Crystallinity-dependent surface oxidation in Cu Films revealed by a visualization of surface plasmon

We visualized surface plasmon in poly- and single-crystalline Cu films by exploiting nano-infrared imaging. We clearly observed oscillating patterns in both films which are attributed to the surface plasmon launched from the film edge and the atomic force microscope tip. The surface plasmons observed for poly- and single-crystalline Cu films have different oscillating periods for the given wavelength of incident beam, and different slopes of the surface plasmon dispersion. These behaviors could be understood by a corresponding difference in dielectric constants of the dielectric layer on top of the Cu films; a relatively smaller dielectric constant is required to fit the surface plasmon's dispersion relation of the single-crystalline Cu film implying that the oxidized layer formed on the Cu film surface is thinner than for the poly-crystalline film. This result is in good agreement with the previous observation about the robustness of the single-crystalline Cu film against the surface oxidation.