Toward the optimization of SiO2 and TiO2-based metamaterials: Morphological, Structural, and Optical characterization

In recent years, metamaterials have emerged as a crucial technology for designing sub-wavelength thick optical components capable of performing various optical functions. Among the others, these nanostructures could be employed to tune the refractive index, making them useful in various fields (from optoelectronic applications to gravitational wave detectors). In this work, nanostratified structures composed of alternating layers of silica (SiO₂) and titania (TiO₂) were proposed and fabricated using plasma-assisted electron beam deposition. The quality of the deposition was demonstrated using Scanning Transmission Electron Microscopy (STEM), revealing 38 titania/silica doublets with a total thickness compatible with the nominal one of 125.4 nm. X-ray Reflectivity (XRR) and Spectroscopic Ellipsometry (SE) confirmed that the average thicknesses of the titania and silica layers are in good agreement with the expected nominal values even after annealing at 500 °C. Finally, Atomic Force Microscopy (AFM) revealed a very flat surface, both in the as-deposited sample and in the thermally processed one.