Multiple Surface Plasmon Excitations Research Articles

Surface Plasmon Excitation at Topmost Surface in Reflection High-Energy Positron Diffraction

To investigate the excitation process of surface plasmon by fast positrons, we measured the positron energy loss spectra from Si(111)-7×7, Al(111)-1×1, and Bi(001)-1×1 surfaces under the total reflection condition using an energy-filtered reflection high-energy positron diffraction. We observed the multiple surface plasmon excitations, which can be represented by the Poisson distribution with the mean excitation number of 2.4-2.8. The energy loss spectrum is nearly independent of the glancing angle of the incident positron beam. We also measured the electron energy loss spectra at similar glancing angles and determined the mean excitation number to be 1.4-1.8. We found that due to the total reflection positrons are able to excite more surface plasmons as compared to electrons. [DOI: 10.1380/ejssnt.2010.190]

Inelastic scattering processes in reflection high-energy positron diffraction from aSi(111)−7×7surface

To analyze the inelastic processes of totally reflected fast positrons at solid surfaces, we measured the absolute reflectivity, specular beam profile, and energy-loss spectrum from a $\text{Si}(111)\text{\ensuremath{-}}7\ifmmode\times\else\texttimes\fi{}7$ surface during the reflection high-energy positron diffraction. The absolute reflectivity of positrons was more than 1 order of magnitude greater than that of electrons; however, it was well below 100% even under the total-reflection condition. The specular beam profile of positrons exhibited a broad feature. The energy-loss spectrum showed that more surface plasmons are excited by positrons as compared to electrons. The degraded absolute reflectivity and the broadening of specular beam profile are explained by the multiple surface-plasmon excitations by positrons.

Molecular thin film structure and multiple surface plasmon excitations at nano-interfaces in the attenuated total reflection Kretschmann configuration

Relationships between molecular thin film structure and multiple surface plasmon (SP) excitations at nano-interfaces have been investigated for prism/metal thin film/molecular thin films in the attenuated total reflection Kretschmann configuration. Recently, emission light through the prism that strongly depended upon the emission angles was observed using the reverse irradiation, that is, direct irradiation of a laser beam from air to molecular thin films. Emission light in the reverse irradiation has investigated in detail for organic thin films with various structures. From the dispersion property of the emission spectra at various emission angles, it was estimated that the emission light was caused by excitation of multiple SPs at the nano-interfaces. The emission properties also depended upon the amount of dye molecules, nano-spacing between the metal and dyes, and polarizations of the laser beam. It is thought that the phenomenon is useful for application to new devices utilizing multiple SP excitations.

Emission Light and Multiple Surface Plasmon Excitations at Prism/Ag/Merocyanine Langmuir-Blodgett Films

Emission light through a prism has been investigated for prism/silver (Ag) thin film/merocyanine (MC) Langmuir-Blodgett (LB) films in the Kretschmann configuration. Emission light was observed by means of direct irradiation of a laser beam from air to the MC LB films, that is, reverse irradiation. The emission properties coincided with resonant conditions of surface plasmon (SP) excitations in the Kretschmann configuration. Emission due to SP excitations depended upon the position of the MC LB film in the LB hetero films of arachidic acid (C20)/MC/C20 on the Ag thin film. The strongest emission was observed at some separation of the MC LB layer from the metal surface. Emission properties were also investigated for the hetero LB films of MC and C20 on aluminum (Al) thin film and for the MC LB films with various thicknesses. It is thought that the phenomenon is useful for application to new devices utilizing multiple SP excitations.

MULTIPLE SURFACE PLASMON EXCITATIONS AND NANOSTRUCTURED DEVICES OF ORGANIC ULTRATHIN FILMS

Surface plasmon (SP) excitations have been investigated in the attenuated total reflection (ATR) Kretschmann configuration of prism/metal/organic ultrathin films. Structure and optical properties of organic ultrathin films have been evaluated using the ATR measurement due to SP excitations. Recently, emission light through the prism was observed using direct irradiation of a laser beam from air to the organic films, that is, reverse irradiation. The emission spectra strongly depended upon the emission angles through the prism and were caused by multiple SP excitations. The emission properties also depend upon structure of metal and organic thin films, dye molecules, separation between metal and molecules, molecular interaction, and so on. It is thought that the phenomenon is useful for application to new devices utilizing multiple SP excitations, and nanostructured devices of organic films using multiple SP excitations are described.

Emission light from prism/silver/rhodamine-B LB film and multiple surface plasmon excitations in the ATR Kretschmann configuration

Emission light through the prism in the Kretschmann configuration of prism/Ag thin film/rhodamine-B (RB) Langmuir–Blodgett (LB) film has been observed by means of direct irradiation of a laser beam from air to the RB LB film, that is, the reverse irradiation method against the conventional attenuated total reflection (ATR) method. The emission light intensities and the spectra strongly depended upon the emission angle at the prism. The relation between the peak wavelengths of the spectra and the emission angles corresponded to the dispersion property of the resonant excitations of surface plasmons (SPs) in the ATR configuration. It was concluded that the emission light was caused by multiple excitations of SPs in the ATR configuration. Emission light through the prism was also observed below the reflection angle of the resonant one when the SP was resonantly excited in the conventional ATR measurement. This emission light also showed the same property as the one in the reverse irradiation method. It is thought that the phenomenon will be used as a new sensing device.

NANOSTRUCTURED LB FILMS AND EMISSION LIGHT DUE TO MULTIPLE SURFACE PLASMON EXCITATIONS IN THE KRETSCHMANN CONFIGURATION

Surface plasmon (SP) excitations have been investigated in the attenuated total reflection (ATR) Kretschmann configuration of prism/metal/Langmuir–Blodgett (LB) films containing dyes. The emission light through the prism was observed using direct irradiation of a laser beam from air to the LB films, i.e., reverse irradiation. The emission intensities depend on the emission angles through the prism, nanostructure of metal and LB films, dye molecules, separation between metal and dye molecules, interactions of dye molecules, etc. The spectra is strongly depended on the emission angles, and the emission light was caused by multiple SP excitations. Nanostructured devices of LB films using SP excitations are described.

Multiple surface plasmon excitations in overlayers of K and Na on Ru(001)

Electron energy loss spectra in the reflection geometry have been measured for potassium and sodium layers on Ru(001) for coverages ranging from N = 1 up to 16–20 layers. The experimental conditions (primary energy, angle-of-incidence) allowed excitation of multiple surface plasmons. For all systems, energy and damping of the surface plasmons together with the integral probability for surface plasmon excitation have been determined. For the variation of these parameters with alkali layer thickness, two coverage regimes can be distinguished that are correlated to different types of excitations. For N ⩽ 1 one-electron excitations are very important; for N ⩾ 2 a collective response (well-defined surface plasmon excitations) takes place. The slowly decreasing energy of the surface plasmon with increasing alkali thickness to the bulk values is in qualitative agreement with both macroscopic and microscopic descriptions. The thickness dependences of the damping and the integral excitation probability indicate that one-electron contributions which are very important for N = 1 are also present for N = 2 and only slowly decrease with increasing thickness of the alkali layer. The analysis of the EELS data for N ⩾ 2 shows that the excitation probability for multiple surface plasmons follows the Poisson distribution; the data are consistent with the consecutive excitation of individual surface plasmons.

Quantum theory of electron energy loss spectra in thin films

An exact theory of the interaction of a fast electron with plasmons in thin films is presented. The general shape of the electron energy loss spectrum is described briefly. Multiple surface plasmon excitations are shown to be important for the specularly reflected beam at grazing incidence.