Thickness dependence of infrared optical properties of ultrathin MoSi2-based thin films

Abstract

This study investigates the thickness-dependent infrared (IR) optical properties of magnetron-sputtered MoSi₂ thin films, demonstrating how precise control over film thickness enables targeted tuning of reflectance, transmittance, and absorbance for IR applications. Fourier-transform IR spectroscopy reveals a twofold mechanism behind the optical behavior of these films. For thicknesses larger than approximately 20 nm, the observed changes in optical response are predominantly governed by multiple reflections at the film interfaces, as described by the Fresnel equations. In the ultrathin regime below 20 nm, however, the optical constants themselves evolve significantly with decreasing thickness, leading to changes in the interactions of the films with IR radiation. This behavior allows for continuous and versatile tuning of optical properties across a broad thickness range. These findings show the potential of MoSi₂ films as highly adaptable materials for advanced IR applications, such as radiative cooling, nanobolometry and IR radiation detectors, for which thickness serves as a key design parameter for tailoring performance.