Size characteristics of surface plasmons and their manifestation in scattering properties of metal particles

The change of the scattering properties of sodium, gold and silver spherical particles with size is discussed in the context of surface multipolar plasmon resonances. The presented surface plasmon size characteristics are abstracted from the quantity which is observed and deliver multipolar plasmon resonance frequencies and plasmon damping rates in the form of a continuous function of particle radius. The performed analysis of the plasmon dispersion relation is analogous to the problem of surface plasmon localized at a semi-infinite, flat metal/dielectric interface.Correlation between the multipolar plasmon resonance parameters, and the spectroscopic optical properties of conductive nanoparticles appearing as peaks in the measurable light intensities is analyzed. We discuss the fact, that such peaks arise from interference of all the electromagnetic fields contributing to the measured intensity, and not solely to the fields due to surface plasmon multipolar modes.We describe the results of light scattering experiment in orthogonal polarization geometries with use of spontaneously growing sodium droplets. The polarization geometry of the experiment allows for distinct separation of resonant contribution of dipole and quadrupole plasmon TM mode contributions to the measured intensities as a function of size.Predictions concerning size characteristics for dipole and quadrupole plasmons are compared with the results of light scattering experiments using spherical sodium droplets (our results) and gold and silver particles in suspension [other authors: Sönnichsen C, Franzl T, Wilk T, von Plessen G, Feldmann J. Plasmon resonances in large noble-metal clusters. New J Phys 2002; 4:93.1-8; Haiss W, Thanh NTK, Aveyard J, Fernig DG. Determination of size and concentration of gold nanoparticles from UV-vis spectra. Anal Chem 2007; 79:4215-21; Njoki PN, Lim I-IS, Mott D, Park H-Y, Khan B, Mishra S, et al. Size correlation of optical and spectroscopic properties for gold nanoparticles. J Phys Chem C 2007; 111:14664-9; Mock JJ, Barbic M, Smith DR, Schultz DA, Schultz S. Shape effects in plasmon resonance of individual colloidal silver nanoparticles. J Chem Phys 2002; 116:6755-9].