Tuning optical properties of atomically heterogeneous systems created by plasma-based low-energy ion beams

The optical properties (reflectivity, transmissivity, and absorptivity) of metallic thin films (MTFs) of copper, silver, gold, and aluminum upon irradiation by low-energy (∼0.5keV) inert gaseous argon (Ar⁺) ion beams are investigated using UV-VIS-NIR spectrophotometry. The optical constants (real and imaginary parts of the refractive index) of both pristine as well as irradiated MTFs are measured by employing the pseudo-Brewster angle technique. The implanted low-energy Ar⁺ ions modify the dielectric constant of pure MTFs, which in turn changes the refractive index and therefore alters the optical properties of MTFs. Results indicate that the reflectivity decreases, whereas the transmissivity increases with Ar⁺ ion fluence. Absorptivity, calculated using the energy conservation law, increases with ion fluence. The optical modification of MTFs is discussed in light of Maxwell-Garnett theory, and possible applications are outlined.