Surface plasmon spectroscopy for the optical characterization of thin metal films and their surfaces

Abstract

Surface plasmons are surface electromagnetic waves. That is, they are travelling waves whose electric and magnetic fields are localized at the interface between a metal and a dielectric. Their propagation characteristics (dispersion) are functions of the optical properties of both the metal and the medium in contact with it. Since they are localized at the interface, they are also sensitive to thin films on the metal surface. Quantitative measurement of surface plasmon resonances can thus yield the optical constants of any one of these three regions. For instance, we can determine the thickness and the dielectric constant (real and imaginary parts) of metal films less than 70 nanometers thick; measure the thickness or refractive index of organic coatings in the 1 to 30 nanometer range; observe the orientation of molecules near a surface in a liquid crystal cell; detect submonolayer adsorption of ionic species from an electrolyte solution. While both prism and grating coupling can be used to excite surface plasmons, we will describe the prism coupling or attenuated total reflection method we commonly use and discuss the sensitivity and range of applicability of the technique. © 1981 SPIE.