Laser induced densification of cerium gadolinium oxide: application to single-chamber solid oxide fuel cells

International audienceIn single-chamber solid oxide fuel cells (SC-SOFC), anode and cathode are placed in a gas chamber where they are exposed to a fuel/air mixture. Similarly to conventional dual-chamber SOFC, the anode and the cathode are separated by an electrolyte. However, as in the SC-SOFC configuration the electrolyte does not play tightness role between compartments, this one can be a porous layer. Nevertheless, it is necessary to have a diffusion barrier to prevent the transportation of hydrogen produced locally at the anode to the cathode that reduces fuel cell performances. This study aims to obtain directly a diffusion barrier through the surface densification of the electrolyte Ce0.9Gd0.1O1.95 (CGO) by a laser treatment. KrF excimer laser and Yb fiber laser irradiations were used at different fluences and number of pulses to modify the density of the electrolyte coating. Microstructural characterizations confirmed the modifications on the surface of the electrolyte for appropriate experimental conditions showing either grain growth or densified but cracked surfaces. Gas permeation and electrical conductivities of the modified electrolyte were evaluated. Finally SC-SOFC performances were improved for the cells presenting grain growth at the electrolyte surface

New trends in femtosecond Pulsed Laser Deposition and femtosecond produced plasma diagnostics

International audienceThe availability of compact table top amplified femtosecond lasers and the technical simplicity of experimental design have opened the way to many recent and fast developments towards thin film elaboration by Pulsed Laser Deposition (PLD) with ultra short laser pulses, with the aim of producing materials of high quality previously unattainable or attainable only through more complex means. The first developments of PLD using femtosecond lasers were made on Diamond-Like Carbon thin films elaboration, with the attempt to reach high sp3 content. PLD with ultra short pulses was used recently to deposit several systems such as quasicrystals or oxides with a transfer of the target composition to the deposited films, even for compounds with complex stoechiometry. Femtosecond laser ablation from solid targets has shown its capability in producing nanoparticles of different materials, even in high vacuum conditions. Nanostructured films of doped Diamond-Like Carbon were obtained recently, opening the way to large applications towards functional materials. The characteristics of the plasma are a well-suited signature of the physics of laser-matter interaction and plasma plume creation and expansion. Recent studies on the control of the film growth and femtosecond PLD processes will be reported. Emphasis on actual capability of the existing sources to elaborate high quality materials will be questioned in terms of energy per pulse, time width, repetition rates but also in the need for further source development and beam shaping improvement

Plasmonic and Hydrodynamic Effects in Ultrafast Laser-Induced Periodic Surface Structures on Metals

International audienceWe report results on the development of laser-induced periodic surface structures produced by ultrashort laser pulses irradiating metallic surfaces. The surface topology features are discussed in terms of periodicity and amplitude contrast of the pattern formation, and in relation to the chrono-logical sequence of laser-induced events. Resonant excitation of Surface Plasmons in metallic grat-ings show that the surface wave excited during the femtosecond laser pulse can initiate the observed patterning. Metallic behavior under nonequilibrium conditions on the picosecond timescale is then investigated to correlate the amount of material experiencing solid-to-liquid transitions and the sub-sequent structure amplitude. With the derived observation, the calculation of the transient nonequi-librium thermodynamic characteristics of excited nickel is performed, allowing to define character-istic timescales of thermocapillary processes which may occur under multi-pulse irradiation

Graphene-based textured surface by pulsed laser deposition as a robust platform for surface enhanced Raman scattering applications

International audienceWe have developed a surface enhanced Raman scattering (SERS)-active substrate based on gold nanoparticles-decorated few-layer (fl) graphene grown by pulsed laser deposition. Diamond-Like Carbon film has been converted to fl-graphene after thermal annealing at low temperature. The formation of fl-graphene was confirmed by Raman spectroscopy, and surface morphology was highlighted by scanning electron microscopy. We found that textured fl-graphene film with nanoscale roughness was highly beneficial for SERS detection. Rhodamine 6G and p-aminothiophenol proposed as test molecules were detected with high sensitivity. The detection at low concentration of deltamethrin, an active molecule of a commercial pesticide was further demonstrated

Characterization of different DLC and DLN electrodes for biosensor design

International audienceDiamond-Like Carbon and Carbon-Like Nanocomposite electrodes, novel materials in the field of biosensors, made with different ratio of sp3/sp2 carbon hybridization or doped with elements such as Ni, Si and W, were characterized electrochemically by cyclic voltammetry and by amperometric measurements towards hydrogen peroxide. SiCAr1 and SiCNi5% were chosen as sensitive transducers for elaboration of amperometric glucose biosensors. Immobilization of glucose oxidase was carried out by cross-linking with glutareldehyde. Measurements were made at a fixed potential + 1.0 V in 40 mM phosphate buffer pH 7.4. SiCAr1 seems to be more sensitive for glucose (0.6875 µA/mM) then SiCNi5% (0.3654 µA/mM). Detections limits were respectively 20 µM and 30 µM. Michaelis-Menten constants for the two electrodes were found around 3 mM. 48% and 79% of the original response for 0.5 mM glucose remained respectively for both electrodes after 10 days

Structure, electrochemical properties and functionalization of amorphous CN films deposited by femtosecond pulsed laser ablation

Amorphous carbon nitride (a-C:N) material has attracted much attention in research and development. Recently, it has become a more promising electrode material than conventional carbon based electrodes in electrochemical and biosensor applications. Nitrogen containing amorphous carbon (a-C:N) thin films have been synthesized by femtosecond pulsed laser deposition (fs-PLD) coupled with plasma assistance through Direct Current (DC) bias power supply. During the deposition process, various nitrogen pressures (0 to 10 Pa) and DC bias (0 to ¿ 350 V) were used in order to explore a wide range of nitrogen content into the films. The structure and chemical composition of the films have been studied by using Raman spectroscopy, electron energy-loss spectroscopy (EELS) and high-resolution transmission electron microscopy (HRTEM). Increasing the nitrogen pressure or adding a DC bias induced an increase of the N content, up to 21 at.%. Nitrogen content increase induces a higher sp2 character of the film. However DC bias has been found to increase the film structural disorder, which was detrimental to the electrochemical properties. Indeed the electrochemical measurements, investigated by cyclic voltammetry (CV), demonstrated that a-C:N film with moderate nitrogen content (10 at.%) exhibited the best behavior, in terms of reversibility and electron transfer kinetics. Electrochemical grafting from diazonium salts was successfully achieved on this film, with a surface coverage of covalently bonded molecules close to the dense packed monolayer of ferrocene molecules. Such a film may be a promising electrode material in electrochemical detection of electroactive pollutants on bare film, and of biopathogen molecules after surface grafting of the specific affinity receptor.This work is produced with the financial support of the Future Program Lyon Saint-Etienne (PALSE) from the University of Lyon (ANR-11-IDEX-0007), under the “Investissements d'Avenir” program managed by the National Agency Research (ANR)

Nanostructured materials elaborated by femtosecond pulsed laser deposition

International audienc

Laser ablation for carbon-based thin films and graphene synthesis

International audienc

Ablation laser femtoseconde pour le dépôt de couches minces

This research report concern the elaboration of thin films by femtosecond Pulsed laser deposition (PLD) and the characterization of the plasma plume. An overview of the results obtained on pure Diamond-Like Carbon (DLC) thin films are presented with the goal of depositing films with high hardness and low friction and wear coefficients, with good adhesive properties on various biomedical substrates, including stainless steel or polyethylene. Thin films have been successfully deposited on the femoral head of hip joints. The properties of DLC films elaborated by femtosecond and nanosecond PLD are compared through the optical properties of the films and the properties of the laser-induced plasma plume. Nanoparticles have been also deposited by femtosecond PLD and included in an amorphous matrix of DLC. By this way, we deposited metal-doped DLC films with tantalum or nickel due to their different chemical affinity with respect to carbon. Two different crystalline phases are obtained in the case of the tantalum-doped DLC film, with the surprising presence of a metastable β-Ta phase, which is correlated to the properties of the plasma plume. Tantalum carbide is also evidenced in a thin layer at the edge of the tantalum clusters.Pure DLC and metal-doped DLC films have been investigated in the frame of electrodes for biosensors. The possibility of using such materials with high sensitivity and low detection limits is shown. The optimization through the incorporation of an other dopant (boron) is dicussed.The possibility of using such boron-doped DLC films for thermal and nanocalorimetric sensors in investigated through another ANR support framework. The DLC thermometers with high TCR coefficient (Temperature Coefficient of Resistance) are integrated in suspended isolated structures and show already suitable properties, In the last part of this research report, propects of our works are presented through the temporal shaping of the laser beam. The outcome has potential interest for thin films elaboration or nanoparticles synthesis. Indeed, a possible way to achieve higher film quality and better control of the ablation process is to regulate the interaction process via spatio-temporal modification of the laser beam. We have developped an experimental tool allowing the possibility of tailoring the plasma plume by adaptive temporal shaping. Preliminary results on the use of an adaptive feedback optimization procedure that adjust the laser temporal form for modulating plasma optical properties are presented. This work is focused on the enhancement of the ionic emission with respect to the neutral emission lines of the plasma induced by laser irradiation of an aluminum sample. Such an optimization leads to plasma plume properties rather different from conventional femtosecond pulses (such as double or long pulses) and to films with lower density of nanoparticles, which is promising for future works.Ce mémoire concerne l'élaboration de couches minces par ablation laser femtoseconde (Pulsed Laser Deposition, PLD) et la caractérisation du panache plasma. Les résultats obtenus pour le dépôt de couches minces de Diamond-Like Carbon (DLC) sont présentés avec l'objectif de déposer des couches à grande dureté et faible coefficient de frottement, avec de bonnes propriétés d'adhérence sur divers substrats d'intérêt biomédical. Des couches minces ont pu être déposées avec succès sur une tête fémorale de prothèse de hanche. Les propriétés des DLC élaborés par PLD femtoseconde et nanoseconde PLD ont été comparées au travers des propriétés optiques des films et d'une caractérisation du plasma.Des nanoparticules ont été déposées par PLD femtoseconde, et incluses dans une matrice DLC. Des films de DLC dopés au nickel ou tantale (en raison de leur différente affinité chimique avec le carbone) ont été synthétisés. Deux différentes phases cristallines sont obtenues dans le cas du DLC dope Ta, avec la présence surprenante d'une phase métastable β-Ta, qui est corrélée aux propriétés du plasma. La présence de carbure de tantale est également mise en évidence sur les bords des clusters de tantale. Les films de DLC pur et de DLC dopé aux métaux sont caractérisés pour l'application aux électrodes pour biocapteurs, avec une sensibilité élevée et une faible limite de détection. L'optimisation avec l'incorporation d'un autre dopant, tel que le bore est discutée. La possibilité d'utiliser ces couches de DLC dopé au bore pour des capteurs thermiques et nanocalorimétriques est étudiée dans le cadre d'un projet ANR. Les thermomètres à base de DLC avec un fort TCR (Coefficient de Température de Resistance) sont intégrés dans des structures suspendues, et montrent de bonnes propriétés. Dans la dernière partie de ce mémoire, les perspectives envisagées pour ce travail sont présentées, avec l'introduction d'une mise en forme temporelle de l'impulsion laser femtoseconde et d'une boucle adaptative d'optimisation. Ces premiers travaux mettent bien en évidence les potentialités de cette technique, pour le dépôt couches minces et la synthèse de nanoparticules, permettant un contrôle de la nature et de l'énergie cinétique des particules du plasma. La suite de ce travail envisage donc de mieux comprendre les effets d'une mise en forme temporelle de l'impulsion laser femtoseconde sur les propriétés des produits d'ablation et donc des couches minces élaborées

New trends in femtosecond Pulsed Laser Deposition and femtosecond produced plasma diagnostics

International audienceThe availability of compact table top amplified femtosecond lasers and the technical simplicity of experimental design have opened the way to many recent and fast developments towards thin film elaboration by Pulsed Laser Deposition (PLD) with ultra short laser pulses, with the aim of producing materials of high quality previously unattainable or attainable only through more complex means. The first developments of PLD using femtosecond lasers were made on Diamond-Like Carbon thin films elaboration, with the attempt to reach high sp3 content. PLD with ultra short pulses was used recently to deposit several systems such as quasicrystals or oxides with a transfer of the target composition to the deposited films, even for compounds with complex stoechiometry. Femtosecond laser ablation from solid targets has shown its capability in producing nanoparticles of different materials, even in high vacuum conditions. Nanostructured films of doped Diamond-Like Carbon were obtained recently, opening the way to large applications towards functional materials. The characteristics of the plasma are a well-suited signature of the physics of laser-matter interaction and plasma plume creation and expansion. Recent studies on the control of the film growth and femtosecond PLD processes will be reported. Emphasis on actual capability of the existing sources to elaborate high quality materials will be questioned in terms of energy per pulse, time width, repetition rates but also in the need for further source development and beam shaping improvement