Showing papers on "Plasmon published in 2002"

Shape effects in plasmon resonance of individual colloidal silver nanoparticles

Abstract: We present a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. An experimental method has been developed that begins with the detection and characterization of isolated nanoparticles in the optical far field. The plasmon resonance optical spectrum of many individual nanoparticles are then correlated to their size and shape using high-resolution transmission electron microscopy. We find that specific geometrical shapes give distinct spectral responses. In addition, inducing subtle changes in the particles’ morphology by heating causes a shift in the individual particle spectrum and provides a simple means of tuning the spectral response to a desired optical wavelength. Improved colloidal preparation methods could potentially lead to homogeneous populations of identical particle shapes and colors. These multicolor colloids could be used as biological labels, surface enhanced Raman scattering substrates, or near field optical microscopy sources cove...

Drastic reduction of plasmon damping in gold nanorods.

Abstract: The dephasing of particle plasmons is investigated using light-scattering spectroscopy on individual gold nanoparticles. We find a drastic reduction of the plasmon dephasing rate in nanorods as compared to small nanospheres due to a suppression of interband damping. The rods studied here also show very little radiation damping, due to their small volumes. These findings imply large local-field enhancement factors and relatively high light-scattering efficiencies, making metal nanorods extremely interesting for optical applications. Comparison with theory shows that pure dephasing and interface damping give negligible contributions to the total plasmon dephasing rate.

Luttinger liquid theory as a model of the gigahertz electrical properties of carbon nanotubes

Abstract: Presents a technique to directly excite Luttinger liquid collective modes in carbon nanotubes at gigahertz frequencies. By modeling the nanotube as a nano-transmission line with distributed kinetic and magnetic inductance as well as distributed quantum and electrostatic capacitance, we calculate the complex frequency-dependent impedance for a variety of measurement geometries. Exciting voltage waves on the nano-transmission line is equivalent to directly exciting the yet-to-be observed one-dimensional plasmons, the low energy excitation of a Luttinger liquid. Our technique has already been applied to two-dimensional plasmons and should work well for one-dimensional plasmons. Tubes of length 100 microns must be grown for gigahertz resonance frequencies. Ohmic contact is not necessary with our technique; capacitive contacts can work. Our modeling has applications in potentially terahertz nanotube transistors and RF nanospintronics.

Two-dimensional optics with surface plasmon polaritons

Abstract: We report the experimental realization of highly efficient optical elements built up from metal nanostructures to manipulate surface plasmon polaritons propagating along a silver/polymer interface. Mirrors, beamsplitters, and interferometers produced by electron-beam lithography are investigated. The plasmon fields are imaged by detecting the fluorescence of molecules dispersed in the polymer.

Observation of coupled plasmon-polariton modes in Au nanoparticle chain waveguides of different lengths: Estimation of waveguide loss

Abstract: Near-field interactions between closely spaced Au nanoparticles were characterized by studying the spectral position of the extinction bands corresponding to longitudinal (L) and transverse (T) plasmon-polariton modes of Au nanoparticle chains. Far-field spectroscopy and finite-difference time-domain simulations on arrays of 50 nm diameter Au spheres with an interparticle spacing of 75 nm both show a splitting DeltaE between the L and T modes that increases with chain length and saturates at a length of seven particles at DeltaE = 65 meV. We show that the measured splitting will result in a propagation loss of 3 dB/15 nm for energy transport. Calculations indicate that this loss can be reduced by at least one order of magnitude by modifying the shape of the constituent particles.

Plasmon-assisted transmission of entangled photons

Abstract: The state of a two-particle system is said to be entangled when its quantum-mechanical wavefunction cannot be factorized into two single-particle wavefunctions. This leads to one of the strongest counter-intuitive features of quantum mechanics, namely non-locality1,2. Experimental realization of quantum entanglement is relatively easy for photons; a starting photon can spontaneously split into a pair of entangled photons inside a nonlinear crystal. Here we investigate the effects of nanostructured metal optical elements3 on the properties of entangled photons. To this end, we place optically thick metal films perforated with a periodic array of subwavelength holes in the paths of the two entangled photons. Such arrays convert photons into surface-plasmon waves—optically excited compressive charge density waves—which tunnel through the holes before reradiating as photons at the far side4,5,6,7. We address the question of whether the entanglement survives such a conversion process. Our coincidence counting measurements show that it does, so demonstrating that the surface plasmons have a true quantum nature. Focusing one of the photon beams on its array reduces the quality of the entanglement. The propagation of the surface plasmons makes the array effectively act as a ‘which way’ detector.

Drastic reduction of plasmon damping in gold nanorods

Abstract: Summary form only given. Samples of gold nanospheres and nanorods are investigated in a conventional dark-field microscope For spectral investigations, the scattered light from single particles is focused with the microscope onto the entrance slit of a spectrometer coupled to a cooled CCD camera. This dark-field spectroscopy provides a nearly background free measuring technique and allows to record spectra with excellent signal to noise ratio.

Plasmon resonances in large noble-metal clusters

Abstract: We investigate the optical properties of spherical gold and silver clusters with diameters of 20 nm and larger. The light scattering spectra of individual clusters are measured using dark-field microscopy, thus avoiding inhomogeneous broadening effects. The dipolar plasmon resonances of the clusters are found to have nearly Lorentzian line shapes. With increasing size we observe polaritonic red-shifts of the plasmon line and increased radiation damping for both gold and silver clusters. Apart from some cluster-to-cluster variations of the plasmon lines, agreement with Mie theory is reasonably good for the gold clusters. However, it is less satisfactory for the silver clusters, possibly due to cluster faceting or chemical effects.

Plasmon-assisted Quantum Entanglement

Abstract: The state of a two-particle system is called entangled when its quantum mechanical wave function cannot be factorized in two single-particle wave functions Entanglement leads to the strongest counter-intuitive feature of quantum mechanics, namely nonlocality Experimental realization of quantum entanglement is relatively easy for the case of photons; a pump photon can spontaneously split into a pair of entangled photons inside a nonlinear crystal In this paper we combine quantum entanglement with nanostructured metal optics in the form of optically thick metal films perforated with a periodic array of subwavelength holes These arrays act as photonic crystals that may convert entangled photons into surface-plasmon waves, ie, compressive charge density waves We address the question whether the entanglement survives such a conversion We find that, in principle, optical excitation of the surface plasmon modes of a metal is a coherent process at the single-particle level However, the quality of the plasmon-assisted entanglement is limited by spatial dispersion of the hole arrays This spatial dispersion is due to the nonlocal dielectric response of a metal, which is particularly large in the plasmonic regime; it introduces "which way" labels, that may kill entanglement

Terahertz photoconductivity and plasmon modes in double-quantum-well field-effect transistors

Abstract: Double-quantum-well field-effect transistors with a grating gate exhibit a sharply resonant, voltage tuned terahertz photoconductivity The voltage tuned resonance is determined by the plasma oscillations of the composite structure The resonant photoconductivity requires a double-quantum well but the mechanism whereby plasma oscillations produce changes in device conductance is not understood The phenomenon is potentially important for fast, tunable terahertz detectors

Nanophotonics: design, fabrication, and operation of nanometric devices using optical near fields

Abstract: This paper reviews progress in nanophotonics, a novel optical nanotechnology, utilizing local electromagnetic interactions between a few nanometric elements and an optical near field. A prototype of a nanophotonic integrated circuit (IC) is presented, in which the optical near field is used as a carrier to transmit a signal from one nanometric dot to another. Each section of this paper reviews theoretical and experimental studies carried out to assess the possibility of designing, fabricating, and operating each nanophotonic IC device. A key device, the nanophotonic switch, is proposed based on optical near-field energy transfer between quantum dots (QDs). The optical near-field interaction is expressed as the sum of the Yukawa function, and the oscillation period of the nutation of cubic CuCl QDs is estimated to be less than 100 ps. To guarantee one-directional (i.e., irreversible) energy transfer between two resonant levels of QDs, intrasublevel transitions due to phonon coupling are examined by considering a simple two-QD plus phonon heat bath system. As a result, the state-filling time is estimated as 22 ps for CuCl QDs. This time is almost independent of the temperature in the Born-Markov approximation. Using cubic CuCl QDs in a NaCl matrix as a test sample, the optical near-field energy transfer was experimentally verified by near-field optical spectroscopy with a spatial resolution smaller than 50 nm in the near-UV region at 15 K. This transfer occurs from the lowest state of excitons in 4.6-nm QDs to the first dipole-forbidden excited state of excitons in 6.3-nm QDs. To fabricate nanophotonic devices and ICs, chemical vapor deposition using an optical near field is proposed; this is sufficiently precise in controlling the size and position of the deposited material. A novel deposition scheme under nonresonant conditions is also demonstrated and its origin is discussed. In order to confirm the possibility of using a nanometric ZnO dot as a light emitter in a nanophotonic IC, spatially and spectrally resolved photoluminescence imaging of individual ZnO nanocrystallites was carried out with a spatial resolution as high as 55 nm, using a UV fiber probe, and the spectral shift due to the quantum size effect was found. To connect the nanophotonic IC to external photonic devices, a nanometer-scale waveguide was developed using a metal-coated silicon wedge structure. Illumination (wavelength: 830 nm) of the metal-coated silicon wedge (width: 150 nm) excites a TM plasmon mode with a beam width of 150 nm and propagation length of 2.5 /spl mu/m. A key device for nanophotonics, an optical near-field probe with an extremely high throughput, was developed by introducing a pyramidal silicon structure with localized surface plasmon resonance at the metallized probe tip. A throughput as high as 2.3% was achieved. Finally, as an application of nanophotonics to, a high-density, high-speed optical memory system, a novel contact slider with a pyramidal silicon probe array was developed. This slider was used for phase-change recording and reading, and a mark length as short as 110 nm was demonstrated.

Non?diffraction-limited light transport by gold nanowires

Abstract: We show that metal nanowires sustaining collective electron oscillations (surface plasmon polaritons) can be used as optical waveguides. Thereby, the use of a metal allows to overcome the limitations of miniaturization imposed on conventional dielectric waveguides due to diffraction. To demonstrate this effect we investigate a 200 nm wide and 50 nm high gold nanowire locally excited at a light wavelength of 800 nm. By direct imaging the optical near-field with subwavelength-resolution photon scanning tunneling microscopy we observe light transport along the nanowire over a distance of a few μm. Besides the realization of unprecedented integration densities of photonic devices, metal nanowires could be effectively used to optically address individual nanostructures or molecules.

Fluorescence imaging of surface plasmon fields

Abstract: We demonstrate that surface plasmon fields can be imaged in real time by detecting the fluorescence of a molecular film close to the plasmon carrying metal surface. We use this method to image the field profile of surface plasmons launched at lithographically designed nanoscopic defects.

Plasmon modes in metal nanowires and left-handed materials

Abstract: The electromagnetic eld distribution for thin metal nanowires is found, by using the discrete dipole approximation. The plasmon polariton modes in wires are numerically simulated. These modes are found to be dependent on the incident light wavelength and direction of propagation. The existence of localized plasmon modes and strong local eld enhancement in percolation nanowire composites is demonstrated. Novel left-handed materials in the near-infrared and visible are proposed based on nanowire composites.

Relative contributions to the plasmon line shape of metal nanoshells

Abstract: Nanoshells are mesoscopic particles consisting of a dielectric core coated with a metal shell, in particular gold or silver, of uniform nanometer scale thickness. This topology supports plasmon excitations with frequencies that are sensitively dependent on the relative radii of the nanoparticle's core and shell. The plasmon linewidth for this geometry is typically quite broad, nominally 100 nm or more in wavelength at plasmon resonance wavelengths in the near infrared. Several distinct physical mechanisms control the plasmon lineshape: phase retardation effects, including multipolar plasmon contributions; inhomogeneous broadening due to core and shell size distributions; and electron scattering at the shell interfaces. These mechanisms are examined in terms of their relative contributions to the plasmon line shape for nanoshells fabricated with diameters of 100--250 nm.

Low-threshold terahertz quantum-cascade lasers

Abstract: A quantum-cascade laser operating at λ=66 μm is demonstrated. It consists of a three-quantum-well chirped-superlattice active region embedded in a waveguide based on a single interface plasmon and a buried contact. A threshold current density of 210 A/cm2 at T=12 K, a maximum peak optical power of 4 mW, and operation up to T=44 K are achieved in a 2.7 mm long device with a high reflectivity backfacet coating.

Electrically controlled light scattering with single metal nanoparticles

Abstract: A concept to electrically control the scattering of light is introduced. The idea is to embed noble metal nanoparticles in an electro-optical material such as a liquid crystal in order to induce a spectral shift of the particle plasmon resonance by applying an electric field. Light scattering experiments on single gold nanoparticles show that spherically shaped nanoparticles become optically spheroidal when covered by an anisotropic liquid crystal. The two particle plasmon resonances of the optically spheroidal gold nanoparticles can be spectrally shifted by up to 50 meV when electric fields of more than 10 kV/cm are applied.

Composite Plasmon Resonant Nanowires

Abstract: We present an experimental study of the polarization-dependent scattering of light from homogeneous and multisegment silver, gold, and nickel nanowires. The metallic nanowires are prepared within a polycarbonate membrane template by a combination of electroplating (gold and nickel) and electroless (silver) growth processes. The size range of the nanowire segments is such that surface plasmon resonances are supported, dominating the optical spectra. We characterize the light scattering properties of individual composite nanowires using an optical microscope configured for single particle spectroscopy. Because of the scattering efficiency associated with the plasmon resonance, very narrow (∼30 nm diameter) nanowires can be readily observed under white-light illumination, with the spectral characteristics of each subsection easily distinguishable. Because of their compactness, these simply prepared multiisegment plasmon resonant nanowires are capable of hosting a large number of segment sequences over a comp...

Optical transmission through subwavelength metallic gratings

Abstract: We present measurements of enhanced resonant transmission of infrared radiation through subwavelength metallic gratings made of rectangular grooves. This is achieved either by exciting a resonant waveguide mode in the cavities, or when the field is large enough above the groove, which is particulary satisfied close to surface plasmon excitation conditions at the air/metal interface. Moreover, we show that a model with plasmons on the incident side only explains this result very well.

Ultrafast dephasing of surface plasmon excitation in silver nanoparticles: influence of particle size, shape, and chemical surrounding.

Abstract: By combination of two special methods, ie, persistent spectral hole burning and laser assisted nanoparticle preparation, the dephasing time ${T}_{2}$ of surface plasmon excitation in silver nanoparticles was systematically investigated A strong dependence of ${T}_{2}$ on the plasmon energy is found which reflects the relevance of interband damping and makes necessary a precise control of the particle shape when measuring ${T}_{2}$ The influence of the reduced dimension on the dephasing dynamics was observed as a decrease of ${T}_{2}$ with shrinking particle size In addition, for silver nanoparticles on quartz substrates, a considerable amount of chemical interface damping was observed

Enhanced substrate-induced coupling in two-dimensional gold nanoparticle arrays

Abstract: The influence of substrate induced coupling on plasmon excitations is probed by means of visible and near-infrared extinction microspectroscopy on various arrays of gold oblate spheroidal particles deposited onto a 20-nm-thick gold film. At zero incidence angle and for an interparticle spacing smaller than 250 nm, the spectra exhibit two bands instead of the single one observed for similar particles but deposited on indium tin oxide coated glass. We suggest that the short-wavelength band proceeds from two simultaneous mechanisms: (i) Excitation of a surface-plasmon resonance localized on the particles. (ii) Generation at the gold-glass interface of a propagating surface-plasmon wave due to the fact that the gold particles can act as a grating coupler. Surface-enhanced Raman-scattering experiments performed on oblate spheroid arrays give arguments in favor of the attribution of the long-wavelength band to surface-plasmon resonance of an ensemble of strongly coupled particles. When increasing the spacing between particles of the array beyond 250 nm, extinction spectra display the emergence of a new band. Calculations suggest that this new band proceeds from the excitation of a surface-plasmon standing wave on the film due to Bragg scattering. This assignment to Bragg scattering is supported by the investigation of the effect of varying the incidence angle under both transverse magnetic and transverse electric polarizations.

The Effect of Mutual Orientation on the Spectra of Metal Nanoparticle Rod−Rod and Rod−Sphere Pairs

Abstract: A simple quasistatic treatment for the plasmon resonance spectra of nanoparticle rod−rod and rod−sphere pairs is presented. Spectra are calculated for gold particle pairs at different distances and mutual orientations. For rod−rod and rod−sphere pairs, the spectral changes that occur as a result of interparticle interaction are different for end-to-end (axial) and side-to-side (lateral) orientations. Axial interactions generally lead to a red shift of the most intense (longitudinal axis) plasmon resonance band. Lateral interactions usually lead to a blue shift of the main plasmon band. In general, lateral orientation yields more pronounced spectral changes than the axial case, especially as the aspect ratio of the rod member(s) increases.

Increased data storage in optical data storage and retrieval systems using blue lasers and/or plasmon lenses

Abstract: A optical recording medium (10) includes a crystallizing layer (7,8) for enhancing the crystallization of a phase change memory layer (3), an energy storage layer for aiding the state transformations of a phase change memory layer (3), and/or a modifying element for increasing absorption and contrast at short wavelengths. An optical data storage and retrieval system (figure 3) containing same. A light-plasmon coupling lens including an optically transparent substrate having a light incident surface and a light-plasmon coupling surface opposite the light incident surface. The light-plasmon coupling surface including at least a set of circular concentric peaks/valleys which form a Fourier sinusoidal pattern in the radial direction of the circular concentric peaks/valleys. A conformal layer of metal is deposited on the light-plasmon coupling surface of the substrate and has aperture at the center of thereof through which plasmons are transmitted.

Photoinduced charge separation reactions of J-aggregates coated on silver nanoparticles.

Abstract: The photochemistry of cyanine J-aggregates on the surface of colloidal Ag nanoparticles is reported. The photochemistry is initiated through ultrafast photoexcitation of the plasmon band in Ag nanoparticles, producing an enhanced near-field that interacts with the J-aggregate monolayer. Through transient absorption spectroscopy, we show that photoexcitation of the plasmon in Ag nanoparticles leads to exciton dynamics that differ strongly from J-aggregates alone or for J-aggregate monolayers on bulk metal surfaces. Specifically, charge-separated states with a lifetime of ∼300 ps between the J-aggregate and Ag colloid are formed. The reduction of the Ag nanoparticles is shown to be a multielectron process.

Transmission surface-plasmon resonance (T-SPR) measurements for monitoring adsorption on ultrathin gold island films.

Abstract: Evaporation of ultrathin (1.3-10 nm nominal thickness) gold films onto quartz or mica leads to the formation of a layer of rather uniform gold islands on the transparent support. The morphology of ultrathin gold island films of various thicknesses was studied by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging. The surface plasmon (SP) absorption characteristic of such films is highly sensitive to the surrounding medium, with the plasmon band changing in intensity and wavelength upon binding of various molecules to the surface. The binding process can be monitored quantitatively by measuring the changes in the gold SP absorption, by using transmission UV/Vis spectroscopy. The method, termed transmission surface plasmon resonance (T-SPR) spectroscopy, is shown to be applicable to both chemically and physically adsorbed molecules, in liquid or gas phase, with measurements carried out either ex situ or in situ (real-time measurements) using a variety of molecular probes. Binding to a preformed molecular layer on the Au surface produces a similar response, suggesting the possible use of T-SPR for selective sensing. The sensitivity of T-SPR spectroscopy in detecting molecular binding to the gold depends strongly on the film preparation conditions, and may be comparable to that obtained in surface plasmon resonance (SPR) sensing.

Surface Plasmon Resonance(SPR)Theory: Tutorial

Abstract: In the surface plasmon resonance (SPR) measurement we can detect the change of the film thickness (refractive index change) in the sub-nonometer scale using a low-cost home-made appratus (He-Ne laser, rotating stage, photo-diode detector, prism, maching oil, and 50 nm gold film on a glass plate, See Appendix). In this sense SPR is widely used, in particular, as the immunoassay to detect label-free antigen-antibody reaction. When light is irradiated to the optical prism |thin metallic film (usually 50 nm gold film is used)| sample system, the reflectivity of the light becomes almost zero at the angle of incidence where the surface plasma wave of gold surface can couple to the part of the incident light. 1 This angle is called SPR angle and is very sensitive to the film thickness (refractivity) of the sample. In the usual automated SPR measurementanalysis routine one can get the SPR angle shift and the the change of the film thickness (and/or refractivity), thereby the measurement may be one of the ”black-box”. However I think it is important to know the principle for the people to do something new by an detailed analysis of the measurements. From the name ”plasmon” one may misunderstand that the quantum mechanical understanding is required for SPR principles, but the phenomena can be understood from the classical optics (or electromagnetic theory) which explain the light reflection, transmission, and absorption for the multi-layer medium. In the famous book by Raether the principle of SPR was written completely, but at least for me it is not easy to understand because the book may be for specialist. 2 This note is written for my self-study of SPR principle in order to analyze the SPR curves, 3 . ,later was publish in ”Review of Polarography, 48, No3. 2002, 209 ”, and posted the revised version at http://www.scl.kyoto-u.ac.jp/ masahiro/sprtheory.html. (I am very happy that many people give me contacts and some comments.) In this note on SPR theory I also describe the basics of the light reflection, transmission, absorption at the surface of dielectrics or metal, then it is my pleasure that

Photonic crystals for confining, guiding, and emitting light

Abstract: By using the photonic crystals, we can confine, guide, and emit light efficiently. By precise control over the geometry and three-dimensional design, it is possible to obtain high quality optical devices with extremely small dimensions. Here we describe examples of high-Q optical nanocavities, photonic crystal waveguides, and surface plasmon enhanced light-emitting diode (LEDs).