Interaction Of Surface Plasmons Research Articles

Long-range interaction of localized surface plasmons in periodic and random patterns of Au nanoparticles

The plasmon resonance of periodic and random arrays of Au-nanodiscs and nano-squares was investigated experimentally and numerically. By randomization, plasmon resonance spectra become broadened, however, the electro-magnetic field enhancement is augmented by a factor of 10–10\(^2\) times at some specific wavelength as shown by the finite-element time-domain calculations. The spatial localization takes place at a fewer hot-spots. The randomized structures are promising for the applications in opto-electronics, sensing and light harvesting.

Holographic plasmonic lenses for surface plasmons with complex wavefront profile

We present a direct-method solution toward the general problem of plasmonic wavefront manipulation and shaping to realize pre-designated functionalities based on the surface-wave holography (SWH) method. We demonstrate theoretically and experimentally the design and fabrication of holographic plasmonic lenses over surface plasmons with complex wavefront profiles. We show that visible light at 632.8 nm transmitting through a high-aspect-ratio slit or a micro-rectangle hole in a silver film can be focused to a preset three-dimensional point spot in free space via appropriately manipulating the interaction of excited surface plasmons with the nanoscale groove pattern of the holographic lens. The experiment results of scanning near-field optical microscopy for measuring the three-dimensional optical field distribution agree well both with designs and with numerical simulations, and this strongly supports the effectiveness and efficiency of the SWH method in the design of plasmonic devices that can fulfill manipulation and transformation of complicated-profile surface plasmons.

Interaction of surface and interface plasmons in extremely thin Al films on Si(111)

The collective electronic excitations in Al thin films with thickness down to mono-atomic layer were studied by scanning tunneling microscopy and angle-resolved high resolution electron energy loss spectroscopy. Clear evidences for a coupling of the Al surface plasmon and Al/Si interface plasmon were observed for the film thickness below 3 ML, which induces a splitting of the normal Al surface plasmon mode. The experimental results can be well explained by a classical model for surface plasmon excitations.

Surface plasmon interactions between the grating with slanted sidewall and a metallic film

Based on the finite difference time domain method, the optical properties and the plasmonic interactions between the grating with slanted sidewall and a thin gold film were investigated theoretically. We compare the similarities and differences of transmission, reflection, and absorption spectra of the composite system and the single grating with slanted sidewall. When the thicknesses of the two films and the slit widths are changed, the resonance peaks show blue-shifts, red-shifts, split, decrease and other physical phenomena. Based on the distributions of electric field component Ex, Ey and the total energy, we explain the physical mechanism of light passing through the grating/film nanosystem. The adiabatic nanofocusing of the system is also discussed.

Surface Plasmon-Coupled Emission of Rhodamine 110 Aggregates in a Silica Nanolayer.

First analysis of strong directional surface plasmon-coupled emission (SPCE) of ground-state formed intermolecular aggregates of Rhodamine 110 (R110) in silica nanofilms deposited on silver nanolayers is reported. Until now, the processes of energy transport and its trapping due to aggregate formation have not been studied in the presence of SPCE. A new approach to multicomponent systems with weakly and strongly fluorescent centers making use of fluorophore-surface plasmon interaction is presented. The analysis is based on comparison of experimental free-space emission spectra (F-SE), experimental SPCE with theoretical surface plasmon resonance spectra (SPR). It is shown that, due to the dispersion of SPCE, the detection of weak aggregate emission is straightforward if only the monomers and aggregates fluorescence spectra are somewhat spectrally shifted. SPCE studies confirmed the formation of weakly fluorescent higher order aggregates of R110 in silica films. The results indicate that the increase of energy transfer from monomers to aggregates is due to fluorophore-plasmon interaction.

Surface plasmon effects in the absorption enhancements of amorphous silicon solar cells with periodical metal nanowall and nanopillar structures

The authors numerically investigate the absorption enhancement of an amorphous Si solar cell, in which a periodical one-dimensional nanowall or two-dimensional nanopillar structure of the Ag back-reflector is fabricated such that a dome-shaped grating geometry is formed after Si deposition and indium-tin-oxide coating. In this investigation, the effects of surface plasmon (SP) interaction in such a metal nanostructure are of major concern. Absorption enhancement in most of the solar spectral range of significant amorphous Si absorption (320-800 nm) is observed in a grating solar cell. In the short-wavelength range of high amorphous Si absorption, the weakly wavelength-dependent absorption enhancement is mainly caused by the broadband anti-reflection effect, which is produced through the surface nano-grating structures. In the long-wavelength range of diminishing amorphous Si absorption, the highly wavelength-sensitive absorption enhancement is mainly caused by Fabry-Perot resonance and SP interaction. The SP interaction includes the contributions of surface plasmon polariton and localized surface plasmon.

Understanding the effects of dielectric medium, substrate, and depth on electric fields and SERS of quasi-3D plasmonic nanostructures

The local electric field distribution and the effect of surface-enhanced Raman spectroscopy (SERS) were investigated on the quasi-3D (Q3D) plasmonic nanostructures formed by gold nanohole and nanodisc array layers physically separated by a dielectric medium. The local electric fields at the top gold nanoholes and bottom gold nanodiscs as a function of the dielectric medium, substrate, and depth of Q3D plasmonic nanostructures upon the irradiation of a 785 nm laser were calculated using the three-dimensional finite-difference time-domain (3D-FDTD) method. The intensity of the maximum local electric fields was shown to oscillate with the depth and the stronger local electric fields occurring at the top or bottom gold layer strongly depend on the dielectric medium, substrate, and depth of the nanostructure. This phenomenon was determined to be related to the Fabry-Pérot interference effect and the interaction of localized surface plasmons (LSPs). The enhancement factors (EFs) of SERS obtained from the 3D-FDTD simulations were compared to those calculated from the SERS experiments conducted on the Q3D plasmonic nanostructures fabricated on silicon and ITO coated glass substrates with different depths. The same trend was obtained from both methods. The capabilities of tuning not only the intensity but also the location of the maximum local electric fields by varying the depth, dielectric medium, and substrate make Q3D plasmonic nanostructures well suited for highly sensitive and reproducible SERS detection and analysis.

Electromagnetic contribution to surface-enhanced Raman scattering from rough metal surfaces: A transformation optics approach

The propagation of surface plasmons along rough metal surfaces is investigated with transformation optics. The roughness is modeled on a nanometer scale either by partly embedding a cylinder of metal into the surface (convex rough surface) or by excavating a cylindrical cavity from it (concave rough surface). These two structures can be treated analytically by means of conformal transformation. The interaction of surface plasmons with the singularities of these structures is shown to induce extreme field enhancements. These modes dominate the surface-enhanced Raman-scattering response and enhancement factors of the order of ${10}^{7}$ are predicted. Interestingly, concave rough surfaces are shown to be the best candidates for surface-enhanced Raman scattering due to a stronger field enhancement and a lower sensitivity to the incident light polarization. Our analytical approach also points out the influence of the contact angle between the asperities and the metal surface on the bandwidth and the efficiency of the light-harvesting process.

Optical constants detection in tin dioxide nano-size layers by surface plasmon resonance investigation

Optical constants of tin dioxide nano-size layers were detected using surface plasmons resonance research technique. Squared reflectance indexes difference as well as the ones with s- and p-polarized light are measured simultaneously. Obtained in the work the refraction coefficient of the tin dioxide film gives the possibility to judge about the structural perfection of the layer and confirms that the film has significant porosity, which is created during the decomposition of the polymer materials used as structuring additives. It is shown that the resonance condition for surface plasmons may be destroyed through the interaction of surface plasmons with surface roughness potential of the film (medium dielectric properties variation).

Modeling and calculation of light absorption in silicon/metal nanocomposites

Silicon thin films over a glass substrate has been considerate an economical and viable alternative for the photovoltaic industry. Implementation of this technology will contribute to preserve a clean environment helping to reach a sustainable future. Nevertheless, by their own nature, Silicon thin films present small light absorption, and its electrical energy conversion mechanisms, besides their non ideal character, are not completely understood. The inclusions of metal nanoparticles in semiconductors can modify and improve the light absorption properties of these materials by surface plasmon interaction. It is well known that metal nanoparticles, deposited on the surface of Si-Solar cells, improve considerable the efficiency of the cell and it has been shown that there is a strong correlation between the surface plasmon excitation frequency and that of the exciting light. To study the light interactions on such material, we have developed a theoretical model that takes into account the incorporation of metallic nano-particles over Silicon thin films. We have obtained an analytical expression for the effective permittivity of the Semiconductor/Nano-particle system, ϵeff using this result we have analyzed the light absorption process in the case of Silicon with two types of metallic inclusions.

Lighting Up Multipolar Surface Plasmon Polaritons by Collective Resonances in Arrays of Nanoantennas

We demonstrate the coupling of multipolar surface plasmons with photonic modes in periodic arrays of metallic nanoantennas. This coupling leads to sharp resonances known as lattice surface modes. In spite of the weak interaction of multipolar surface plasmons with light, lattice surface modes provide an efficient radiative decay channel for emitters in the proximity of the array. We observe a tenfold emission enhancement of dyes coupled to lattice resonances. Lattice surface modes light up multipolar plasmonic resonances, opening new possibilities for fluorescence spectroscopies.

Interaction of surface plasmons with fluxes of charged particles crossing the interface between two media

Surface plasmon instability appearing during the interaction of plasmons with a flux of charged particles crossing the interface between media with different electromagnetic properties is predicted. The conditions under which instability appears are determined and the increments are found. The influence of the potential barrier at the interface on the interaction of surface plasmons with charged particles is investigated.

Enhancing InGaN-based solar cell efficiency through localized surface plasmon interaction by embedding Ag nanoparticles in the absorbing layer

The use of localized surface plasmon (LSP) interaction for significantly enhancing InGaN absorption near its band edge and the overall efficiency of an InGaN-based solar cell by embedding Ag nanoparticles (NPs) in the InGaN absorbing layer is numerically demonstrated. The generation of LSP resonance on the embedded Ag NPs and the NP scattering can produce a field distribution in the InGaN layer for enhancing absorption. It is shown that the embedded Ag NPs do not significantly affect the transport of the photo-generated carriers. The distortion of static electrical stream lines in the solar cell due to the embedded Ag NP leads to a decrease of photocurrent by only a few percents. Based on the material parameter values we use, unless the surface recombination velocity at the interface between the Ag NP and surrounding InGaN is extremely high, Ag NP embedment in the absorbing layer of an InGaN-based solar cell can enhance its efficiency by up to 27%. Such an increase is significantly larger than that achieved by depositing metal NP on the top surface of a solar cell.

Mechanically tunable surface plasmon resonance based on gold nanoparticles and elastic membrane polydimethylsiloxane composite

Surface plasmon in nanoscaled materials has recently attracted a great deal of attention due to its possibility in a wide range of application. From a practical standpoint, it is desirable for the devices having a tunability of surface plasmon frequency. To achieve this goal, in this study, a composite consisting of two-dimensional gold nanoparticles array embedded in elastic polydimethylsiloxane (PDMS) membrane has been synthesized. Because the elastic PDMS membrane has a high malleability, with an external stress, it is very easy to regulate the interparticle distance in the gold nanoparticle array. The change in the distance between each nanoparticle will alter the surface plasmon interaction, and hence surface plasmon frequency can be manipulated. It is found that when the interparticle distance increases, the enhanced surface plasma mutual coupling will cause the blueshift of surface plasmon resonance frequency. The observed result satisfies the forecast based on electromagnetic theory.

Controlling polarization twisting of light resulting from surface plasmon interactions with threefold symmetric nanostructures

The design and architecture of nanostructures for the purpose of controlling and manipulating surface plasmon polariton (SPP) dynamics is currently a focal point of research. It is driven by the predicted impact that plasmonic components will have on many future technologies. In this paper, we demonstrate the first instance of plasmon-mediated polarization reorientation observed in the far field with no associated re-emission directional change. Specifically, it is demonstrated that, as a result of the interaction between SPPs and tailor-designed nanostructures of threefold symmetry characteristics, a polarization twisting of the SPP-mediated reradiated light is attained. It is shown that the dynamics of such an interaction can be controlled externally, enabling active control of the outgoing polarization orientation. In order to further understand the origin of the processes involved, Green's function based simulations of the interactions are presented and confirm that the origin of the polarization twisting can be explained via asymmetrical in-plane SPP scattering.

P53 Detection by Fluorescence Lifetime on a Hybrid Fluorescein Isothiocyanate Gold Nanosensor

p53 is a tumor suppressor whose detection in the body is highly valuable as marker for early cancer diagnosis and prognosis. In this report we have studied constructs based on gold nanoparticles (NPs) functionalized with specific anti-p53 antibodies and with a fluoresceine derivative, FITC. The interaction of surface plasmons on gold NPs few nm in size, with fluorophores bound within few nanometers from the surface, induces changes in the fluorophore excited state lifetime. This parameter follows linearly the p53 concentration in solutions up to 200-400 pM, depending on the size of the NP, with an uncertainty approximatley =25 pM. We have evaluated the specificity of the nanosensor for p53 by testing it against bovine serum albumin, beta-lactoglobulin and lysozyme solutions. The titration of total cell extracts from p53 positive or p53-null cells with the anti-p53 antibody decorated gold NPs indicates that this construct is promising for possible applications to in vivo screening.

Reversible Thermochromic Nanocomposites Based on Thiolate-Capped Silver Nanoparticles Embedded in Amorphous Polystyrene

Technologically useful reversible thermochromic materials can be prepared using very simple polymer-embedded nanostructures. In particular, silver nanoparticles capped by long-chain alkyl-thiolate molecules (i.e., Agx(SCnH2n+1)y, with n > 10) spontaneously organize in aggregates because of the interdigitation phenomenon involving the linear alkyl chains bonded at surfaces of neighboring nanoparticles. Owing to the alkyl-chain interdigitation, nanoparticles very close to each other result and an interaction among their surface plasmon resonances may take place. Surface plasmon interaction causes a splitting of the absorption band whose characteristics depend on the aggregate shape. Since shape-less aggregates are generated, a multiple-splitting of the silver surface plasmon absorption band is observed, which causes a broad absorption spreading on the whole visible spectral region. Amorphous polystyrene containing interdigitated silver nanoparticles has a dark-brown or black coloration, depending on the nanoparticle numerical density, but since the inter-particle distance slightly increases at melting point of interdigitation crystallites a reversible termochromic effect is observed at this special temperature. In particular, the material coloration changes from dark-brown to yellow which is the coloration produced by the surface plasmon absorption of isolated silver nanoparticles. This reversible thermochromism can be finely controlled by modifying the structure of thiolate groups, and precisely, the strength of interactions acting inside the interdigitation crystallites.

An Equivalent Circuit Modeling of an Equispaced Metallic Nanoparticles (MNPs) Plasmon Wire

Based on the electric dipole moment (EDM) model of free oscillating electrons inside a single metallic nanoparticle (MNP), a comprehensive methodology is presented in the paper for calculating the equivalent circuit elements associated with an MNP. To find out the passive circuit elements for the MNP, the electromagnetic (EM) power flows are calculated by deriving the relaxation damping, radiation outflow, host matrix EM coupling, and applied signal interaction. The law of conservation of energy is then used to compute the extended oscillatory equation motion of a spherical MNP. The resonant behavior of a single MNP is represented by a lumped resonant circuit model, where the circuit parameters <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">RLC</i> are derived from the equation of motion of the EDM and EM near-field energy outside the MNP. Finally, equivalent circuit of a linearly equispaced MNPs plasmon wire is modeled as a voltage-controlled voltage source by using the nearest surface plasmon interactions.

Long Range Enhancement of Molecular Fluorescence by Closely Packed Submicro-scale Ag Islands

We found that closely packed submicro-scale Ag islands (each ∼370 nm across and ∼90 nm in height on the average) produced not only extremely short-range fluorescence enhancement for rhodamine dye (RhB) placed only ∼1 nm away from the metal surface, but also a novel, long-range enhancement for the same dye for the metal—molecule distance up to ∼50 nm. The net enhancement factor for the spin-coated RhB, with a fluorescence quantum yield of ∼2 % in the absence of Ag islands, was as high as ∼20-folds at the metal--molecule distance of ∼30 nm. We propose that strong interparticle surface plasmon interactions involving such large Ag islands play crucial roles for the long-range fluorescence enhancement. [DOI: 10.1380/ejssnt.2009.653]

Analytical Investigation of Transmission Properties of Metallic Gratings

We re-examine the classical one-dimensional transmission grating to explain the enhanced transmission in the surface impedance approximation. The nearly zero transmission and extraordinary transmission phenomena related to the surface plasmon are presented by analysing the scattering amplitude of waveguide mode at the output surface of grating. It is revealed that the transmission peaks are related to the Fabry–Perot factor and the interaction of surface plasmon and other diffractive orders.