Modelling the optical properties of magnesium thin films determined by ellipsometry and reflectometry

The optical constants of magnesium (Mg) based films, such as the complex refractive index, are poorly reported in the literature. Consequently, this work presents two self-consistent ellipsometry models capable of determining the optical constants of electron beam evaporated Mg thin films of different thicknesses within a wavelength range from 250 to 1600 nm. These models were validated by fitting spectroscopic ellipsometry measurements at three different incident angles and reflectance measurements. The optical constants of the thinnest film indicate absorption losses due to the influence of voids observed in Field Emission Gun-Scanning Electron Microscopy images. When these voids are considered in the ellipsometry model, a reduction in the extinction coefficient (k) from 4.4 to 3.6 at a wavelength of 800 nm is observed. Thicker films present a different morphology resulting in a drastic change in the optical response leading to reflectivity and k reduction.