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The unique architecture of iridescent Morpho butterfly scales is known to exhibit different optical responses to various vapours. However, the mechanism behind this phenomenon is not fully quantitatively understood. This work reports on process developments in the micro-fabrication of a Morpho-inspired photonic structure in atomic layer deposited (ALD) materials in order to investigate the vapour optical sensitivity of such artificial nanostructures. By developing recipes for dry and wet etching of ALD oxides, we micro-fabricated two structures: one combining Al2O3 and TiO2, and the other combining Al2O3 and HfO2. For the first time, we report the optical response of such ALD Morpho-like structures measured under a controlled flow of either ethanol or isopropyl alcohol (IPA) vapour. In spite of the small magnitude of the effect, the results show a selective vapour response (depending on the materials used).

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In this work, porous silicon (PSi) samples were conformally coated with ultrathin films of aluminum oxide (Al 2 O 3 ) and hafnium oxide (HfO 2 ) using atomic layer deposition (ALD) to passivate their internal surface and improve their overall stability in aqueous media. Their porosity and optical properties were characterized before and after ALD treatment. The stability over time in aqueous media of the ALD passivated porous layers was then evaluated and compared to PSi layers oxidized at 800 °C (PSiO 2 ), which is a treatment widely used in the literature for biosensing applications. The ALD oxide-covered samples performed equally to the oxidized PSi samples, but exhibited a higher mean refractive index, which results in a better contrast. These improved optical properties resulted in a signal exhibiting a significantly decreased noise. This in turn leads to a theoretical limit of detection improved by a factor 13 and 16 for PSi/Al 2 O 3 and PSi/HfO 2 , respectively, compared to the standard PSiO 2 . This could thus result in an improved sensitivity for biosensing applications.

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