Energy Transfer Across a Metal Film Mediated by Surface Plasmon Polaritons

Direct evidence for surface plasmon-mediated enhanced light transmission through metallic nanohole arrays

This paper provides direct evidence for the role of surface plasmons in the enhanced optical transmission of light through metallic nanoscale hole arrays. Near-field optical images directly confirmed the presence of surface plasmons on gold nanohole arrays with interhole spacings larger than the surface plasmon wavelength. A simple interference model provides an intuitive explanation of the two types of fringe wavelengths observed in the near-field optical images. Far-field spectroscopy revealed a surface plasmon band that contributed a factor > 8 to the transmission enhancement. Furthermore, silicon nanohole arrays did not exhibit any features in the near-field, which demonstrates that metallic materials are necessary for enhanced light transmission through nanohole arrays.

Self-consistent quantum mechanical model for the description of excitation energy transfers in molecules at interfaces

In this paper we present a quantum mechanical model to study excitation energy transfers in molecular systems located in the vicinity of an interface. The model is based on an approximate solution of the time-dependent density functional theory equations and solvent effects are introduced in terms of the integral equation formalism version of the polarizable continuum model. A unique characteristic of this model is that environment induced polarizing effects on the interacting molecules and screening effects on their interaction are included in a coherent and self-consistent way. The model is applied to different situations of the ethylene dimer in the vicinity of an air/water interface and compared with an alternative quantum electrodynamics approach.

Surface Plasmon−Quantum Dot Coupling from Arrays of Nanoholes

The coupling of semiconductor quantum dots (QDs) to the surface plasmon (SP) modes of nanohole arrays in a metal film was demonstrated for the first time, showing enhancement in the spontaneous emission by 2 orders of magnitude. The SP-enhanced transmission resonances of the nanohole arrays were tuned around the photoluminescence (PL) peak of polystyrene-b-poly(acrylic acid) (PS-b-PAA)-stabilized cadmium sulfide (CdS) quantum dots (QDs) in contact with the arrays. As a result the overall PL from the SP-QD system was enhanced by 2 orders of magnitude, even after excluding the enhanced transmission of the nanohole array without the QDs. The maximum enhancement occurred when the resonance from the nanohole array matched the QD PL spectrum. Time-resolved PL measurements were used to estimate the relative contribution of different physical mechanisms to the enhanced spontaneous emission. The increased spontaneous emission in the SP-QD system is promising for prospective plasmonic light-emitting devices incorporating QDs.

Right bipyramids of silver: a new shape derived from single twinned seeds

Silver nanoparticles with a single (111) twin were selectively nucleated and grown for the first time to produce right bipyramids 75-150 nm in edge length. Key to the production of single twinned seeds was the addition of NaBr to a polyol synthesis in which AgNO3 is reduced by ethylene glycol in the presence of poly(vinyl pyrrolidone). Examination of nanoparticles at different stages of the reaction with electron microscopy revealed that the spherical, single twinned seeds grew to become right bipyramids through enlargement of their (100) facets. The UV-vis-NIR spectrum exhibited by right bipyramids is distinct from that of any other silver nanostructure, and their sharp corners make these new nanoparticles especially promising for enhancement of Raman scattering.

Optically produced arrays of planar nanostructures inside fused silica

Linearly polarized femtosecond light pulses, focused inside fused silica to an intensity that leads to multiphoton ionization, produce arrayed planes of modified material having their normal parallel to the laser polarization. The planes are < or = 10 nm thick and are spaced at approximately lambda/2 in the medium for free space wavelengths of both 800 and 400 nm. By slowly scanning the sample under a fixed laser focus, order is maintained over macroscopic distances for all angles between the polarization and scan direction. With the laser polarization parallel to the scan direction we produce long-range Bragg-like gratings. We discuss how local field enhancement influences dielectric ionization, describe how this leads to nanoplane growth, why the planes are arrayed, and how long-range order is maintained.

Plasmonics: merging photonics and electronics at nanoscale dimensions

Electronic circuits provide us with the ability to control the transport and storage of electrons. However, the performance of electronic circuits is now becoming rather limited when digital information needs to be sent from one point to another. Photonics offers an effective solution to this problem by implementing optical communication systems based on optical fibers and photonic circuits. Unfortunately, the micrometer-scale bulky components of photonics have limited the integration of these components into electronic chips, which are now measured in nanometers. Surface plasmon-based circuits, which merge electronics and photonics at the nanoscale, may offer a solution to this size-compatibility problem. Here we review the current status and future prospects of plasmonics in various applications including plasmonic chips, light generation, and nanolithography.

Gold–conductive polymer nanoparticles: A hybrid material with enhanced photonic reactivity to environmental stimuli

We have designed a simple synthetic procedure to encapsulate colloidal gold nanoparticles by electrostatic adsorption with water-soluble poly(aniline-2-carboxylic acid). The composite nanoparticles are stable in aqueous buffer and retain the respective optical reactivity of the gold colloid to refractive index increases, and of the conductive polymer to pH changes and oxidoreduction. The new composite displays, however, significant enhancements in photonic performance when compared to the individual components, which seem to result from electronic interplay between the two materials in the hybrid structure. The enhanced photonic reactivity of the composite structure offers new opportunities for biosensing application.

Conducting Polymer Electrochemical Switching as an Easy Means for Designing Active Plasmonic Devices

Due to the continuously increasing demand for ultimate miniaturization of electronic and photonic systems, molecular electronics and plasmonic devices are currently booming as alternative technologies because of their very promising potential in writing, reading, storing, and processing information at the nanoscale. Conducting polymers or oligomers have been proposed and used as basic building blocks in molecular and plastic electronics since the end of the 80s. Plasmonics is, on the other hand, an emerging branch of photonics which uses nanostructured materials that support surface plasmons. Among plasmonic devices, active plasmonic devices are still lacking. In this work, we report on new active molecular plasmonic devices in which the electrochemical switching of a nanometric film of conductive polymer between its reduced and oxidized state is used in order to control, switch, and modulate localized surface plasmon (LSP) resonance of gold nanoparticle arrays.

Analytic design and visualization of multiple surface plasmon resonance excitation using angular spectrum decomposition for a Gaussian input beam

We propose an exact design, analysis, and visualization method for multiple surface plasmon resonance (MSPR) mode excitation phenomena for a structure composed of an optimized-thickness polymethyl-methacrylate layer and a gold thin-film layer. The proposed simulation method is based on a recursive transfer matrix method (R-TMM) and Gaussian angular spectrum decomposition. Our method illustrates, under the Kretchmann-Raether attenuated total reflection (ATR) geometry, the response for an angle-modulated Gaussian incident beam. To verify the simulation results we also performed experiments to excite MSPR modes under the ATR geometry. Our fast and exact R-TMM with the Gaussian angular spectrum method can be widely applied to the design and analysis of metal- and dielectric-composed thin film structures.

Surface Plasmon Resonance-Mediated Colloid Gold Monolayer Junctions

Because of the localized field amplification that occurs, excitation of surface plasmons (SPs) in metal nanoparticle-based current-carrying nanoelectronic devices is expected to lead to new and interesting applications. We report a simple way to prepare surface plasmon resonance (SPR)-mediated colloid Au monolayer junctions by a wet chemistry and soft top electrode deposition. The SPR-enhanced junction current is observed upon illumination with light of energies close to the nanoparticle plasmon resonance wavelengths. This current is superimposed on tunneling current observed in the absence of surface plasmons.

Anisotropic Metal Nanoparticles: Synthesis, Assembly, and Optical Applications

This feature article highlights work from the authors' laboratories on the synthesis, assembly, reactivity, and optical applications of metallic nanoparticles of nonspherical shape, especially nanorods. The synthesis is a seed-mediated growth procedure, in which metal salts are reduced initially with a strong reducing agent, in water, to produce approximately 4 nm seed particles. Subsequent reduction of more metal salt with a weak reducing agent, in the presence of structure-directing additives, leads to the controlled formation of nanorods of specified aspect ratio and can also yield other shapes of nanoparticles (stars, tetrapods, blocks, cubes, etc.). Variations in reaction conditions and crystallographic analysis of gold nanorods have led to insight into the growth mechanism of these materials. Assembly of nanorods can be driven by simple evaporation from solution or by rational design with molecular-scale connectors. Short nanorods appear to be more chemically reactive than long nanorods. Finally, optical applications in sensing and imaging, which take advantage of the visible light absorption and scattering properties of the nanorods, are discussed.

Heterodimers of nanoparticles: formation at a liquid-liquid interface and particle-specific surface modification by functional molecules

On the basis of a fundamental property of nanoparticles, the self-assembling at a liquid-liquid interface to form "colloidosomes", a heterogeneous reaction takes place on the exposed surface of the nanoparticles to produce the heterodimers of two distinct nanospheres, which can be modified by two different functional molecules in a particle-specific manner.