Effect of Different Roughnesses on the Excitation by Photons of the Surface Plasmon of Aluminum

Abstract

Different roughnesses induce changes of the interaction of incident light with surface-plasma oscillations. We observed those changes in the optical properties of aluminum. Identical aluminum films were deposited in ultrahigh vacuum (uhv) on substrates of varying roughnesses. We measured the reflectance at photon energies in the vicinity of the surface plasmon energy (1000–1600 A). We used overcoated substrates of different dielectrics (CaF2, MgF2, and LiF). In the terms of existing theories, we show that the curves are conveniently interpreted by taking into consideration (a) the light scattering by the surface characterized by the rms roughness σ and (b) the plasmon-photon interaction closely related to the roughness σand correlation length a. Thus, within the limit of accuracy (ΔR = ±0.5%) the roughness can be determined; σ is a function of the dielectric’s thickness with Δσ<0.5 A and the correlation length a (5 A<Δa<10 A) appears to be a characteristic of the nature of the dielectric. A study under an electron microscope confirms the theoretical strong value of roughnesses and shows the condensation process of aluminum on the rough substrates.