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In this work, a versatile method is proposed to increase the sensitivity of optical sensors based on the localized surface plasmon resonance (LSPR) phenomenon. It combines a physical deposition method with the oblique angle deposition technique, allowing the preparation of plasmonic thin films with tailored porosity. Thin films of Au-TiO2 were deposited by reactive magnetron sputtering in a 3D nanostructure (zigzag growth), at different incidence angles (0° ≤ α ≤ 80°), followed by in-air thermal annealing at 400 °C to induce the growth of the Au nanoparticles. The roughness and surface porosity suffered a gradual increment by increasing the incidence angle. The resulting porous zigzag nanostructures that were obtained also decreased the principal refractive indexes (RIs) of the matrix and favoured the diffusion of Au through grain boundaries, originating broader nanoparticle size distributions. The transmittance minimum of the LSPR band appeared at around 600 nm, leading to a red-shift to about 626 nm for the highest incidence angle α = 80°, due to the presence of larger (scattering) nanoparticles. It is demonstrated that zigzag nanostructures can enhance adsorption sites for LSPR sensing by tailoring the porosity of the thin films. Atmosphere controlled transmittance-LSPR measurements showed that the RI sensitivity of the films is improved for higher incidence angles., This research was sponsored by the Portuguese Foundation for Science and Technology (FCT) in the framework of Strategic Funding UID/FIS/04650/2013; project POCI-01-0145-FEDER-016902, with FCT reference PTDC/FIS-NAN/1154/2014; and project POCI-01-0145-FEDER-032299, with FCT reference PTDC/FIS-MAC/32299/2017. This work was also developed within the scope of the project CICECO-Aveiro Institute of Materials, FCT Ref. UID/CTM/50011/2019, financed by national funds through the FCT/MCTES. Manuela Proença acknowledges her PhD grant from FCT, with reference SFRH/BD/137076/2018. Joel Borges acknowledges FCT for his Post-Doc grant SFRH/BPD/117010/2016. Marco S Rodrigues acknowledges FCT for his PhD grant with reference SFRH/BD/118684/2016. Konstantin Romanyuk wish to thank the Portuguese FCT for the financial support (grant SFRH/BPD/88362/2012)., info:eu-repo/semantics/publishedVersion

"Available online 08 April 2019", Nanocomposite thin films, composed of monometallic Au and Ag, and bimetallic AuAg nanoparticles, dispersed in a CuO matrix were prepared, characterised and tested for Localized Surface Plasmon Resonance (LSPR) sensing. The films were deposited by reactive magnetron sputtering, followed by a post-deposition thermal annealing to modify the size and shape of the nanoparticles distribution within the oxide matrix. Regarding the main results of the monometallic systems, the Au:CuO films showed LSPR bands from 800 nm to 650 nm, which reveal a progressive narrowing and a continuous blue-shift with increasing temperature (400–700 °C). The Ag:CuO films evidenced plasmonic bands at about 400 nm for temperatures of 500 °C and above. The bimetallic system, Au-Ag:CuO, showed LSPR bands in the range between those of the corresponding monometallic systems, due to the presence of Ag enriched AuAg alloy nanoparticles, taking part of Janus-like structures in some cases. In terms of LSPR sensing, Au:CuO films revealed the highest values of refractive index sensitivity since the nanoparticles are more exposed to the surrounding environment., This work was supported by the Portuguese Foundation for Scienceand Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019; and by the projects NANOSENSING, POCI-01-0145-FEDER-016902, with FCT reference PTDC/FIS-NAN/1154/2014; andNANO4BIO, POCI-01-0145-FEDER-032299, with FCT reference PTDC/FIS-MAC/32299/2017. Manuela Proença acknowledges her PhD grantfrom FCT, with reference SFRH/BD/137076/2018. Joel Borges ac-knowledges FCT for his Post-Doc grant SFRH/BPD/117010/2016.Marco S. Rodrigues acknowledges FCT for his PhD grant with referenceSFRH/BD/118684/2016. The authors would like to thank E. Alves(Instituto de Plasmas e Fusão Nuclear, Instituto Superior Técnico,Universidade de Lisboa) and N. P. Barradas (Centro de Ciências eTecnologias Nucleares, Instituto Superior Técnico, Universidade deLisboa) for the RBS analysis., info:eu-repo/semantics/publishedVersion

Nanocomposite thin films, with noble nanoparticles dispersed in a dielectric matrix, are known to present unique optical properties. Based on the Localized Surface Plasmon Resonance (LSPR) phenomenon, these "nanoplasmonic" materials are the basis of a wide range of technological applications, namely (bio)molecular LSPR-sensors. They are regulated by the concentration, size, shape and distribution of the nanoparticles and dielectric environment properties. In this work, the possibility of using aluminium nitride (AlN) as a host dielectric matrix for LSPR films was evaluated. For this purpose, nanocomposite Au:AlN films were prepared by magnetron sputtering, followed by thermal annealing to promote the growth of the nanoparticles. Three sets of films were deposited with atomic Au concentrations of 2.2, 4.4 and 6.0 at.%. LSPR bands appeared from the temperature of 500 degrees C, with resonance positions of 520-540 nm. The films showed potential to be tested in LSPR-sensing applications due to their optical responses., This work is financed by National Funds through FCT - Portuguese National Funding Agency for Science, Research and Technology, in the framework of the project PTDC/FIS-NAN/1154/2014 (FCT Projet 9471-RIDTI Reforcar a Investigacao, o Desenvolvitnento Tecnologico e a Inovactio), co-financed by FEDER (POCI-01-0145-FEDER-016902). This research was also sponsored by FCT in the framework of the Strategic Funding UID/FIS/04650/2013. The authors also acknowledge project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. Joel Borges acknowledges FCT for his Post-Doc Grant SFRH/BPD/117010/2016, Marco S. Rodrigues acknowledges his PhD-Grant from FCT, with reference SFRH/BD/118684/2016. The authors also acknowledge P. Pedrosa from Institut FEMTO-ST, Universite Bourgogne Franche-Comte, Besancon, France, for SEM analysis., info:eu-repo/semantics/publishedVersion

Nanocomposite thin films, containing Au nanoparticles dispersed in a CuO matrix, were prepared by reactive DC magnetron sputtering and post-deposition thermal annealing. The CuO matrix was found to be stoichiometric and the atomic concentration of Au was determined to be about 12.3 at.%. After the annealing process, the average size of the crystalline domains of the Au nanoparticles (fcc structure) increased from about 6 nm (at an annealing temperature of 300 °C) to approximately 13 nm (after annealing at 800 °C), with a progressive crystallization of the CuO matrix in the monoclinic structure. A nanoplasmonic effect due to the localized surface plasmon resonance (LSPR) phenomenon appeared in the films after annealing temperatures of 400 °C and higher. The correspondent LSPR bands appeared in the visible range of the transmittance spectra, becoming progressively narrower. Angle Resolved X-ray Photoelectron Spectroscopy results indicated that the surface of Au/CuO nanocomposite thin film is contaminated with a sub-nanometric layer (~ 0.6 nm) of hydrocarbons and that the Au nanoparticles are relatively homogenously dispersed inside the CuO dielectric matrix. Furthermore, the results seem also to indicate that the Au nanoparticles are covered with about 0.2 nm of CuO. Although further studies need to be performed to make clear the particular features of the present nanocomposite thin films’ system, this work shows promising results concerning some particular applications that are envisaged, namely their use as LSPR sensing platforms for particular molecules detection (e.g. gases)., National Funds through FCT - Portuguese National Funding Agency for Science, Research and Technology, in the framework of the project PTDC/FIS-NAN/1154/2014 (FCT Projet 9471-RIDTI Reforçar a Investigação, o Desenvolvimento Tecnológico e a Inovação), co-financed byFEDER (POCI-01-0145-FEDER-016902). This research was also sponsored by FCT in the framework of the Strategic Funding UID/FIS/04650/2013. Joel Borges acknowledges FCT for his Post-Doc Grant SFRH/BPD/117010/2016 and Marco S. Rodrigues acknowledges his PhD-Grant from FCT with reference SFRH/BD/118684/2016. The authors would like to thank Paulo Pedrosa and Nicolas Martin (Université Bourgogne Franche-Comté) for SEM measurements and E. Alves (Instituto de plasmas e fusão nuclear-IST-Universidade de Lisboa) and N. P. Barradas (Centro de Ciências e Tecnologias Nucleares-IST-Universidade de Lisboa) for the RBS analyses, info:eu-repo/semantics/publishedVersion

Thin films containing monometallic (Ag,Au) and bimetallic (Ag-Au) noble nanoparticles were dispersed in TiO2, using reactive magnetron sputtering and post-deposition thermal annealing. The influence of metal concentration and thermal annealing in the (micro)structural evolution of the films was studied, and its correlation with the localized surface plasmon resonance (LSPR) and surface enhanced Raman spectroscopy (SERS) behaviours was evaluated. The Ag/TiO2films presented columnar to granular microstructures, developing Ag clusters at the surface for higher annealing temperatures. In some cases, the films presented dendrite-type fractal geometry, which led to an almost flat broadband optical response. The Au/TiO2system revealed denser microstructures, with Au nanoparticles dispersed in the matrix, whose size increased with annealing temperature. This microstructure led to the appearance of LSPR bands, although some Au segregation to the surface hindered this effect for higher concentrations. The structural results of the Ag-Au/TiO2system suggested the formation of bimetallic Ag-Au nanoparticles, which presence was supported by the appearance of a single narrow LSPR band. In addition, the Raman spectra of Rhodamine-6G demonstrated the viability of these systems for SERS applications, with some indication that the Ag/TiO2system might be preferential, contrasting to the notorious behaviour of the bimetallic system in terms of LSPR response., CNPq - Conselho Nacional de Desenvolvimento Científico e Tecnológico(CFUM-BI-23/2016-UID/ FIS/04650/2013), info:eu-repo/semantics/publishedVersion