Due to the ongoing improvement in nanostructuring technology, ultrathin metallic nanofilms have recently gained substantial attention in plasmonics, e.g. as building blocks of metasurfaces. Typically, noble metals such as silver or gold are the materials of choice, due to their excellent optical properties, however they also possess some intrinsic disadvantages. Here, we introduce niobium nanofilms (~10 nm thickness) as an alternate plasmonic platform. We demonstrate functionality by depositing a niobium nanofilm on a plasmonic fiber taper, and observe a dielectric-loaded niobium surface-plasmon excitation for the first time, with a modal attenuation of only 3–4 dB/mm in aqueous environment and a refractive index sensitivity up to 15 μm/RIU if the analyte index exceeds 1.42. We show that the niobium nanofilm possesses bulk optical properties, is continuous, homogenous, and inert against any environmental influence, thus possessing several superior properties compared to noble metal nanofilms. These results demonstrate that ultrathin niobium nanofilms can serve as a new platform for biomedical diagnostics, superconducting photonics, ultrathin metasurfaces or new types of optoelectronic devices.

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A novel fabrication strategy is introduced for the synthesis of 3D silver–silica hybrid nanostructures by employing the plasma‐enhanced atomic layer deposition (PE‐ALD) on the templated substrates with enzymatically generated silver nanoparticles (EGNPs). Comparing with the conventional PE‐ALD process for the silica deposition (by using the precursors of tri‐dimethyl‐amino‐silane (TDMAS) and oxygen plasma), here the EGNPs play a key role for the formation of 3D hierarchical structures. During the oxygen plasma step, a metastable silver oxide surface is formed, and then thermally decomposes and releases excess oxygen during the next TDMAS step. A side reaction for the deposition of silica occurs with the excess released oxygen. The formation of the metastable silver oxide and its decomposition repeat cyclically during the PE‐ALD process, thereby, the side reaction is going on progressively, and finally, the 3D silver–silica hybrid nanostructures are formed with this novel strategy of metastable state assisted atomic layer deposition. Various 3D silver–silica composite nanostructures, such as nanosponges and nanoflowers, can be fabricated easily by tuning the PE‐ALD parameters. With each additional ALD cycle, the silver particle size decreases which also further reduces side reactions. The observed growth‐effect thus seems to be limited by the amount of silver used.

In utilizing the exceptional optical properties of metallic nanoparticles, surface enhanced Raman spectroscopy (SERS) is an excellent candidate for analytical detection schemes due to its molecular specificity and high sensitivity. To record reliable SERS signals, impurifications on the metallic surface contributing to the overall SERS signal, have to be removed. In this context, it is important to improve the nanostructures’ quality to implement SERS in routine analytical applications. Here, we report about an easy to handle and fast protocol for the generation of SERS active nanoparticles by enzymatically reducing silver ions to their elementary state and oxidizing hydroquinone (HQ) to p-benzoquinone (p-BQ). However, these SERS substrates lead to a strong background signal overlapping with the actual analyte Raman bands. In order to quench this background signal and to protect the silver nanoparticles from oxidation we covered metallic nanoparticles with a dielectric layer of alumina (Al2O3) by applying plasma enhanced atomic layer deposition (PE-ALD). This coating guarantees the stability of these SERS substrates for at least 4 weeks after preparation under ambient storing conditions. The sensitivity of these enzymatically generated nanoparticles (EGNPs) coated with a 1 nm Al2O3 layer allows for a background free detection of riboflavin down to less than 10 nM. Furthermore, the improved specificity of these background-free and bottom-up produced plasmonic arrays has also been demonstrated by detecting a retinol monolayer.

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