Showing papers on "Plasmon published in 1976"

Introduction to solid state physics

Abstract: Mathematical Introduction Acoustic Phonons Plasmons, Optical Phonons, and Polarization Waves Magnons Fermion Fields and the Hartree-Fock Approximation Many-body Techniques and the Electron Gas Polarons and the Electron-phonon Interaction Superconductivity Bloch Functions - General Properties Brillouin Zones and Crystal Symmetry Dynamics of Electrons in a Magnetic Field: de Haas-van Alphen Effect and Cyclotron Resonance Magnetoresistance Calculation of Energy Bands and Fermi Surfaces Semiconductor Crystals I: Energy Bands, Cyclotron Resonance, and Impurity States Semiconductor Crystals II: Optical Absorption and Excitons Electrodynamics of Metals Acoustic Attenuation in Metals Theory of Alloys Correlation Functions and Neutron Diffraction by Crystals Recoilless Emission Green's Functions - Application to Solid State Physics Appendix: Perturbation Theory and the Electron Gas Index.

A Monte Carlo approach to the direct simulation of electron penetration in solids

Abstract: A new Monte Carlo approach to the direct simulation of scattering process of a penetrating electron in matter has been attempted. The theoretical stopping powers for elementary excitation processes (conduction-electron, plasmon and L-shell electron excitations) were used instead of Bethe's stopping power equation to describe the energy loss process in the electron penetration. The result obtained for aluminium describes the energy as well as the angular distribution of the transmitted electrons satisfactorily. This approach has also been applied to copper as a preliminary example. The theory describes qualitatively the energy and angular distributions of the transmitted electrons fairly well, but there is some discrepancy between theory and experiment in the energy distribution.

Electron energy loss studies in solids; The transition metal dichalcogenides

Abstract: The theory of characteristic electron energy losses is discussed in terms of the electronic band structure of a solid. The relationship between the observed plasmon energies, the average interband energy gap and the background dielectric constant of the solid is developed. The transmission energy loss spectra of a number of the layer-type transition metal dichalcogenides, MX2, where M=Zr, Hf, Nb, Ta, Mo and W and X=S and Se, have been measured in the range of 0–50 eV. In the experiments, a beam of 50 keV electrons is incident along the c-axis of the crystals and electrons inelastically scattered through an angle of 1 m radian are selected for energy analysis. This ensures that the momentum transfer and hence the electric vector for the excitations lies in the basal plane of the crystal (E⊥c). Kramers-Kronig analysis has been applied to the energy loss data to deduce the complex dielectric function of each material. From this function, all other ‘optical’ constants, such as the reflectivity, and t...

A model for energy deposition in liquid water.

Abstract: both a redistribution of oscillator strengths relative to the gas phase, and the possible existence of a collective oscillation (plasmon). We investigate the effects of such a plasmon on the partition of energy deposited by fast electrons. To accomplish this, we develop a heuristic model of the liquid based primarily upon the extensive body of gas phase generalized oscillator strength data. The model has one major free parameter, the strength of the 21.4 eV plasmon. Using standard resonance shapes to approximate the energy loss spectrum of the plasmon, we estimate that the water plasmon has an oscillator strength of 2 (+J about 0.6) and a half-width of about 3.5 eV. We then calculate the slowing down of an electron in liquid water according to continuous-slowing-down theory, and after allowing for plasmon decay, compare the yields for the liquid and gas phases. Our results indicate that when the plasmon decays by ionization it produces a spectrum of only subexcitation electrons. We find a modest change in the yields with the eV per-ion-pair lowered from 30.7 in the gas to 28.5 in the liquid.

High resolution microanalysis in materials science using electron energy loss measurements

Abstract: SUMMARY The physical basis of microanalysis using measurements of electron energy losses associated with atom ionization or plasmon excitation in thin electron microscope specimens is explained in a simple manner. In addition the equipment used to resolve both the high and low energy regions of the loss electron spectrum is described. It is shown that ionization loss analysis is still in its infancy, but plasmon loss analysis has now been providing quantitative microanalytical data on light metal alloys for 8 years. The results obtained from both techniques and their application to specific metallurgical problems are reviewed. Conclusions are drawn concerning the future use of these techniques in high resolution microanalysis.

Analysis of the electron excitation spectra in heavy rare earth metals, hydrides and oxides

Abstract: 2014 The energy loss spectra of 75 keV electrons transmitted through thin evaporated foils of heavy rare earths (Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in three different chemical states (metal, hydride and oxide) exhibit two main peaks due to collective « plasmon » excitations in the 10-17 eV energy range and to inner 5p excitations between 30 and 40 eV. A quantitative analysis of the intensity spectral distribution allows one to calculate the energy loss function and, through a KramersKrönig inversion, the dielectric constant and the dipole oscillator strength. Various results are then explained in terms of band structure, so that we are lead to propose a simple model for the interband transitions occuring in oxides. LE JOURNAL DE PHYSIQUE TOME 37, AVRIL 1976, Classification Physics Abstracts 2.820 8.800 8.120

Plasmon Dispersion and Anisotropy in Polymeric Sulfur Nitride, (SN) x

Abstract: Plasmon dispersion and anisotropy in the metallic polymer ${(\mathrm{SN})}_{x}$ were investigated directly by electron-energy-loss spectroscopy. A positive dispersion relation was observed for plasmons propagating along the polymer-chain $b$ axis. As the plasmon wave vector changes from parallel to perpendicular to the $b$ axis, the plasmon energy decreases from 2.5 to 1.5 eV consistent with the view that ${(\mathrm{SN})}_{x}$ is a poor conductor in the perpendicular direction rather than a quasi-one-dimensional metal.

Comment on Plasmon Linewidth Experiments for Electrons on a Helium Surface

Abstract: We show that the proper application of the established theory of electron-ripplon scattering for electrons trapped on helium correctly predicts the absolute linewidth, as a function of external electric field, observed in a recent plasmon experiment.

Structure-Related Optical Characteristics of Thin Metallic Films in the Visible and Ultraviolet.

Abstract: Surface irregularities and crystalline order strongly influence both the scattered light and absorption of metallic films. These effects extend through all spectral regions but are particularly important in the visible and ultraviolet. Scattered light arises from several scattering mechanisms. Macroscopic irregularities such as dust, scratches and particulates are typically much less important than are microirregularities only a few tens of angstroms in height but covering the entire surface. For metals such as silver and aluminum, which have plasma edges in the ultraviolet, the excitation of surface plasmons resulting from these microirregularities causes additional incoherently reemitted or "scattered" light. Surface plasmon excitation also causes increased absorption in some wavelength regions. These effects are enhanced by dielectric overcoating layers, which both increase the absorption and scattering and shift the wavelength at which the peak occurs. Surface plasmon excitation is particularly important in the ultraviolet region, where the dielectric overcoating applied to prevent formation of an oxide film on aluminized mirrors, for example, can significantly change the mirror reflectance. Plasmon excitation is made possible by a momentum conserving process associated with material inhomogeneities and hence can presumably be caused by crystalline disorder in the metal surface as well as surface irregularities. If the disorder is present on a sufficiently fine scale, it also affects the band structure of the metal and hence its optical absorption. Examples of the effect of film structure on the optical properties of evaporated and sputtered metal films will be given.

Optical and electrical studies of Ti- and Ta-dichalcogenides: Plasmons

Abstract: We have measured the room temperature reflectance of the Ti and (1T) Ta dichalcogenides as well as TiSe2 alloyed with TaSe2. Two types of carriers with different relaxation times are required to account for the observed plasma reflection. Both of these plasma frequencies in TiSe2 increase with increasing Ta content, suggesting they are associated with electrons. The resistivity of these alloys falls on decreasing the temperature with a knee occurring at a temperature where electron diffraction shows the appearance of a superlattice. This knee diminishes and moves to lower temperature with increasing carrier concentration.

Pseudopotential theory of the width of the long wavelength plasmon in simple metals

Abstract: The full width at half maximum (FWHM) of long wave-length plasmons in simple metals is derived in a form convenient for application. The line width is a measure of the strength of the pseudopotential, and very good agreement with recent experimental measurements is found for a representative set of nearly-free-electron (NFE) metals. The dispersion of the FWHM is also discussed.

Oscillations of a two-dimensional classical plasma

Abstract: We have calculated the complex dispersion relation of the two-dimensional classical plasmon within the framework of the Vlasov or random-phase approximations.

Stimulated electron tunneling in metal‐barrier‐metal structures due to surface plasmons

Abstract: It is shown that electron tunneling can be stimulated by electron–plasmon–virtual photon interactions. Negative differential resistance exhibiting a threshold voltage and current density is expected for metal‐barrier‐metal structures.

Energieverlustmessungen von schnellen Elektronen an Oberflächen von Ga, In, Al und Si

Abstract: The excitation of surface plasmons on liquid indium, gallium and aluminum surfaces as well as on silicon cleavage faces is studied by reflection of 10 keV electrons at grazing incidence (80° up to 89°). Due to the high excitation probability of surface plasmons at these large angles of incidence multiples of surface plasmons are observed. (Except on Si.) The Poisson distribution of the intensity of these energy losses is verified quantitatively as well as the dependence on (cosα)−1. The value of the excitation probability indicates that at grazing incidence the electrons are reflected just at the surface without penetrating into the volume. This is further demonstrated by the lack of volume plasmons. The surface loss positions in the solid and the liquid state show the calculated differences due to the density difference of both phases

Plasmon dispersion in single-crystal magnesium

Abstract: Plasmon dispersion and damping along the a and c axes in single-crystal magnesium were measured directly by electron energy-loss spectroscopy. No significant anisotropy in dispersion was observed; however, the damping was found to be anisotropic.

Physics of compact radio sources. I. Particle acceleration and flux variations

Abstract: The observed patterns of variability of compact radio sources may be explained by assuming that the radio components are plasmons containing relativistic particles, and by applying a model with the following features: (1) the plasmons are ejected at high speed into the interstellar medium in the nuclei of active galaxies: (2) ram pressure confinement of the plasmons leads to Rayleigh-Taylor and Kelvin-Helmholtz instabilities therein; (3) turbulence is thereby introduced into the plasmons; (4) the turbulence amplifies the plasmon magnetic field (for a short period) and this leads to betatron aceleration of the relativistic particles; (5) the turbulence vortices continue to accelerate the particles by the second-order Fermi acceleration mechanism. The emission patterns are the result of the combination of these accelerations and adiabatic losses. (AIP)

Plasmon Bands and Gaps in Metal Crystals

Abstract: We consider the influence of a periodic lattice upon the plasmon energy in a metal, by means of the equation of motion proposed by March and Tosi. The solution, within the random-phase approximation and for a weak periodic potential, shows the existence of two plasmon bands separated by a complex energy gap near the Brillouin zone border. This gap, due to plasmon Bragg diffraction, is rapidly quenched in presence of damping in simple metals. Group-IV metals and semiconductors should offer better chances for the observation of these "nearly-free-plasmon" bands near the Brillouin zone border.

Direct observation of the optical plasma resonance of Ag by photon-assisted tunneling

Abstract: Photon-assisted tunneling is proposed for the investigation of optical plasma resonances; this is demonstrated by the direct observation of the Ag resonance in appropriate Ag-Al2O3-Al structures. A spectral scan of the ratio of the signals photoinduced by the p and s polarizations shows a large enhancement corresponding to the plasma resonance of Ag.

Plasmon divergence in peanuts (Arachis hypogaea): A third plasmon and locus affecting growth habit.

Abstract: In a series of reciprocal crosses between peanut (Arachis hypogaea L) cultivars from different regions and known testers, the cultivar HG1 from India was shown to have a third plasmon type, designated [G] HG1 also has a third locus, Hb5 , which interacts with the plasmons and the loci described earlier In the [G] plasmon, Hb1 and Hb5 are additive: plants having three or four dominant alleles have a trailing habit while the other nuclear genotypes produce in [G] erect plants In the [V4] plasmon, Hb2 and Hb5 are complementary, [V4] Hb2-, Hb5-plants being trailing, the others erect In the [G] plasmon, Hb2 and Hb5 are complementary, while in the [O] plasmon they are additive