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We report a drastic enhancement of electrocatalytic activity toward glucose oxidation by using novel electrocatalysts on the basis of "bare" unprotected Au nanoparticles synthesized by methods of laser ablation in pure deionized water. The recorded current density of 2.65 A cm -2 mg -1 for glucose electrooxidation was higher than a relevant value for conventional chemically synthesized Au nanoparticles by an order of magnitude and outperformed all data reported in the literature for metal and metal alloy-based electrocatalysts. The enhanced electrocatalytic characteristics of laser-synthesized nanoparticles are explained by the absence of any organic contaminants or protective ligands on their surface, relatively small size of nanoparticles and their particular crystallographic structure. The employment of bare nanomaterials in glucose electrooxidation schemes promises a radical improvement of current biofuel cell technology and its successful application in bio-implantable devices.

The physical phenomena involved in the interaction of a laser-generated plasma plume with a background gas are studied numerically. A three-dimensional combined model is developed to describe the plasma plume formation and its expansion in vacuum or into a background gas. The proposed approach takes advantages of both continuous and microscopic descriptions. The simulation technique is suitable for the simulation of high-rate laser ablation for a wide range of background pressure. The model takes into account the mass diffusion and the energy exchange between the ablated and background species, as well as the collective motion of the ablated species and the background-gas particles. The developed approach is used to investigate the influence of the background gas on the expansion dynamics of the plume obtained during the laser ablation of aluminum. At moderate pressures, both plume and gas compressions are weak and the process is mainly governed by the diffusive mixing. At higher pressures, the interaction is determined by the plume-gas pressure interplay, the plume front is strongly compressed, and its center exhibits oscillations. In this case, the snowplough effect takes place, leading to the formation of a compressed gas layer in front of the plume. The background pressure needed for the beginning of the snowplough effect is determined from the plume and gas density profiles obtained at various pressures. Simulation results are compared with experimentally measured density distributions. It is shown that the calculations suggest localized formation of molecules during reactive laser ablation.

Fine electrically-conductive patterns of silver nanoparticles ink have been laser printed using the laser-induced forward transfer (LIFT) technique. LIFT is a technique that offers the possibility of printing patterns with high spatial resolution from a wide range of materials in solid or liquid state. Influence of drying the ink film, previous to its transfer, on the printed droplet morphology is discussed. The laser pulse energy and donor-receiver substrate separation were systematically varied and their effects on the transferred droplets were analyzed. The use of an intermediate titanium dynamic release layer was also investigated and demonstrated the possibility of a better control of both the size and shape of the printed patterns. Conditions have been determined for printing flat-top droplets with sharp edges. 21 µm width silver lines with 80 nm thickness have been printed with a smooth convex profile. Electrical resistivities of the transferred patterns are only 5 times higher than the bulk silver.

International audienceSurface modifications by nanostructuring present a new laser application for improvement of surface properties such as adhesion, mechanical characteristics or corrosion protection. In this study, we report the formation of nanoparticles by laser irradiation of a steel surface. The influence of laser parameters such as pulse duration (25–30 ns, 500 fs), wavelength (248 nm, 308 nm), and the background gas pressure (10 mbar− 1 bar) on the formation of this back deposition layer composed of aggregated iron oxide nanoparticles were investigated. Scanning electron microscopy and atomic force microscopy were used to characterise the irradiated steel surface and the particle morphology deposited by backward flux. In the nanosecond laser ablation regime, films are formed by aggregated nanoparticles with well developed cauliflower like structures, the size and the morphology depending on the nature and pressure of the background gas. In the femtosecond regime, we observed the formation of micrometer sized structures at the steel surface. In particular, a non-conventional mechanism of nanocluster condensation and growth is revealed since two different ablation rates corresponding to two different predominant processes are observed. These analyses demonstrate the possibility of controlling the distribution and the size of particles by varying the laser parameters and the background gas pressure and natur

International audienceUsing various band-gap materials and tightly focused femtosecond laser pulses with wavelengths in the range 1200-2200 nm, we show that nonlinear absorption is independent of the wavelength except for narrow gap semiconductor materials. This observation corresponds to a transition between multiphoton ionization and tunnel ionization for an adiabaticity parameter of about 3, which compares favorably with Keldysh predictions. Our results indicate that long wavelengths must open up an alternative to pulse shortening for ultraprecision optical breakdown in dielectrics

Organic thin-film transistors have been fabricated using laser-induced forward transfer as spatially resolved laser-printing method. Using this technique, source and drain electrodes were deposited from silver nanoparticle ink and the copper phthalocyanine (CuPc) was used to form the active layer. Both kinds of materials were transferred from a donor substrate onto a receiver substrate upon irradiation with laser pulses in the picosecond regime. The latter substrate formed the gate and the dielectric of the transistor. Electrical characterizations showed that the transistors are fully operative, showing well-defined linear and saturation regimes in the I-V curves.

We produce and characterize high-angle femtosecond Bessel beams at 1300-nm wavelength leading to nonlinearly ionized plasma micro-channels in both glass and silicon. With microjoule pulse energy, we demonstrate controlled through-modifications in 150-lm glass substrates. In silicon, strong two-photon absorption leads to larger damages at the front surface but also a clamping of the intensity inside the bulk at a level of %4 Â 10 11 W cm À2 which is below the threshold for volume and rear surface modification. We show that the intensity clamping is associated with a strong degradation of the Bessel-like profile. The observations highlight that the inherent limitation to ultrafast energy deposition inside semiconductors with Gaussian focusing [Mouskeftaras et al., Appl. Phys. Lett. 105, 191103 (2014)] applies also for high-angle Bessel beams. V C 2015 AIP Publishing LLC. [http://dx