scispace - formally typeset
Search or ask a question

Showing papers on "Plasmon published in 1996"


Journal ArticleDOI
TL;DR: A mechanism for depression of the plasma frequency into the far infrared or even GHz band is proposed: Periodic structures built of very thin wires dilute the average concentration of electrons and considerably enhance the effective electron mass through self-inductance.
Abstract: The plasmon is a well established collective excitation of metals in the visible and near UV, but at much lower frequencies dissipation destroys all trace of the plasmon and typical Drude behavior sets in. We propose a mechanism for depression of the plasma frequency into the far infrared or even GHz band: Periodic structures built of very thin wires dilute the average concentration of electrons and considerably enhance the effective electron mass through self-inductance. Computations replicate the key features and confirm our analytic theory. The new structure has novel properties not observed before in the GHz band, including some possible impact on superconducting properties.

3,954 citations


Journal ArticleDOI
TL;DR: For the first time it is possible to handle surfaces consisting of complex particles close enough to interact strongly, and a fully retarded implementation of Maxwell's equations on adaptive meshes allows treatment of large particles as well as small.
Abstract: We present an implementation of Maxwell's equations on adaptive meshes in order to study interaction of light with metal surfaces. For the first time it is possible to handle surfaces consisting of complex particles close enough to interact strongly. A fully retarded implementation allows treatment of large particles as well as small. By way of example we model a rough silver surface as an array of half-cylinders embedded in a silver surface. Very localized plasmon modes, created by strong electromagnetic coupling between touching metallic objects, dominate the surface enhanced Raman scattering response.

830 citations


Journal ArticleDOI
TL;DR: In this article, an analysis of the transient absorption of colloidal gold nanoparticles with an average radius of 15 nm has been carried out and two time constants: 2.5 ps and a slower component of > 50 ps.
Abstract: Colloidal gold nanoparticles with an average radius of 15 nm have a surface plasmon absorption band at 530 nm. Excitation by laser pulses of 450 fs duration, and wavelength of 600 or 380 nm “bleached” the plasmon band and produced a transient absorption at the wings of the “bleach” spectrum. The transient absorption was found to have a similar temporal behavior at different wavelengths. Analysis of their temporal behavior showed two time constants: 2.5 ps, and a slower component of >50 ps. Laser excitation close to the plasmon band at 600 nm leads to the formation of “hot” non-Fermi electronic distribution within the colloidal particles. Transient absorption from these “hot” electrons led to different absorptions from that of the plasmon absorption of “cold” electrons. The “hot” electrons relax via electron−phonon coupling in 2.5 ps, and the phonon−phonon relaxation of the lattice occurs in >50 ps. At 380 nm excitation, the amplitude of the blue wing becomes smaller, and the slow component becomes longer...

341 citations


Journal ArticleDOI
TL;DR: In this article, the use of surface plasmons on planar surfaces for the characterisation of those surfaces is analysed, and analytic expressions for the sensitivity of such characterisation to the variation of bulk refractive indices, and to the addition of thin dielectric layers on the plasmon supporting surface.

166 citations


Journal ArticleDOI
TL;DR: It is found that, within a certain range of size, a hill on an otherwise flat surface can be a source of a micrometer wide plasmon beam, and the effective cross section of a defect can be substantially larger than its visible geometrical size.
Abstract: A new technique for direct-write ablation on a 100 nm scale has been implemented in a photon scanning tunneling microscope setup. This combination allows us, for the first time, to study surface plasmon scattering by in situ created individual surface defects, while the sizes and shapes of the defects are varied. It is found that, within a certain range of size, a hill on an otherwise flat surface can be a source of a micrometer wide plasmon beam. Another new observation is that the effective cross section of a defect can be substantially larger than its visible geometrical size. These results suggest possible practical applications of surface plasmons in two-dimensional optical arrangements.

125 citations


Journal ArticleDOI
TL;DR: The cumulant expansion approach is used to obtain the spectral functions of Na and Al from ab initio calculations including the effects of band structure and the GW spectral functions are dramatically improved.
Abstract: he valence photoemission spectra of alkali metals exhibit multiple plasmon satellite structure. The calculated spectral functions within the GW approximation show only one plasmon satellite at too large binding energy. In this Letter we use the cumulant expansion approach to obtain the spectral functions of Na and Al from ab initio calculations including the effects of band structure. The GW spectral functions are dramatically improved and the positions of the multiple plasmon satellites are in very good agreement with experiment while their intensities cannot be explained from intrinsic effects only.

116 citations


Patent
30 May 1996
TL;DR: In this paper, an electro-optic medium formed between two spatially disposed electrodes was used to induce a lossy condition on the propagating radiation in an optical waveguide for modulating or interacting with radiation guided and propagating along an optical longitudinal axis of an optical fiber.
Abstract: An optical device for modulating or interacting with radiation guided and propagating along an optical longitudinal axis of an optical waveguide, such as, an optical fiber, has a different directional geometry compared to conventionally comparable devices such as, for example, plasmon or planar surface modulators for optical fibers. The geometry includes a nonlinear, electro-optic medium formed between two spatially disposed electrodes. The medium/electrode sandwich is aligned along the waveguide longitudinal propagating axis and extends in a radial direction from the optical waveguide core with the inner end of the medium in spatial proximity to the waveguide core for evanescent coupling with the radiation field propagating in the waveguide. An applied electric field to the spatially disposed electrodes varies the refractive index of the electro-optic medium from just below the effective refractive index of the waveguide to just above the effective refractive index waveguide to induce a lossy condition on the propagating radiation. Modulation of the applied electric field will bring about intensity modulation of the propagating radiation.

109 citations


Journal ArticleDOI
TL;DR: In this article, the energy dependence of electron inelastic mean free path and stopping power in alkali halides and metal oxides has been investigated in the 50 eV to 10 keV energy range.
Abstract: Calculations of electron inelastic mean free paths and stopping powers for several alkali halides (KF, KC1, KBr, and KI) and metal oxides (BeO, MgO, SiO 2 and Aj 2 O 3 ) have been performed in the 50 eV to 10 keV energy range The complex dielectric formalism, improved to include the energy gap, was used for estimating the valence part of the transport characteristics, whereas the part related to electron-core interactions was evaluated according to Gryzinski's theory An extended comparison of these calculations with the available experimental data as well as with other theoretical predictions is presented Trends of the energy dependence of the inelastic mean free path and stopping power in alkali halides are studied The role of the plasmon deexcitation process as a source for low-energy electrons in secondary electron emission spectra is discussed The presented data can be used in Monte-Carlo simulations of electron transport in the considered materials

102 citations


Journal ArticleDOI
01 Jun 1996-Micron
TL;DR: In this paper, a systematic description on the classical electron energy-loss theory and its applications in characterizing interband transition and plasmon excitations in thin films, surfaces, interfaces, isolated particles and supported particles of different geometrical configurations is given.

96 citations


Journal ArticleDOI
TL;DR: It is found that bulk plasmons are excited even under conditions where the majority of the ions do not penetrate the surface, provided the energy released in neutralizing the incoming ion exceeds the plasmon energy.
Abstract: We find structure in the energy spectra of electrons not explainable by an Auger neutralization mechanism. This structure, which can be a dominant feature in the spectra, can be caused by a neutralization mechanism involving the excitation of both surface and bulk plasmons, provided the energy released in neutralizing the incoming ion exceeds the plasmon energy. We find that bulk plasmons are excited even under conditions where the majority of the ions do not penetrate the surface. The experiments were done in ultrahigh vacuum s,1 3 10 210 Torrd in a Perkin-Elmer 560 x-ray photoemission spectroscopy (XPS) and Auger microprobe system equipped with a double-pass cylindrical mirror electron energy spectrometer. For these experiments, the spectrometer was operated at a constant pass energy of 40 eV, a resolution of 0.16 eV, and an approximately constant transmission over the measured electron energy range. The energy scale of the spectrometer was calibrated with XPS photoelectron spectra of Au and high energy cutoff of the Al LVV Auger spectrum. To ease discussion of the results, the energy scale was

95 citations


Journal ArticleDOI
TL;DR: Direct crossover from a one-dimensional to a three-dimensional regime is found under readily fulfilled conditions for carbon nanotubes in the case of small finite longitudinal momentum transfer \q, while for q50 bulk graphitic plasmons fail to develop, and a two-dimensional behavior is found.
Abstract: s and p plasmons in coaxial carbon nanotubes and multishell fullerenes are modeled in analogy with coupled collective excitations in finite, layered, two-dimensional-electron-gas, planar semiconductor superlattices. The curvature of the surface of these complex carbon clusters plays an important role in shaping the dimensionality ~one dimensional, two dimensional, or three dimensional! of the plasmons. Direct crossover from a one-dimensional to a three-dimensional regime is found under readily fulfilled conditions for carbon nanotubes in the case of small finite longitudinal momentum transfer \q , while for q50 bulk graphitic plasmons fail to develop. For large q , a two-dimensional behavior is found. The case of multishell fullerenes resembles in all instances the q50 behavior of carbon nanotubes. Such behavior correlates with the observed systematic redshift of the strong interstellar absorption band as compared to the p plasmon of bulk oriented graphite ~i.e., the 5.7 eV position of the former compared to the 6.2 eV energy of the latter!. Furthermore, in the case of p plasmons in carbon nanotubes, a special surface mode can develop for large q , due to the difference in the values of the dielectric constants between the graphitic structures and the surrounding medium.

Journal ArticleDOI
TL;DR: A self-contained theoretical analysis of the dynamical response of a one-dimensional electron system, as confined in a semiconductor quantum wire, within the random-phase approximation is provided.
Abstract: We provide a self-contained theoretical analysis of the dynamical response of a one-dimensional electron system, as confined in a semiconductor quantum wire, within the random-phase approximation. We carry out a detailed comparison with the corresponding two- and three-dimensional situations, and discuss the peculiarities arising in the one-dimensional linear response from the nonexistence of low energy single-particle excitations and from the linear nature of the long wavelength plasmon mode. We provide a critical discussion of the analytic properties of the complex dielectric function in the complex frequency plane. We investigate the zeros of the complex dielectric function, and calculate the plasmon dispersion, damping, and plasmon spectral weight in one dimension. We consider finite temperature and impurity scattering effects on one-dimensional plasmon dispersion and damping. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: In this paper, a blue shift and sharpening of the peak corresponding to the plasmon resonance was observed as the distance between particles decreased to a value comparable to, or less than, their diameter.
Abstract: Two-dimensional arrays of 1000 A silver particles were prepared by adsorption from colloidal suspensions onto glass slides derivatized with (3-mercaptopropyl)trimethoxysilane. By variation of the concentration of the colloidal suspensions, slides with different interparticle distances were obtained, and their extinction spectra were measured in water. A blue shift (up to 90 nm) and sharpening of the peak corresponding to the plasmon resonance was observed as the distance between particles decreased to a value comparable to, or less than, their diameter. The angular dependence of the extinction spectra was studied for s- and p-polarized light. The data are interpreted to result from coherent coupling of the plasmon resonances in closely spaced silver particles upon irradiation with light.

Journal ArticleDOI
TL;DR: In this paper, coupled layers of electron and hole liquids in semiconductor heterostructures in zero magnetic field were investigated using the Singwi-Tosi-Land-Sjǫolander self-consistent formalism generalized for layers of unequal density.
Abstract: We have investigated coupled layers of electron and hole liquids in semiconductor heterostructures in zero magnetic field for densities ${\mathit{r}}_{\mathit{s}}$\ensuremath{\lesssim}20 using the Singwi-Tosi-Land-Sj\"olander self-consistent formalism generalized for layers of unequal density. We calculate susceptibilities, local fields, pair correlation functions, and the dispersion of the collective modes for a range of layer spacings. We include cases where the densities in the two layers are not equal. We find generally that static correlations acting between layers do not have a large effect on the correlations within the layers. For coupled electron-hole layers we find that as the spacing between the layers decreases there is a divergence in the static susceptibility of the liquid that signals an instability towards a charge-density-wave ground state. When the layer spacing approaches the effective Bohr radius the electron-hole correlation function starts to diverge at small interparticle separations. This effect is a precursor to the onset of excitonic bound states but this is preempted by the charge-density-wave instability. The acoustic plasmon exhibits a crossover in behavior from a coupled mode to a mode that is confined to a single layer. Correlations sometimes push the acoustic plasmon dispersion curve completely into the single-particle excitation spectrum. For layers with different densities the Landau damping within the single-particle excitation region is sometimes so weak that the acoustic plasmon can exist inside the region as a sharp resonance. We find for the electron-hole case that proximity to the charge-density-wave instability has an unusual effect on the dispersion of the optical plasmon mode. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: In this article, the authors discuss the possible existence of transverse optical plasmons in superlattices consisting of Josephson coupled superconducting layers, as opposed to the usual plasmon which are poles in the density-density channel.
Abstract: We discuss the possible existance of transverse optical plasma modes in superlattices consisting of Josephson coupled superconducting layers. These modes appear as resonances in the current-current correlation function, as opposed to the usual plasmons which are poles in the density-density channel. We consider both bilayer superlattices, and single layer lattices with a spread of interlayer Josephson couplings. We show that our model is in quantitative agreement with the recent experimental observation by a number of groups of a peak at the Josephson plasma frequency in the optical conductivity of La1.85Sr0.15CuO4.

Journal ArticleDOI
TL;DR: A 10(3) signal enhancement of THG that is due to the excitation of a surface plasmon in thin silver films by an attenuated-total-internal-ref lection geometry is reported.
Abstract: Optical third-harmonic generation (THG) is dipole allowed. I report a 10(3) signal enhancement of THG that is due to the excitation of a surface plasmon in thin silver films by an attenuated-total-internal-ref lection geometry. Because the THG signal depends on the cube of the incident intensity and the second-harmonic generation depends on the square of the intensity, the THG overtakes the second-harmonic generation at laser intensities beyond 6 x 10(11) W/cm(2).

Journal ArticleDOI
TL;DR: In this paper, the intrinsic optical bistability of nanometer-size spherical CdS particles coated with silver was investigated and the shell thickness was adjusted to obtain maximum plasmon resonance at the wavelength 514.5 nm, thus enabling measurements with a 2 Wargon ion laser.
Abstract: We report about the observation of intrinsic optical bistability of nanometer‐size spherical CdS particles coated with silver. The particles were chemically prepared as isolated CdS clusters in aqueous suspensions and coated with silver by chemical reduction from added AgNO3. They exhibit intrinsic optical bistability due to high third order susceptibility in the CdS core particle. The effect was enhanced by the silver shell which yields strong enhancement of the local field at the frequencies of the plasmon resonances. The shell thickness was properly adjusted to obtain maximum plasmon resonance at the wavelength 514.5 nm, thus enabling measurements with a 2 W‐argon ion laser. The obtained results show a strong dependence on the shell thickness. The third order susceptibility χ(3) of the CdS particle material was determined to χ(3)=(5.1±2.3)×10−11 (m/V)2 in agreement with theoretical work on the optical bistability of heterogeneous semiconductor systems.

Journal ArticleDOI
TL;DR: It is shown that the regime of SPP scattering and, consequently, near-field optical images, are determined by the topography of a local surface area with the size limited by the SPP propagation length.
Abstract: Localization phenomena in the elastic scattering of surface plasmon polaritons (SPP{close_quote}s), i.e., in the SPP scattering in the surface plane, are related to the appropriate characteristics of SPP and surface roughness. Optical fields of SPP{close_quote}s, which are excited at two different wavelengths (488 and 633 nm) used in turn for each surface region of four different metal (silver and gold) films, are imaged simultaneously with surface topography by use of a photon scanning tunneling microscope with shear force feedback. Single scattering and weak and strong localization of SPP{close_quote}s are observed depending on the sample and the light wavelength. This is a direct demonstration of different regimes of the elastic SPP scattering realized at the same surface region for different light wavelengths. It is shown that the regime of SPP scattering and, consequently, near-field optical images, are determined by the topography of a local surface area with the size limited by the SPP propagation length. {copyright} {ital 1996 The American Physical Society.}

Journal ArticleDOI
TL;DR: In this article, the Raman spectra of GaN films grown by molecular beam epitaxy and hydride vapor phase epitaxy on GaAs and Al2O3 substrates have been studied.
Abstract: Raman spectra of GaN films grown by molecular‐beam epitaxy and hydride vapor‐phase epitaxy on GaAs and Al2O3 substrates have been studied. It was found that longitudinal phonon modes disappear from the spectra of n+ films due to screening by free carriers, but coupled plasmon phonon modes of the higher‐energy branch are not observed because of strong damping of plasmons. Precise values for phonon frequencies and linewidths are presented. No differences in phonon frequencies for the films of different thicknesses grown on different substrates have been found which indicates that the strain due to lattice and thermal‐expansion mismatch is relaxed by the formation of the dislocations very close to the substrate–film interface.



Journal ArticleDOI
TL;DR: It is shown that backscattering enhancement requires the excitation of counterpropagating polaritons, whereas surface waves traveling in one direction produce diffuse scatter without a strong back scattering peak.
Abstract: The effects of plasmon polariton excitation on a metal surface with weak one-dimensional roughness are studied experimentally. It is shown that backscattering enhancement requires the excitation of counterpropagating polaritons, whereas surface waves traveling in one direction produce diffuse scatter without a strong backscattering peak.

Journal ArticleDOI
Xudong Jiang1
TL;DR: In this article, the collective electronic excitations on graphene tubules are discussed using an empirical infinitely thin cylindrical shell model within the framework of a two-fluid hydrodynamic description.
Abstract: Due to the inherent simplicity of the graphene tubule systems, it is expected that these systems will become model systems for the calculation of the mechanical and electronic properties of idealized carbon fibers. In this paper the collective electronic excitations on graphene tubules are discussed. The frequencies of the plasmons on graphene tubules are calculated using an empirical infinitely thin cylindrical-shell model within the framework of a two-fluid hydrodynamic description. There are two parameters involved in our calculation which are calibrated on graphite. The variations of plasmon frequencies and oscillator strength with the size of tube and longitudinal plasmon wavelength are discussed. \textcopyright{} 1996 The American Physical Society.

Patent
28 Oct 1996
TL;DR: A tapered probe tip for use in near-field scanning optical microscopy is coated with a sheath of metal material having a plasma frequency comparable to optical frequencies as discussed by the authors, and the preferred sheath material is silver.
Abstract: A tapered probe tip for use in near-field scanning optical microscopy is coated with a sheath of metal material having a plasma frequency comparable to optical frequencies. Alternatively, the sheath material has lower energy plasmons. The preferred sheath material is silver. Other preferred sheath materials are potassium, Rb, cesium, tungsten oxide, sodium tungsten oxide and Re oxide.

Journal ArticleDOI
TL;DR: In this article, the dispersion properties of plasmon surface polaritons (PSP) were used as a contrast giving mechanism for ultrathin-film characterization using white light instead of a laser for resonant PSP excitation.
Abstract: We report on experiments, applying a novel microscopy method for ultrathin‐film characterization which uses the dispersion properties of plasmon surface polaritons (PSP) as a contrast giving mechanism. In contrast to prior methods, we apply white light instead of a laser for resonant PSP excitation. For a given incident angle and an area of given thickness, a narrow spectral band of the incident light is at resonance for PSP excitation. Therefore, we obtain images with areas of different thickness appearing in different color. As an example, we present microscopic images taken from a thin Cu–phthalocyanine film, evaporated onto solid support through a mask. In addition, we compare the obtained images to theoretical considerations on the contrast mechanism.

Journal ArticleDOI
TL;DR: In this paper, the authors examined the possibility of strongly non-monotonic behavior arising from a resonance process between plasmons and two-pair excitations, and evaluated with the help of sum rules and selfconsistency requirements within a single-pole approximation for the dielectric function.
Abstract: Electron energy-loss experiments have shown a rapid softening of the bulk plasmon dispersion across the series of the alkali metals. Motivated by these observations, we reconsider the evaluation of the dynamic, long-wavelength exchange - correlation potential in the electron fluid, which is of interest for applications in time-dependent density functional theory. The value of at the plasma frequency determines the exchange - correlation contribution to the leading plasmon dispersion coefficient in the homogeneous electron fluid. Whereas an interpolation scheme originally proposed by Gross and Kohn assumes a monotonic increase of across the plasma frequency, we examine the possibility of strongly non-monotonic behaviour arising from a resonance process between plasmons and two-pair excitations. This process is evaluated with the help of sum rules and selfconsistency requirements within a single-pole approximation for the dielectric function. The cases of a fermion plasma and of a boson plasma are treated in parallel and the reliability of the results for the fermion plasma at low coupling is tested by calculations within a random-phase approximation for the dielectric function. In all cases it is found that the resonance process accumulates oscillator strength in the neighbourhood of , thus decreasing the value of below the static value fixed by the compressibility sum rule. Although this lowering does not suffice to account by itself for the measured plasmon dispersion coefficient in the low-density alkali metals, our results provide useful input for combined band-structure and exchange - correlation calculations.

Journal ArticleDOI
TL;DR: The coupling of the coherent, longitudinal-optic~LO! phonons to collective carrier excitations oscillating parallel to the growth direction of GaAs/Al is illustrated.
Abstract: Coherent longitudinal-optical phonons are generated in semiconductor heterostructures. The coupling of the coherent, longitudinal-optic (LO) phonons to collective carrier excitations oscillating parallel to the growth direction of GaAs/${\mathrm{Al}}_{0.36}$${\mathrm{Ga}}_{0.64}$As quantum wells is investigated with femtosecond time-resolution. This coupling is found to be weak for small well widths and evolves towards the bulk plasmon phonon coupling at increased well widths. We present a theory for the dielectric function in the growth direction of the heterostructure and calculate the frequency response of the system on the pulsed optical excitation. It is shown that the observations are based on the coupling of coherent phonons to intersubband plasmons. \textcopyright{} 1996 The American Physical Society.

Journal ArticleDOI
TL;DR: The 2-loop resummed propagator in hot $g~2\phi~4$ theory has a cut along the whole real axis in the complex energy plane, but for small $g$ the spectral density is sharply peaked around the plasmon, and the spectral width vanishes at large momenta.
Abstract: We study the two-loop resummed propagator in hot {ital g}{sup 2}{phi}{sup 4} theory. The propagator has a cut aong the whole real axis in the complex energy plane, but for small {ital g} the spectral density is sharply peaked around the plasmon. The dispersion relation and the width of the plasmon are calculated at zero {ital and} finite momentum. At large momenta the spectral width vanishes, and the plasmon loses its collectivity and behaves like a noninteracting free particle. {copyright} {ital 1996 The American Physical Society.}

Journal ArticleDOI
TL;DR: In this paper, the effect of the dielectric permittivity on the number of hot excitations produced by a fast particle was investigated using the polarization approximation, which allows the peculiarities of the permittivities to be accounted for.
Abstract: The electron cascade after the absorption of a high-energy photon or collision of a high-energy particle is studied using the polarization approximation, which allows the peculiarities of the dielectric permittivity to be accounted for. The main effect of the frequency dependence of the dielectric function can be observed for secondary electrons with energies between the threshold of the inelastic scattering and a few plasmon energies. The expression for the threshold energy for Wannier-Mott exciton production is obtained in the parabolic band approximation. The competition of strongly inelastic scattering and phonon-assisted relaxation influences the total number of hot excitations produced by a fast particle. The role of dielectric properties is important for solids with a complicated electron energy structure, such as systems with d and f bands (e.g., rare earth compounds) and with high-lying outermost core bands (crystals with so-called crossluminescence, e.g. BaF2).

Journal ArticleDOI
TL;DR: In this article, the surface plasmon excitations on n-type InAs(001) surfaces prepared either by decapping a protective As layer or by argon ion bombardment and annealing procedures were studied.