2D reproduction of the face on the Turin Shroud by infrared femtosecond pulse laser processing.

Femtosecond pulse laser processing concentrates a huge quantity of light energy in extremely short pulses of a few tens to hundreds of femtoseconds, enabling superficial laser machining or marking of any kind of materials, with a reduced or insignificant heat affected area. A digitized paper printed image of the face on the Turin Shroud was used to monitor a scan head intercalated between a femtosecond pulsed laser source and a linen fabric sample, enabling the direct 2D reproduction of the image of the face with a laser beam size corresponding to one pixel of the digitized image. The contrast in the marked image was controlled by adjusting the energy density, the number of superimposed pulses per pixel, and the distance between successive impacts. The visual aspect of the laser-induced image is very similar, at naked eye, to the source image. The negative photograph of the marked linen fabric reveals a face remarkably close to the well-known negative picture of the face on the Turin Shroud. Analyses by infrared spectroscopy, Raman spectroscopy, and scanning electron microscopy were performed to characterize the laser marked areas.

Efficient reversible phase mask for TiO2 submicron gratings directly printed on cylindrical surfaces.

In this article we present a radial phase mask specially designed and manufactured for direct micro-structuration under UV photolithography of a cylindrical surface covered by a photoresist TiO2 film. The period of the phase mask is sub-micron (between 480 nm and 720 nm) and allows direct printing on several types of cylindrical components. With this dedicated reversible phase mask we have demonstrated the feasibility of a TiO2 grating with a period of 960 nm, printed on a SiO2 cylinder or inside a SiO2 tube of 8 mm diameter.

Polarization-driven self-organization of silver nanoparticles in 1D and 2D subwavelength gratings for plasmonic photocatalysis.

One of the main challenges in plasmonics is to conceive large-scale, low-cost techniques suitable for the fabrication of metal nanoparticle patterns showing precise spatial organization. Here, we introduce a simple method based on continuous-wave laser illumination to induce the self-organization of silver nanoparticles within high-index thin films. We show that highly regular and homogeneous nanoparticle gratings can be produced on large areas using laser-controlled self-organization processes. This very versatile technique can provide 1D and 2D patterns at a subwavelength scale with tunable features. It does not need any stabilization or expensive devices, such as those required by optical or electron lithography, and is rapid to implement. Accurate in-plane and in-depth characterizations provide valuable information to explain the mechanisms that lead to pattern formation and especially how 2D self-organization can fall into place with successive laser scans. The regular and homogeneous 2D self-organization of metallic NPs with a single laser scan is also reported for the first time in this article. As the reported nanostructures are embedded in porous TiO2, we also theoretically explore the interesting potential of organization on the photocatalytic activity of Ag-NP-containing TiO2 porous films, which is one of the most promising materials for self-cleaning or remediation applications. Realistic electromagnetic simulations demonstrate that the periodic organization of silver nanoparticles can increase the light intensity within the film more than ten times that produced with randomly distributed nanoparticles, leading as expected to enhanced photocatalytic efficiency.

Growth of single gold nanofilaments at the apex of conductive atomic force microscope tips.

This paper describes a fast and one-step technique to grow single gold filaments at the apex of commercial conductive AFM tips. It is implemented with an atomic force microscope in air with a high relative humidity at room temperature and is based on a bias-assisted electro-reduction of gold ions directly at the tip apex. The technique requires only ad hoc substrates made of a mesoporous silica layer loaded with gold salt deposited on a conductive electrode. It leads to the growth, at the tip apex, of filaments whose length can be monitored and controlled during the growth between tens and hundreds of nanometers and whose radius of curvature can be as low as 3 nm. Made of polycrystalline gold nanostructures, the filaments are chemically and mechanically stable and conductive.

Large Area Fabrication of Periodic TiO2 Nanopillars Using Microsphere Photolithography on a Photopatternable Sol-Gel Film.

The authors demonstrate a unique low cost process to print 2D, submicron size, and high refractive index nanopillars using a direct colloidal-photolithography process. A well collimated i-line source emitting at 365 nm wavelength illuminates a mono layer of silica microspheres of 1 µm diameter deposited on a photosensitive TiO2-based sol-gel layer. No etching process is needed since this layer is directly UV photo patternable like a negative photoresist. Furthermore, this thin layer offers interesting optical properties (high refractive index and optical transparency) and good mechanical and chemical stability and thus can be directly used as a functional microstructure (for PV or sensor applications, for example). The paper describes the modeling of the electric field distribution below the spheres during the illumination process, the photochemistry of the TiO2 sol-gel layer process, and preliminary results of TiO2 nanopillars of around 200 nm in diameter fabricated on a three-inch substrate.

Influence of reduction processes on the colour and photochromism of amorphous mesoporous TiO(2) thin films loaded with a silver salt.

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 TiO(2) films. 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.

Comparison of initial photocatalytic degradation pathway of aromatic and linear amino acids.

Amino acids are at the origin of the formation of odourous compounds after chlorination treatment. Our objectives were to test the efficiency of a photocatalytic process to remove these types of compounds. Five amino acids (AA)-phenylalanine, tyrosine, tryptophan, glycine and alanine--have been chosen as model molecules. The photocatalytic degradation has been investigated in aqueous solutions containing TiO2 suspensions as photocatalysts, in order to assess the adsorption, the disappearance rate and the mechanism of degradation. Results showed that only a small amount of amino acid is adsorbed corresponding to less than 1% of OH covered for aromatic amino acids and about 10% for linear amino acids. A comparison of disappearance rate, total organic carbon (TOC) removal and intermediate for these five amino acids are presented and discussed, taking into account their nature.

Coupling process between solid-liquid extraction of amino acids by calixarenes and photocatalytic degradation.

The removal of biological or pharmaceutical compounds through the wastewater treatment becomes relevant. These compounds are present as traces in sewage. In this work, we propose a coupling process which combines the pre-concentration of the pollutant by selective extraction and then degradation of these pollutants by photocatalysis in presence of TiO2. This process is efficient at room temperature by activation of a photocatalyst (TiO2) under UV light. Aromatic amino acids were chosen as model of pharmaceutical pollutants. Their extraction from water, ensured by calixarene derivatives, and their photocatalytic degradation were investigated. It was shown that photodegradation follows a first-order kinetic and that the rate constant enhances with amino acid concentration. The effect of the pH on the rate constant will be discussed.

Investigation of host-guest stability constants of calix[n]arenes complexes with aromatic molecules by RP-HPLC method.

Under reversed-phase high-performance liquid chromatographic conditions [Spherisorb ODS 1 stationary phase, UV detection at 254 nm, and acetonitrile-dichloromethane-acetic acid-methyl-tert-butylether (84.6/4.5/0.9/10, v/v/v/v) as the mobile phase], adding p-tert-butylcalix[8] (10(-5)-3.10(-5))-[12]arenes (10(-5)-4.10(-5) mol/L) to the mobile phase leads to decreased sorption of aromatic solutes on the surface of the sorbent because of the formation of host-guest inclusion complexes between the calixarenes and the aromatic molecules. Stability constants of the complexes (781-9338M(-1)) are determined from the relationship between the solute capacity factors and the calixarene concentration in the mobile phase.

Enhancement of the ionic response of field effect transducers using porous silicon.

Oxidised porous silicon samples prepared from highly and weakly doped p-type silicon substrates, have been functionalised with calix[4]arene (CA) molecules. They have been used for sodium detection as electrolyte/insulator/silicon (EIS) structures. An over Nernstian behaviour was observed and correlated with physical parameters of porous silicon samples (porosity, resistivity). A generalised Nernstian equation was proposed in order to describe this property. CA functionalised EIS structures based on porous silicon present higher lifetime compared to flat structures.