Low-loss magnesium films for plasmonics

The optical properties of pure nanostructured magnesium films deposited on glass, Si and GaAs substrates using DC magnetron sputtering are examined in this work to determine the potential of Mg as plasmonic material in the ultraviolet (UV) to near-infrared (NIR) spectral range. Using film thicknesses ranging from 210 to 910 nm, the corresponding optical constants over the wavelength range of 250–1700 nm were measured using a variable angle spectroscopic ellipsometer and these results are compared to reference Al thin films. The optical constants of Mg depend on the film thickness. From the perspective of plasmonics applications, we find that the best values are observed in this work for the 910 nm thick Mg film on glass substrates. The film morphology and structure of the Mg films were characterized using atomic force microscopy, scanning electron microscopy, stylus profilometry and X-ray diffraction. The optical dielectric constants and plasmonic figures of merit are strongly influenced by the film structure. The results show that smooth and [0 0 0 2] textured magnesium films have extremely low loss, superior or comparable to aluminum films in portions of the UV spectrum.