Showing papers on "Plasmon published in 1979"

Vector Scattering Theory

Abstract: Vector theories dealing with the interaction of light with surface roughness are reviewed. Light scattering from microirregularities whose heights are much smaller and much larger than the wavelength of the incident light are discussed. The theories apply to metal-coated surfaces and, in addition, surfaces covered with multilayer dielectric stacks. Surface plasmon effects, which are also discussed, include the decrease in the specular reflectance caused by conversion of photon energy into surface plasmons (i.e., additional absorption due to surface plasmons), as well as the radiative decay of surface plasmons into photons (i.e., surface plasmon "scattering"). There is a brief discussion of how to use experimental surface height data in the theoretical formulae. Finally, published experimental data on scattering and surface plasmon effects are compared to theoretical predictions.

Exciton–surface plasmon interactions

Abstract: A thin film possessing excitonic states within the range of energies of a plasmon surface polariton of a metallic substrate can strongly influence this surface electromagnetic wave either by a resonance interaction or a quenching interaction. We have analyzed this coupling and present our results showing the effects of an anisotropic orientation in the molecular film compared to an isotropic orientation and the effects of damping of the molecular electronic transition in the film. In a typical attenuated total reflection (ATR) experiment either an angular scan or a wavelength scan is usually used. A comparison of these two situations is given and sample calculations are displayed with perspective figures of reflectivity versus both angle and wavelength. The results show that a combination of both types of scans, i.e., angular scans at a series of wavelengths or wavelength scans at a series of angles or some combination to follow along the dispersion curve, are necessary to map the dispersion. Further isot...

Stimulated raman scattering by an intense relativistic electron beam subjected to a rippled electric field

Abstract: Generation of submillimeter radiation by stimulated Raman scattering in an intense relativistic electron beam subjected to a spatially periodic transverse electric field is examined. The requisite electric field modulation can be obtained by rippling the wall of the conducting drift tube. When the electron beam is subjected to a periodic longitudinal electric field, short‐wavelength plasmons, rather than photons, are generated. The growth rate and other parameters related to this instability are discussed.

Plasmon Spectra of Ferric-Chloride-Intercalated Graphite

Abstract: High-resolution electron energy-loss spectra show unexpected features of electronic excitations in stage-1 Fe${\mathrm{Cl}}_{3}$-intercalated graphite. A sharp 1-eV plasmon surprisingly exhibits positive quadratic dispersion and damping characteristic of a free three-dimensional electron gas. However, the dispersion coefficient is very large and the intensity falls unusually sharply with increasing momentum, indicating the likelihood of strong band-structure effects. An intense 5.9-eV energy loss is identified with a shifted $\ensuremath{\pi}$ plasmon in graphite consistent with only weakly perturbed carbon $\ensuremath{\pi}$ bands.

Possible Observation of Local Plasmon Modes Excited by Electrons Tunneling through Junctions

Abstract: The light emitted by small-particle tunnel junctions is partially polarized. The excess light polarized perpendicular to the junctions is possibly due to the radiative decay of localized surface plasmons that are excited by tunneling electrons. Both the angular distribution and the intensity versus photon energy of this light are in agreement with recent theoretical calculations based on the excitation and radiative decay of surface plasmons in a small metal particle located above a metal film.

Self-image excitation mechanism for fast ions scattered by metal surfaces at grazing incidence

Abstract: Energy-loss spectra and electronic-transition probabilities of atomic and molecular ions scattered by surface plasmons are evaluated for experiments in which fast ions are specularly reflected from a metal surface at grazing incidence. The coupling between plasmons and the ion monopole charge governs the scattered-ion loss spectrum. For ion velocities not small compared to plasmon phase velocities and for small grazing angles, large numbers of surface plasmons may be excited, resulting in large average energy losses and broad loss spectra, as observed experimentally. Further, the interaction between the ion multipole moments with the surface plasmons induces transitions between ground and excited states of the ions. For molecular ions this may result in their dissociation when the state produced is unstable. The final electronic states populated by the plasmon scattering mechanism are shown to exhibit a high degree of orientation, as required by the observation of elliptically polarized fluorescence emitted by the scattered beam. As applications, we calculate explicitly the dissociative scattering of H/sup +//sub 2/ and the production of coherently oriented 2P states in He/sup +/ and compare with available experimental results.

Calculations of the electron-energy-loss probability in thin uniaxial crystals at oblique incidence

Abstract: The complete differential electron-energy-loss probability is calculated for scattering of a fast electron by a thin uniaxial crystal foil at oblique incidence. Retardation effects are considered in the present calculation. In the long-wavelength limit the local dielectric tensor lim/sub q/..-->..o epsilon-arrow-right (q,..omega..) is expected to give a good description of the response of the electron gas in solids to the fields of the incident electron. Using this dielectric approach, the scattering cross section of both volume and surface excitations are obtained. Plasmon anisotropy and the excitation of both extraordinary and ordinary Cerenkov radiation are discussed. The dispersion relations for both extraordinary and ordinary surface waves are also obtained and studied in detail. As an example, we have calculated the scattering probability distribution function for a 500-A-thick graphite foil under normal incidence of 75-keV electrons.

Dynamic screening of core hole. I. Semiclassical model

Abstract: Creation of a deep hole and a fast electron in a metal by an X-ray photon produces a dynamic relaxation of the surrounding electrons of the Fermi sea which is treated here in a semiclassical way. The authors emphasise the contribution of the plasmons which should be predominant far from threshold. They construct an energy-dependent effective potential acting on the photoelectron. They show the existence of a characteristic time t0 (a fraction of the plasmon period) necessary for the creation of plasmons: at a given distance r from the hole, the potential seen by the photoelectron of velocity nu is a statically screened potential when r/ nu >t0; when r/ nu

Plasmon behavior at the charge-density-wave onset in 2 H -Ta Se 2

Abstract: We have studied experimentally and theoretically the thermoreflectance of $2H$-Ta${\mathrm{Se}}_{2}$ in the neighborhood of the plasmon resonance near 1 eV, as a function of temperature. An extensive red shift and change of width of the plasmon (a narrowing at first, then a broadening) occur as one heats up through the 90-120-K range where charge-density waves (CDW) disappear. From a close inspection of the dielectric response as a function of frequency and temperature we find that optical transitions disappear in the 0.2-0.8-eV region in correspondence with the weakening of CDW upon heating, while new intrabrand (0.2 eV) and interband (g1 eV) transitions replace them. This transfer of oscillator strength, entirely expected on the basis of a model CDW band structure, accounts qualitatively for both shift and narrowing (broadening) of the plasmon. A theory of the plasmon shift caused by the new CDW periodicity is developed, and applied to the present case, by means of a model umklapp response. The results show that the shift is chiefly due to the presence of the new CDW transitions in the 3 \ifmmode\times\else\texttimes\fi{} 3 band structure. The temperature-induced change of optical response at the CDW onset is also found to be smooth and broad with temperature, unlike that of other properties, like specific heat, which exhibit a clear critical behavior. This indicates a "slow" change in the energy-band structure, for $T\ensuremath{\sim}120$ K, probably mostly a change of electron lifetime, whose rate of increase seems maximum around 110 K.

Plasmon Mechanism for the Energy Loss, Dissociation, and Orientation of Fast Ions Excited by Surface-Grazing Collisions

Abstract: An interaction mechanism is proposed for the inelastic, grazing-incidence scattering of fast ions by metal surfaces which involves coupling of the ion multipoles with surface plasmons. The monopole-plasmon coupling governs the energy-loss spectrum, whereas the higher-multipole interactions raise the ion into electronic excited states. The proposed mechanism is very efficient in dissociating unstable excited molecular ions and in producing atomic excited states with a high degree of orientation.

Investigation of metallic surface layers on metals by surface plasmon ATR spectroscopy

Abstract: 2014 The optical properties of very thin Ag layers on Al surfaces were investigated in the vicinity of the Ag effective plasma frequency, by attenuated total reflection with surface plasma wave excitation. The complex dielectric constant of the adsorbed layers is found to be similar to that of bulk Ag provided non-local effects (longitudinal plasma waves) are taken into account. LE JOURNAL DE PHYSIQUE LETTRES TOME 40, 15 JUILLET 1979, F Classification Physics Abstracts 78.65 73.60D 71.45G

Comment on the plasmon model for image-potential-induced surface states

Abstract: Calculations of the binding energy of bound positron states in metal surfaces, with explicit inclusion of plasmon dispersion and single-particle effects, are presented. The binding energy is greatly reduced with respect to the undispersed case.

Elemental Analysis Using Inner-Shell Excitations: A Microanalytical Technique for Materials Characterization

Abstract: Experiments based on transmission electron microscopy play an extremely important role in materials characterization and diagnostics. The high resolution which can be achieved by modern commercial instruments is being used routinely to derive structural and crystallographic information from both the image and diffraction pattern. In materials diagnostics, these two capabilities are enhanced greatly by the ability to obtain direct elemental information at a comparable spatial resolution (i.e. ≲ 10 nm) and thereby place this elemental information in the context of the microstructure and micro-crystallography of the specimen. This combination of techniques, in part, has been the goal of analytical electron microscopy. The principle of microarea analyses is to probe a small volume of a specimen and to detect the many signals which are generated as a result of the interaction between the incident-electron beam and this volume. The desired elemental information is carried either: i) in the secondary emission of X-rays or Auger electrons which occur during the decay of the primary excitation process; or ii) in the transmitted-electron energy-loss spectrum which reflects the primary excitations (i.e. plasmons, valence-shell electrons and inner-shell electrons). Since the preliminary work of WITTRY, FERRIER and COSSLETT (1969) was reported, there has been considerable interest in the use of inner-shell excitations for direct elemental analysis and it is this aspect of electron energy-loss spectroscopy that will be detailed here. Those interested in the analysis techniques and materials applications of plasmon excitations should see a recent review by WILLIAMS and EDINGTON (1976).

Surface Exciton Polaritons

Abstract: Surface polaritons are elementary excitations which are propagating along the boundary between a crystal and an outside dielectric medium. The energy range of surface polaritons lies in the gap between the corresponding transverse and longitudinal bulk excitation energies. When this bulk excitation is a plasmon or a phonon or an exciton, the associated surface mode is called a surface plasmon or a surface phonon or a surface exciton polariton.

Plasmon loss and plasmon gain in Mg-Cd alloys

Abstract: The energy and intensity of the plasmon loss lines accompanying X-ray photoemission and Auger emission lines in the spectra of Mg, Mg88Cd12, Mg75Cd25, Mg50Cd50, Mg25Cd75, Cd and Mg97Ag3 have been measured. The probability of plasmon excitation is found to decrease rapidly with increasing Cd or Ag concentration. The energy and intensity of a weak satellite line on the high kinetic energy side of the MgKL2.3L2.3(1D) line has been measured for five of the alloys and these results confirm that the satellite is due to plasmon gain.

Plasmon dispersion in two-metal systems

Abstract: The hydrodynamic model incorporating spatial dispersion is used to investigate the nonretarded plasmon dispersion for a bimetallic interface and for two arbitrary metal half-spaces separated by a vacuum. For the bimetallic interface, the full curve for the well known interface plasmon, starting at omega 2=1/2( omega p12+ omega p22), is given. It is shown that a similar plasmon mode exists when the metals are cleaved and separated, but which corresponds to a different form of density fluctuation and has a dependence on the separation distance. In addition, a new 'image' plasmon omega im is predicted. This arises from the image of the denser metal 2 ( omega p2> omega p1) forming as a result of the density response of the bulk electrons in metal 1, and is independent of the parameters of the less dense metal. The generalisations of the well known symmetric ( omega +) and antisymmetric ( omega -) surface plasmons, seen for two identical metals, are also derived. The generalised upper branch omega + only appears if omega p1> omega p2/ square root 2 and forms the continuation of omega im below the bulk continuum region of the less dense metal.

High-frequency conductivity of a two-dimensional, two-component electron gas

Abstract: A first-principles calculation of the high-frequency conductivity for a two-dimensional, two-component electron gas is presented. Both frequency and temperature dependence are considered. The influence of electron-electron collisions on the two-dimensional plasmon is discussed in relation to possible experiments in MOS structures.

Stimulated plasmon emission in semiconductors

Abstract: This paper reinvestigates the possibility of coherent plasma-wave oscillations in direct-gap semiconductors when the plasma frequency is near the band gap. A theory of plasma instability is developed, based on the collective-coordinate method. Threshold, the nonlinear region above threshold, and the electric field are investigated from the perspective of the collective-coordinate method, and the results are applied to specific narrow-gap semiconductors. When the plasma-wave emission is coherent, the cross section for light-plasmon scattering can be enhanced many orders of magnitude. Experiments are proposed.