8.
We fabricated inclined Au nanocup arrays by using the nanosphere lithography method combined with dichloromethane etching and investigated their optical properties. The transmittance spectra of these Au nanocup arrays under different polarizations and incident angles were detected and discussed. Surface plasmon resonance was employed to explain the peaks in the spectra. These inclined Au nanocup arrays may be useful for the potential applications in plasmonic devices. 相似文献
9.
A high performance plasmonic sensor based on a metal-insulator-metal (MIM) waveguide coupled with a double-cavity structure consisting of a side-coupled rectangular cavity and a disk cavity is proposed. The transmission characteristics of the rectangular cavity and disk cavity are analyzed theoretically and the improvements of performance for the double-cavity structure compared with a single cavity are studied. The influence of structural parameters on the transmission spectra and sensing performance are investigated in detail. A sensitivity of 1136 nm/RIU with a high figure of merit of 51,275 can be achieved at the resonant wavelength of 1148.5 nm. Due to the high performance and easy fabrication, the proposed structure may be applied in integrated optical circuits and on-chip nanosensors. 相似文献
10.
We report the remote excited Raman optical activity (ROA) of adenine along Ag plasmonic waveguide. First, the surface plasmons that propagate along Ag nanowire is demonstrated experimentally. Second, the Raman spectra of adenine are measured experimentally. Third, the remote exited ROA by plasmonic waveguide are measured and compared. It is found that the plasmon chirality strongly influenced the molecular ORA by the local surface plasmon and remote plasmon waveguide. The plasmon chirality of nanostructures and the chirality plasmon waveguide should be considered in the experiments for the local and remote measurement. 相似文献
11.
In this paper, the simultaneous switching and sensing capabilities of a compact plasmonic structure based on a conventional rectangular hole in a silver film are proposed and investigated. The proposed structure has ultrahigh sensitivity up to 3000 nm/RIU and high figure of merit of 170 RIU−1. Also, the simulation results show the potential of the presented refractive index sensor to detect malaria infection, cancer cells, bacillus bacteria, and solution of glucose in water. Simultaneously, by changing the incident lightwave polarization, the structure behaves like a plasmonic switch, which has high extinction ratios of 15.81, 31.20, and 25.03 dB at three telecommunication wavelengths of 850, 1310, and 1550 nm, respectively. The ultrafast response time of 20 fs is achieved for the wideband application of the switching capability at the wavelength range of 1056 to 1765 nm. Moreover, the equivalent circuit model and transmission (ABCD) matrix methods are derived to validate the simulated results. Simple design, good agreement between the numerical and analytical results, biomedical applications, ultrahigh sensitivity, and ultrafast performance of the proposed structure help this idea to open up paths for design and implementation of other multi-application plasmonic devices in near-infrared region. To the best of our knowledge, the mentioned analytical methods have not been studied former at near-infrared wavelengths. Therefore, the achievements could pave the way for verifying the simulation results of plasmonic nanostructures in future investigations. 相似文献
12.
The double-layered hexagonal disks of the extracellular hemoglobin of the annelid worm Ophelia bicornis form two types of two-dimensional crystalline arrays. The hexagonal type exhibited a typical honeycomb pattern of top views with a center-to-center distance of 26.2 nm. Laterally oriented molecules formed rectangular crystals with lattice constants a = 26.7 run and b = 19.8 nm. The three-dimensional structure was determined from both crystal forms by reconstruction from images of tilt series. At the resolutions obtained, 1.8 nm for the hexagonal form and 2.5 nm for the rectangular form, flattening of the hemoglobin molecules against the support was observed. Nevertheless the two independent reconstructions provided information about the mass distribution within the main subunit and the connectivity between different parts of the molecule. 相似文献
13.
The chiroptical response of plasmonic chiral nanostructures can be tuned by combining different structures. In this paper, an L-shaped metal strip is introduced into a rectangular metal nanohole to generate absorption circular dichroism (ACD). The results of a finite-element method calculation show that ACD effects result from contorted electrical oscillations in the L-shaped strip. Additional calculations show that the ACD effects of the proposed metasurface depend strongly on the structure parameters. These findings provide not only a mechanism for enhancing chiroptical responses in planar structures but also a general strategy for the chiral manipulation of light and creation of chiroptical devices. 相似文献
14.
Circular and bow tie-shaped Au nanoholes arrays were fabricated on gold films deposited on the tips of single-mode optical fibers. The nanostructures were milled using focused ion beam with a high quality control of their shapes and sizes. The optical fiber devices were used for surface-enhanced resonance Raman scattering (SERRS) measurements in both back- and forward-scattering geometries, yielding promising performance in both detection arrangements. The effect of the hole shape on the SERRS performance was explored with the bow tie nanostructures presenting a better SERRS performance than the circular holes arrays. The results present here are another step towards the development of optical fiber tips modified with plasmonic nanostructures for SERRS applications. Figure Circular and bow tie-shaped nanohole arrays were milled on gold films deposited on the tips of single-mode optical fibers. The arrays were fabricated by focused ion beam milling, which allowed good control over the sizes and the shapes of the nanostructures. The optical fiber devices were used for surface-enhanced resonance Raman scattering (SERRS) measurements in both back- and forward-scattering geometries. This work represents another step towards the development of optical fiber tips modified with plasmonic nanostructures for SERRS applications 相似文献
15.
A compact plasmonic lens is proposed in this paper. This plasmonic lens consists of rectangular holes etched on the silver film and arranged on one straight line and possesses the characteristics of short focus length, ultrathin thickness, and strong focus ability. The theoretical design for the plasmonic lens abides by the constructive interference theorem, and the surface plasmon polaritons excited by the holes with linearly polarized light illumination focuses effectively. The plasmonic lenses with single and double focus spots are provided, and the simulation experiment gives the powerful verification. The distinct structure feature and the excellent focusing characteristic of this plasmonic lens are benefit for its applications in optical integration. 相似文献
16.
Glancing angle deposition is a powerful method for direct fabrication of nanostructures on various substrates. In this research, GLAD method has been used to fabricate Ag nanostructures with columnar morphology for refractive index sensing applications. The morphology and plasmonic properties of the nanostructures are controlled by changing deposition parameters such as glancing angle, speed of azimuthal rotation of the substrate, and the height of deposited nanostructures. The results show that increasing the deposition thickness from 200 to 500 nm leads to narrowing the plasmonic peak, which mainly relates to increment of the distance between larger nanostructures. By changing the glancing angle between 86° to 80°, the narrowest plasmonic peak corresponding to the greatest sensitivity has been obtained for the film deposited at the angle of 82°. Also, increment of the rotation speed of the samples leads to narrowing of the plasmonic peaks. By measuring the refractive index sensitivity (RIS) of the nanostructures, a best sensitivity of 154 nm/RIU has been obtained. Finally, we investigated the stability of Ag nanostructures in deionized water by introducing a new stabilizing technique in which a thin Au layer is coated on the Ag nanostructures. This technique has the merits of simultaneously protecting the Ag nanostructures against oxidation and keeping their refractive index sensitivity high enough for long time usages. 相似文献
17.
The sensitivity of the wavelength position of localized surface plasmon resonance (LSPR) in metal nanostructures to local changes in the refractive index has been widely used for label-free detection strategies. Tuning the optical properties of the nanostructures from the visible to the infrared region is expected to have a drastic effect on the refractive index sensitivity. Here, we theoretically investigate the optical response of a newly designed plasmonic interface to changes in the bulk refractive index by the finite difference time domain method. It consists of a structured interface, where the planar interface is superposed with dielectric pillars 30 nm in height and 125 nm in length with a separation distance of 15 nm. The pillars are covered with U-shaped gold nanostructures of 50 nm in height, 125 nm in length, and 5 nm of gold base thickness. The whole structure is finally covered with a 5-nm thick dielectric layer of n 2?=?2.63. This plasmonic structure shows bulk refractive index sensitivities up to 1750 nm/RIU (RIU : refractive index unit) in the near infrared ( λ?=?2621 nm). The enhanced sensitivity is a consequence of the extremely enhanced electrical field between the gold nanopillars of the plasmonic interface. 相似文献
18.
Plasmonic Fano resonances arise in symmetric single-layer conical nanoshells, which can be switched on and off by changing the polarization of the incident electric field. By breaking the symmetry, higher-order dark hybridized modes emerge in the spectrum, which couple to the superradiant bright mode and induce higher-order plasmonic Fano resonances. From a comparison with spherical nanostructures, it comes out that single-layer conical nanoshells are found to be highly capable in the generation of higher-order Fano resonances with larger modulation depths in the optical spectra. Such nanostructures are also found to offer high values of figure of merit and contrast ratio due to which they are highly suitable for biological sensors. 相似文献
19.
Small metal nanostructures, especially gold and silver nanoparticles, are known for their interesting optical properties caused by plasmonic effects. Molecular plasmonics, a combination of these optically active nanostructures with the molecular world, opens new possibilities for bioanalytics and (bio-) nanophotonics. Isotropic or anisotropic, homogeneous or heterogeneous metal nanoparticles provide a platform for different, highly defined functional units with interesting optical properties such as plasmon waveguides or molecular beacons. Nanohole arrays in metal layers are another promising component for nanophotonics. New photonic materials were realized from combinations of single metal nanoparticles with individual nanoholes in metals. Atomic force microscopic imaging was used to determine the particle location as well as the lateral dimensions and the topography of the resulting structures. Besides ultramicroscopic characterization of the nanoarrangements, such as nanoparticles positioned in nanoholes, far-field optical methods were also applied to investigate their optical properties. 相似文献
20.
The structure of the human low-density lipoprotein (LDL) was analyzed in vitreous ice using cryo-electron microscopy (cryo-EM). In relatively thick cryo-EM preparations, random orientation of LDL particles produced various types of projections on the microscope screen, including circular projections with a high-density ring and rectangular projections with two high-density bands. However, in especially thin preparations, preferred, non-random orientations of the LDL particle produced only circular projections of the lipoprotein structure. In preparations with high LDL concentrations, ordered two-dimensional arrays, including hexagonal arrangements of circular projections and short stacks of rectangular projections, were observed. These observations are consistent with a discoid shape of the LDL particle, and suggest that surface tension forces may influence orientation of the LDL disc in thin aqueous films. Face-on orientation of LDL in especially thin cryo-EM preparations may explain earlier difficulties in identifying discoid features of the lipoprotein particle, and illustrates that some caution is warranted when attempts are made to reconstruct the three-dimensional structure of LDL from cryo-electron micrographs. 相似文献
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