Optical characterization of nanostructured silver thin films studied by spectroscopic ellipsometry

The evolution of optical properties of nanostructured thin films of silver grown by pulsed DC magnetron sputtering is presented in this paper. The thicknesses of the films varied from ~58 nm to ~98 nm by changing the time of deposition, namely, 180, 240 420 and 600 seconds. The void fraction and surface roughness were extracted from the optical constants using to Bruggemen Effective Medium Approximation (BEMA). With increase in thickness, the void fraction decreased while the surface roughness increased indicating a transition from smooth to hillock like grains with valleys between them. An analysis of the data using Drude´s free electron theory revealed that the unscreened plasma frequency Dpu increased with thickness which is in line with the increase in electron density due to decrease in void fraction.