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Mesoporous TiO 2 films loaded with silver nanoparticles grown photocatalytically, which are initially brown, change their color under visible laser irradiations. In this article, we compare the multicolor photochromisms of amorphous and anatase phases of TiO 2. The mesoporous films are impregnated with silver salt and then exposed to a low-intensity UV laser light to grow silver nanoparticles. The Ag–TiO 2 films are then exposed to visible laser beams, and the influences of several exposure parameters on the photochromic behavior are examined. Most of the previous studies have reported a poor stability of the photoinduced colors under day light or even in the dark, and few of them demonstrated the ability to get various colors on the same sample. These inconveniences limit the application field of such materials. On the other hand, except in our previous studies, only crystalline TiO 2 is generally used, in its anatase or rutile phase. In this article we show that mesoporous films of amorphous and anatase phases of TiO 2 respond in an efficient manner to light excitation and that multiple colors can be obtained on both kinds of films. For the first time on such Ag–TiO 2 films we show that the various photoinduced colors are stable over considerable months. Visible intensity is shown to have a significant influence on the film behavior, which was not identified in previous studies. The laser-induced spectral changes are also shown to depend on the incident laser polarization. The photochromic behaviors are characterized in terms of color changes and spectral variations. The reproducibility of the photochromic process along reduction/oxidation cycles is demonstrated, and the stability of different laser-induced colors is reported on 6-month-old samples. [ABSTRACT FROM AUTHOR]

Silver nanoparticles were created inside mesoporous titania thin films by different reduction processes. We investigated the influence of the reduction method on the colour and photochromism of these amorphous TiO2films. The results highlight brown films by optical reduction, gray films by thermal reduction, and red, purple or orange films by chemical reduction. The different size distributions and localizations of the nanoparticles, characterized by UV-visible spectroscopy and electron microscopy, give various photochromic behaviours when exposed to visible laser light. We especially report the bleaching of different film colours under laser exposure. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance is an effect widely used for biosensing. Biosensors based on this effect operate in different configurations, including the use of diffraction gratings as couplers. Gratings are highly tunable and are easy to integrate into a fluidic system due to their planar configuration. We discuss the optimization of plasmonic grating couplers for use in a specific sensor configuration based on the optical switch. These gratings present a sinusoidal profile with a high depth/period ratio. Their interaction with a p -polarized light beam results in two significant diffracted orders (the 0th and the -1st), which enable differential measurements cancelling noise due to common fluctuations. The gratings are fabricated by combining laser interference lithography with nanoimprinting in a process that is aligned with the challenges of low-cost mass production. The effects of different grating parameters such as the period, depth and profile are theoretically and experimentally investigated.

A deep metal grating enables quasi-phase-matched simultaneous excitation of two counterpropagating surface plasmon modes by means of its +1st and -2nd diffraction orders. The resulting angular reflection spectra of the scattered -1st and zeroth orders exhibit three interleaved zeros and maxima in a range centered around the Littrow angle. The spectra differ thoroughly from the usual reflection dip resulting from single-order plasmon coupling that produces strong absorption. The zeroth and -1st orders exhibit two crossing angles enabling high-sensitivity common-mode detection schemes designed to reject variations in source power and environmental noise. The proof of concept and experimental assessment of this new surface plasmon resonance (SPR) sensing scheme are demonstrated by monitoring gases in a pressure-controlled chamber. A limit of detection (LOD) of 2 × 10 -7 refractive index unit (RIU) was achieved.

A new plasmonic configuration is proposed for application in a sensor and demonstrated for the detection of variations in the bulk refractive index of solutions. The configuration consists of monitoring two diffracted orders resulting from the interaction of a TM-polarized optical beam incident on a grating coupler, operating based on an effect termed the "optical switch". The two monitored diffracted orders enable differential measurements which cancel the drift and perturbations common to both, leading to an improved detection limit, as demonstrated experimentally. The measured switch pattern associated with the grating coupler is in good agreement with theory. Bulk sensing is demonstrated under intensity interrogation via the sequential injection of solutions comprised of glycerol in water into a fluidic cell. A limit of detection of about 10-6 RIU was achieved. The optical switch configuration is easy to implement and is cost-effective, yielding a highly promising approach for the sensing and the real-time detection of biological species.

Zirconium oxide (ZrO 2 ) is a well-studied and promising material due to its remarkable chemical and physical properties. It is used, for example, in coatings for corrosion protection layer, wear and oxidation, in optical applications (mirror, filters), for decorative components, for anti-counterfeiting solutions and for medical applications. ZrO 2 can be obtained as a thin film using different deposition methods such as physical vapor deposition (PVD) or chemical vapor deposition (CVD). These techniques are mastered but they do not allow easy micro-nanostructuring of these coatings due to the intrinsic properties (high melting point, mechanical and chemical resistance). An alternative approach described in this paper is the sol-gel method, which allows direct micro-nanostructuring of the ZrO 2 layers without physical or chemical etching processes, using optical or nano-imprint lithography. In this paper, the authors present a complete and suitable ZrO 2 sol-gel method allowing to achieve complex micro-nanostructures by optical or nano-imprint lithography on substrates of different nature and shape (especially non-planar and foil-based substrates). The synthesis of the ZrO 2 sol-gel is presented as well as the micro-nanostructuring process by masking, colloidal lithography and nano-imprint lithography on glass and plastic substrates as well as on plane and curved substrates.

Surface micro-nanostructuring can provide new functionalities and properties to coatings. For example, it can improve the absorption efficiency, hydrophobicity and/or tribology properties. In this context, we studied the influence of micro-nanostructuring on the photocatalytic efficiency of sol-gel TiO 2 coatings during formic acid degradation under UV illumination. The micro-nanostructuring was performed using the UV illumination of microspheres deposited on a photopatternable sol-gel layer, leading to a hexagonal arrangement of micropillars after development. The structures and coatings were characterized using Raman spectroscopy, ellipsometry, atomic force microscopy and scanning electron microscopy. When the sol-gel TiO 2 films were unstructured and untreated at 500 °C, their effect on formic acid's degradation under UV light was negligible. However, when the films were annealed at 500 °C, they crystallized in the anatase phase and affected the degradation of formic acid under UV light, also depending on the thickness of the layer. Finally, we demonstrated that surface micro-nanostructuring in the form of nanopillars can significantly increase the photocatalytic efficiency of a coating during the degradation of formic acid under UV light.

The microstructuring of the distribution of silver nanoparticles (NPs) in mesoporous titania films loaded with silver salts, using two-beam interference lithography leading to 1 Dimension (1D) grating, induces variations in the photocatalytic efficiency. The influence of the structuration was tested on the degradation of methyl blue (MB) under ultraviolet (UV) and visible illumination, giving rise to a significant improvement of the photocatalytic efficiency. The periodic distribution of the NPs was characterized by transmission electron microscopy (TEM), high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and scanning electron microscopy (SEM)., Competing Interests: The authors declare no conflict of interest.