Size and shape effects in light scattering from small silver, copper, and gold particles

Abstract

Spectra of light scattered from small particles of silver, copper, and gold have been observed between 220 and 500 nm, and interpreted on the basis of size measurements of particle samples taken concurrently with the spectra. Particles were formed by homogeneous nucleation in a flowing inert gas bath containing vapor from the bulk metal. Mean particle diameters between 2 and 150 nm were measured by electron microscopy. A resonance peak was observed at 367 ± 5 nm (3.80 ± 0.06 eV) in the scattered light spectrum of silver particles, principally due to the collective oscillation of conduction electrons. An analysis of the scattered light resonance of silver particles was made using measured particle size distributions, and exact calculations of scattering from spheres including damping predicted by the free-electron gas model. Significant differences between observed spectra and calculations indicate that the width of the resonance is influenced by non-spherical shapes as well as by collisions of conduction electrons with the particle surface.