Small metal particles: Non-local optical properties and quantum-size effects

Abstract
In this work we survey some recent results concerning non-local optical effects and particle-size dependence for the optical properties of individual metallic particles. We start by giving a historical overview and a conceptual discussion on the subject of small particles, underlining their potential applications. Simplified optical response functions for a metallic sphere are introduced and duly illustrated to bring out the physical content. Particular emphasis is given to optical absorption, resonance effects and far-infrared properties exhibited by simple and noble metal particles having less than 100 Å radii. A comparison between the traditional (Mie) approach and the proposed non-local scheme is made and it leads to an increased understanding of the various mechanisms a small particle exhibits when screening an external electromagnetic field.