Effect of Surface Morphology on the Optical Properties in Metal-Dielectric-Metal Thin Film Systems

The effect of surface morphology on the optical properties in a metal-dielectric-metal (MDM) thin film was investigated. Ag films were thermally evaporated at different rates to obtain different surface roughnesses and grain sizes. The reflectance spectra of the Ag/MgF2/Ag films show a dip due to surface-roughness-induced excitation of surface plasmon polaritons. The dip position varies from 650 to 800 nm, depending on the surface morphology of the multilayered film. An empirical relationship was found between the optical properties (i.e., the dip position and its linewidth) and the Ag film structural properties (i.e., surface roughness, grain size, and filling factor). The causes of and contributions to the shift of the dip position and the linewidth of the dip were discussed. The study is important to metal-dielectric-based structures, and the unique feature of such a MDM film could be used for color filters.