Excitation Of Localized Surface Plasmons Research Articles

Ti–PS nanocomposites by plasma immersion ion implantation and deposition

We synthesize Ti–PS nanocomposites by plasma immersion ion implantation and deposition (PIII&D) technique. Ti nanoparticles at size of 5–15 nm are found in PS matrix. We propose the formation of Ti nanoparticles as a result of the combined effect of ion implantation and ion condensation in PIII&D process. X-ray photoelectron spectroscopy measurements reveal that Ti atoms have three different chemical states, metal, oxide and carbide. While surface Ti atoms are oxidized, embedded Ti atoms keep their metallic states by surrounding PS matrix. We characterize optical absorbance of Ti–PS nanocomposites by UV–VIS measurements. An adsorption peak due to the excitation of localized surface plasmon is found at wavelength 337.5 nm and the fractal nature of Ti–PS nanocomposites broaden absorption wavelength from UV to infrared. In addition, we use a protein assay to measure protein immobilization. It is found that the amount of protein immobilized on Ti–PS nanocomposites is almost twice than that on pristine PS. The enhancement mechanisms are attributed to the increased surface roughness as well as covalent linkages between protein molecules and functional groups on the surface of Ti–PS nanocomposites.

Single live cell refractometer using nanoparticle coated fiber tip

We present a nano-optical probe for real-time refractive index measurement of single live cell. The probe was made of a tapered fiber tip coated with 13 nm diameter gold nanoparticles. The evanescent wave near the tip excited localized surface plasmon resonance of gold nanoparticles. By measuring the optical intensity scattered from the nanoparticles, the probe showed an intensity sensitivity up to ∼5400% per refractive index unit. The 3T3 fibroblast cell was tested by inserting the probe into the cytoplasm. Refractive index as measured by the localized plasmonic effect was 1.3506, consistent with the results measured by holographic methods.

Localized surface plasmon resonance effects on the magneto-optical activity of continuous Au/Co/Au trilayers

We study how the magneto-optical activity in polar configuration of continuous Au/Co/Au trilayers is affected by the excitation of localized plasmon resonances of an array of Au nanodiscs fabricated on top of them over a dielectric SiO(2) spacer. We show that the effect of the nanodiscs array is twofold. First, it optimizes the absorption of light at specific photon energies corresponding to the localized surface plasmon excitation of the array, modifying the reflectivity of the system (we define this effect as the purely optical contribution). Second, upon localized plasmon resonance excitation, the electromagnetic field in the whole system is redistributed, and an enhanced magneto-optical activity occurs at those energies where the electromagnetic field in the magnetic layer is increased (this effect is identified as the purely magneto-optical contribution of the nanodiscs array).

Optical forces on metallic nanoparticles induced by a photonic nanojet

We investigate the optical forces acting on a metallic nanoparticle when the nanoparticle is introduced within a photonic nanojet (PNJ). Optical forces at resonance and off-resonance conditions of the microcylinder or nanoparticle are investigated. Under proper polarization conditions, the whispering gallery mode can be excited in the microcylinder, even at off resonance provided that scattering from the nanoparticle is strong enough. The optical forces are enhanced at resonance either of the single microcylinder or of the nanoparticle with respect to the forces under off-resonant illuminations. We found that the optical forces acting on the nanoparticle depend strongly on the dielectric permittivity of the nanoparticle, as well as on the intensity and the beam width of the PNJ. Hence, metallic sub-wavelength nanoparticle can be efficiently trapped by PNJs. Furthermore, the PNJ's attractive force can be simply changed to a repulsive force by varying the polarization of the incident beam. The changed sign of the force is related to the particle's polarizability and the excitation of localized surface plasmons in the nanoparticle.

High Sensitivity Transmission-Type SPR Sensor by Using Metallic–Dielectric Mixed Gratings

We theoretically investigate transmission-type SPR sensors with novel metallic-dielectric mixed gratings by rigorous coupled-wave analysis (RCWA), compared to the conventional dielectric gratings based structure. It is found that the transmittance efficiency and the full width at half-maximum (FWHM) of the transmission curve can be modulated by increasing or decreasing the metallic part. Therefore, appropriate proportion of metal part will induce enhancement factor of sensor merit. Furthermore, this novel structure will also bring enhancement of resonant angle shift, which can be explained by plasmonic interpretation based on a surface limited increase of interaction area and excitation of localized surface plasmons (LSPs). The proposed configuration has a wide range of potential applications not only as sensor but also other optical devices.

Characteristics of light intensity enhancement of a silver nanoprism with rounded corners

We have fabricated silver nanoprisms of 100-600 nm side length by focussed ion beam lithography and measured the light intensity scattering spectra using dark-field microscopy. Two resonance peaks due to localized surface plasmon excitation were observed in the spectra and their central frequency shown to depend on the prism size. The near-field electromagnetic intensity distribution with TE-polarized light at the vacuum wavelength of 632.8 nm was measured. We have obtained a much lower light intensity enhancement than previously numerically predicated. However, scattering spectra obtained numerically, taking into account roundness of the prism corners, agree well with experimental ones. At the same time, the numerically determined field distribution was different to the near-field intensity obtained experimentally. Our results suggest the particular shape of the corner region of the prism is a key factor for obtaining a large light intensity enhancement and shaping the local field distribution.

Raman and near‐field spectroscopic study on localized surface plasmon excitation from the 2D nanostructure of gold nanoparticles

We have studied electromagnetic field on the surface of two-dimensional nanostructure of gold nanoparticles through two-photon-induced photoluminescence images by using scanning near-field optical microscope and far-field surface-enhanced Raman scattering measurements. The near-field two-photon-induced photoluminescence image shows that strong inhomogeneous enhancement in two-photon-induced photoluminescence occurs over the two-dimensional nanostructure, representing localized surface plasmon excitations. The results suggest that the local structure of the two-dimensional nanostructure influences the distribution of localized surface plasmon excitation.

Time‐Resolved 2PPE and Time‐Resolved PEEM as a Probe of LSP′s in Silver Nanoparticles

The time‐resolved two‐photon photoemission technique (TR‐2PPE) has been applied to study static and dynamic properties of localized surface plasmons (LSP) in silver nanoparticles. Laterally, integrated measurements show the difference between LSP excitation and nonresonant single electron‐hole pair creation. Studies below the optical diffraction limit were performed with the detection method of time‐resolved photoemission electron microscopy (TR‐PEEM). This microscopy technique with a resolution down to 40 nm enables a systematic study of retardation effects across single nanoparticles. In addition, as will be shown in this paper, it is a highly sensitive sensor for coupling effects between nanoparticles.

带纳米小孔的高灵敏度局域增强表面等离子体传感器优化设计

For breaking through the sensitivity limitation of conventional surface plasmon resonance (SPR) biosensors, novel highly sensitive SPR biosensors with Au nanoparticles and nanogratings enhancement have been proposed recently. But in practice, these structures have obvious disadvantages. In this study, a nanohole based sensitivity enhancement SPR biosensor is proposed and the influence of different structural parameters on the performance is investigated by using rigorous coupled wave analysis (RCWA). Electromagnetic field distributions around the nanohole are also given out to directly explain the performance difference for various structural parameters. The results indicate that significant sensitivity increase is associated with localized surface plasmons (LSPs) excitation mediated by nanoholes. Except to outcome the weakness of other LSP based biosensors, larger resonance angle shift, reflectance amplitude, and sharper SPR curves' width are obtained simultaneously under optimized structural parameters.

Comparative study of atomic force mode and tunneling mode tip-enhanced Raman spectroscopy

In Tip-Enhanced Raman Spectroscopy (TERS) a metal (or metallized) sharp tip is used to enhance the electromagnetic field by a localized surface-plasmon excitation. Two different modes - atomic force mode (AFM) and scanning tunneling mode (STM) - together with their respective types of probe tips are used in TERS experiments. We have compared the efficiency in enhancing the Raman signal on a thin dye layer for metal-coated AFM tips as well as for electrochemically etched metal STM tips. A much higher enhancement factor and better reproducibility were found when using STM tips. The very different performance is mainly attributed to the more efficient plasmonic excitation when using bulk-metal tips and possibly to the morphological differences in the tip and apex shapes existing between the two tip types.

Electric Field Enhancement of Nano Gap of Silver Prisms

Using numerical calculation, we examine the effects of gap distance ofa pair of nano gap silver prisms with rounded corners on the locallight intensity enhancement. Two peaks due to localized surface plasmon(LSP) excitation are observed in a wavelength range from 900 nm to300 nm. The results demonstrate that peaks at a longer and a shorterwavelength corresponded to dipole-like and quadrupole-like LSPresonances, respectively. It is found that a gap distance up to 20 nmprovides larger light intensity enhancement than that of a singlesilver nano prism with rounded corners. Furthermore, nano gap silverprisms are fabricated by direct focused ion beam processing, and wemeasure the scattering light spectrum of a pair of nano prisms by aconfocal optical system. However, the two LSP peaks are not observed invisible range because the sizes of the nano gap and prisms are toolarge.

Crystalline structure’s influence on the near-field optical properties of single plasmonic nanowires

The finite difference time domain method is employed to study the crystalline structure’s influence on the propagation of a local excitation along metallic nanowires of subwavelength cross section. The metallic nanowires are elongated cylinders deposited on a transparent substrate. A tightly focused gaussian beam illuminates one end of the nanowires. According to recent experimental studies, the authors show that the propagation length of the localized surface plasmon excitations depends on the crystalline structure of the nanowire. Thus, they are able to determine the effective permittivity of metals in such a nanostructure versus its crystalline properties. The authors also demonstrate that the field of optical information transport could greatly benefit from the care of the subwavelength optical waveguide’s crystallinity.

Surface plasmon interference excited by tightly focused laser beams

We show that interfering surface plasmon polaritons can be excited with a focused laser beam at normal incidence to a plane metal film. No protrusions or holes are needed in this excitation scheme. Depending on the axial position of the focus, the intensity distribution on the metal surface is either dominated by interferences between counterpropagating plasmons or by a two-lobe pattern characteristic of localized surface plasmon excitation. Our experiments can be accurately explained by use of the angular spectrum representation and provide a simple means for locally exciting standing surface plasmon polaritons.

Optical gas sensitivity of a metaloxide multilayer system with gold-nano-clusters

Abstract In this paper we report on the optical gas sensitivity of a sputtered multilayer system consisting of InxOyNz thin films and gold-nano-clusters. This system shows a reversible change in the optical absorption (increase or decrease of absorbance) during exposure to reducing or oxidizing gases in air. The gold-nano-clusters are randomly distributed on and inside the multilayer system. Here, we demonstrate the optical gas sensitivity at a temperature of 400 °C and three exemplary gas samples: carbon monoxide in dry synthetic air, nitrogen dioxide in dry synthetic air and hydrogen in dry synthetic air. We show that the incorporation of the gold-clusters leads to a broad absorption peak in the range of visible light due to the excitation of localized surface plasmons. The corresponding resonance wavelength is shifted by gas exposure that in turn changes the optical behavior of the multilayer system.

Controlling surface plasmon excitation of pair arrays of metallic nanocylinders

Surface plasmon excitation of pair arrays of silver nanocylinders is studied using finite-difference time-domain simulations. Strong local fields are generated around the nanocylinders due to excitation of localized surface plasmon and electromagnetic fields are confined effectively in the gaps between the nanocylinders. Surface plasmon resonance and local-field enhancement of two-pair arrays can be controlled by changing the illumination direction of the incident light due to induced asymmetric polarization charges. Complex resonant modes could be excited with increasing number of silver nanocylinder pairs. Selective local-field enhancement is observed in the gaps of the pairs by changing the interpair distance of four-pair arrays.

Extraordinary optical transmission in the ultraviolet region through aluminum hole arrays

We investigated the extraordinary optical transmission phenomenon in the UV range by fabricating large-area, free-standing aluminum hole arrays using extreme UV interference lithography and shadow thermal evaporation. Transmission spectra show strong peaks in the UV region resulting from both surface plasmon polariton and localized surface plasmon excitations. The results indicate that the high plasmon frequency of Al is directly responsible for the presence of strong resonance peaks in the UV region, which supports the role of plasmonic phenomena in the extraordinary transmission. The simple fabrication method enables large-area production of such structures for research and industrial production purposes.

Near-field optical properties of single plasmonic nanowires

The authors apply the finite difference time domain method to study the propagation of a local excitation along metallic nanowires of subwavelength cross section. The metallic nanowires are elongated cylinders deposited on a transparent substrate. A tightly focused Gaussian beam illuminates one end of the nanowires. The localized surface plasmon excitations propagate along the nanowire over distances much larger than the incident wavelength. According to recent experimental studies, they show that such nanostructures behave like a Fabry-Pérot cavity with large value of surface plasmon propagation length.

Surface enhanced Raman scattering phenomenon

Surface enhanced Raman scattering and surface enhanced fluorescence phenomena are the result of resonance excitation of localized surface plasmons in nanoparticles of some metals. By appropriate choice of the shape and size of metallic nanoparticles, the kind of adsorbed molecules and the wavelength of the exciting light, it is possible to achieve enhancement of the intensity of Raman scattering equal to 1012-1014. This means that only some molecules inside the exciting light beam are sufficient to record the Raman spectrum. Electromagnetic and chemical mechanisms of enhancement of Raman scattered light and methods of roughness investigation of surfaces exhibiting this promising phenomenon are described in this paper. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Nanowire-based enhancement of localized surface plasmon resonance for highly sensitive detection: a theoretical study

A nanowire-based localized surface plasmon resonance (LSPR) biosensor has been investigated to evaluate the impact of design parameters of nanowires on the excitation of localized surface plasmons (LSPs) and the sensitivity enhancement of a LSPR biosensor. The results based on rigorous coupled wave analysis and finite difference time domain method indicate that significant sensitivity increase is associated with LSP excitation mediated by nanowires and that resonant coupling of LSPs through a nanogroove achieves larger field enhancement and sensitivity improvement than LSP excitation in a single nanowire. A specific optimization provided a nanowire-based structure with the sensitivity increase by more than 23 times as well as good linear detection properties.

Fabrication of Silver Probes for Localized Plasmon Excitation in Near-field Raman Spectroscopy

Abstract We present a new method for preparing a silver probe for tip-enhanced near-field Raman spectroscopy. In this method, the probe is coated with silver colloids by a simple chemical reaction known as a mirror reaction. Silver particles ≈40 nm in diameter, which is ideal for localized surface plasmon excitation in the visible wavelength range, are formed at the tip apex with high reproducibility. Futhermore, tip-enhanced Raman spectra of single-walled carbon nanotubes were measured by using the probe.