Surface-plasmon radiation from ellipsoidal silver spheroids

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Abstract
We have studied the radiation resulting from 15keV-electron bombardment of thin silver films and of particles formed by heat treating these films. The particles were treated as oblate and prolate spheroids on which resonant surface-charge-density oscillations (surface plasmons) were excited by electron bombardment. We have calculated the energy associated with various surface-plasmon modes as a function of the shape of the spheroid using nonretarded electrodynamics and the optical properties of bulk silver. We have obtained good agreement between the calculations and the experimental observations of the wavelength, polarization, and angular intensity distributions of radiation emitted by silver particles which were characterized as to size and shape with the use of scanning electron microscopy. The emission from one type of sample was found to be the result of the radiative decay of a dipole and a quadrupole oscillation on oblate spheroids. The radiation from another type of sample showed evidence of the decay of dipole plasmons on prolate particles.