Showing papers on "Plasmon published in 2001"
TL;DR: This light-driven process results in a colloid with distinctive optical properties that directly relate to the nanoprism shape of the particles, which could be useful in developing multicolor diagnostic labels on the basis of nanoparticle composition and size but also of shape.
Abstract: A photoinduced method for converting large quantities of silver nanospheres into triangular nanoprisms is reported. The photo-process has been characterized by time-dependent ultraviolet-visible spectroscopy and transmission electron microscopy, allowing for the observation of several key intermediates in and characteristics of the conversion process. This light-driven process results in a colloid with distinctive optical properties that directly relate to the nanoprism shape of the particles. Theoretical calculations coupled with experimental observations allow for the assignment of the nanoprism plasmon bands and for the first identification of two distinct quadrupole plasmon resonances for a nanoparticle. Unlike the spherical particles they are derived from that Rayleigh light-scatter in the blue, these nanoprisms exhibit scattering in the red, which could be useful in developing multicolor diagnostic labels on the basis not only of nanoparticle composition and size but also of shape.
3,256 citations
TL;DR: In this paper, a point dipole analysis predicts group velocities of energy transport that exceed 0.1c along straight arrays and shows that energy transmission and switching through chain networks such as corners and tee structures is possible at high efficiencies.
Abstract: The further integration of optical devices will require the fabrication of waveguides for electromagnetic energy below the diffraction limit of light. We investigate the possibility of using arrays of closely spaced metal nanoparticles for this purpose. Coupling between adjacent particles sets up coupled plasmon modes that give rise to coherent propagation of energy along the array. A point dipole analysis predicts group velocities of energy transport that exceed 0.1c along straight arrays and shows that energy transmission and switching through chain networks such as corners (see Figure) and tee structures is possible at high efficiencies. Radiation losses into the far field are expected to be negligible due to the near-field nature of the coupling, and resistive heating leads to transmission losses of about 6 dB/lm for gold and silver particles. We analyze macroscopic analogues operating in the microwave regime consisting of closely spaced metal rods by experiments and full field electrodynamic simulations. The guiding structures show a high confinement of the electromagnetic energy and allow for highly variable geometries and switching. Also, we have fabricated gold nanoparticle arrays using electron beam lithography and atomic force microscopy manipulation. These plasmon waveguides and switches could be the smallest devices with optical functionality.
1,650 citations
TL;DR: A fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface.
Abstract: We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interface. Different regimes of tunneling (resonant through a ``surface plasmon molecule,'' or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.
1,577 citations
TL;DR: It is shown that the onset of collective behaviour such as Coulomb screening and plasmon scattering exhibits a distinct time delay of the order of the inverse plasma frequency, that is, several 10-14 seconds after ultrafast excitation of an electron–hole plasma in GaAs.
Abstract: Electrostatic coupling between particles is important in many microscopic phenomena found in nature. The interaction between two isolated point charges is described by the bare Coulomb potential, but in many-body systems this interaction is modified as a result of the collective response of the screening cloud surrounding each charge carrier. One such system involves ultrafast interactions between quasi-free electrons in semiconductors-which are central to high-speed and future quantum electronic devices. The femtosecond kinetics of nonequilibrium Coulomb systems has been calculated using static and dynamical screening models that assume the instantaneous formation of interparticle correlations. However, some quantum kinetic theories suggest that a regime of unscreened bare Coulomb collisions might exist on ultrashort timescales. Here we monitor directly the temporal evolution of the charge-charge interactions after ultrafast excitation of an electron-hole plasma in GaAs. We show that the onset of collective behaviour such as Coulomb screening and plasmon scattering exhibits a distinct time delay of the order of the inverse plasma frequency, that is, several 10(-14) seconds.
551 citations
TL;DR: In this paper, the spectrum of plasmon resonances for metallic nanowires with a non-regular cross section, in the 20-50 nm range, was investigated numerically.
Abstract: We investigate numerically the spectrum of plasmon resonances for metallic nanowires with a nonregular cross section, in the 20‐50 nm range. We first consider the resonance spectra corresponding to nanowires whose cross sections form different simplexes. The number of resonances strongly increases when the section symmetry decreases: A cylindrical wire exhibits one resonance, whereas we observe more than five distinct resonances for a triangular particle. The spectral range covered by these different resonances becomes very large, giving to the particle-specific distinct colors. At the resonance, dramatic field enhancement is observed at the vicinity of nonregular particles, where the field amplitude can reach several hundred times that of the illumination field. This near-field enhancement corresponds to surface-enhanced Raman scattering~SERS! enhancement locally in excess of 10 12 . The distance dependence of this enhancement is investigated and we show that it depends on the plasmon resonance excited in the particle, i.e., on the illumination wavelength. The average Raman enhancement for molecules distributed on the entire particle surface is also computed and discussed in the context of experiments in which large numbers of molecules are used.
476 citations
TL;DR: In this paper, surface plasmons are realized by a prism coupling arrangement involving an opaque aluminum screen for a distinct separation of excitation and propagation region, and the surface plasmon propagation length as a function of film widths is measured by detecting stray light due to surface plasar scattering with a conventional optical microscope.
Abstract: Addressing the fundamental question of miniaturization of light guiding and routing towards nanoscale optics, we study experimentally surface plasmon propagation in silver and gold thin films of finite widths in the micrometer range. Spatially confined excitation of surface plasmons is realized by a prism coupling arrangement involving an opaque aluminum screen for a distinct separation of excitation and propagation (measurement) region. The surface plasmon propagation length as a function of film widths is measured by detecting stray light due to surface plasmon scattering with a conventional optical microscope.
374 citations
TL;DR: The plasmon resonances of interacting silver nanowires with a 50 nm diameter are investigated and a dramatic field enhancement between the particles is observed, where the electric field amplitude reaches a hundredfold of the illumination.
Abstract: We investigate the plasmon resonances of interacting silver nanowires with a 50 nm diameter. Both non–touching and intersecting configurations are investigated. While individual cylinders exhibit a single plasmon resonance, we observe much more complex spectra of resonances for interacting structures. The number and magnitude of the different resonances depend on the illumination direction and on the distance between the particles. For very small separations, we observe a dramatic field enhancement between the particles, where the electric field amplitude reaches a hundredfold of the illumination. A similar enhancement is observed in the grooves created in slightly intersecting particles. The topology of these different resonances is related to the induced polarization charges. The implication of these results to surface enhanced Raman scattering (SERS) are discussed.
333 citations
TL;DR: In this paper, a photon scanning tunneling microscope was used to probe the field of surface plasmon polariton modes excited on finite-width thin metal films (metal stripes).
Abstract: We use a photon scanning tunneling microscope to probe the field of surface plasmon polariton modes excited on finite-width thin metal films (metal stripes). We first investigate the coupling between surface plasmons launched by a focused beam on a homogeneous thin film and the modes sustained by metal stripes of different widths. We show that, if the width of the metal stripe is about a few micrometers, a strong coupling with the stripe modes can be achieved at visible frequencies. A sharp transverse confinement of the field associated with the surface plasmon modes propagating on the metal stripe is unambiguously observed on the constant height photon scanning tunneling microscope images. The back-reflection of these modes at the end of the stripe leads to a surface-wave interference pattern from which the wavelength of the stripe surface plasmon modes is directly measured. We finally demonstrate that metal stripes could be used for optical addressing purposes at the micrometer scale since a stripe with a triangularly shaped termination performs the focusing of the stripe surface plasmon field.
310 citations
TL;DR: In this article, the authors presented the application of long-range surface plasmons to a wavelength-modulated surface plasmon resonance sensor, using either magnesium fluoride or Teflon AF-1600 as a dielectric buffer layer.
Abstract: We present the application of long-range surface plasmons to a wavelength-modulated surface plasmon resonance sensor. Theoretical design parameters and experimental data are presented for two sensor designs, using either magnesium fluoride or Teflon AF-1600 as a dielectric buffer layer. The demonstrated sensitivity of the long-range surface plasmon resonance sensor in refractometric experiments is up to seven times higher than that of an equivalent conventional surface plasmon resonance (SPR) sensor, while the measured resolution is comparable. According to theoretical design calculations presented, further optimization of materials and layer thickness could reduce the resonance width while achieving even higher sensitivities, thereby creating a sensor with significantly better resolution than conventional SPR sensors.
296 citations
TL;DR: The first optical images taken with a probe consisting of a single gold nanoparticle for apertureless scanning near‐field optical microscopy are presented and plasmon resonances of gold particles are recorded.
Abstract: We report on the fabrication, characterization and application of a probe consisting of a single gold nanoparticle for apertureless scanning near-field optical microscopy. Particles with diameters of 100 nm have been successfully and reproducibly mounted at the end of sharp glass fibre tips. We present the first optical images taken with such a probe. We have also recorded plasmon resonances of gold particles and discuss schemes for exploiting the wavelength dependence of their scattering cross-section for a novel form of apertureless scanning near-field optical microscopy.
TL;DR: Variation of the structure parameters allows continuous tuning of these high-transmission bands across the particle-plasmon resonance.
Abstract: The interaction of visible light with the particle-plasmon resonance of metallic nanoparticles can be controlled by geometrical arrangement of nanoparticle arrays. These arrays are placed on a substrate that supports guided modes in the wavelength range of the particle plasmon. Coupling of this particle-plasmon resonance to the directly incident light and to the waveguide modes results in almost complete suppression of light extinction within narrow spectral bands due to destructive interference. Variation of the structure parameters allows continuous tuning of these high-transmission bands across the particle-plasmon resonance.
TL;DR: In this paper, the authors used nanowire gratings produced by electron beam lithography to study the effect of the polarization direction of the incident light on optical extinction spectroscopy.
Abstract: The optical response of regularly arranged noble metal wires with nanoscopic cross sections (nanowire gratings) strongly depends on the polarization direction of the incident light. We use silver and gold nanowire gratings produced by electron beam lithography to study this effect by optical extinction spectroscopy. For a polarization direction perpendicular to the wire axis, the excitation of a dipolar plasmon mode dominates the extinction spectrum. The spectral position of the plasmon resonance can be tuned by an appropriate choice of nanowire geometry and material. For a polarization direction parallel to the wire axis, the profile of the extinction spectrum varies mainly as a function of the grating constant. In particular, a transmission maximum for small grating constants is found. By combining the surface plasmon excitation and grating effect for orthogonal polarization directions, a spectrally selective polarizer with an extinction ratio of 26 is demonstrated.
TL;DR: In this paper, a light detection system combined with a 200kV transmission electron microscope was used to measure the photon emission spectra from submicron silver particles induced by an electron beam.
Abstract: Photon emission spectra from submicron silver particles induced by an electron beam have been measured using a light detection system combined with a 200-kV transmission electron microscope. Multiple peaks appear in the spectra associated with collective plasmon excitations produced in the particles by the incident electrons. The wavelengths of these peaks are observed to shift towards larger values with increasing particle diameter, as predicted by Mie theory. Moreover, photon maps have been obtained in a scanning mode and they indicate that those peaks correspond to the multipole modes of electromagnetic oscillations in metallic spheres (Mie resonances). The spectral shape of the emission and the dependence on particle size, impact parameter, and electron energy are well explained from theoretical calculations of the photon emission probability derived from a fully retarded analytical treatment of the interaction of fast electrons with metallic spheres.
TL;DR: In this article, numerically the plasmon resonances of 10-50 nm nanowires with a non-elliptical section were investigated and the field distribution at the surface of these wires exhibits a dramatic enhancement, up to several hundred times the incident field amplitude.
TL;DR: The coupling induced by retardation effects when two plasmon-resonant nanoparticles are interacting leads to an additional resonance, the strength of which depends on a subtle balance between particle separation and size.
Abstract: We study the coupling induced by retardation effects when two plasmon-resonant nanoparticles are interacting. This coupling leads to an additional resonance, the strength of which depends on a subtle balance between particle separation and size. The scattering cross section and the near field associated with this coupled resonance are studied for cylindrical particles in air and in water. Implications for surface-enhanced Raman scattering and nano-optics are discussed.
TL;DR: The properties of gold surfaces patterned using a nanoscale "lost wax" technique by electrochemical deposition through a self-assembled latex template support localized surface plasmons which couple strongly to incident light, appearing as sharp spectral features in reflectivity measurements.
Abstract: We investigate the properties of gold surfaces patterned using a nanoscale "lost wax" technique by electrochemical deposition through a self-assembled latex template. Near-spherical gold nanocavities within the resulting porous films support localized surface plasmons which couple strongly to incident light, appearing as sharp spectral features in reflectivity measurements. The energy of the resonances is easily tunable from ultraviolet to near infrared by controlling the diameter and height of the nanocavities. The energies of these features agree well with the Mie resonances of a perfect spherical void.
IBM1
TL;DR: In this paper, the dispersion of interface plasmons in poly-Si/SiO2/Si structures with polycrystalline Si gates has been investigated and the effect of plasmon scattering on the effective electron mobility in Si inversion layers has been shown.
Abstract: In metal–oxide–semiconductor structures with polycrystalline Si gates, electrons in the inverted channel of the substrate scatter with electrons in the gate via long-range Coulomb interactions. For thin oxides, these interactions can cause a significant transfer of momentum from the channel to the gate, thus reducing the effective mobility of the two-dimensional electron gas in the substrate. We present calculations of the dispersion of the interface plasmons in poly-Si/SiO2/Si structures, comparing the results obtained in the long-wavelength limit to those obtained using the random-phase approximation. Employing the former model, we compute the effect of plasmon scattering on the effective electron mobility in Si inversion layers. We find a significant reduction of the mobility for oxides thinner than about 3 nm.
TL;DR: The surface of gold nanorods is coated with thickness controlled silver by reducing AgCl43- exclusively on the metallic surface to form AucoreAgshell nanorod and then restored by selectively remov...
Abstract: The surface of gold nanorods is coated with thickness-controlled silver by reducing AgCl43- exclusively on the metallic surface to form AucoreAgshell nanorods and then restored by selectively remov...
TL;DR: The magneto-optical properties of noble-metal-ferromagnetic-metal multilayer thin films have been investigated as a function of the incidence angle, including the total reflection range, in the polar, longitudinal, and equatorial geometries, and for different values of the photon energy in the near infrared and visible spectrum as discussed by the authors.
Abstract: The magneto-optical properties of noble-metal--ferromagnetic-metal multilayer thin films have been investigated as a function of the incidence angle, including the total reflection range, in the polar, longitudinal, and equatorial geometries, and for different values of the photon energy in the near-infrared and visible spectrum. The experimental and theoretical results are obtained on a Au/Co/Au model system. They demonstrate that the resonant coupling of the p component of the light electric field with the gold surface plasmon, which occurs in the total reflection range, yields a strong enhancement of the magneto-optical response and signal-to-noise ratio of the system for the three magnetization directions. This resonant coupling and the resulting enhancement of the relevant magneto-optical quantities are achieved for any photon energy in the near infrared and visible range simply by tuning the incidence angle. The efficiency of this enhancement effect is shown to increase towards the infrared region of the spectrum following the rise of the quality factor of the surface plasmon resonance.
Dissertation•
24 Jul 2001
TL;DR: In this paper, the dephasing times and local field enhancement factors of plasmons in noble metal nanoparticles are determined by spectrally investigating the light-scattering from individual nanoparticles in a dark-field microscope setup.
Abstract: Plasmon excitations, i.e. collective oscillations of the conduction electrons, strongly influence the optical properties of metal nanostructures and are of great interest for future photonic devices. Here, plasmons in metal nanostructures are investigated by nearand far-field optical microscopic techniques. Emphasis is placed on the study of the linear interaction of light with individual nanostructures. Specifically, the light transmission through individual nanometer-sized holes in opaque metal films is investigated using a scanning near-field optical microscope (SNOM). It is shown unambiguously that excitation and lateral propagation of surface plasmons support the light transmission through these nanoholes. This process has been under discussion recently. The propagation direction is given by the light polarization, thus allowing controlled addressing of individual holes — a process that may figuratively be described as “nanogolf”. This polarization controlled addressing of specific holes may be applicable for de-multiplexing purposes in future optical systems. Furthermore, the dephasing times and local field enhancement factors of plasmons in noble metal nanoparticles are determined by spectrally investigating the light-scattering from individual nanoparticles in a dark-field microscope setup. It is found that radiation damping limits the plasmon dephasing time, T2, in the gold nanospheres studied here to 25 fs, whereas suppression of interband damping in gold nanorods leads to surprisingly long particle plasmon dephasing times and large local field enhancement factors. The record value of T2=18 fs approaches the theoretical limit given by the free-electron relaxation time. The results of this first systematic and conclusive experimental study on individual particles answer the long debated question of the amount of plasmon damping in gold nanoparticles. Good agreement with calculations using the bulk dielectric function of gold shows that purely collective dephasing and surface effects contribute negligibly to the overall damping in the particles under investigation. The experimental results allow to deduce the relative contributions of radiation, interand intraband damping in gold nanoparticles. Also, the “true” particle plasmon dephasing time is determined in the sense of a pure plasmon oscillation without coupling to photons or interband excitations. The spectroscopic investigation of plasmons in single nanoparticles can also be used to determine the refractive index of the medium surrounding the particles. It is demonstrated for the first time how this can be used to build optical nanosensors based on particle plasmons. Applications for local concentrations, binding events and redox reactions are shown. The sensing volume of such a nanosensor is on the order of attoliters. First experiments towards increasing the sensitivity show the prospect of this technique. Actively changing the environment around metal particles by electrically aligning liquid crystal molecules allows the shift of the resonance frequency over a wide spectral range. The experiments presented here show that this novel effect can be used for electrically controlled light scattering with high contrast and spectral selectivity.
TL;DR: Devaux et al. as mentioned in this paper studied the effect of varying the cylinder radius on the surface plasmon dispersion, thus justifying that the cylinder is a useful model for near-field probes in spite of their slightly conical shape.
Abstract: Metal-cladded dielectric cylinders with submicron diameters may serve to model coated tips used in nearfield scanning optical microscopy. The signal measured may be greatly influenced by resonance effects due to eigenmodes of the probe. Especially, using a photon scanning tunneling microscope setup, gold-coated tips have been found to detect a signal proportional to the magnetic field distributions [E. Devaux et al.. Phys. Rev. B 62, 10 504 (2000)]. This effect is attributed to cylindrical surface plasmons. We present here fully retarded calculations of the dispersion and field patterns of the nonradiative plasmon modes in cylindrical geometry. We study the effect of varying the cylinder radius on the surface plasmon dispersion, thus justifying that the cylinder is a useful model for near-field probes in spite of their slightly conical shape.
TL;DR: In this article, the surface plasmons in silver films with narrow straight grooves were visualized in unprecedented detail by means of near-field optical techniques, and their values were determined semiquantitatively.
Abstract: Excitation and propagation of surface plasmons in silver films structured with narrow straight grooves were visualized in unprecedented detail by means of near-field optical techniques. Reflectivity, transmissivity, and scattering loss of the grooves are demonstrated. Their values are determined semiquantitatively. The surface plasmon attenuation are found to be dominated by material and surface/interface imperfections.
TL;DR: The energy and the linewidth dispersion of a plasmon in a dense two-dimensional electron system in a metallic surface-state band on a silicon surface is studied for the first time.
Abstract: We have studied, for the first time, the energy and the linewidth dispersion of a plasmon in a dense two-dimensional electron system in a metallic surface-state band on a silicon surface. As expected from the considerably high effective density and long Fermi wavelength of the system, the plasmon energy dispersion exhibited an excellent agreement with the nearly free-electron theory. However, in a small wave number region below the Landau edge, we have observed an anomalous linewidth dispersion which nearly free-electron theories do not predict.
Book•
01 Jan 2001
TL;DR: In this paper, an apertureless metallic probe was used for near-field microscopy using surface plasmon polaritons and a focused laser beam was used to control light confinement by localized surface plasmons.
Abstract: Near-Field Optics and the Surface Plasmon Polariton.- Near-Field Microscope Probes Utilizing Surface Plasmon Polaritons.- Apertureless Metallic Probes for Near-Field Microscopy.- Controlling Light Confinement by Excitation of Localized Surface Plasmons.- Spectroscopy of Gap Modes in Metal Particle-Surface Systems.- Near-Field Spectral Analysis of Metallic Beads.- Forces in Optical Near-Fields.- Laser Trapping of a Metallic Probe for Near Field Microscopy.- Surface-Enhanced Infrared Absorption.- Excitation of Surface Plasmon Polaritons by a Focused Laser Beam.
TL;DR: A plasmon waveguide was designed and fabricated using a metal-coated silicon wedge structure that converted propagating far-field light to the near field illumination as discussed by the authors, and the waveguide's beam width and propagation length were determined using a near-field microscope.
Abstract: A plasmon waveguide was designed and fabricated using a metal-coated silicon wedge structure that converts propagating far-field light to the near field Illumination (λ=830 nm) of the waveguide (plateau width 150 nm) caused transverse magnetic plasmon-mode excitation Use of a near-field microscope allowed us to determine its beam width and propagation length as 150 nm and 25 μm, respectively
TL;DR: In this paper, the authors employed numerical field calculations to study quantitatively the wavelength-dependent interaction of visible light with nanometric holes in metallic screens and found that the transmission efficiency through holes in an ideally conducting screen of finite thickness was found to follow a power law as a function of wavelength with an exponent close to −4.
TL;DR: In this article, the size-dependent absorbance properties of Au and Ag nanoclusters dispersed in organic solvents were investigated using high pressure liquid chromatography (HPLC) and transmission electron microscopy.
Abstract: We report high-pressure liquid chromatography (HPLC) and transmission electron microscopy studies of the size-dependent absorbance properties of Au and Ag nanoclusters dispersed in organic solvents. These nanosize metal clusters are synthesized by an inverse micelle synthetic technique at room temperature in inert oils and those investigated range in diameter from 1.3–8 nm. HPLC allows us to separate the clusters from all other chemicals and size select to a resolution of ±2 A. We use an on-line photodiode array to study the size-dependent absorbance properties of these clusters. For both Au and Ag clusters in the size range d=8 to d=1.5 nm, the plasmon linewidth broadens following a 1/R linewidth size dependence whose slope is greatest for Au. The peak asymmetry in the plasmon band shape is greatest for Au and increases with decreasing size for both Au and Ag clusters. The plasmon peak energy blue shifts with decreasing size for Au clusters while in the case of Ag nanoclusters a red shift is observed.
TL;DR: In this article, a shift in plasmon surface resonance is measured for colloidal solutions of gold nanoparticles upon adsorption of polyampholyte (gelatin), and it is demonstrated that the shift in wavelength of the absorption maximum can quantitatively yield measurements of the adsorbed amount as well as information about the structure of the adorbed polymer layer.
Abstract: A shift in plasmon surface resonance is measured for colloidal solutions of gold nanoparticles upon adsorption of polyampholyte (gelatin). It is demonstrated that the shift in wavelength of the absorption maximum can quantitatively yield measurements of the adsorbed amount as well as information about the structure of the adsorbed polymer layer. Semiquantitative agreement is found with calculations based on the Mie theory in the quasi-static limit. The method is demonstrated to provide quantitative measurements of the kinetics of biopolymer adsorption onto colloidal nanoparticles in solution.
TL;DR: In this article, a nanostructured surface in the form of a bi-grating is shown to efficiently couple surface plasmon polaritons to free-space radiation in the visible part of the spectrum.
Abstract: A nanostructured surface in the form of a bi-grating is shown to efficiently couple surface plasmon polaritons to free-space radiation in the visible part of the spectrum. Coupling was achieved for all propagation directions of the surface mode and the efficiency found to be independent of the propagation direction, taking a mean value of 60% for the structure examined. The consequences of the findings for emissive devices that make use of surface plasmons are discussed.