Showing papers on "Plasmon published in 1991"
TL;DR: Light emission characteristics from the tunnel gap of a scanning tunneling microscope are used to elucidate the interaction of tunneling electrons with tip-induced plasmon modes on Ag, Au, and Cu surfaces.
Abstract: Light emission characteristics from the tunnel gap of a scanning tunneling microscope are used to elucidate the interaction of tunneling electrons with tip-induced plasmon modes on Ag, Au, and Cu surfaces. Enhanced redshifted spectra are observed in the tunneling regime. Model calculations of optical spectra in this range agree well with the experimental data. Isochromat spectra are used to demonstrate that the principal excitation process occurs via inelastic tunneling.
396 citations
262 citations
TL;DR: In the 1D quantum limit the intrasubband plasmon displays the linear dispersion characteristic of 1D free-electron behavior and collective 1D intersubband excitations appear as dispersion-less and have a negligible shift from the single-particle energy.
Abstract: The energy and the wave-vector dispersion of single-particle and collective excitations of the one-dimensional (1D) electron gas in GaAs quantum wires have been determined by resonant inelastic light scattering. In the 1D quantum limit the intrasubband plasmon displays the linear dispersion characteristic of 1D free-electron behavior. Quantitative agreement is found with calculations based on the random-phase approximation. In contrast, collective 1D intersubband excitations appear as dispersion-less and have a negligible shift from the single-particle energy
234 citations
TL;DR: In this article, the authors discussed the determination of the thickness and dielectric constant of thin layers by means of surface plasmon resonance and showed that it appears to be impossible to determine these parameters from one single surface-plasmon response experiment.
155 citations
TL;DR: In this article, the exact solutions of Laplace's equations for the tip/sample geometry were presented, and it was shown that the field enhancement associated with such tip plasmons is instrumental for inelastic tunneling and light emission during scanning tunneling microscopy.
Abstract: The electromagnetic fields that can build up around metallic or dielectric pointed tips are of increasing interest in context with the new scanning probe microscopies (tunneling, near‐field optics, Coulomb and van der Waals forces etc.). The paper presents exact solutions of Laplace’s equations for the tip/sample geometry. For suitable media, plasmons are found whose electric fields are highly localized in the gap region. We believe that the field enhancement associated with such tip plasmons is instrumental for inelastic tunneling and light emission during scanning tunneling microscopy.
154 citations
TL;DR: The most prominent feature of the one-dimensional plasmon is a wire-width-dependent negative dispersion in a magnetic field, which is a unique property of edge-plasmon-type oscillations.
Abstract: Quasi-one-dimensional electronic systems have been realized in deep-mesa-etched AlGaAs/GaAs quantum wires. By means of a metallic grating coupler oriented perpendicularly to the wires, we could couple far-infrared radiation to one-dimensional plasmons propagating along the wires. The most prominent feature of the one-dimensional plasmon is a wire-width-dependent negative dispersion in a magnetic field, which is a unique property of edge-plasmon-type oscillations. In addition, we observe a rich spectrum of further modes which arise from the mixing between the one-dimensional plasmon and a charge oscillation perpendicular to the wires.
101 citations
TL;DR: The width of the electron temporal profile, measured utilizing this nonlinear photoelectric effect, however, fails to show the narrowing commensurate with the higher-order nonlinearity.
Abstract: We report a study of surface-plasmon-mediated multiphoton photoelectric emission from thin films of Ag, Au, Cu, and Al. The experiments were performed in the Kretchmann attenuated-total-internal reflection geometry while the excitation source was an unamplified femtosecond colliding-pulse mode-locked ring laser. Contrast to the electron emission obtained by irradiating the laser on a metal surface, electron yield increases by several orders of magnitude with fairly high quantum efficiency, is observed when photons are coupled to the surface-plasmon modes of these films. Although the photon absorption reaches its maximum when the reflectivity exhibits a deep minimum at the surface-plasmon resonance angle, it is found that the maximum electron yield occurs at a slightly different angle than the reflectivity dip. The results of these measurements favor the field-density calculations using the Fresnel equations. The width of the electron temporal profile, measured utilizing this nonlinear photoelectric effect, however, fails to show the narrowing commensurate with the higher-order nonlinearity.
96 citations
IBM1
TL;DR: In this article, the dependence of electron mobility in n-type and p-type Si on the impurity concentration is studied using a simplified picture that, hopefully, retains the essential physics.
Abstract: The dependence of the electron mobility in n-type and p-type Si on the impurity concentration is studied using a simplified picture that, hopefully, retains the essential physics. The momentum relaxation time is calculated including interactions between electrons and phonons, electrons, and ionized impurities using a phase-shift analysis, short-range intercarrier interactions, and, most importantly, the scattering of electrons by plasmons. It is found that this process has a very strong effect at large impurity concentrations, particularly in p-type Si. Recent experimental results for the minority-electron mobility in the base of p-n-p bipolar transistors can be explained in terms of the proposed model, although only qualitative aspects can be considered, since the scatter of the experimental data is often larger than the differences caused by the various approximations employed.
95 citations
TL;DR: In this article, a hydrodynamic model was used to estimate the frequencies of plasmons in the range between 6 and 8 eV and near and above 25 eV for fullerenes C60 and C70.
Abstract: The fullerenes C60 (quasispherical though actually icosahedral) and C70 (quasispheroidal) are very like hollow shells (graphiteroles) made from a single hexagonal layer from a graphite crystal. They should support multipolar (l≥1) plasma oscillations, closely related to the plasmons seen in graphite. We estimate their frequencies using the so‐called hydrodynamic model, with (provisionally) just one parameter calibrated on graphite. We predict π plasmons in the range between 6 and 8 eV, and σ plasmons near and above 25 eV. The best, if not the only way to observe them is by electron energy‐loss spectroscopy. Only the dipole (l=1) excitation is allowed optically; in the solid, its frequency should be shifted according to the Lorentz–Lorenz formula. If, improbably, the l=1 π plasmon is observable in solution, its frequency should be unprecedentedly sensitive to the refractive index of the solvent. On C70, the multipoles are split and shifted relative to C60, but only by surprisingly little.
81 citations
TL;DR: In this paper, the authors calculated the rate of light emission from a scanning tunneling microscope with an Ir tip probing a silver film and found that one out of 104 tunneling electrons will emit a photon in the visible range.
Abstract: We have calculated the rate of light emission from a scanning tunneling microscope with an Ir tip probing a silver film. In the calculation we model the tip by a sphere. We find a considerable enhancement of the light emission compared with for example inverse photoemission experiments. This enhancement is explained as the result of an amplification of the electromagnetic field in the area below the microscope tip due to a localised interface plasmon. We estimate that one out of 104 tunneling electrons will emit a photon in the visible range. Due to an electromagnetic decoupling of the sphere from the sample the enhanced emission is lost for photon energies above a certain value. We also find that the experimentally observed maximum in the light emission as a function of bias voltage is related to the behavior of tip-sample separation versus bias voltage.
74 citations
TL;DR: The theoretical results allow us to explain the existence of the experimentally observed modes, as well as the dependence of the loss function on the electron trajectory, and the loss probability for fast electrons scattered inelastically by spheres of equal or different radii is obtained.
Abstract: We have determined the surface-plasmon modes of interacting spherical particles as a function of the particle radii, the separation R, and the dielectric constant of the surrounding medium. The coupling between the two particles produces a shift of all surface-plasmon eigenfrequencies leading, in the case of Al particles embedded in Al oxide, to a bispherical plasmon mode in the 3--4-eV range. Using a second-quantization description of the surface plasmons, the loss probability for fast electrons scattered inelastically by spheres of equal or different radii is obtained. Application to Al particles surrounded by Al oxide yields results that are compared with the experimental data obtained by Batson using scanning transmission electron microscopy. The theoretical results allow us to explain the existence of the experimentally observed modes, as well as the dependence of the loss function on the electron trajectory.
TL;DR: In this article, the use of evanescent light for the optical characterization of polymer thin films and interfaces is described. But it is not shown that the excitation of these waves allows for a sensitive determination of the optical architecture of the interface(s) involved.
Abstract: This paper describes the use of evanescent light for the optical characterization of polymer thin films and interfaces. Firstly, a few basic concepts of evanescent wave phenomena, including total internal reflection, plasmon surface polaritons and guided optical modes, are reviewed. It is shown that the excitation of these waves allows for a sensitive determination of the optical architecture of the interface(s) involved. This “surface light” can then be used for the same broad range of optical techniques as it is known from experimental set-ups designed for the investigation of various optical properties of polymer samples using plane electromagnetic waves, i.e. “normal” photons. This is demonstrated for diffraction experiments, microscopic investigations, inelastic scattering, e.g. Brillouin- or Raman-spectroscopies, etc. The examples given include thin polymer films prepared by spin-coating or by the Langmuir-Blodgett-Kuhn technique. It is shown that properties and processes at solid-solution interfaces can be investigated equally well, and even surfaces of bulk samples can be characterized.
TL;DR: High-resolution electron-energy-loss spectroscopy of the surface of graphite reveals a discrete loss feature attributed to the excitation of a π-band plasmon polarized with E∥c, found to be strongly temperature dependent.
Abstract: High-resolution electron-energy-loss spectroscopy of the surface of graphite reveals a discrete loss feature attributed to the excitation of a π-band plasmon polarized with E∥c. The frequency of the plasmon is found to be strongly temperature dependent. This arises from the contribution of thermally generated carriers to the plasma frequency, as confirmed by explicit calculations using the graphite band structure
TL;DR: In this paper, a tunnelling microscope is used to detect surface plasmons (SPs) on a silver-vacuum interface excited by a He-Ne laser.
Abstract: A tunnelling microscope is used to detect surface plasmons (SP) on a silver-vacuum interface excited by a He-Ne laser The decay length of the SP is determined experimentally, and the detection mechanism of the SP in the tunnelling microscope is discussed
TL;DR: In this paper, the influence of surface plasmons excited in polycrystalline silver film on the tunneling current of a scanning tunneling microscope (STM) has been analyzed.
Abstract: The influence of surface plasmons excited in a polycrystalline silver film on the tunneling current of a scanning tunneling microscope (STM) has been analyzed. The plasmons cause an additional flow of electrons from the tungsten tip to the silver surface on the order of up to 50 pA. This process is independent of the polarity of the applied bias voltage, thereby excluding effects of thermal expansion. The different nature of the ordinary tunneling current and the surface plasmon induced current is clearly revealed by their different dependence on the gap distance. The local distribution of the intensity of the surface plasmon induced signal reveals structures on a nanometer scale. Some of them are correlated to the surface topography.
TL;DR: In this article, a theoretical expression for the Raman scattering rate by a coupled phonon-damped plasmon mode has been derived from a dielectric model and compared to the experimental data.
Abstract: Raman spectroscopy measurements have been performed on GaAs:Be samples with high crystalline quality and exceptional heavy doping level ranging from 1019 to 1.4×1021 cm−3. The recorded spectra show a structure we assigned to a coupled LO phonon‐damped plasmon mode. A theoretical expression for the Raman scattering rate by this mode has been derived from a dielectric model and compared to the experimental data. Using a fitting procedure the doping level of the samples has been estimated in agreement with Hall measurements. Moreover, the study of the Raman intensity evolution of both unscreened‐LO and coupled phonon‐plasmon structures, provided a convenient and rapid method to determine the activated carrier density in p‐doped polar semiconductors. Disorder effects due to the dopant impurities have been also observed and analyzed using a spatial correlation model description.
TL;DR: Long-range surface plasmon-polaritons are shown to be supported even by highly asymmetric configurations, even when the metal film thickness and the superstrate refractive index are varied.
Abstract: Surface plasmon–polariton modes supported by thin metal films surrounded by dissimilar semi-infinite dielectrics are studied. The dispersion of the modes is evaluated, and their characteristics are investigated when the metal film thickness and the superstrate refractive index are varied. Long-range surface plasmon–polaritons are shown to be supported even by highly asymmetric configurations.
TL;DR: In this article, electron diffraction patterns recorded along several zone axes indicated that C60 has a face centered cubic unit cell with Fm3m space group symmetry and lattice parameter of 1.42 nm within 5% experimental error.
TL;DR: Aldred et al. as mentioned in this paper obtained energy-filtered convergent-beam electron diffraction (CBED) patterns from a 10A˚region of the specimen in a scanning transmission electron microscope (STEM) equipped with a digital image-acquisition system.
TL;DR: In this article, a 200 keV transmission electron microscope equipped with an electron energy analyzer was used to obtain electron energy loss spectra in a low loss region from solid C60.
Abstract: Electron energy-loss spectra in a low loss region have been obtained from solid C60 by a 200 keV transmission electron microscope equipped with an electron energy analyzer. Bulk plasmons are observed at two characteristic energies, 6.5 and 26 eV, being attributed to collective oscillation of π-electrons, and to that of all the valence electrons (both the π- and σ-electrons), respectively.
TL;DR: In this paper, a two-dimensionalally modulated electron gas as well as arrays of quantum dots and anti-dots were prepared on GaAs and AlGaAs heterostructures.
TL;DR: In the high-temperature limit, the use of the current ultrarelativistic dispersion relations increases the emissivity by a factor of 3.185, which may have a significant effect on the initial cooling rate for the core of a neutron star.
Abstract: Previous calculations of the emissivity of a plasma due to the decay of transverse photons and plasmons into neutrino pairs have used dispersion relations that are inaccurate at relativistic temperatures or densities. In the high-temperature limit, the use of the current ultrarelativistic dispersion relations increases the emissivity by a factor of 3.185. This may have a significant effect on the initial cooling rate for the core of a neutron star.
TL;DR: It is shown that the plasmon-phonon coupling can appreciably shift the dispersion curves, and additional plAsmonlike intersubband modes that exist in regions observable in far-infrared optical spectroscopy are found.
Abstract: The spectrum of the coupled plasmon-phonon collective excitations of a quasi-one-dimensional quantum-well wire is analyzed. Using a three-subband model the electronic polarization function is treated in detail within the random-phase approximation. It is found that, in comparison with the quasi-two-dimensional electron gas, the excitation spectrum of the quasi-one-dimensional electron gas contains additional regions free of Landau damping. The dispersion curves of the collective excitations are calculated and presented in graphical form for three different cases of subband population. It is shown that the plasmon-phonon coupling can appreciably shift the dispersion curves. In the case that more than one subband is populated, we have found additional plasmonlike intersubband modes that exist in regions observable in far-infrared optical spectroscopy.
TL;DR: In this article, the effects of structural damage, induced by low energy ion bombardment, on the conduction band plasmon energy has been monitored as a function of post-bombardment annealing temperature.
TL;DR: Edge magnetoplasma excitations in a two-dimensional electron system have been studied in radio-frequency experiments which exhibit a strong nonlocal behavior of the plasmon dispersion.
Abstract: Edge magnetoplasma excitations in a two-dimensional electron system have been studied in radio-frequency experiments which exhibit a strong nonlocal behavior of the plasmon dispersion. The nonlocality is shown to be caused by the diagonal conductivity σ xx , which, via a length l ∞ σ xx , governs the spatial distribution of the plasma charge oscillations in the direction perpendicular to the plasmon wave vector, i.e., to the edge of the two-dimensional layer
TL;DR: In this article, high-resolution electron energy-loss spectra were obtained from solid C60 and two bulk plasmon peaks were observed at 6.4 eV and 25.5 eV.
Abstract: High-resolution electron energy-loss spectra were obtained from solid C60. Two bulk plasmon peaks were observed at 6.4 eV and 25.5 eV. Eleven fine features due to single electron excitations were observed as shoulders of the two plasmon peaks at 2.1, 2.8, 3.7, 5.1, 6.1, 7.5, 9.5, 10.7, 15, 18 and 20 eV. The `Einsatz' point at 1.4 eV in the imaginary part e2 of the dielectric function, which was obtained by Kramers-Kronig analysis of the spectra, may be due to the interband transition (band gap) between the highest occupied electronic state and the lowest unoccupied state.
TL;DR: In this paper, the collective-mode spectrum for layered superconductor structures was investigated and it was shown that the plasmon modes remain below the superconducting gap edge.
Abstract: We investigate the collective-mode spectrum for a layered superconductor structure. For wave vectors directed close to the superlattice axis, we find that the plasmon modes remain {ital below} the superconducting gap edge. This is in sharp contrast with the situation for isotropic superconductors in three dimensions, for which the Anderson-Higgs mechanism lifts all such modes out of the gap. We also find that, as a mode crosses the gap edge, either by increasing the wave vector or tilting its direction with respect to the superlattice axis, there is a unique mode-coupling effect between pair-breaking excitations and the collective mode. This manifests itself as a line splitting in the dielectric response, which may in principle be used to determine the gap of such a system. We also calculate the effect of interplane tunneling on the collective-mode spectrum. We find that, if the tunneling rate is large enough, the plasmon modes may all be lifted out of the gap. We show that estimates for the plasmon energy based on the effective-mass approximation can grossly {ital overestimate} its minimum value.
TL;DR: In this paper, pyridine and a number of related molecules were used to lower the work function of thin Ag films so as to compare the effects of various molecular properties on the photoemission process and on surface electronic modes.
Abstract: We have used pyridine and a number of related molecules to lower the workfunction of thin Ag films so as to compare the effects of various molecular properties on the photoemission process and on surface electronic modes We find that a nitrogen lone pair electronic orbital is essential for a large threshold shift Other molecular properties, such as dipole moment and polarizability have a very small effect The films are rough, therefore we see strong photoyields at the energy of the surface plasma mode, 36 eV There is also a peak in the photoyield at 385 eV, the energy of the bulk plasmon