Grain size effect on the optical properties of thin silver films

The characterization of the optical constants of metals is an extensive task and dates back to many decades ago. In present work, particular emphasis has been placed on calculations of the dielectric function of thin silver films performed using both photometric (reflection and transmission) measurements. Silver thin films were deposited on glass substrates via radio-frequency sputtering. The thickness of the thin films is in the range of 10 to 100 nm. The optical constants (refractive index and extinction coefficient) and the parameters for the Drude optical model (damping constant, Gamma and plasma frequency, omega(p)) of the films were calculated. It was established that the value of Gamma strongly depends on the thickness due to a size effect in the metal films. When the thickness of the silver films decreases, the magnitude of the imaginary part of the dielectric function becomes smaller than its bulk value. This feature should be taken into account in the design and simulation of the most optical metamaterials with metal-dielectric meta-atoms.