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Fano-like resonances in modulated single layers for angular and frequency selectivity of light

This study was aimed to investigate the growth process of thin films on a pre-structured surface using different optically transparent materials and their optical properties. As results of conformal deposition of ion beam sputtered dense single layers on nano-modulated surfaces showed, replicability of surface modulation depends on the layer’s material itself. Among investigated metal oxides, namely tantalum, niobium, hafnium, and silicon oxides, materials with higher molecular weight tend to better repeatability of the initial structure. As an example, the surface modulation depth of tantalum oxide single layer of ~1 μm thickness has preserved almost 97 % of the initial structure, while the silica layer showed the most rapid smoothening of modulation since preserved only ~ 65 %. Considering that tantalum oxide single layers showed the best replicability results, its optical properties were investigated in a more detailed way. Optical characterization revealed the presence of Fano-like resonance phenomenon in such single-layer structure with high refractive index, surrounded by a lower refractive index media. Due to the coupling of thin film's waveguided modes with excited Fabry-Perot modes this phenomenon results in extremely low transmittance lines in the transmittance maps in a plane of the angle of incidence θ and wavelength λ. Moreover, these resonance lines show sensitivity to the angle and the wavelength of the incident light, which can serve as a demonstration of spatial and spectral filtering properties in such compact photonic single-layer structures.