Showing papers on "Plasmon published in 2000"
15 Dec 2000
TL;DR: In this article, the authors proposed coupled plasmon modes for energy transfer in chains of closely spaced metal nanoparticles, which can be obtained at a length scale much less than wavelength of visible light.
Abstract: Electromagnetic energy transfer in plasmon wires consisting of chains of closely spaced metal nanoparticles can occur below the diffraction limit by means of coupled plasmon modes. Coherent propagation with group velocities that exceed 0.1 c is possible in straight wires and around sharp corners (bending radius much less than wavelength of visible light). Energy transmission through chain networks is possible at high efficiencies and is a strong function of the frequency and polarization direction of the plasmon mode. Although these structures exhibit transmission losses due to heating of about 3 dB/500 nm, they have optical functionality that cannot be obtained in other ways at a length scale ≪1 μm.
689 citations
TL;DR: In this article, the authors proposed coupled plasmon modes for energy transfer in chains of closely spaced metal nanoparticles, and showed that they can be obtained at a length scale that cannot be obtained in other ways.
Abstract: Electromagnetic energy transfer in plasmon wires consisting of chains of closely spaced metal nanoparticles can occur below the diffraction limit by means of coupled plasmon modes. Coherent propagation with group velocities that exceed 0.1 c is possible in straight wires and around sharp corners (bending radius much less than wavelength of visible light). Energy transmission through chain networks is possible at high efficiencies and is a strong function of the frequency and polarization direction of the plasmon mode. Although these structures exhibit transmission losses due to heating of about 3 dB/500 nm, they have optical functionality that cannot be obtained in other ways at a length scale \ensuremath{\ll}1 \ensuremath{\mu}m.
668 citations
TL;DR: A strong dependence of the plasmon lifetime and resonance wavelength on the grating constant is found and it is found that gold nanoparticles arranged in regular two-dimensional patterns have regular grating effects.
Abstract: We probe the influence of grating effects on plasmon excitations in gold nanoparticles arranged in regular two-dimensional patterns. Samples produced by electron-beam lithography are investigated by femtosecond time-resolved and spectroscopic methods. We find a strong dependence of the plasmon lifetime and resonance wavelength on the grating constant.
575 citations
TL;DR: In this article, the effect of solvent refractive index and core charge on the surface plasmon absorbance of alkanethiolate monolayer-protected gold clusters (MPCs) was investigated.
Abstract: This report describes the effect of solvent refractive index and core charge on the surface plasmon absorbance of alkanethiolate monolayer-protected gold clusters (MPCs). Solution spectra of dodecanethiolate MPCs (5.2 nm average diameter) reveal an 8-nm shift in plasmon band position as the solvent refractive index is varied from nd20 = 1.33 to 1.55. The spectral shift agrees with predictions of Mie theory when the alkanethiolate monolayer is accounted for in the calculations. Electronic charging of the MPC gold core by electrolysis, from its rest potential (−0.16 V) to +0.82 V vs a Ag quasi-reference electrode, causes a 9-nm (516 to 525 nm) shift in the surface plasmon band position. The shift in surface plasmon band position with core charge is compared to the predictions of the concentric sphere model for MPC capacitance and Mie theory, as a first step toward probing effects of quantized core charging on this important optical property.
512 citations
TL;DR: The absorption spectra of the the gold colloid monolayers, which were immersed in liquid samples or coated with thin films, were measured and increases of both the resonance wavelength and the absorbance as the refractive indices of the sample liquids or the thickness of the coated films increased.
Abstract: A new optical sensor that uses local plasmon resonance is proposed. A peak that is due to the local plasmon resonance appears in the absorption spectrum of a gold colloid suspension in the visible region, and its height and wavelength depend on the refractive index of the suspension. These properties are used for optical sensors. We used gold colloid monolayers in which colloidal gold particles a few tens of nanometers in diameter were immobilized upon a glass slide by a functional organic coupling agent. We measured the absorption spectra of the the gold colloid monolayers, which were immersed in liquid samples or coated with thin films. We observed increases of both the resonance wavelength and the absorbance as the refractive indices of the sample liquids or the thickness of the coated films increased. The proportional constants of the resonance wavelength to the film thickness were 3.6 and 5.7 for a 13.9- and a 20.2-nm gold colloid monolayer, respectively.
431 citations
TL;DR: In this paper, a Schottky junction formed at the interface of ITO and zinc phthalocyanine was investigated to study the influence of the metal particles on the optical extinction spectra and on the short circuit photocurrent spectra of such constructed organic solar cells.
422 citations
TL;DR: In this paper, the authors demonstrate the selective coupling of photons into the plasmon mode of a 20 nm diameter nanowire, which then propagates in a nonemissive fashion down the wire length before being emitted as an elastically scattered photon at distal end.
Abstract: We report the observation of unidirectional plasmon propagation in metallic nanowires over distances >10 μm. Through control of the incident excitation wavelength and rod composition, we demonstrate the selective coupling of photons into the plasmon mode of a 20 nm diameter nanowire. This mode then propagates in a nonemissive fashion down the wire length before being emitted as an elastically scattered photon at the distal end. As expected from previous studies of plasmon excitation in nanoparticles and thin films, we observe a strong wavelength and material dependence of this phenomenon. This metal-dependent plasmon propagation is exploited to produce a wire through which plasmons propagate unidirectionally. A bimetallic wire with a sharp Au/Ag heterojunction is shown to display both wavelength dependence and unidirectionality with respect to plasmon propagation across the heterojunction. It is expected that these results will contribute to the growing interest in optical energy transport in molecular-le...
419 citations
TL;DR: In this article, a simple, fast, and flexible technique to measure optical scattering spectra of individual metallic nanoparticles was developed to measure the effect of particle diameter on the dephasing time of the particle plasmon resonance in gold nanoparticles.
Abstract: We have developed a simple, fast, and flexible technique to measure optical scattering spectra of individual metallic nanoparticles. The particles are placed in an evanescent field produced by total internal reflection of light from a halogen lamp in a glass prism. The light scattered by individual particles is collected using a conventional microscope and is spectrally analyzed by a nitrogen-cooled charge-coupled-device array coupled to a spectrometer. This technique is employed to measure the effect of particle diameter on the dephasing time of the particle plasmon resonance in gold nanoparticles. We also demonstrate the use of this technique for measurements in liquids, which is important for the potential application of particle plasmons in chemical or biological nanosensors.
394 citations
TL;DR: In this paper, the structural basis for the aggregation-induced optical properties of colloidal gold nanosphere aggregates is examined by means of electrodynamics calculations, using accurate nanoparticle polarizabilities determined from Mie theory, an iterative conjugate-gradient solution algorithm, and fast Fourier transform methods for efficient solution of the electrodynamic interacting nanoparticle equations.
Abstract: The structural basis for the aggregation-induced optical properties of colloidal gold nanosphere aggregates is examined by means of electrodynamics calculations. Recently developed methods for calculating the electrodynamic response of aggregates composed of large numbers of small metal nanospheres in a dielectric medium are used to determine the optical changes associated with the formation of spherical aggregates. The calculations use accurate nanoparticle polarizabilities determined from Mie theory, an iterative conjugate-gradient solution algorithm, and fast-Fourier transform methods for efficient solution of the electrodynamic interacting nanoparticle equations. The UV extinction lowering and the shifting and broadening of the visible plasmon peak observed experimentally in solutions of DNA-linked gold nanospheres are explained as the collective electromagnetic response of thousands of nanoparticles.
312 citations
TL;DR: What are believed to be the first experimental observations of the existence of long-range plasmon-polariton waves, guided by a thin metal film of finite width, are presented.
Abstract: What are believed to be the first experimental observations of the existence of long-range plasmon–polariton waves, guided by a thin metal film of finite width, are presented. A waveguide composed of an 8-µm-wide, 20-nm-thick, 3.5-mm-long Au metal film embedded in SiO2 was successfully excited at a free-space wavelength of 1.55 µm in an end-fire experiment. The theoretical nature of the phenomenon is described, and experimental observations of field confinement provided by this metal waveguide are presented in detail.
308 citations
TL;DR: In this paper, a method for enhancing the emission properties of light-emitting diodes, by coupling to surface plasmons, is analyzed both theoretically and experimentally, and the analyzed structure consists of a semiconductor emitter layer thinner than /spl lambda//2 sandwiched between two metal films.
Abstract: A method for enhancing the emission properties of light-emitting diodes, by coupling to surface plasmons, is analyzed both theoretically and experimentally. The analyzed structure consists of a semiconductor emitter layer thinner than /spl lambda//2 sandwiched between two metal films. If a periodic pattern is defined in the top semitransparent metal layer by lithography, it is possible to efficiently couple out the light emitted from the semiconductor and to simultaneously enhance the spontaneous emission rate. For the analyzed designs, we theoretically estimate extraction efficiencies as high as 37% and Purcell factors of up to 4.5. We have experimentally measured photoluminescence intensities of up to 46 times higher in fabricated structures compared to unprocessed wafers. The increased light emission is due to an increase in the efficiency and an increase in the pumping intensity resulting from trapping of pump photons within the microcavity.
TL;DR: At resonance frequencies, extremely large enhancements of the electromagnetic fields occur near the surface of the particle, with amplitudes several hundred-fold that of the incident field.
Abstract: We study the plasmon resonances of 10–100(nm) two-dimensional metal particles with a non-regular shape. Movies illustrate the spectral response of such particles in the optical range. Contrary to particles with a simple shape (cylinder, ellipse) non-regular particles exhibit many distinct resonances over a large spectral range. At resonance frequencies, extremely large enhancements of the electromagnetic fields occur near the surface of the particle, with amplitudes several hundred-fold that of the incident field. Implications of these strong and localized fields for nano-optics and surface enhanced Raman scattering (SERS) are also discussed.
TL;DR: In this article, the extinction bands of the respective multipolar plasmons overlap considerably to form a broad spectrum, spectrally well-separated extinction bands corresponding to multipolar order up to n=6 are found.
Abstract: We report on the experimental observation of multipolar plasmon excitations in lithographically designed elongated silver particles. In contrast to spheres, where the extinction bands of the respective multipolar plasmons overlap considerably to form a broad spectrum, spectrally well-separated extinction bands corresponding to plasmons of multipolar order up to n=6 are found. The results agree well with numerical simulations based on the Green’s Dyadic method.
TL;DR: In this paper, a study of the surface-enhanced infrared absorption (SEIRA) spectroscopy of para-nitrobenzoic acid (PNBA) adsorbed on thermally evaporated silver films has been conducted to determine the effect of film architecture on the magnitude of SEIRA enhancement.
Abstract: A study of the surface-enhanced infrared absorption (SEIRA) spectroscopy of para-nitrobenzoic acid (PNBA) adsorbed on thermally evaporated silver films has been conducted to determine the effect of film architecture on the magnitude of the SEIRA enhancement. Ordered arrays of uniformly sized silver nanoparticles, termed periodic particle arrays (PPAs), were prepared on several different infrared transparent substrates (germanium, silicon, and mica) by nanosphere lithography (NSL). It was found that the ordered arrays deposited by NSL produced well-defined and intense surface plasmon resonance (SPR) bands in the infrared at frequencies between 1500 and 4000cm -1. The peak frequency of these infrared SPR bands depended on the array architecture and the substrate material. By appropriate design of the nanoparticle array, the infrared SPR band can be made to be coincident with the SEIRA sensitive infrared bands of the PNBA. The trends in the infrared SPR peak frequencies and band shapes were consistent with predictions from electrodynamic theory. The SEIRA responses per unit area of deposited metal obtained with the PPA-type films were at best comparable to results obtained with disordered silver and gold films deposited on the same substrate materials by thermal evaporation (i.e., in the absence of any NSL masking spheres). The results of this study are most consistent with theories and models that attribute SEIRA to the dielectric constant and optical extinction spectrum of the metal film. Index Headings: Infrared spectroscopy; Surface-enhanced infrared absorption; Plasmon; SEIRA.
TL;DR: In this article, the ultrafast surface plasmon resonance nonlinearities and their connection with the conduction band electron dynamics are discussed in metal nanoparticles in the light of the results of high sensitivity femtosecond pump-probe experiments in silver nanoparticles embedded in a glass matrix.
TL;DR: The collective mode structure of a strongly correlated Yukawa fluid is determined, with the purpose of analyzing wave propagation in a strongly coupled dusty plasma, and a longitudinal plasmon and a transverse shear mode are identified.
Abstract: We determine the collective mode structure of a strongly correlated Yukawa fluid, with the purpose of analyzing wave propagation in a strongly coupled dusty plasma. We identify a longitudinal plasmon and a transverse shear mode. The dispersion is characterized by a low- k acoustic behavior, a frequency maximum well below the plasma frequency, and a high- k merging of the two modes around the Einstein frequency of localized oscillations. The damping effect of collisions between neutrals and dust grains is estimated.
TL;DR: In this paper, an extensive electron energy loss spectroscopy study of the low-loss energy region, recorded on multishell carbon and boron-nitride nanotubes and carbon hyperfullerenes, is presented.
Abstract: We present an extensive electron energy loss spectroscopy study of the low-loss energy region, recorded on multishell carbon and boron-nitride nanotubes and carbon hyperfullerenes. Collections of spectra were recorded in a scanning transmission electron microscope by scanning a subnanometer probe from vacuum into the center of the nano-objects. This experimental technique provides the unique ability of disentangling and identifying the different excitation modes of a nanoparticle. We concentrate on the study of surface modes excited in a near-field geometry where the coupling distance between the electron beam and the surface of the nano-objects is accurately monitored. Similarities between surface collective excitations in the different layered nanostructures (cylindrical or spherical, boron nitride, or carbon constituted) are pointed out. Two surface modes at 12--13 eV and 17--18 eV are experimentally clearly evidenced. We show that these modes are accurately described by a classical continuum dielectric model taking fully into account the anisotropic character and the hollow geometry of the nanoparticles. These two modes are shown to be directly related to the in-plane and out-of-plane components of the dielectric tensor. The higher-energy mode (in-plane mode) is shown to shift to higher energy with decreasing impact parameter, as a result of an increase in the weights of the high-order multipolar modes while reaching the surface of the nano-objects.
TL;DR: The properties of some purely bound plasmon-polariton modes guided by an asymmetric waveguide structure composed of a thin lossy metal film of finite width supported by a dielectrics substrate and covered by a different dielectric superstrate are presented for what is believed to be the first time.
Abstract: The properties of some purely bound plasmon-polariton modes guided by an asymmetric waveguide structure composed of a thin lossy metal film of finite width supported by a dielectric substrate and covered by a different dielectric superstrate are presented for what is believed to be the first time. The mode spectrum supported by these structures is quite different from the spectrum supported by corresponding asymmetric slab structures or similar finite-width symmetric waveguides. Unlike these limiting cases, the dispersion with film thickness exhibits an unusual oscillatory character that is explained by a “switching” of constituent interface modes. This mode switching is unique to asymmetric finite-width structures. Above a certain cut-off film thickness, the structure can support a long-ranging mode and its attenuation decreases very rapidly with decreasing film thickness, more so than the long-ranging mode in symmetric structures. Also, the cutoff thickness of the long-ranging mode is larger than the cutoff thickness of the long-ranging mode in the corresponding asymmetric slab waveguide, which implies that propagation along finite-width films is more sensitive to the asymmetry in the structure than propagation along a similar slab structure. Both of these results are potentially useful for the transmission and control of optical radiation.
TL;DR: In this paper, the authors used grazing-incidence X-ray reflectivity (XRR) to validate the density of a variety of amorphous carbon thin films derived from the valence plasmon in electron energy loss spectroscopy measurements.
TL;DR: In this article, a promising optical system and technique for detection, imaging, and visualization of minimal changes, of the order of 10−6 in refractive index, in the near field is presented.
Abstract: We present a promising optical system and technique for detection, imaging, and visualization of minimal changes, of the order of 10−6 in refractive index, in the near field. The system is based on phase imaging of excited surface plasmons in a conducting layer in contact with a sample. This technique is shown here to be sensitive enough to image the flow of helium and argon gas in a nitrogen atmosphere. Its application to biological and chemical research is suggested.
TL;DR: In this paper, the plasmon resonances for small two-dimensional silver particles (nanowires) with elliptical or triangular shapes in the 20 nm size range were investigated.
Abstract: We study the plasmon resonances for small two-dimensional silver particles (nanowires) with elliptical or triangular shapes in the 20 nm size range. While the elliptical particle has only two resonances, a well known fact, we demonstrate that the triangular particle displays a much more complex behaviour with several resonances over a broad wavelength range. Using animations of the field amplitude and field polarization, we investigate the properties of these different resonances. The field distribution associated with each plasmon resonance can be related to the polarization charges on the surface of the particles. Implications for the design of plasmon resonant structures with specific properties, for example, for nano-optics or surface enhanced Raman scattering are discussed.
TL;DR: In this article, the authors used femtosecond laser pulses to investigate the excitation and decay mechanisms of the surface plasmon resonance in Ag nanoparticles grown on graphite and found that the resonant excitation of this collective excitation leads to a two-orders-of-magnitude-enhanced two-photon photoemission yield from a graphite surface with ag nanoparticles compared to the yield from pure graphite.
Abstract: Two-photon photoemission spectroscopy using femtosecond laser pulses is used to investigate the excitation and decay mechanisms of the surface plasmon resonance in Ag nanoparticles grown on graphite. The resonant excitation of this collective excitation leads to a two-orders-of-magnitude-enhanced two-photon photoemission yield from a graphite surface with Ag nanoparticles compared to the yield from pure graphite. From the shape of the photoemission spectra, the polarization dependence of the photoemission yield and the excitation probabilities for different excitation pathways we conclude that excitation with 400-nm femtosecond laser pulses leads to the coherent multiple excitation of the surface plasmon in the Ag nanoparticles. This multiply excited plasmon mode can decay via the coupling to a single-particle excitation leading to the emission of an electron if its final state is located in the continuum. The surface plasmon in metallic nanoparticles is a model system to investigate collective excitations in multiphoton processes.
TL;DR: In this paper, the influence of the probe composition on the formation of constant-height photon scanning tunneling microscope images when observing a dielectric sample was studied and dramatic effects due to the metallization of the tip were presented and discussed in detail.
Abstract: We present a study of the influence of the probe composition on the formation of constant-height photon scanning tunneling microscope images when observing a dielectric sample. Dramatic effects due to the metallization of the tip are presented and discussed in detail. We show how the recorded images can look quite different when the probe is dielectric or coated with gold. Comparison with numerical calculations indicate that the experimental signals are of electric or magnetic nature depending on the composition of the tip. For well-defined conditions, gold-coated tips provide images of the distribution of the magnetic field intensity associated with the optical near field. To get more insight into the origin of this effect, we have performed a careful analysis of the plasmon modes associated with a gold-coated dielectric cylinder. We conclude that the detection of the optical magnetic field is related to the conditions of excitation of circular symmetry plasmon, or ring plasmon, in the gold-coated tip.
Patent•
03 Nov 2000
TL;DR: In this article, metal-doped sol-gel materials, suitable for use as sensors for surface-enhanced Raman spectroscopic analysis for trace chemical detection, are produced by effecting gelation and solvent removal of a doped solgel.
Abstract: Metal-doped sol-gel materials, suitable for use as sensors for surface-enhanced Raman spectroscopic analysis for trace chemical detection, are produced by effecting gelation and solvent removal of a doped sol-gel. Reaction and drying may be effected in an oxygen-starved environment. The metal of the sol-gel material functions, when irradiated, to produce a plasmon field for interaction with molecules of analyze in contact therewith, increasing by orders of magnitude Raman photons that are generated by excitation radiation. The sensors (1) provided may be in the form of glass vials, fiber optics, multi-well micro-sample plates, etc., having a substrate (2) and surface coatings of the sol-gel material (3) doped with metal particles (4) of size to optimize generation of aplasmon field (7), to provide sampling sytems for use in a Raman instrument, the flow of molecules being depicted by (8).
TL;DR: The bias-dependent spatial distribution of the photon emission rates reveals the electric-field distribution ofthe different coupled plasmon modes in this model.
Abstract: We report on the experimental observation of STM-induced photon emission in ultrahigh vacuum on a network of 4-nm silver spheres. The spheres are covered by a dielectric, electrically insulating, organic layer and deposited on Au(111). The bias-dependent spatial distribution of the photon emission rates reveals the electric-field distribution of the different coupled plasmon modes in this model.
TL;DR: In this article, it was pointed out that the variation of the plasmon frequency of metal with temperatures, though generally extending to a very limited amount, could have significant effects on the recently observed dependence of surface-enhanced Raman scattering (SERS) on substrate temperatures.
Abstract: It is pointed out that the variation of the plasmon frequency of metal with temperatures, though generally extending to a very limited amount, could however have significant effects on the recently observed dependence of surface-enhanced Raman scattering (SERS) on substrate temperatures.
TL;DR: The experimental results show that within the wave inelastically scattered at aluminium plasmons there is in fact an area of about 10 nm diameter with coherence sufficient to take electron holograms.
TL;DR: A carrier-density dependent oscillation is predicted, which is superimposed on the decay of the coherent control photon echo signal of a semiconductor, that reflects the oscillatory transfer of excitation back and forth between electrons and a mixed plasmon-phonon mode.
Abstract: We predict a carrier-density dependent oscillation, which is superimposed on the decay of the coherent control photon echo signal of a semiconductor. It reflects the oscillatory transfer of excitation back and forth between electrons and a mixed plasmon-phonon mode. This signature provides obvious and unique evidence for the finite duration of the interaction process, i.e., evidence for the collective Coulomb quantum kinetics. The theoretical predictions for the model semiconductor GaAs are reproduced in corresponding experiments.
TL;DR: In this article, a simple model in which the conduction electron plasmon is coupled to the continuum of electron-hole pairs is described by means of ab initio calculations.
Abstract: The delicate interplay between plasmonic excitations and interband transitions in noble metals is described by means of ab initio calculations and a simple model in which the conduction electron plasmon is coupled to the continuum of electron-hole pairs. Band-structure effects, especially the energy at which the excitation of the d-like bands takes place, determine the existence of a threshold plasmonic mode, which manifests itself in Ag as a sharp resonance experimentally observed at 3.8 eV. However, such a resonance does not appear in the spectra of the other noble metals. Here this different behavior is also analyzed, and an explanation is provided.
TL;DR: In this article, surface plasmons are excited by using an oil-immersion lens, which forms one arm of an interferometer, and the characteristic output variation with defocus is determined by the propagation properties of the surfaces.
Abstract: Surface plasmons are electromagnetic surface waves whose k vectors are greater than that of free-space radiation. We excite surface plasmons by using an oil-immersion lens, which forms one arm of an interferometer. We demonstrate the way in which the characteristic output variation with defocus is determined by the propagation properties of the surface plasmons, which leads to diffraction-limited surface plasmon microscopy in the far field.