Showing papers on "Plasmon published in 2004"
TL;DR: It is established that electromagnetic waves in both materials are governed by an effective permittivity of the same plasma form, which allows the creation of designer surface plasmons with almost arbitrary dispersion in frequency and in space.
Abstract: Metals such as silver support surface plasmons: electromagnetic surface excitations localized near the surface that originate from the free electrons of the metal. Surface modes are also observed on highly conducting surfaces perforated by holes. We establish a close connection between the two, showing that electromagnetic waves in both materials are governed by an effective permittivity of the same plasma form. The size and spacing of holes can readily be controlled on all relevant length scales, which allows the creation of designer surface plasmons with almost arbitrary dispersion in frequency and in space, opening new vistas in surface plasmon optics.
2,740 citations
TL;DR: The discrete dipole approximation is used to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces.
Abstract: We use the discrete dipole approximation to investigate the electromagnetic fields induced by optical excitation of localized surface plasmon resonances of silver nanoparticles, including monomers and dimers, with emphasis on what size, shape, and arrangement leads to the largest local electric field (E-field) enhancement near the particle surfaces. The results are used to determine what conditions are most favorable for producing enhancements large enough to observe single molecule surface enhanced Raman spectroscopy. Most of the calculations refer to triangular prisms, which exhibit distinct dipole and quadrupole resonances that can easily be controlled by varying particle size. In addition, for the dimer calculations we study the influence of dimer separation and orientation, especially for dimers that are separated by a few nanometers. We find that the largest /E/2 values for dimers are about a factor of 10 larger than those for all the monomers examined. For all particles and particle orientations, the plasmon resonances which lead to the largest E-fields are those with the longest wavelength dipolar excitation. The spacing of the particles in the dimer plays a crucial role, and we find that the spacing needed to achieve a given /E/2 is proportional to nanoparticle size for particles below 100 nm in size. Particle shape and curvature are of lesser importance, with a head to tail configuration of two triangles giving enhanced fields comparable to head to head, or rounded head to tail. The largest /E/2 values we have calculated for spacings of 2 nm or more is approximately 10(5).
1,778 citations
TL;DR: In this paper, the authors apply the plasmon hybridization method to nanoparticle dimers, providing a simple and intuitive description of how the energy and excitation cross sections of dimer plasmons depend on nanoparticle separation.
Abstract: We apply the recently developed plasmon hybridization method to nanoparticle dimers, providing a simple and intuitive description of how the energy and excitation cross sections of dimer plasmons depend on nanoparticle separation. We show that the dimer plasmons can be viewed as bonding and antibonding combinations, i.e., hybridization of the individual nanoparticle plasmons. The calculated plasmon energies are compared with results from FDTD simulations.
1,577 citations
TL;DR: The results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.
Abstract: Since 1993, InGaN light-emitting diodes (LEDs) have been improved and commercialized, but these devices have not fulfilled their original promise as solid-state replacements for light bulbs as their light-emission efficiencies have been limited. Here we describe a method to enhance this efficiency through the energy transfer between quantum wells (QWs) and surface plasmons (SPs). SPs can increase the density of states and the spontaneous emission rate in the semiconductor, and lead to the enhancement of light emission by SP–QW coupling. Large enhancements of the internal quantum efficiencies (etaint) were measured when silver or aluminium layers were deposited 10 nm above an InGaN light-emitting layer, whereas no such enhancements were obtained from gold-coated samples. Our results indicate that the use of SPs would lead to a new class of very bright LEDs, and highly efficient solid-state light sources.
1,349 citations
TL;DR: Using electrodynamics calculations, one dimensional array structures built from spherical silver nanoparticles that produce remarkably narrow plasmon resonance spectra upon irradiation with light that is polarized perpendicular to the array axis are discovered.
Abstract: Using electrodynamics calculations, we have discovered one dimensional array structures built from spherical silver nanoparticles that produce remarkably narrow (∼ meV or less) plasmon resonance spectra upon irradiation with light that is polarized perpendicular to the array axis. The narrow lines require a minimum particle radius of about 30 nm to achieve. Variations of the plasmon resonance wavelength, extinction efficiency and width with particle size, array structure, interparticle distance and polarization direction are examined, and conditions which lead to the smallest widths are demonstrated. A simple analytical expression valid for infinite lattices shows that the sharp resonance arises from cancellation between the single particle width and the imaginary part of the radiative dipolar interaction.
710 citations
TL;DR: In this paper, the optical response of periodic arrays of metallic nanoparticles composed of a pair of particles on each lattice site was investigated, and the interparticle separation within the pairs from dielectric proximity to conductive contact on a nanometer scale was observed.
Abstract: We have investigated the optical response of periodic arrays of metallic (gold) nanoparticles composed of a pair of particles on each lattice site. By varying the interparticle separation within the pairs from dielectric proximity to conductive contact on a nanometer scale, we observe an abrupt, large renormalization as well as a splitting of the surface plasmon polariton energy. These spectral anomalies are ascribed to a transition whereupon the interparticle dipole−dipole interaction is shunted and the plasmon polaritons exhibit multipolar behavior, including a very high local concentration of electromagnetic energy in the vicinity of their conductive contact.
653 citations
TL;DR: In this article, two opposing tip-to-tip Au triangles have been fabricated with triangle lengths of 75 nm and gaps ranging from 16 to 488 nm, and the plasmon scattering resonance first blue shifts with increasing gap, and then red shifts as the particles become more and more uncoupled, while perpendicularly polarized excitation shows little dependence upon gap size.
Abstract: Metallic “bowtie” nanoantennas consisting of two opposing tip-to-tip Au triangles have been fabricated with triangle lengths of 75 nm and gaps ranging from 16 to 488 nm. For light polarized along the line between the two triangles, the plasmon scattering resonance first blue-shifts with increasing gap, and then red-shifts as the particles become more and more uncoupled, while perpendicularly polarized excitation shows little dependence upon gap size. This behavior may be approximately understood in a coupled-dipole approximation as changes in the phase between static dipole−dipole interactions and dipole radiative interaction effects.
645 citations
TL;DR: In this article, the optical properties of silver nanoparticles used in tandem ultrathin-film organic photovoltaic cells were investigated, and it was shown that the enhancement of an incident optical field persists into an organic dielectric for distances of up to 10nm from the center of an array of approximately 5-nm-diameter nanoparticles.
Abstract: We investigate the optical properties of silver nanoparticles used in tandem ultrathin-film organic photovoltaic cells. Experimental results indicate that the enhancement of an incident optical field persists into an organic dielectric for distances of up to 10nm from the center of an array of approximately 5-nm-diameter nanoparticles. Furthermore, this enhancement exists far from the resonant particle surface-plasmon excitation energy. We propose a model to explain this long-range enhancement and investigate the role that cluster spacing, shape, and an embedding dielectric medium with a complex dielectric constant play in determining plasmon enhancement. This effect is shown to increase the efficiency of tandem organic solar cells, and the implications for further solar cell efficiency improvements are discussed.
614 citations
TL;DR: It is found that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles.
Abstract: Au and Ag nanoshells are investigated as substrates for surface-enhanced Raman scattering (SERS). We find that SERS enhancements on nanoshell films are dramatically different from those observed on colloidal aggregates, specifically that the Raman enhancement follows the plasmon resonance of the individual nanoparticles. Comparative finite difference time domain calculations of fields at the surface of smooth and roughened nanoshells reveal that surface roughness contributes only slightly to the total enhancement. SERS enhancements as large as 2.5 × 1010 on Ag nanoshell films for the nonresonant molecule p-mercaptoaniline are measured.
602 citations
TL;DR: In this paper, a promising nanofabrication method, used to fabricate fine patterns beyond the diffraction limit, by employing surface plasmon polariton (SPP) resonance was demonstrated.
Abstract: We demonstrate a promising nanofabrication method, used to fabricate fine patterns beyond the diffraction limit, by employing surface plasmon polariton (SPP) resonance. Sub-100 nm lines were patterned photolithographically using surface plasmon polaritonic interference in the optical near field excited by a wavelength of 436 nm. The unperforated metallic mask approach which has corrugated surfaces on both sides is proposed for arbitrary patterning. The corrugated surface of the metallic mask on the illuminated side collects light through SPP coupling, and SPP on the exit side of metallic mask redistributes the light into nanoscale spatial distribution, which can be used to fabricate nanostructures. Preliminary numerical simulations support the experimental results.
525 citations
TL;DR: It is shown that the plasmon resonances in single metallic nanoshells and multiple concentric metallic shell particles can be understood in terms of interaction between the bare plAsmon modes of the individual surfaces of the metallic shells.
Abstract: We show that the plasmon resonances in single metallic nanoshells and multiple concentric metallic shell particles can be understood in terms of interaction between the bare plasmon modes of the individual surfaces of the metallic shells. The interaction of these elementary plasmons results in hybridized plasmons whose energy can be tuned over a wide range of optical and infrared wavelengths. The approach can easily be generalized to more complex systems, such as dimers and small nanoparticle aggregates.
TL;DR: This work combines confocal microscopy using supercontinuum laser illumination and an interferometric detection technique to identify single nanoparticles of diameter below 10 nm and records the plasmon resonance of a single nanoparticle.
Abstract: We combine confocal microscopy using supercontinuum laser illumination and an interferometric detection technique to identify single nanoparticles of diameter below 10 nm. Spectral analysis of the signal allows us to record the plasmon resonance of a single nanoparticle. Our results hold great promise for fundamental studies of the optical properties of single metal clusters and for their use in biophysical applications.
TL;DR: In this article, the particle plasmon frequency was observed in optically excited spherical gold nanoparticles and a photoluminescence efficiency of 10 − 6 was determined. But this was independent of particle size and four orders of magnitude higher than the efficiencies determined from metal films.
Abstract: Light emission at the particle plasmon frequency is observed in optically excited spherical gold nanoparticles. We find a photoluminescence efficiency of ${10}^{\ensuremath{-}6}$, which is essentially independent of particle size and four orders of magnitude higher than the efficiencies determined from metal films. Our experimental findings are explained with a process in which excited $d$-band holes recombine nonradiatively with $\mathit{sp}$ electrons, emitting particle plasmons. These plasmons subsequently radiate, giving rise to the photoluminescence observed in the experiment. We determine the quantum efficiencies involved in this process.
TL;DR: In this paper, a dipole-limit calculation based on confocal ellipsoids was used to simulate the spectra of the core/shell nanorods using bulk dielectric functions.
Abstract: Au/Ag core/shell nanorods with different shell thickness were synthesized in aqueous solution by chemically depositing silver on gold nanorods surface. With the silver coating, the longitudinal plasmon mode of the nanorods shifted blue and was enhanced. A dipole-limit calculation, based on confocal ellipsoids, simulates the spectra of the core/shell nanorods using bulk dielectric functions. Good agreement with the experimental result was achieved. Light scattering spectra of single nanorods were taken by dark-field microscopy to measure the homogeneous line width. The scattering spectra of single gold nanorods are less than 10% broader than the theoretical value, while the spectra of silver-coated nanorods are systematically 40−50% broader. The additional damping of the plasmon was modeled as the extra scattering at the Au−Ag interface and the nanorods surface. A model for evaluating the plasmon damping in inhomogeneous metallic systems with interfaces is presented.
TL;DR: In this paper, a new paradigm for tuning the optical properties of gold nanorods by organizing them longitudinally, using thioalkylcarboxylic acid based bifunctional molecules is reported.
Abstract: We report a new paradigm for tuning the optical properties of gold nanorods by organizing them longitudinally, using thioalkylcarboxylic acid based bifunctional molecules. The rationale behind the selection of the bifunctional molecule is based on the fact that the thiol group binds to the ends of the nanorods, which further assembles in a longitudinal fashion through cooperative hydrogen bonding between the carboxylic groups. A generalized procedure for uniaxial plasmon coupling through longitudinal self-assembly of Au nanorods, initially to dimers and further to linear assemblies, is presented. Uniaxial modulation of interplasmon coupling through stepwise self-assembly of Au nanorods will have application in nanoelectronics and plasmonics.
TL;DR: Nanoporous TiO(2) films loaded with gold and silver nanoparticles exhibit negative potential changes and anodic currents in response to visible light irradiation, so that the films would potentially be applicable to inexpensive photovoltaic cells, photocatalysts and simple plasmon sensors.
TL;DR: It is shown that the presence of the gain medium can compensate for the absorption losses in the metal and suggest that lossless gainassisted surface plasmon polariton propagation can be achieved in practice.
Abstract: The propagation of surface plasmon polaritons on metallic waveguides adjacent to a gain medium is considered. It is shown that the presence of the gain medium can compensate for the absorption losses in the metal. The conditions for existence of a surface plasmon polariton and its lossless propagation and wavefront behavior are derived analytically for a single infinite metal-gain boundary. In addition, the cases of thin slab and stripe geometries are also investigated using finite element simulations. The effect of a finite gain layer and its distance from the SPP waveguide is also investigated. The calculated gain requirements suggest that lossless gainassisted surface plasmon polariton propagation can be achieved in practice.
TL;DR: In this paper, the authors apply the plasmon hybridization method to a solid nanosphere interacting with a metallic surface and show that the plasm energies of the nanoparticle exhibit strong shifts with nanoparticle−surface separation.
Abstract: We apply the recently developed plasmon hybridization method to a solid nanosphere interacting with a metallic surface. We show that the plasmon energies of the nanoparticle exhibit strong shifts with nanoparticle−surface separation. Depending on the energy of the surface plasmon, nanoparticle plasmons can either red shift or blue shift with decreasing nanoparticle−surface separation. The shifts can be explained as resulting from image-like interactions with the metal surface and, more importantly, through hybridization between the nanoparticle plasmons and the delocalized surface plasmons of the substrate.
TL;DR: This paper overviews recent studies of anisotropic noble metal nanoparticles, in which a combination of theory and experiment has been used to elucidate the extinction spectra of the particles, as well as information related to their surface enhanced Raman spectroscopy.
Abstract: In this paper we overview our recent studies of anisotropic noble metal (e.g. gold and silver) nanoparticles, in which a combination of theory and experiment has been used to elucidate the extinction spectra of the particles, as well as information related to their surface enhanced Raman spectroscopy. We used wet-chemical methods to generate several structurally well-defined nanostructures other than solid spheres, including silver nanodisks and triangular nanoprisms, and gold nanoshells and multipods. When solid spheres are transformed into one of these shapes, the surface plasmon resonances in these particles are strongly affected, typically red-shifting and even splitting into distinctive dipole and quadrupole plasmon modes. In parallel, we have developed computational electrodynamics methods based on the discrete dipole approximation (DDA) method to determine the origins of these intriguing optical features. This has resulted in considerable insight concerning the variation of plasmon wavelength with nanoparticle size, shape and dielectric environment, as well as the use of these particles for optical sensing applications.
TL;DR: The results show that the narrow lines are remarkably robust to array disorder, but vacancy defects can easily destroy the effect, and it is shown that the arrays have greater sensitivity than isolated nanoparticles.
Abstract: The interaction of light with silver nanoparticle arrays can in some cases produce mixed plasmonic/photonic bands that have extremely narrow (<1 meV) line shapes in extinction and scattering. In this paper we extend computational electrodynamics results of a recent communication [S. Zou, N. Janel, and G. C. Schatz, J. Chem. Phys. 120, 10871 (2004)] where this effect was first described to study how these narrow bands are influenced by a number of structural factors, and to determine how useful these arrays might be for sensing applications. Included are studies of the effect of disorder in the array structure on plasmon intensity and width, of the effect of orientation of the array relative to the polarization and propagation direction of the incident light, and of the effect of particle shape (comparing results for silver spheres and cylindrical disks). Our results show that the narrow lines are remarkably robust to array disorder, but vacancy defects can easily destroy the effect. The narrowest lines are associated with one dimensional arrays in which both polarization and wave vectors are perpendicular to the array axis. For two dimensional arrays, the narrowest lines are associated with the wave vector perpendicular to the plane of the array and polarization in the plane. Arrays composed of oblate cylinders generate more intense and more redshifted plasmon/photonic peaks than do prolate or spherical particles under comparable conditions. Finally, for sensing applications in which analyte binding is determined by the plasmon wavelength shift associated with change in the surface refractive index, we show that the arrays have greater sensitivity than isolated nanoparticles.
TL;DR: It is demonstrated that the localization of the predicted plasmons in acute grooves may be substantially stronger than what is allowed by the diffraction limit.
Abstract: One-dimensional localized plasmons (channel polaritons) guided by a triangular groove on a metal substrate are investigated numerically by means of a finite-difference time-domain algorithm. Dispersion, existence conditions, and dissipation of these waves are analyzed. In particular, it is demonstrated that the localization of the predicted plasmons in acute grooves may be substantially stronger than what is allowed by the diffraction limit. As a result, the predicted waves may be significant for the development of new subwavelength waveguides and interconnectors for nano-optics and photonics.
TL;DR: In this paper, single particle dark field spectroscopy has been combined with high-resolution scanning electron and atomic force microscopy to study the scattering spectra of single gold/silica nanoshells.
Abstract: Single particle dark field spectroscopy has been combined with high-resolution scanning electron and atomic force microscopy to study the scattering spectra of single gold/silica nanoshells. The plasmon resonant peak energies match those calculated by Mie theory based on the nanoshell geometry. The resonance line widths fit Mie theory without the inclusion of a size-dependent surface scattering term, which is often included to fit ensemble measurements. These results suggest that plasmon spectral measurements of nanoparticle ensembles are broadened due to particle inhomogeneity.
TL;DR: The reversible charging and discharging effects associated with photoexcitation of a TiO2 shell in a Ag@TiO2 composite are described and the charging of the silver core is associated with the shift in the surface plasmon band from 460 to 430 nm.
Abstract: The reversible charging and discharging effects associated with photoexcitation of a TiO2 shell in a Ag@TiO2 composite are described. The photoinduced charge separation in the TiO2 shell is followed by electron injection into the silver core. Interestingly, the charging of the silver core is associated with the shift in the surface plasmon band from 460 to 430 nm. The stored electrons are discharged upon exposure of the charged Ag@TiO2 composite to an electron acceptor. As the electrons from the silver core are discharged, the original surface plasmon absorption of the Ag core is restored.
TL;DR: In this article, isolated nanometric holes in optically thin Au films exhibit a localized surface plasmon resonance in the red to near-infrared region, analogous to a dipolar particle plasmoron.
Abstract: Elastic scattering measurements show that isolated nanometric holes in optically thin Au films exhibit a localized surface plasmon resonance in the red to near-infrared region. The hole plasmon red shifts with increasing hole diameter or increasing refractive index of the surrounding medium, analogous to a dipolar particle plasmon. A pronounced blue shift is observed when the distance between holes is decreased, indicating an enhanced coupling between holes mediated by surface plasmon polaritons of the intervening flat film surface.
TL;DR: In this article, a combination of theory and experiment designed to elucidate the properties of gold nanoshells is presented, showing that 2−5 nm pinholes have only a small effect on the extinction spectra; however, they lead to local electric fields that are enhanced by a factor of 3−4 close to the plasmon maximum.
Abstract: We present a combination of theory and experiment designed to elucidate the properties of gold nanoshells. Wet chemistry methods are used to prepare the nanoshells, and transmission electron microscopy (TEM) analysis is used to characterize the shell structure, demonstrating the presence of pinholes in the shells. Both Mie theory and the discrete dipole approximation (a numerical method) are used to characterize the electrodynamics of the shell structures, including both perfect and pinhole defected shells. The calculations show that 2−5 nm pinholes have only a small effect on the extinction spectra; however, they lead to local electric fields that are enhanced by a factor of 3−4 close to the plasmon maximum. This makes metal nanoshells (with holes) attractive materials for surface enhanced Raman spectroscopy applications.
TL;DR: In this paper, the authors investigate the geometrical parameters that control the sensitivity of the plasmon resonance wavelength of a silica−gold nanoshell to changes in its dielectric environment.
Abstract: In this study, we investigate the geometrical parameters that control the sensitivity of the plasmon resonance wavelength of a silica−gold nanoshell to changes in its dielectric environment. It was found that the magnitude of the SPR frequency shift upon a change in refractive index of the embedding medium depends primarily on total nanoparticle size and less sensitively on the core/shell ratio. Immobilized nanoshells on a glass substrate showed a 25% decrease in magnitude of the SPR shifts; however, sensitivities as large as Δλ/Δn = 555.4 nm/RIU were obtained for this geometry.
TL;DR: The authors' plasmonic-type glucose nanosensors with regard to particle stability, pH effects, the dynamic range for glucose sensing, and the observation wavelength are optimized to be compatible with clinical glucose requirements and measurements.
TL;DR: In this article, the plasmon resonance peak wavelengths of finite one-dimensional chains of Au nanoparticles excited by evanescent light waves with polarization parallel to the chains were investigated.
Abstract: We report experimental and theoretical studies on the plasmon resonances of finite one-dimensional chains of Au nanoparticles excited by evanescent light waves with polarization parallel to the chains. The experimental results show that the plasmon resonance peak wavelengths of these finite 1D chains are significantly red-shifted in comparison to that of single Au nanoparticle. Contrary to previous findings, the peak wavelengths are observed to be a nonmonotonic function of particle numbers in the chain. This phenomenon is reproduced in the theoretical results obtained by using the transfer-matrix method and is shown to occur only for larger particles where phase retardation effects are important in plasmon coupling.
TL;DR: It is suggested that, for certain film designs, interlayer interparticle resonance might be revealed as an independent contribution at 800 nm in UV-visible spectra of the SA-LbL films.
Abstract: Nanoscale uniform films containing gold nanoparticle and polyelectrolyte multilayer structures were fabricated by the using spin-assembly or spin-assisted layer-by-layer (SA-LbL) deposition technique. These SA-LbL films with a general formula [Au/(PAH-PSS)nPAH]m possessed a well-organized microstructure with uniform surface morphology and high surface quality at a large scale (tens of micrometers across). Plasmon resonance peaks from isolated nanoparticles and interparticle interactions were revealed in the UV-visible extinction spectra of the SA-LbL films. All films showed the strong extinction peak in the region of 510-550 nm, which is due to the plasmon resonance of the individual gold nanoparticles redshifted because of a local dielectric environment. For films with sufficient density of gold nanoparticles within the layers, the second strong peak was consistently observed between 620 and 660 nm, which is the collective plasmon resonance from intralayer interparticle coupling. Finally, we suggested that, for certain film designs, interlayer interparticle resonance might be revealed as an independent contribution at 800 nm in UV-visible spectra. The observation of independent and concurrent individual, intralayer, and interlayer plasmon resonances can be critical for sensing applications, which involve monitoring of optomechanical properties of ultrathin optically active compliant membranes.
TL;DR: Two-photon-induced photoluminescence images and spectra of single gold nanorods are investigated by using an apertured scanning near-field optical microscope to reveal characteristic features reflecting an eigenfunction of a specific plasmon mode as well as electric field distributions around the nanorod.
Abstract: We have investigated two-photon-induced photoluminescence images and spectra of single gold nanorods by using an apertured scanning near-field optical microscope. The observed PL spectrum of single gold nanorod can be explained by the radiative recombination of the electron−hole pair near the X and L symmetry points. PL images reveal characteristic features reflecting an eigenfunction of a specific plasmon mode as well as electric field distributions around the nanorod.